Prof. E. Wartmann's Sixth Memoir on Induction. 275 



cultivation of science than mine happens to be. I shall merely 

 add, in conclusion, that in order not to encroach unreasonably 

 on these pages, I have transferred two articles connected with 

 the present paper to the Mechanics' Magazine ; they probably 

 appear in the numbers for Sept. 16 and Sept. 23; in the latter 

 of which I have given a short and easy investigation of the 

 theorem of Leibnitz for the advanced differential coefficient of 

 the product of two functions. 

 Belfast, Aug. 26, 1848. 



XLI. Sixth Memoir on Induction. By M. Elie Wartmann, 

 Professor of Natural Philosophy in the Academy of Geneva *. 



[Continued from p. 94.] 



§ XVIII. Does Induction affect the acoustic properties of 



Elastic Bodies ? 



165. V PUBLISHED two years agof some experimental 

 A researches on the causes of the sounds produced by 

 discontinuous electric currents in metallic wires. This phe- 

 nomenon may be viewed under other aspects, and it may be 

 asked whether a permanent electric induction determines in 

 the molecules of sonorous bodies a change of elasticity which 

 is rendered evident by appreciable modifications in their 

 acoustic properties. The following experiments have been 

 undertaken with a view to solve this question. 



166. A disc was selected of m *198 diameter, and m, 0018 

 thickness, forming part of a Marloye's set of plates. This 

 disc was made with the greatest possible care : its texture is 

 remarkably homogeneous, and the acoustic figures, formed of 

 diameters or concentric circumferences, are produced upon 

 it with extreme precision. Its lower surface was covered with 

 a thick layer of gum-lac varnish ; and after strongly electrizing 

 this sort of electrophore, the charge was sustained by means 

 of a good machine. It was however impossible to discover 

 the least difference in its sonorous state, whether it was elec- 

 trified or not. 



167. A glass disc, m, 135 in diameter and m, 002 in thick- 

 ness, was furnished on both its surfaces with a circular arma- 

 ture of tinfoil, m, 117 in diameter. This flat condenser was 



* Communicated by the Author. 



\ Archives des Sciences Physiques et Naturelles, vol. i. p. 419. In the 

 sitting of the 8th of May last, M. Wertheim presented to the Academy of 

 Sciences, of Paris some further researches on this subject, the conclusions 

 of which are identical with those which I then enunciated with respect to 

 the effects of discontinuous currents. See the Institut of the 10th of 

 May, No. 749. 



