80 Intelligence and Miscellaneous Articles. 



(3) The magneto-electrical current is not always proportional to 

 the increase or diminution of the magnetic moment of the magnet ; 

 it depends not only on this quantity, but also on the rapidity with 

 which the magnetic modification is effected. 



(4) This modification is not always proportional to the intensity 

 of the current which produces it, even taking into account the mag- 

 netic capacity of the steel or iron bar in which it is produced. — Pog- 

 gendorff's Annalen, vol. cxxxiii. p. 233 ; Bibliotheque Universelle f 

 May 15, 1868. 



APPLICATION OF THE VIBRATIONS OF COMPOUND BARS TO DE- 

 TERMINING THE VELOCITY OF SOUND. BY J. STEFAN. 



The method introduced by Chladni of determining, from the lon- 

 gitudinal tones of bars, the velocity of sound in these bars, is not 

 applicable to those bodies which have not the form of long bars, 

 or cannot by friction be made to sound. For such cases the new 

 process serves. 



The body to be investigated is constructed in the shape of a small 

 bar, and fastened on a longer bar of wood or glass, which can itself 

 be readily made to sound. This compound bar may now be made 

 to sound by friction, and thus the number of vibrations of the fun- 

 damental note or of a higher tone be determined. Knowing, then, 

 the velocity for the longer bar, that for the smaller one may be de- 

 duced by a formula which, it is true, is somewhat complicated. 



By this method the following observations, among others, were 

 made: — 



The velocity of sound in wax =730 metres, and is thus a little 

 more than twice as great as in air. This number refers to the tem- 

 perature 20° C. ; with increase in temperature the velocity of sound 

 decreases so much that a decrease of 40 metres corresponds to an 

 increase of 1°, and at 30° the velocity of sound in wax and in air are 

 the same. 



The velocity of sound in grease is at 20° C. only half as great as 

 in wax, and with an increase in temperature diminishes somewhat 

 more quickly than in wax. 



For the velocity of sound in caoutchouc, values were found which 

 fall between 30 and 60 metres; the softer the caoutchouc, the 

 less the velocity of sound. 



These results recall those of Helmholtz on the velocity of the pro- 

 pagation of nervous excitation, which are within the same limits as the 

 velocity of sound in soft caoutchouc, and suggest the thought that 

 the velocity of nervous excitation coincides with that of sound, and 

 that nervous excitation can be propagated in longitudinal waves. 

 — Berichte der Kaiserlichen Akademie in Wien, April 30, 1868. 



