M. A. Bravais on Right and Left-handed Oscillations. 197 



On reflecting on the results of the experiments I have now 

 submitted to your readers in connexion with this subject, the 

 view I take of the supposed law of production of cold by elec- 

 tricity is_, that it arises in the action of a battery where the heat 

 developed by resistance to conduction is at its minimum; so 

 that the caloric wanted for the chemical actions going on is exhibited 

 in the joint through the power of a galvanic current of bringing to 

 a state of equilibrium the temperatures in its circuit. In Smee's 

 battery zinc is passing from a solid to a fluid state, and one of 

 the elements of water is assuming a gaseous form. 



XXXI. On Systems in which Right and Left-handed Oscillations 

 are not executed alike. By M. A. Bravais*. 



THE remarkable rotation of the plane of oscillation of a pen- 

 dulum observed by M. Foucault presents a similitude 

 with the rotation of the plane of polarization of a homogeneous 

 luminous ray, passing along the axis of a crystal of quartz, which 

 appears to me to be worthy of the attention of physicists. The 

 rotative phsenomenon of quartz has hitherto had no analogue 

 among determinate natural motions ; but in the beautiful expe- 

 riment of Foucault such an analogue has been discovered. 



The only difference is, that in quartz, according to the theory 

 of undulation, every molecule of sether situate in the axis of the 

 ray imparts to the next following molecule its own motion in 

 the direction of propagation, and returns to a state of rest, until 

 a fresh shock sets it again in motion ; while in the case of a 

 pendulum the oscillating mass moves isolated and as a whole, 

 without imparting its motion to neighbouring particles. 



I propose examining the case where the oscillation is circular. 

 Fresnel has shown that a circular vibration may be regarded as 

 the equivalent of two plane vibrations of the same amplitude, 

 but whose phases are 90° different. Starting from this, he has 

 proved that if the planes of the two component vibrations rotate 

 with a certain common velocity, the propagation of the corre- 

 sponding circular motion will be altered, plus or minus, according 

 as the rotation is right- or left-handed. From this he concluded 

 that these two kinds of vibration cannot propagate themselves 

 with the same velocity, — a result which he confirmed by direct 

 experiment. 



The same conclusion being applied to the lineal and very 

 small vibrations of a pendulum, we observe that when the motion 

 is circular, as in the case of the conical pendulum, the duration 

 of a vibration cannot be the same when the motion is in the 



* Comptes Rendiis, vol. xxxii. p. 166, 



