proceedings: philosophical society 127 



of rotations must have occurred during the intervals, it was possible to 

 determine a period of rotation appljdng, perhaps, to the Sun as a whole, 

 the preliminary synodic period thus found was nearly 33 days; (4) the 

 solar magnetic field is as complex as that of the Earth and the distorting 

 systems which are superposed upon a primary, simple magnetic field 

 follow laws very similar to those disclosed in the study of the Earth's 

 field. The paper was illustrated by lantern slides. Mr. Burgess dis- 

 cussed the question of magnetic state under high temperature and pres- 

 sure; Messrs. Swann and White also discussed the paper. 



]\Ir. W. F. G. Swann then gave an illustrated paper on The atmospheric 

 potential gradient and a theory as to its connection with other phenomena 

 in atmospheric electricity. The application of the ordinary theory of 

 conduction of electricity in gases to the atmosphere shows the mere 

 existence of an atmospheric potential gradient of the kind found carries 

 with it the following requirements: (1) the ratio of number of positive 

 ions per cc. at the Earth's surface to the number of negative ions shall 

 be greater than unity; (2) the above ratio shall increase with potential 

 gradient ; (3) neither the number of positive ions per cc. nor the number 

 of negative ions per cc. at the Earth's surface are the same thing as the 

 numljers which would, if the atmospheric field were absent, exist in ordei 

 to result in a balance between recoml)ination and formation; (4) the 

 atmospheric potential gradient, in a homogeneous atmosphere, shall 

 decrease with the height in the neighborhood of the Earth's surface ; (5) 

 there should be an apparent, but not necessarily true, increase of the 

 rate of ionization with the height. The problem of the conduction of 

 electricity between parallel plates immersed in a gas shows that the usual 

 solution is quite inapplicable when the rate of formation of ions is small 

 and the plates are a finite distance apart; accordingh% a new calculation 

 is given. The paper was discussed by Messrs. Bauer, Marvin, Sosman, 

 and Humphreys, particularly in reference to the present rather primitive 

 state of the science of atmospheric electricity. 



The 731st meeting was held on December 4, 1913, at the Cosmos Club, 

 being a joint meeting with the Washington Academy of Sciences. 

 President Tittmann, of the Academy, in the chair; about 150 persons 

 present. 



Professor Jean Perrin, of the University of Paris, spoke on Brownian^ 

 movement and molecidar reality. The paper gave a brief review of the 

 history of the subject and of the author's work, and was illustrated by 

 cinematographic photographs showing three experiments to illustrate 

 the BroA\'nian movement. 



The chair called for a rising vote of thanks to the speaker for his very 

 interesting and instructive address. 



The 732d meeting, 43d annual meeting, was held on December 20, 

 1913, at the Cosmos Club, President Abbot in the chair; 28 persons 

 present. The minutes of the 42d annual meeting were read. The 

 report of the Secretaries was read by IMr. Humphreys, showing an active 



