On an Electrical Apparatus which acts the part of a Valve. 207 



very much. This is a very clear proof of the reaction of the 

 induction current upon the extra current. 



It may also be mentioned, that when the hammer vibrates in 

 a vacuum, and when the parts which beat against one another 

 are of platinum, the latter are very much attacked. The platinum 

 part of the tongue, the brass part above it, the screw of the pin, 

 and the mountings are all greatly blackened. This black powder 

 evidently consists of tinely pulverized platinum, which, when the 

 hammer is in activity, can be seen scattered in small sparks from 

 the point of the pin around in all directions. 



Owing to this strong action upon the hammer, the above- 

 described method of increasing the intensity of the induction 

 current is scarcely to be recommended in practice ; neverthelesSj 

 theoretically considered, it is certainly not less interesting than 

 the three methods already known ; by the condenser, by allowing 

 the hammer to vibrate under water, and by interrupting the 

 current between the poles of a magnet, which last method was 

 investigated by Rijke. 



The action upon the hammer, however, can be considerably 

 diminished by substituting a silver in place of the platinum pin. 

 The sparks then assume a green colour, which is particularly 

 visible in daylight. 



XXIV. On an Electrical Apparatus which acts the part of a Valve. 

 By M. J. M. Gaugain. 



MGAUGAIN has recently communicated to the Academy 

 • of Sciences in Paris, a Note on an Electrical Apparatus 

 which acts the part of a valve*. The subject has been further 

 examined by M. liiess, an account of whose researches we intend 

 to appear in a subsequent Number of the Philosophical IMaga- 

 zine. M. Gaugain remarks, that there is a numerous class of 

 electric currents which are considered as being formed by the 

 succession of several other currents, with directions alternately 

 opposed to each other. To fix definitely the true constitution of 

 these composite currents, it was thought useful to isolate the 

 partial currents which form them ; and to attain this end, he 

 proposed to devise an apparatus which should possess (like a 

 valve) the power of arresting currents having a certain direction, 

 while it should leave to those flowing in an opposite direction 

 perfect freedom of passage. Several combinations which fulfil 

 this condition more or less completely were successively studied; 

 they were based on the known properties of points, and on the 

 experiment of the pierced card. We will here, however, limit 



* Comptes Rmdus, vol. xl. No. 12. 



