METEOROLOGY AND ALLIED SUBJECTS. 



321 



rents, and Lemstrom deduces for the whole magnetic moment (M), iu 

 the direction of the axis of the earth, 



M = f -2 [r - hy 11 J 



where ii is the magnetic moment of a unit's mass, J is the inductive 

 action of a unit of current, r radius of the earth, h the distance of the 

 magnetic stratum from the limits of the atmosphere. This explanation 

 agrees entirely with the formula of Gauss, and the discussion of it ex- 

 plains equally the average position of the magnetic action and its secu- 

 lar annual and daily variations. It is also in conformity with the acci- 

 dental phenomena of magnetic storms and auroras. [Z. 0. G. M., XVI, 

 1881, p. 108.) 



Denza has determined the law of diurnal variations of atmospheric 

 electricity at Moncalieri, and by means of hourly observations on 215 

 days, distributed through the years 1871 and 1878. The following tables 

 give his resulting averages (a) for the 215 days or a whole year, and {b) 

 for the days on which no irregular disturbances took place. The anal- 

 ogy between this diurnal i>eriod and that of atmospheric pressure is 

 similar to that pointed out by Neumayer. {Z. 0. G. ill., XVI, p. 88.) 



Warren De La Rue and H. W. Miiller have arrived at some interesting 

 conclusions in reference to the altitude of the aurora. They find experi- 

 mentally that the least pressure under which the aurora has been seen 

 in their experiments, is 0.38°^"", corresponding to an elevation of 37 or 38 

 miles. The following table collects the results of their observations: 



S. MiA J£)9 21 



