14 Prof. E. Edlund on the Path of Electrical Induction- and 



but variable, and there is constantly nutation of the axis as well as 

 precession, the action above described will be somewhat modified; 

 and the elasticity of the solid material may be expected to have 

 some influence on the result. This influence, however, will be 

 minute, as the part of the disturbing force which is variable and 

 produces nutation is very much smaller, even at its maximum, 

 than the precessional force. The consideration of this matter, 

 however, has no bearing upon the validity or not of Mr. Hop- 

 kins's method, but simply upon the numerical value of his final 

 result, not upon the question of the fluidity or solidity of the 

 earth's mass. 



6. It will appear then, I think, to your readers that the stric- 

 tures of M. Delaunay upon this method, which the genius of 

 Mr. Hopkins devised, betray an oversight of the real point upon 

 which the success of his method depends, and that this method 

 stands unimpaired. 



I am, 



Yours faithfully, 



Murree, Himalayas, John H. Pratt. 



May 17, 1870. 



III. On the Path of Electrical Induction- and Disjunction- Cur- 

 rents through Gases of various Densities, and between Poles of 

 different shapes. By E. Edlund*. 



1. Ij^OR shortness' sake I will, in what follows, apply the term 

 -*- electrical disjunction- currents to those currents which 

 have their origin in the voltaic arc or in the electrical spark, and 

 in the same connexion will speak of the force to which they owe 

 their origin as the electromotive force of disjunction. This name 

 indicates that to produce these currents the conduction must be 

 broken, in order that a luminous arc or spark may be formed, 

 as well as that the poles between which the luminous pheno- 

 menon is formed are mechanically disintegrated f. 



In the investigation I used the same electrophorus machine 

 as that employed in my earlier experiments on these currents. 

 An insulated copper wire, ac, is directly connected with the 

 knob a (see the figure) on one absorber, while the insulated 



* Translated from Poggendorff's Annalen for March 1870, having been 

 read before the Swedish Royal Academy of Sciences at Stockholm, Octo- 

 ber 13, 1869. 



t In the sequel I shall use the term "disintegration of the poles" to 

 denote the whole mechanical work which the current performs in the spark, 

 although this work is consumed not only in disintegrating the poles, but 

 also in imparting velocity to the detached particles, in putting masses of 

 air in motion, &c. 



