C. GENERAL PHYSICS. 157 



of the roof, and especially to the rain-water pipes, in order 

 that greater facility may be offered to the electric fluid in 

 its passage to the earth. American Engineer ', I., 122. 



ATMOSPHERIC ELECTRICITY IN SPITZBERGEN". 



In reference to the observations of atmospheric electricity 

 in high northern latitudes, in which, as yet, our instruments 

 have generally given negative results, Wijkander states 

 that the late Swedish polar expedition gave special atten- 

 tion to this subject, and that all their observations show 

 that at relatively high temperatures the air conducts elec- 

 tricity very well, to which fact is ascribed the absence of 

 lightning and the presence of the Northern Lights. It has 

 been said that these latter phenomena depend upon the 

 great moisture of the air in these regions ; but it seems clear 

 that the polar light is conditioned by other circumstances, 

 since the same temperature and the same degree of humidity 

 do not bring forth these results in other latitudes. 19 C\ 

 VII, 422. 



VELOCITY OF THE TRANSMISSION OF ELECTRIC FORCE. 



The question as to whether electric and magnetic forces 

 require sensible time to exert their influence, at a distance, 

 has been made the subject of numerous investigations, one of 

 the most interesting of which is that of Herwicr, who has 

 endeavored to conduct experiments upon as large a scale 

 as possible. The preliminary results to which he was led 

 have, he thinks, justified him in formulating the conclusion 

 that if the terrestrial magnetic influence has any definite 

 velocity of transmission whatever, it must be at least at the 

 rate of half a million of miles per second ; and that the in- 

 fluence of the earth's magnetism at any point of the earth's 

 surface attains its full degree within -g-^-jj of a second. 19 

 (7, VIII, 30. 



edlltnd's theory of the nature of electricity. 



In a report on the theory lately advanced by Professor Ed- 

 lund as to the nature of electricity, Dr. Emsmann states that 

 apparently Edlnnd has, in this matter, taken such a step for- 

 ward as was made when previous investigators were able, 

 by means of one aether, to explain both optical and thermal 



