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The increased use of large areas of flat paved and sodded surfaces not only in airport-construction but in express highways, parking-lots, roofs of large buildings, etc., makes desirable the hydraulic investigation which Messrs. IZZARD and AUGUSTINE have reported as accomplished and projected for future experimentation [see 1 of “References” at end of paper]. They are to be commended for the precision of experimental measurements on the smooth, plane surface which is the base from which the investigation will be expanded to include the rougher-paved and sodded surfaces which prevail in actual practice. (Note: Attention is called to an error in printing the line following equation (11) where “(p/43560d)” should read “(pl/43560d)”.

This paper is a discussion of the question “Do climatological averages serve adequately as normals?”, as presented by George W. Kindling of the Atlanta (Georgia) United States Weather Bureau before the American Meteorological Society In Milwaukee, Wisconsin, June, 1939. All tabulations used to supplement this discussion were abstracted from his original manuscript. The present practice of the United States Weather Bureau is to show climatological normals as arithmetical averages. The question is, do these averages serve adequately as normals? To answer the question, one must state explicitly what interpretation is attached to the normal and then review the climatological records from all parts of the country for possible discrepancies.

This paper describes an easily constructed instrument for the purpose of obtaining a continuous record of the time of occurrence and duration of shower-type rains and their range of raindrop sizes. A battery-driven motor pulls paper tape, previously treated with the water-soluble dye, methylene blue, past an opening exposed to the rain. The spot diameters left by the rain on the tape may be related to raindrop size by laboratory calibration. During a week's run on the island of Oahu, Hawaii, a total of 119 rains were recorded. Although many of these passed in a minute or so and were only a few minutes apart, less than 40 were recorded by nearby recording rain gages.

Explanatory note by N. W. Cummings—The original paper as submitted by Messrs. Kennedy contained an explanation of the terms of the energy-equation which duplicated in large measure that presented by me at the Pasadena meeting. At the suggestion of Mr. Harding these and some other parts of the paper have been deleted or condensed, and at the suggestion of R. E. Kennedy, I took a few liberties in making some other minor changes. No computations have been changed or omitted, and it is believed that all are substantially correct, although time did not permit a complete check. There may be some slight mistakes in s. for the pan. Mr. Kennedy has made use of Richardson's equation for back-radiation, using Fahrenheit temperatures and B.t.u's. per square inch for a 30.4-day month instead of Centigrade temperatures and calories per square centimeter per minute.

The work reported by Blanchard in this paper must be regarded as an important effort in the experimental study of the stability of large raindrops. Stroboscopic photography has been admirably adapted by Blanchard to the task of revealing rapid changes in drop shape as well as showing details of drop breakup. Since publication of Blanchard's work provides virtually the sole source of observational information relative to raindrop dynamics, the writer would like to ask several questions in an effort to elucidate several points that arose in his mind in studying the paper.

The development of useful rainfall-runoff relations for small basins is an extremely useful extension of this valuable hydrologic tool. The authors are to be congratulated upon a n excellent paper on an interesting subject presented in a clear and concise manner. The writer is particularly interested in the subject because of his own efforts to develop some methods of computing approximate rainfall-runoff relations in various areas of the world, given a minimum amount of climatological facts and runoff data. I n the course of the writer's investigations, he came to several conclusions which seem to be at variance, to some degree, with the authors'. Firstly, the authors state that experience has shown that the seasonal factor in the rainfall-runoff relation shows little change with in a physiographicaUy homogeneous region. The writer believes that authors may have meant to include similar climate as well as similar physiography. By definition, seasonal curves properly established should largely reflect the influence of the annual climatic cycle on runoff. In many areas of similar physiography, considerable differences have been known to exist in the evapotranspiration losses reflecting the effect of climatic differences. In place of accepting the seasonal curve from an area of one climate and using it foe an area of another climate, the writer has obtained some workable runoff relations by adjusting the seasonal curves for variations in seasonal factors. The factors used included the mean air temperature in January and July, plus the length of the growing season and other climatic data. It seems to the writer, that if acceptable results were obtained by the authors in Georgia, using the seasonal curves of a rainfall-runoff relation developed in Maryland, the effect of differences in climate may have been only partially compensated in the hourly rainfall-hourly runoff portion of the runoff relation. If this were the case, the procedure illustrated in the paper will have limited application.

For years Hydrology enjoyed the position of being the largest Section in the American Geophysical Union, and we contributed something like 40 % of the scientific papers in the Transactions. It was a rather comfortable arrangement, because we were numerically dominant in a prestige organization. Starting in January of 1959 something strange started to happen. Our familiar gray publication got a new name and a yellow cover, and there were some articles about outer space. This was not objectionable, because outer space had become a very popular subject in the World, and we took a certain amount of pride in being associated with it. As the months went by it became a bit troublesome, because the publication became larger with almost each monthly issue, and it was becoming difficult to find items about hydrology. Some complaints came along later in the year, and these gave rise to a letter from the President of the Section. We were still getting as many papers dealing with hydrology as ever, he said, it was just that there was more of this new material.

In two recent papers I dealt with the aperiodic changes of temperature on Mount Washington [see 1 of “References” at end of paper]. The present investigation is a continuation of the former attempts.

In recent studies of stream-flow determination from rainfall-records much emphasis has been placed on antecedent weather. The soil-moisture deficiencies that occur on a watershed as a result of weather preceding rainfall could be rather closely estimated if the amount of moisture lost by evaporation and transpiration between storms were known. Instruments designed to secure measurements of such losses are only now being perfected [see 5 of “References” at end of paper] and it was in anticipation of them that a proposed method has been developed for calculating contributions of runoff to stream-flow by reference to soil-moisture deficiencies at the beginning of rainfall. The details of the method are tentative. Only a brief outline of the procedure and of the results obtained is therefore presented in this paper.

The use of precipitation-runoff relations for water supply forecasting has been discussed in numerous papers. This paper describes the details of the techniques developed by the United States Weather Bureau in connection with its program of water-supply forecasting. In addition to its use as a forecasting tool, the method may also be employed for interpolation or extrapolation of stream-flow records, and for the evaluation of water resources. Because the analysis involves a long period of record, time trends in the data must be considered. The downward trend of runoff in the Colorado River Basin as compared to observed precipitation is discussed.

The principle of pattern-repetition as a means for forecasting the annual runoff- and flood-peaks of major rivers was first presented in a brief paper by the author under date of April 9, 1942. Therein was submitted a preliminary application of the pattern-principle to the problem of forecasting the summer peak and total annual runoff of the Columbia River at Cascade Locks, Oregon, for the year 1941–42. Pattern-analysis as presented in our paper of April 1942 introduced an entirely new departure so far as we know in forecasting river-flow. The Present paper has been prepared in an effort to amplify the annual preliminary procedure and to extend original studies by further investigation.

During recent years numerous methods for the prediction of rate of snow-melt and resultant runoff have been presented [see 1, 2, 3,4 of “References” at end of paper]. Some solutions were based on thermodynamic principles. Others made use of simple empiricisms. As yet however, no procedure has completely supplanted the use of the degree-day factor [4, 5]. The outstanding virtue of the degree-day method is its extreme simplicity. Only records of dry-bulb temperature are necessary to compute degree-days and a simple multiplication by a degree-day “factor” completes the computation of the volume of snow-melt. The great disadvantage of the procedure is that it neglects humidity, radiation, and other factors known to influence the melting-rates of snow. It is the purpose of this paper to outline the methods developed by the office of the Weather Bureau at Sacramento, California, for applying the degree-day procedure to river-forecasting in the Sacramento and San Joaquin river-basins.

It seems fortunate that two papers concerning the relationship between wind velocity and movement of the surface water appeared in the same issue. Since both papers show apparently different results, it seems necessary to point out difference in the methods used to obtain these results. The first paper shows evidence for a discontinuity of the wind-water movement relationship between wind force groups 1 to 4 and 5 to 8 of the Beaufort scale, and a decrease of the ratio k, current velocity/wind velocity, for stronger winds. The second paper reports an indication for a possible increase of this ratio at wind forces above 3 Beaufort. A corne a of both papers, therefore, is called for. Lawford and Veley do not include wind forces above Beaufort 5, and as indicated in their Figures 1 and 2, many values for force 5 are extrapolations from current curves a t forces 1 to 4. If any discontinuity should occur between 4 and 5 or at a higher forces, it cannot be discovered or will be veiled. Whether any change in the ratio k occurs at force 3 as indicated by the curves for Varne and S.2 could not be detected at Amrum bank. The method used by Mandelbaum does not permit the interpolation of intermediate values. As pointed out by Lawford and Veley, the conversion of wind velocities estimated by the Beaufort scale to a unit scale of cm/sec or mi/hr is always inherently arbitrary. This conversion scale also depends on where the wind velocity is estimated, at the masthead; on deck of the vessel, three to four meters above the water surface; or directly at the water surface. As indicated by Mandelbaum (Fig. 1) the various attempts for such conversions differ greatly from each other. A slightly different position given to forces 4 and 5 light alter the appearance of the curves completely. The results of both papers have this same inherent uncertainty.

In a paper entitled “Progress toward a rational program of snow-melt forecasting [see 1 of “References” at end of paper] MERRILL BERNARD outlined and presented graphically the relations between the factors involved in the snow-melt phenomenon. This outline is an expression of a forecasting-procedure development for which this paper may be considered a progress-report

Snow-reporting in New England is used in this paper to refer to reports of snow-conditions for winter sports primarily, although such reports are also of service to highway engineers, long-distance shippers, and power-companies. Stream-flow and even floods are less dependent on snow-accumulations than on occasional torrential rains, and differ thus from Western conditions. Since snow-depth, its quality, and distribution vary extremely from place to place in New England, as well as from day to day and hour to hour, many agencies such as railroads which run “snow-trains” have been receiving and publishing snow-reports for several years. These reports are carried by most metropolitan and local daily papers, as well as by special publications like The Ski Bulletin published every Friday in Boston.

This report of an investigation to determine a multiple correlation equation for use in relating various hydrologic factors is an extremely worthwhile presentation. As the authors point out, there have been numerous papers reporting results of statistical analyses of hydrologic data. However, there have been too few papers devoted to a description of the techniques used in selecting and designing empirical equations for use in regression analysis in hydrologic studies. The recent rapid increase in the application of electronic computers emphasizes the need for increased familiarity with basic mathematical and numerical methods.

At the Annual Meeting for 1945, a paper was presented on degree-day units, especially on the regional contrasts in their range or variation. That paper was published in the Transactions for August, 1945 (v. 26, pp. 45–48). The term “degree-day,” invented by a heating engineer and adopted by the United States Weather Bureau, has been applied hitherto to the sums below 65°F, for which the term “cold degree-day units” is here proposed. The sums of the temperatures above 70°F, calculated in the same way as cold degree-day units, is the subject of this paper. A day having a daily mean temperature of 71° has one hot degree-day unit; a day with a mean of 85° has 15 units. Twenty days with means of 85° have a total of 300 units. The annual average number of hot degree-day units in the United States has been laboriously calculated from “Daily Normal Temperatures in the United States,” Supplement 26 of the Monthly Weather Review, published in 1925.

To deduce the size, shape, and density of the anomalous masses which produce the Vening Meinesz belts of negative gravity-anomalies is an important problem. This calculation has been carried out by Vening Meinesz [see 1 of “References” at end of paper] for a profile from Java to Christmas Island and by Jung [2] for a profile across the Nares Deep and also for one across East Timor. The present paper considers the possibility of increasing the accuracy of this calculation in future work. Three possibilities are discussed.

In an earlier paper [see 1 of “References” at end of paper] the influence of altitude on the annual course of air-pressure was examined. The annual and semiannual waves were considered. It was shown that the annual wave is a thermal wave, the amplitude of which increases with altitude above sea-level in a strictly linear way. The semiannual wave resulted as a pressure-wave and seems to be a forced wave because the amplitude is invariant with altitude. It was stated that the Fourier series which represents the annual variation did not converge well, so that it was necessary to consider also the third wave.

This year the Committee on Runoff had three major objectives: (1) to report on runoff research projects now in progress or proposed for. action in the immediate future; (2) to follow up through correspondence on a number of selected papers that have appeared in the Transactions during the few years; and (3) to solicit discussion of current papers from qualified members. Under (1), reports have been received listing runoff research projects of the U.S. Forest Service, Geological Survey, Bureau of Reclamation, Corps of Engineers, Bureau of Public Roads, aid also projects of the New Jersey Division of Water Policy and Supply and the University of Illinois. These condensed reports have been grouped by subject matter and made a part of this report.

A brief though concise statement of the history of ground-water studies on Long Island, beginning with the early water-level observations in Brooklyn by STODDARD in 1854, was given by THOMPSON [see 7 of “References” at end of paper]. These and other early data were considered later by LEGGETTE [8]. He evaluated them by means of a graph of the cumulative departure of precipitation. More recent studies by LEGGETTE [9] and by the writer have lead to the procedure outlined in Part I of this paper [10], which was founded upon an empirical approach suggested by LEGGETTE and was later justified by analysis based on the theory of BOUSSINESQ [11].

Programs of observation of the natural fluctuations of ground water covering an extensive area where there is no continuous aquifer are discouraging for the reason that readings must be made for a considerable period of time before they begin to have meaning. The results are not directly translated into quantitative data in the manner that streamflow records are. Consequently to appreciate the potential value of this work it is necessary to have some perspective of the possible future significance. Otherwise opportunities to gather much needed basic hydrologic data may be lost. Papers by the same author describing the method of analysis and the practical application in forecasting assured river flow have appeared in previous Transactions of the American Geophysical Union. This paper deals primarily with the precautions believed to be essential in maintaining the high standard of consistency in order to make the effort expended on observation of greatest use in the future.

In a previous paper entitled “stream-flow from rainfall by unit method” (Eng. News-Record, April 7, 1932), the writer defined a unit graph as the hydrograph of runoff from a given area, due to a one-inch runoff-depth applied in one day or in any other convenient unit of time. A procedure for deriving the unit graph from observed rainfall- and runoff-records was presented. After the unit graph has been derived a runoff-record for the given area, for any rain or series of rains, may be computed by a simple summation process. Figure 1, from the aforesaid paper, graphically illustrates the summation process and it will not be described further here.

(In connection with this paper, S. O. Harper, acting Chief Engineer of the Bureau of Reclamation, writes as follows to Dr. Church: “I am forwarding herewith a paper prepared by Mr. O. C, Reedy of this office, discussing the plan of the Bureau of Reclamation to utilize measurements of precipitation in conjunction with snow-course measurements as a means of forecasting the probable inflow to Lake Mead. You will note from reading the paper that presentation of the material may be a bit premature in that the Bureau has not made sufficient use thereof to be able to state any conclusions. However, it may be that by presenting our ideas on the subject, and getting other people to think along these lines, we may secure some suggestions as to our plan of attack, and I assure you that these will be welcome.”)

This paper is written in an effort to introduce a comparatively new research tool to American meteorologists. Of the many instruments available to the research meteorologist, the sailplane or high performance glider is least known. However, immediately after the War the sailplane began to be used in such applications as thunderstorm exploration and studies of airflow over ridges. Since the acceptance of this new tool depends mainly upon the researchers' appreciation of its advantages as well as its limitations, this paper attempts to present some of the characteristics of the sailplane as a probe and as an elevated platform for other meteorological instruments. Certain instruments used in the sailplane are also described since they are not generally known by the meteorologists.

The first part of the Committee's Report appeared in December 1953 issue of the Transactions, pages 938–944. Attention was there directed to a second part of the Report to appear later. It was stated that this would consist of a paper by F. J. Veihmeyer and A. H. Hendrickson: Does Transpiration Decrease as the Soil Moisture Decreases? This paper was presented before the Section of Hydrology on May 4, 1953. After reading all contributions here presented upon the question provided by the title of the paper itself, it is evident that wide differences of opinion prevail concerning the answer. The Chairman of the Committee will simply point out that there may be two possible explanations of these differences: (1) all participants are not, in actual fact, considering precisely the same phenomenon, and (2) the phenomenon under discussion has not, in all cases cited in support, been directly measured.

Resistivity-surveys were made at the Legrande oil-pool in Hart County, Kentucky, to correlate, if possible, oil- and gas-structures with resistivity-measurements. The results of this work are presented in Technical Paper 521 (in press). A careful study of magnetic anomalies measured by an Askania balance was made upon three representative iron ore-deposits. From the geophysical viewpoint they represent three different types of deposits. The results of this investigation are very interesting and are being published by the Bureau as Technical Paper 528 (in press).

The flow of cold air down slopes on clear, calm nights is a familiar phenomenon which is of great significance to citrus growers during radiation frost weather. The current is due to the fact that chilled air is more dense than that unchilled and therefore tends to underrun the lighter air. This phenomenon is somewhat similar to the submerged flow of salt water, or of water with solids in suspension, under clear fresh water. The status of knowledge in those fields is seen in papers such as those by O'Brien and Cherno, by Kalinske, and by Dobbins [see 15, 9, 10, 3 of “References” at end of paper]. The authors have not seen an adequate analytical method which would satisfactorily treat buoyancy-stability and account for the eddy-transfer of heat or moisture across fluid planes of zero shear-stress. It is hoped that critical discussions of this paper will lead to that objective.

This paper is a continuation of one given at the Twenty-Fifth Annual Meeting of the American Geophysical Union, in June, 1944, on “A study of the radoncontent of soil-gas” [see 1 of “References” at end of paper]. The present paper covers the period from May 17, 1944, to March 25, 1945. Its main purpose is to consider the meteorological influences upon the radon-content, such as barometricpressure changes, wind-velocity effects, and temperature-variations. Four depths, 25, 75, 150, and 200 cm, were investigated. In the course of 177 days of actual investigation during this period, covering 642 Individual readings, the radon-content of the soil-gas was measured. Ionization-chambers connected with a Wulf bifilar-electrometer were used, and the amount of radon was calculated in (curie/cc) X 10−14 , after calibrating the apparatus by means of a standard solution of radium. From the results obtained the following conclusions can be drawn: (1) Dry ground produces constant values of the radon-content at each depth and shows an increase of the content with depth. (2) A long period of snow-and-ice-coverage of the ground causes all pipes to approach the same value. Frozen ground gives the highest values for the year. (3) Barometric pressure causes, at least to a depth of 200 cm, a variation such that an increasing pressure tends to decrease the radon-content, while a decreasing pressure produces an increase in radon-content. This effect is most pronounced at the 25- and 75-cm levels. (4) A high wind-velocity over a number of hours will noticeably reduce the radon-content in the top layers of the ground. (5) Ground-temperature changes have apparently no great effect upon the radoncontent of soil-gas.

The fundamentals of isentropic analysis of flow-patterns within the atmosphere were set forth last year in a paper presented before the meteorological section of the American Geophysical Union by C.-G. Rossby [see 1 of “References” at end of paper]. Since that time a considerable amount of research has been directed to the application of these charts for use in helping to explain certain weather-phenomena and to develop new tools for use in weather-forecasting. While the technique of constructing these analyses has been appreciably improved within the past year, the underlying procedure and suggestions made by Rossby have been found to be substantially most effective, and for this reason they are being carried out at the Massachusetts Institute of Technology.

Since 1926 the management of the International Power and Paper Company, Ltd., has been forecasting stream-flow for the Grand Lake Basin in western Newfoundland. (Appreciation extended to ERIC HINTON of Bowater's, Newfoundland Pulp and Paper Mills, Ltd., for furnishing data upon which this paper is based.) As the company operates its paper-mill at Corner Brook exclusively by hydroelectric power, it is interested in the magnitude of the spring-flood which produces the major portion of the annual stream-flow. Accordingly, predictions of flood-magnitudes have been obtained in the early spring of each year since 1928 by means of snow-surveys and precipitation-records. The predicted runoff each year consisted simply of the water-content of snow calculated from a snow-survey made about the middle of March, plus precipitation measures until the end of March, plus a constant average figure—based on past records—expressing the most probable precipitation after the end of March. All figures were expressed in billions of cubic feet (BCF). The results of the first ten years from 1926 to 1935 have been summarized and discussed by HINTON [see 1 of ”References“ at end of paper].

Teleseismic work—This was maintained with few exceptions on the same basis as in the previous year. (1) The privately operated station of Mrs. M. M. SEEBERGER at Des Moines, Iowa, resumed routine recording early in 1942. The records are being forwarded to the Coast and Geodetic Survey. (2) A McCOMB-ROMBERG seismograph was installed at the Spring Hill (Alabama) Seismograph-Station through the cooperation of The Franklin Institute and the Coast and Geodetic Survey. (3) WENNER seismometers for the Sitka Observatory were equipped with new coils, dynamic testers, and metal covers which can be oil-sealed; a one-component temporary instrument was in operation at the station during the alterations and a new recorder equipped with a WALLACE and TIERNAN motor modified for accurate control by a pendulum clock was placed in operation. (4) There was some cooperation with the National Park Service in connection with the establishment of a new station at Flagstaff, Arizona. (5) In cooperation with the International Seismological Association, photographic paper and paper for mechanical seismographs were supplied for the Danish stations at Ivigtut and Scoresby Sund, Greenland. (6) Four seismographs are now being operated in the Boulder Dam Area, one having been added in 1941; new stations are being established in the vicinities of Grand Coulee Dam and Shasta Dam; these projects are being conducted jointly with the Bureau of Reclamation and with the cooperation of the National Park Service.

The Chairman, in a letter to members of the Committee and others, stated as follows: “(1) Opportunity for public discussion of important hydrologic papers presented before the American Geophysical Union has not been furnished. Such papers require advance distribution to enable a satisfactory review to be made, and the present facilities of the American Geophysical Union do not permit this. The value of these papers would be greatly enhanced by written discussion.

About 50 delegates, representing 15 countries, were in attendance. The contacts between delegates from the different countries were most stimulating and helpful, and a great deal of benefit- was derived thereby. The basic theme adopted for the Edinburgh Meeting was “The problem of atmospheric disturbances,” which quite naturally resolved itself into six different divisions, as follows: (a) The definition of a disturbance; (b) origin of disturbances; (c) structure of cyclones; (d) Interaction between different layers of the atmosphere; (e) radiation and its role in atmospheric disturbances; and (e) precipitation. A number of instructive papers were read under these six heads and, in addition, there were about a dozen papers of a miscellaneous nature. All were interesting and many evoked discussion.

The simple instrument with which the measurements presented in this paper were made has been described in several papers by Weyde and Frankenburger ([see 1 of “References” at end of paper] and others elsewhere. It may be just stated that it consists mainly of a test-tube with a liquid coloring red under the influence of that part of the ultra-violet spectrum which produces the erythema and which is therefore of particular biological importance. The color of the liquid is compared with a standardized color-wedge that gives units of radiation which are calibrated against erythema-doses. The instrument is not only cheap but also easy to handle and to carry. There exist as yet only a few series of observations, the most important of which have been conducted by Knepple [2] and Ungenheuer [3] at Oberstdorf, Bavaria, Germany, in the high mountains, by Bossolasco [4] during the International Polar Year at Mogadiscio, Italian Somaliland, Africa, and by Fuchs [5] on an expedition through south-central Europe.

This paper is the second statistical study of tornadoes in the United States. The first paper (see Charles W. Brown, A study of the time-, areal-, and type-distribution of tornadoes in the United States, Trans. Amer. Geophys. Union, 14th Annual Meeting, pp. 100–106, 1933) covered only the last 15 years from 1917 to 1931. The present contribution is based upon a study of all the data, which may vary in completeness in the various states and years with the personnel, contained in the publications of the Weather Bureau for 52 years from 1880 to 1931. The previous study, though for a shorter period, included 2017 tornadoes (54.1 per cent) of the total number, 3911, whereas the present study includes for the earlier 37-year period but 1894 tornadoes. Earlier graphs have been revised and the later data have been added thereto. In addition, new studies for the entire time have been made of the hourly occurrence, the frequency, and the damage possibilities of different areas, and all the tornadic tracks of the half-century have been plotted on one map (Fig. 1, which is copyrighted). These latter studies are already serving as a basis in part for revision of tornado-insurance rates. Further theoretical and statistical studies are in progress.

It seems necessary to make some criticism of Baker's paper because the physical problem is much more complex than indicated. Although simplifying assumptions are frequently used to good advantage in the solution of many problems, when the initial assumptions are simplified to the point where they render the final results too unrealistic for practical use, their advantage may be lost. In Baker's paper, this situation may exist. One example of what may be a case of over-simplification is the author's assumption that the included cone-angle of the effective boundary of a stationary jet will be about 24deg;, and, for calculating the mass, inertia, buoyancy, and vertical acceleration of a ‘slice’ of the jet, this constitutes the effective boundary. Another such assumption is that the average density over the cross section thus defined is equal to the arithmetic average of the densities of all parcels of air entrained upstream of the cross section under consideration.

The annual meeting of the Pacific Southwest Region was held January 16–17 at the University of California in Los Angeles with about 100 in attendance. On the evening preceding the meeting continuing into the first meeting day, Los Angeles experienced a 7½ inch rainfall which cut down attendance substantially, and it was necessary to cancel two of the papers because of the circumstances resulting. It was none the less considered to have been a highly successful meeting, and as the address at the banquet concerned the problems of air pollution, some thought was expressed that AGU should have a section particularly concerned with the atmosphere as a resource. Sixteen papers bearing chiefly on hydrology and meteorology were presented.

Ten years ago, the senior writer of this paper engaged in a discussion with a hydrologist on the distinction existing between predicting the flow of a river on which a power-plant was contemplated and predicting the flow of a river on which a power-plant existed. The difference between the two problems produced this paper, which is still unfortunately a progress-report. It was hoped to bring this study to a close at this time but unexpected circumstances rendered that goal impossible. It might be added however that the conclusion-study would not require the time or effort the material in this paper required.

This is a popular presentation of the formal paper on “Evaporation at high altitudes and high latitudes” presented for the writer at the meeting of the Section of Hydrology at Washington, D.C. That paper appears in full in these Transactions.

In this third paper of statistical studies of the distribution of tornadoes in our country in the recent half-century, the writers submit the county-distribution map with comments. It shows the results of the study of the distribution based upon smallest available unit. Of course, it is understood that, under the inspiration of Colonel Finley's enthusiasm, the gathering of tornado-data was fairly comprehensive until the middle of the nineteenth century. A hiatus of a score of years then ensued in which tornado-facts were of rather fragmentary nature. But from 1916 on, some 5000 observers were cooperating in collecting fairly complete field-data. Of the 4000 tornadoes studied in this paper, about three-fifths occurred in this later period, and of the balance, the major portion occurred in the earlier period.

The only matters needing report in connection with my activities in atmospheric electricity are briefly noted in the following paragraphs. (1) I have developed a theory which is explained in its title as follows: A Modification of the Electromagnetic Equations consistent with restricted relativity and providing a possible explanation of the origin of the Earth's, electric charge, of the Earth's magnetic field, and of gravitation. This paper was published in abstract form towards the end of my paper on “The Earth's Electric and Magnetic Phenomena,” in the Journal of the Franklin Institute for February, 1926. It is now in process of publication in extended form in the Philosophical Magazine. It will also appear in the publication of the papers presented at the International Mathematical Congress in Toronto a couple of years ago.

The following summary of the U. S. Geological Survey gravity program in Washington, Idaho, Montana, and Wyoming is one of a series of short papers that outline Geological Survey gravity projects in the western United States. The substance of this summary is a list of references of published papers on U. S. Geological Survey gravity projects in the northwestern states together with an index map (Figure 1) showing the location of the project, the approximate a real coverage reported in the publication, and the contour map given in the publication. Areas in Figure 1 are related to the References (part 2) by a number code. In addition, the gravity projects in progress are listed in Table 1, indicating the area in which the work is being done and the person in charge of the project. Capital letter relate the locations of the projects in Figure 1 to the list of projects in Table 1. No attempt has been made to indicate the areal coverage or contour interval of the projects in progress.

Perhaps the first reaction to the title of this paper may be “why discuss probability? If that approach in hydrology has not already been discarded, it ought to be.” Certainly the critical attitude toward studies of probability expressed in much recent engineering literature would suggest this conclusion. The following quotation from an article “Possible and probable future floods” by William P. Creager in the November, 1939, issue of Civil Engineering is representative: “About 1914 the theory of probabilities was applied to flood studies; that is, curves were derived indicating by past records on a stream the frequency with which, during a long period, a given flood should be expected. Notwithstanding the fact that periods of record sometimes did not exceed 20 years and very seldom exceeded 30 or 40 years, these probability-curves were extrapolated to estimate the flood which would be expected during long periods—once in 1,000, 5,000, 10,000 years, etc. Then, according to the judgment of the engineer, the 1,000-, 5,000-, or 10,000-year flood was selected for the design-capacity of the spillway.

Due to the various defense projects started at Sitka during 1938 and 1939 and the resulting influx of construction workers, there was brought about an acute housing shortage in the town. In order to meet the demand for houses and apartments, a large number of small dwellings were hastily constructed. A number of these new buildings were erected very close to the buildings of the Observatory and the continuity of the magnetic observations at the Sitka Observatory was threatened. Land belonging to the Department of Agriculture and used for an experimental farm was transferred to the Coast and Geodetic Survey as a site for the Observatory. A special appropriation from Congress made it possible to construct new buildings at this site, and the Observatory was moved to this location on the outskirts of the town of Sitka in the fall of 1940 [see 1 of “References” at end of paper].

Investigations into the various factors which influence Beaufort estimates of the wind force at sea are known to have been made on the basis of data of a variety of vessels with and without sail, moving ships and light-vessels. The authors have augmented this list with another set of original data which may be welcomed especially since it is the first time that routine observations of ocean weather ships were used for that purpose. According to the title of their paper the accuracy of the wind-speed estimates was their main object of investigation.

Hayes and Kittredge have contributed useful quantitative information to the old and possibly never-ending problem of measuring precipitation. That the problem is old is indicated in a paper written by Abbe in July 1899, which appeared 50 in the Monthly Weather Review, where he cited articles which were about 50 years old at that time. The authors are to be commended for demonstrating a profile of rainfall catch from the edge of a clearing to a distance where the catch seems to be uninfluenced by the trees. Further, it is gratifying to see two such profiles, thus showing not only an average distribution of catch, but also indicating its variability. The validity of the profiles is based on consistent instrumentation, which in this case, was a set of gages tilted uniformly. It is regretted that details of wind force and direction were not reported. In view of the statement that much of the rain came with southeast winds, and with the map showing the pine stand to the southwest of the gages, the important question still remains: How far do the effects of a timber stand extend to gages down wind from its edge?

Recent intercomparisons of wireless time signals show variations of 0s.2 to 0s.3 in the time from one observatory as compared with that from others, and suggestions have been made that such variations may be due to the astronomical observations, and that longitude work may be subject to similar uncertainties. This paper gives the results of several different investigations into the differences in clock corrections as determined from observations on the different instruments at the U.S. Naval Observatory, on over a thousand nights in the last twenty years. From these comparisons it was found that the clock corrections determined from definitive reductions of simultaneous observations on two standard instruments rarely differ as much as 0s.1, and that the average difference is 0s.03. The probable error of a clock correction is 0s.014. The large instruments hold together within 0s.03 for a number of years at a time.

In the science of hydrometeorology, many attempts have been made to investigate the areal-depth relationship of rainfall, but little information has been obtained sufficiently to draw positive conclusions, particularly in connection with storms occurring in small watersheds. The writer is glad to see that this paper supplies the valuable information, resulting from area-depth studies of rainfall, that maximum rainfall data for thunderstorm rainfall in small basins bear a linear relationship to the square root of area. As this relationship is expressible by a simple and workable equation, it is indeed very useful for many engineering purposes.

By virtue of the Bernoulli effect, the wind blowing over the summit of Mt. Washington, New Hampshire, causes the station barometric reading to be less than the pressure at the same level in the free air near the summit but away from the influence of the mountain. The object of this paper is to determine the amount of pressure fall that results from the Bernoulli effect and to show how it may be compensated for to a good degree of approximation by use of a pitot tube connected to the barometer. The pressure deficiency produced by the wind at Mt. Washington has been ascertained by correlating barometric readings on the mountain with comparable data reported by surrounding low-level radiosonde stations. The latter data were derived by interpolation from synoptic charts giving pressures of the 5000-foot plane or heights of the 850-millibar constant-pressure surface. A curve of pressure correction to overcome the specified deficiency in barometric reading has been prepared, giving the correction as a function of wind velocity. This curve showed that the flow of air over the mountain causes the observed barometric pressure on the summit to decrease relative to free-air pressure nearly in proportion to V2, where V = wind velocity observed on the summit. This fact suggested to the author that the impact pressure of the wind (ρV2/2, where ρ = air density) available from a pitot tube vaned into the wind might be used to compensate automatically for the pressure deficiency produced by the wind, since both impact pressure and pressure deficiency apparently are functions of V2. A vaned pitot-tube assembly was built and mounted on the Observatory tower freely exposed to the wind. Tubing was used to connect the pitot tube to a fixed-cistern mercurial barometer and to a pressure-tight box containing a standard microbarograph. The impact pressure of the wind thus imposed directly on both the barometer and the microbarograph is found to compensate approximately for the deficiency in pressure due to the wind blowing over Mt. Washington. The pressure observed at the station, with the pitot tube connected to the barometer, was compared to the local free-air pressure derived by interpolation from the upper-air synoptic charts. Tables of frequency of various discrepancies between these two pressures are given. These tables show that zero (0) discrepancies occur with greatest frequency, although a discrepancy as large as eight millibars has been observed out of 176 comparisons. It is believed that a major proportion of each large discrepancy results from errors in location of the isograms on the upper-air charts that served as a source for the comparative data. Judging by the data available, the mean discrepancy in station pressure found when using the pitot tube with the barometer at Mt. Washington is of the order of one millibar.