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An axisymmetric static system of charged point particles is investigated in the framework of general relativity. The particles are located on the axis of symmetry; the Einstein-Maxwell equations are solved in second approximation. Equilibrium is maintained by means of 'struts' connecting neighbouring particles. Assumptions are made which make the solution unique. The mass of the whole system and the gravitational mass of individual particles are defined.

(1964). Plancton production in natural lakes and hydro-electric water-basins in the alpine region of the Austrian Alps. SIL Proceedings, 1922-2010: Vol. 15, No. 1, pp. 375-383.

(1966). Salmonideneinsatze in Hochgebirgsseen und -tumpel der Ostalpen. SIL Proceedings, 1922-2010: Vol. 16, No. 2, pp. 1182-1191.

Exploring some aspects of the linearized theory of general relativity, the authors discover new possibilities for experimental tests. A new design for a gravitational wave detector is suggested. The starting point of these investigations is a part of newtonian mechanics whose study helps to understand some of the puzzling features of general relativity. The approximations made are as numerous and as severe as in most similar investigations.

In Lake Erken a conspicuous peak in the standing crop and production rate of phytoplankton occurs regularly in the ice-out period. The environmental changes associated with this outburst were studied in spring 1960. The availability of radiant energy is the key factor for the instigation of the phytoplankton “explosion,” but some lag in the response of the algae to the increase of radiation is caused by the necessity for light adaptation even when the intensities of photosynthetically usable energy are still very low. The growth rates of phytoplankton as measured by cell volume and by chlorophyll content are similar. The specific growth coefficient (in log. units per day) of the dominant species Stephanodiscus hantzschii pusillus is considerably higher (0.09) than that of the entire assemblage of algae (0.065). Two weeks after ice-out the biomass, production rate, and relative photosynthetic efficiency (carbon uptake per unit biomass and unit radiation) of phytoplankton decrease sharply. Depletion of inorganic nutrients, especially nitrogen, is apparently the main cause for the end of the spring bloom. Grazing affects only a small fraction of the phytoplankton; exploitation of diatoms by the zooplankton is negligible during the spring outburst.

Clear lakes above the timber line are inhabited throughout the year by a considerable diversity of nannoplanktic algae. Only a few species are of quantitative importance, but these show a biomass (...

A method of obtaining the explicit form of the gravitational field of multipoles in the second approximation is furnished here. The generalization of this method to any superposition of multipoles is straight‐forward. We obtain as an example the second‐order metric for the superposition of a monopole and a quadrupole.