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Nature photography was almost the first application of the electronic flash system of lighting when it became commonly available.1 Although these first units used paper capacitors charged to high voltages and discharging at microsecond rates, later ``strobes'' employed lower-voltage capacitors and operated at longer flash durations. Hence, today's conventional strobe is not suitable for the rapidly moving subjects of nature photography. This article describes a development in strobe equipment that incorporates new and improved design to create flash units of not only lighter weight, but with exposure times of less than 100 microseconds.

The problem of the pulling into step of a synchronous motor has proved very difficult to solve, since it centres about a non-linear differential equation. One solution of the equation is not enough. All possible solutions with all combinations of the coefficients need to be made and classified into two groups, those that synchronize and those that do not. Until recently this has been practically impossible because of the amount of time required to make the solutions by graphical or point-by-point methods.The development of the integraph by Dr. Bush and his associates at the Massachusetts Institute of Technology has made it possible to solve this problem by machine integration. This integraph, which performs two successive integrations simultaneously, is particularly adapted to the solution of first- and second-order total differential equations. The solutions described in this paper were obtained by using the integraph in this way.This paper presents the complete solution of the problem for the case of a non-salient-pole synchronous motor. The results are put in a simple form convenient for practical use. By means of these results all of the necessary relationships between field current, induction-motor torque and slip, which determine whether or not a given load of a definite flywheel effect can be brought into synchronism, are determined. An example of a practical application is given.

The Rapatronic camera takes still exposures of 2 to 20 μsec with a high degree of resolution. Exposure is easily synchronized with a fast-transient event, and the shutter has at least a 30-deg viewing angle with apertures in the useful range for high-speed photography. The shutter is of the magneto-optic “light valve” type, operating by the rotation of the plane of polarization of light traversing glass in a magnetic field (Faraday effect). Three polarizers, crossed at 0-90-0 deg, produce an open-to-closed transmission ratio in excess of thirty million, and removal of the magnetic field closes the shutter, allowing it to pass only one billionth of the light from the subject.

Mechanical oscillations of synchronous motors following the application of abrupt shaft loads have not heretofore been easily calculated for cases of large angular swings, taking into account the damping currents in the rotor, except by tedious point-by-point methods. The chief difficulty has been due to the form of the basic differential equation upon which the solution of hunting problems depends. Within the last few years, Doctor V. Bush and others at the Massachusetts Institute of Technology have devised the integraph which is capable of solving the equations of the synchronous motor. Into the integraph are put curves representing the non-linear differential equations and the boundary conditions. The desired results come from the integraph as curves. In this paper, the problem of sudden load on the non-salient pole alternator is solved by the integraph for enough different conditions so that the performance of practically any machine of this type may easily be predicted from the compiled results. Knowing the moments of inertia of the machine and its load, the characteristics of the machine running as a synchronous motor and as an induction motor, the maximum amount of sudden load for which the machine will remain in synchronism may be determined for different values of initial load. Other curves give the maximum angle of the first swing of the rotor and the time interval for the rotor to change from Us initial position to this maximum angle. The simplest type of equation representing an ideal synchronous machine is solved in this paper. The integraph is capable of solving problems of a much more complicated nature than those presented. The more complicated problems pertaining to machines with unsymmetrical excitation and salient-pole rotors will probably be the subjects of future papers.

Design details are given for two submicrosecond flash sources for photography by reflected light, silhouette and schlieren techniques. The source for reflected-light photography uses a “guided” air spark operated at 18 kv with 0.05 μf to produce a 0.4-μsec flash with a peak light of 5 million candlepower. The flashtube, a special design, is described, together with its power supply and trigger circuit. The trigger circuit can be operated by a microphone, phototube, contactor or other electrical signal, and incorporates an adjustable time delay. A photograph taken with the unit is shown. — A small spark source capable of producing flashes of about 10 mμsec duration for silhouette and schlieren photography is described. Relative peak light output and flash duration are given as a function of pressure for air, nitrogen, oxygen, carbon dioxide, hydrogen and argon. Gap resistance is given as a function of gap length, for air.

Mechanical oscillations of synchronous motors following the application of abrupt shaft loads have not been hereto-fore easily calculated for cases of large angular swings, taking into account the damping currents in the rotor, except by tedious point-by-point methods. The chief difficulty has been due to the form of the basic differential equation upon which the solution of hunting problems depends. Within the lastfew years Dr. V. Bush and others at the Massachusetts Institute of Technology have devised the integraph which is capable of solving the equations of the synchronous motor. Into the integraph are put curves representing the non-linear differential equations and the boundary conditions. The desired results come from the integraph as curves. In this paper the problem of sudden load on the non-salient pole alternator is solved by the integraph for enough different conditions so that the performance of practically any machine of this type may be easily predicted from the compiled results. Knowing the moments of inertia of the machine and its load, the characteristics of the machine running as a synchronous motor and as an induction motor, the maximum amount of sudden load for which the machine will remain in synchronism may be determined for different values of initial load. Other curves give the maximum angle of the first swing of the rotor and the time interval for the rotor to change from its initial position to this maximum angle. The simplest type of equation representing an ideal synchronous machine is solved in this paper.

This paper describes the electrical characteristics of gas‐filled discharge tubes when flashed by a condenser discharge. The object of the experiments was to determine the effects of tube dimensions, pressure, voltage, and capacity upon the performance. The results are of an experimental nature and cover a limited range of values of tubes and circuit constants. An empirical constant called tube resistance is defined and evaluated. This constant is useful in predicting the performance of tubes in electrical circuits.

An automatic stroboscopic power angle recorder developed to study directly the transient performance of synchronous machines during load disturbances is described in this paper. A portion of the machine under observation is illuminated by stroboscopic light, and its oscillations are recorded directly by a moving-film camera. The operation of the device is made automatic by connecting a suitable relay in its circuit. A typical installation on a hydroelectric generator is described.

The Differential Analyzer at the Massachusetts Institute of Technology has made possible the rapid and accurate solution of the idealized non-linear differential equations of motion of synchronous motors which describe the pulling-into-step transients. The purpose of this paper is to present the results of these solutions in a useable form. These results give a rather complete analysis of the phenomena, and thus enable the determination of the performance of practically any machine. One of the factors which is considered in this paper is the time constant of the field circuit with the armature short-circuited. Curves are given showing the additional load which may be synchronized when the field switching is angularly controlled to the best angle. The influence of salient poles has been considered as well as non-uniformity of the amortisseur winding. The practical application of the study is indicated by a numerical example.

The growth of the luminous area of a high current discharge in an electronic xenon‐filled flashtube has been studied by means of a sequence of timed short‐exposure photographs taken with a magneto‐optic shutter. Electrical measurements show that the tube conductance is approximately proportional to the luminous area of the arc channel. The ionized gas has a volume conductivity of about 90 mho/cm averaged over the luminous path during the buildup for the conditions investigated.

A grid-controlled arc-discharge tube which requires neither power nor time for heating the cathode, but in which a discharge of several hundred amperes is controlled by an extremely small amount of power in the grid circuit, is described in this paper. The tube has characteristics especially useful In circuits requiring large peak current but low average current, some examples of which are given here and is applicable particularly as a light source in stroboscopes.

By means of the “differential analyzer,” the equations describing the pulling-into-step transients of a synchronous motor can be solved readily and accurately. The results of such solutions give a rather complete analysis of pulling-into-step phenomena, and thus make possible the determination of the performance of practically any synchronous motor. Practical application of the study is illustrated by a numerical example.

The boomer, an electromagnetically driven sound source for seismic profiling, consists of a triggered capacitor-bank that discharges through a flat coil or coils. Eddy currents are induced in aluminum plates that are held against the coil by heavy springs or rubber bumpers. The plates are violently repelled, and a cavitation volume is produced in the water which acts as a source of low-frequency sound. The boomer has been used as the transmitter of a continuous seismic profiling system at sea. A 1000-joule system has been used in shallow, fresh and salt water. Reflections from sediment layers at least a kilometer below the bottom of the Puerto Rico trench have been recorded by Hersey and his group aboard the Woods Hole Oceanographic Institution's R.V. Chain with a 13,000-joule (maximum) boomer.

After a brief summary of the theory of electronically produced pulses of light, energy storage systems, and energy converting devices, a review is made of commonly used triggering and controlling elements. A series of practical devices utilizing the previously described methods are discussed, showing typical stroboscopes, high-speed single-flash photographic lights, high-speed motion-picture lights, and flash sequence equipment.

A synchronous motor started as an induction motor must pass through an electro-mechanical transient after the field circuit is supplied with electrical excitation in order to change its action from that of an induction motor to that of a synchronous motor. The calculation of this problem has been difficult because the differential equation of motion is of a non-linear type of which no analytical solution has been made. The integraph at the Massachusetts Institute of Technology has given a new and direct method of solving equations of the type encountered in these pulling-into-step transients. In this paper are compiled the results of many integraph solutions which were made after combining the factors that influence the performance of such machines into ratios and relative factors so that the results will apply to all practical cases. From the solutions several generalizations are made which can be directly applied to determine whether or not any type of salient-pole synchronous motor will synchronize properly. These solutions take into account inertia, saliency, incompleteness of amortisseur windings, load, switching angle, and field current, and assume negligible armature resistance, negligible rotor leakage reactance, no saturation, constant load torque near synchronous speed, and negligible electrical transients. Oscillograph tests of a 160-hp. motor and a sample calculation are given.

By means of moving pictures taken stroboscopically it is possible to see the rotor of a synchronous machine just as though one were actually revolving at synchronous speed with the rotating field of the stator windings. Newly developed thyratron tubes provide sufficient light for taking the pictures.

A sub—microsecond light source was combined with recent improvements in color schlieren optics to photograph transient subjects such as bullets, air flow around propellers, and sub—microsecond electric arcs. The photographs have aesthetic merit as well as technical value. The paper summarizes color schlieren development and theory, and presents calculations for camera lens selection.

An open xenon gas spark between electrodes in a large bulb conveniently forms an intense small—volume source of light, but often shows spacial instability due to heated gas flow from previous discharges, or from electrical breakdown variations. The use of multiple inter—electrode starting wires solves the spacial problems for many applications. Information is presented on the light output, the efficiency, the spectral output, the flash duration, and the size of the emitting source as a function of time, energy, and gap length. Only lamps filled with xenon, and mostly with a small addition of hydrogen, are discussed. The experimental results were taken with 6 sizes of capacitors ranging from 0.005 to 5.6mfd. The properties of the capacitor, such as effective series resistance (ESR) and internal inductance, have been found to be very important when used with gap lamps since the arc resistance is very small.

Discharge lamps filled with xenon gas through which electrical capacitors are discharged have found many applications for producing pulsed energy in photography and energy discharges. The object of this paper is to review sane of the more important characteristics of flash lamps. The flash duration of specific flash lamps when operated from a given capacitor charged to same known voltage is dis-cussed below. The dimensions of the lamp are one of the most impor-tant factors since the response of the lamp to the circuit is greatly influenced. Experimentally measured flash duration as a function of capacitance and voltage is given in graphical form for one type of flash lamp. Rules (approximate) are given for converting the data into data for other flash lamps and circuits. Efficiency of a xenon lamp can be as high as 5 candela/watt for a lamp that is loaded so that the arc fills the inner diameter of the constraining tube. The life of the xenon lamp can be many, many flashes. In fact, this is one of the lamp's strong points. The spectral distribution of the light from a xenon lamp closely approximates daylight with a small shift to the blue if the applied voltage is high. Details of a specific flash lamp showing the nature of the spectral output is given. A list of some of the oractical uses of electronic flash lamps is given and discussed.

Equipment is described to take double‐exposure silhouette photographs of rapidly moving objects. Each exposure time is about ⅕ microsecond, and the time interval between flashes is adjustable. An eight‐inch square Ektalite Fresnel lens is used as a field lens to focus the light from the illuminating spark into the camera lens; it is especially useful for subjects where the lens is frequently damaged.Timing of the first spark is conveniently made for explosions by a photoelectric tube triggered by the light of the explosion. A double exposure photograph of a dynamite blasting cap is given as an example.

An unusual increase in light output results when a neon strobe tube is suddenly short-circuited during the transient. Experimental measurements have been made of the emitted light from the discharge when the capacitor is short-circuited at different times after the initiation of the discharge.

By means of the integraph the differential equation of motion for a synchronous motor during pulling-into-step transients is readily solved. An expression thus can be set up to predetermine the limiting conditions under which such a motor will synchronize.

Electronic flash tubes may be used to illuminate cloud chambers in order to freeze particles in motion and obtain sharp, clear photographs without blurring the image. Introductory theory of flash tubes is given, and the illumination of a 120 × 150 × 60 cm cloud by four 132-cm (54-in.) flash tubes is described. A total energy of 58,800 W-sec is used.

A shutter that closes quickly for capping drum cameras is described. A density of 3 is obtained in about 30 μsec by the sudden evaporation of a network grid of small lead wires. Energy for the evaporation and control of the operation instant are accomplished by a charged capacitor and a series hydrogen thryatron respectively.

Xenon-filled gaseous discharge tubes flashed from energy stored in electrical capacitors are very useful converters of electrical energy into light, for both visual and photographic purposes. The efficiency for a typical tube is about 40 lumens per watt for rated conditions. Measured values of light output and efficiency as functions of energy input are given for the FT-14 flashtube. A method of measuring the integrated light output is described, as well as typical circuits and electrical conditions. The xenon electrical flashtube is particularly useful for color photography since its spectral distribution is similar to that of daylight and since the spectral distribution and efficiency are not appreciably affected by voltage or life. The quantity of light is predictable in terms of energy input from the storage capacitor. The flashtube is proposed as a standard lamp, especially for flash comparison. An approximate relationship useful for calculating the photographic exposure factor or guide factor (distance × aperture) is given in terms of energy in the condenser, the type of reflector used, and film speed.