270 proceedings: philosophical society 



and may not exist as a definite 'surface. It is only in case of a uniform 

 distribution of the compensation that there could be a definite surface 

 limiting the distribution of compensation. It was stated that the uni- 

 form distribution was adopted in the computations to facilitate the 

 progress of the work. Any one of several distributions, other than 

 that of uniform distribution, would give practically the same results. 

 This is somewhat of a surmise, as no elaborate tests were made. 



The application of the theory of isostasy to the gravity data made 

 it possible to derive a formula for giving gravity at sea level at any 

 latitude. 348 stations in the United States and other countries were 

 used in the derivation of a number of formulas on various assumptions. 

 One of them, the best formula probably in the world, is 7 = 978.039 

 (1 4- 0.005294 sin 2 </> - 0.000007 sin 2 20) in which 7 is the value of 

 gravity sought and <£ is the latitude of the station. 



Discussion. Mr. G. K. Burgess asked about the possibility of 

 using the Eotvos torsion balance for determining variations in the 

 intensity of gravity, and about the complete absence of magnetic 

 materials in the pendulum used. 



Mr. Bauer questioned whether the depth of compensation did not 

 vary with the topography, and Mr. Bowie called attention to the 

 fact that the data from stations located on plains did not permit of a 

 solution for the depth. 



Mr. W. F. G. Swann then gave a paper on The origin of the earth's 

 electric charge. Measurements of the variation of the penetrating 

 radiation with altitude point to the upper atmosphere as the origin 

 of a part of this radiation. The whole of the penetrating radiation 

 is probably of the 7 ray type, but the part which reaches the Earth's 

 surface from the outer atmosphere is naturally the most penetrating 

 part. Indeed, it is so penetrating that it passes through a thickness 

 of air which would be equivalent, in absorptive action, to a column of 

 mercury 76 cm. high, if absorption coefficients were simply propor- 

 tional to density and were independent of material. The 7 ray radia- 

 tion from the outer layers of the atmosphere will consequently be very 

 "hard," and, in accordance with the known results of laboratory 

 experiments, we must conclude that the negative corpuscles which it 

 emits from the air molecules are emitted almost entirely in the direc- 

 tion of the radiation, and further, that they can have a range in air 

 at least equal to that of the swiftest /3 rays from radium products. 

 The emission of corpuscles by these 7 rays will consequently result, 

 at each point of the atmosphere, in a downward current of nega- 

 tive electricity, which we shall call the corpuscular current. This 

 corpuscular current will charge the Earth until the return con- 

 duction current balances the corpuscular current at each point of 

 the atmosphere. 



Taking, for the purpose of this abstract, a simplified case where 

 the penetrating radiation considered is all directed vertically down- 

 wards, if q is the number of corpuscles liberated per cubic centimeter 

 per second by the penetrating radiation, and h is the average distance 



