M. E. Edlund 071 the Nature of Electricity. 179 



But evideDtly_, that this may be so, kh (or the velocity of the 

 sether in the inducing circuit multiplied by the constant k) must 

 have a very small numerical value. With regard to the velocity 

 h, experiments have not, as we have seen, led to an accordant 

 result. Fizeau and Gounelle found that the velocity rose in a 

 copper wire to 180 millions, and in an iron wire to 100 millions 

 of metres in a second. Walker estimated the velocity in an iron 

 wire at 30 millions only, and Gould at less than 26 millions in a 

 wire of the same metal. The experiments made on a copper 

 telegraph- v/ire between Greenwich and Edinburgh gave a little 

 more than 12 millions of metres per second; and only 4^ mil- 

 lions was obtained on the telegraphic line which connects Green- 

 wich with Brussels. The small velocity on this last line^ which 

 was also of copper_, may be partly explained by a great length of 

 it being submarine. It must further be remarked that, from 

 the manner in which the experiments were made, the numbers 

 cited express the velocity with which the first quantity of sether 

 propagates itself, at the commencement of the current, from one 

 pole to the other. The ratio of this velocity to the velocity when 

 the current continues with constant intensity has not yet been 

 determined by experiment. Of the velocity of the sether in a 

 wire under the conditions of an ordinary induction experiment 

 we know almost nothing more than that it is very great. 



The constant k enters as a factor in Ampere^s formula for 

 electrodynamic phenomena ; and its value has been determined 

 experimentally by W. Weber and Kohlrausch*. Taking as unit 

 that above given for the measure of the sether, we have from the 

 experiments of those two physicists, in round numbers : — 



— ~ = 440 millions of metres per second. 

 vk 



Admitting for the velocity h a value within the limits of the 

 results of the above-mentioned experiments^ a very small value 

 is obtained for the product kh. Now the constant a of the first 

 term of formula (14) should also have only a trifling numerical 

 value. It follows evidently, from the considerations set forth in 

 these pages, that ah must be less than 1. If^ then, we admit for 

 example the value of h found by Walker, or 30 millions of metres 



per second, the value of « will be < jr^ — 'rrr-. . On this sup- 



^ 30 milhons ^ 



position, the product -- will be =^ titi-f^ — rr } and conse- 



^ ^ 2 12,900 millions 



kh 

 quently a may be 400 times — . This shows that, far from con« 



* Po2;g. A?in, vol. xcix. p. 10. 



N2 



