On Atmospheric Electricity and the Aurora borealis. 423 



This almost total absence of the elongated form arises from 

 Clausius' fundamental hypothesis, that the motions of the 

 molecules emitted by a stratum may be represented by radii 

 drawn to a sphere from an excentric point ; whereas it appears 

 from the discussion in the earlier part of the present memoir 

 that the encounters that take place within each of the two 

 streams into which the gas may be divided, give to the surface 

 to which the radii are to be drawn an elongated form. This 

 omission from Clausius' hypothesis does not sensibly affect 

 the spherical harmonics of the first order, and accordingly his 

 hypothesis is adequate as regards the flow of heat, which de- 

 pends exclusively on one of these ; but it renders the hypo- 

 thesis an insufficient one as regards polarization stress, or any 

 other phenomenon which depends on spherical harmonics of 

 the second order. 



LIY. Researches on Unipolar Induction, Atmospheric Elec- 

 tricity, and the Aurora Borealis. By E. Edlukd, Professor 

 of Physics at the Swedish Royal Academy of Sciences. 



[Concluded from p. 371.] 



AS the magnetic properties of the earth cannot be fully ac- 

 counted for by assuming the existence of a magnet in its 

 interior, it is quite evident that the preceding consideration can 

 only indicate the general course of the phenomena in question. 

 We will now rapidly examine whether the results of that con- 

 sideration are conformable to those given by observation. 



Atmospheric electricity has long been the object of repeated 

 investigations. These have been so numerous that to give an 



two square centimetres at the distance of a fourth-metre asunder and kept 

 at temperatures that differ by 10° 0. To turn this into kinetic measure 

 we must multiply by 41 GOO X 1000000 ; so that Gr would amount to about 

 1144000 in G.C.S. kinetic measure (i. e. in hyper-fifth-grammetres per 

 second). Again, we may take as rough approximations, 



1 



Po ~800' 

 T =T. 



p =p 1 =1000000. 



Introducing these values into equation (18), we find approximately, 



«e=0001 



of a hyper-milligram per square centimetre — an amount which, as it 

 ought to be, is vastly smaller than that indicated by experiment. 



