C. GENERAL PHYSICS. 173 



teristics of the flight of birds. For insects, as well as for 

 iishes, the modes of propulsion involve quite difierent prin- 

 ciples of mechanics. L Aeronaut^ January^ 1873. 



THE SILEXT DISSIPATIOIST OF ELECTRICITY. 



This subject, on which such diverse opinions are maintain- 

 ed in the various treatises on electricity, has been investigated 

 v/ ith great care by Boboulieff, of St. Petersburg. He states 

 as the result of most critical study of the theory of gases, 

 and after prolonged and delicate experiments on dry air and 

 on dry hydrogen gas, that (1) the dissipation of electricity 

 in the air, and in all gases, diminishes with the diminution of 

 the pressure, and that (2) the dissipation in hydrogen is 

 smaller than in the air at the same pressure. These conclu- 

 sions seem to confirm the dynamical theory of gases as pro- 

 pounded by Maxwell and others, and to agree with the re- 

 sults of a portion of the earlier experiments, especially with 

 Coulomb and Warburg. Jour. Rubs. Chem. and JPhys. Soc.y 

 1873. 



EDLIJNd's theory of ELECTRICITY. 



The electrical theory of Professor Edlund, of Stockholm, 

 which was first published in 1870 (in Swedish), has now been 

 translated into French, and seems destined to have a wide 

 circulation. The ease with which it can be submitted to 

 mathematical treatment, and the success that has attended 

 attempts to explain by it some of the more complicated elec- 

 trical phenomena, even in all their details, gives it a very 

 great value, as, in itself, a convenient means of research ; 

 probably, however, we still have to look beyond the theories 

 of Franklin, Thomson, Maxwell, Edlund, etc., for the true 

 physical nature of that which we call electricity. According 

 to Edlund, no hypothesis is necessary other than that already 

 so well established i.e., the existence of an extremely elastic 

 and subtle ether a gas difi*used throughout all space. The 

 properties of this ether are those that have already explained 

 the nature of light and heat e.g., it permeates all transparent 

 bodies as well as the most perfect vacuum, and may exist in 

 all opaque bodies, though in the latter brought under peculiar 

 influences, such that it can no longer transmit light, though 

 it may both heat and electricity. The atoms of ether repel 



