LARGE DOUBLE-CURRENT VOLTA-FARADIC APPARATUS. 263 



sound, ^ I used as a means of chronoscopy the trace left upon a plate 

 of iodized silver by an induction spark proceeding from one of 

 Ruhmkorfif's coils. The interruption of the inducing current was 

 produced mechanically ; but under certain circumstances, instead of 

 a single trace, I observed as many as fifteen traces, corresponding 

 to as many small sparks into which a single discharge had been 

 subdivided. I could distinguish one from another because the 

 plate was in rapid rotation, and the small sparks, being suc- 

 cessive, left their marks on different points ; but the fifteen 

 traces were separated only by the length of a millimetre, which 

 corresponded to a time notably less than the fifty-thousandth 

 part of a second. The sparks were unquestionably successive, 

 because they were all aligned in the direction of the movement 

 of the plate. 



"There is no room to believe but that each of these partial 

 sjDarks corresponded to a vibration produced in the interrupter, 

 for it is manifest that, according to the law of the movement 

 of interruption, the induced discharge, which most commonly 

 manifests itself in a single spark, may divide itself into a certain 

 number of partial discharges. These phenomena were observed 

 with a Ruhmkorff's coil, of moderate dimensions." ^ 



In the tremblers, the point of the screw is platinized, and comes 

 into contact with a plate also platinized, and soldered to the piece 

 which beats against it, so that perfect contact is as little as possible 

 interfered with by oxydation. In time, however, the platinum, 

 burnt by the electric spark, does undergo oxydation ; and the 

 oxyde deposited on its surfaces checks the passage of the current, 

 and weakens the power of the apparatus ; the play of the trembler 

 being 'either hindered or altogether stopped. I have remedied this 

 fault by increasing the thickness of the piece of platinum, and by 

 making it movable, so that when, after working some hours a day 

 for many months, it becomes oxydized, it may be shifted a little 

 to the left or right, and a new place brought into use. It is also 

 necessary to clean the point of the screw from time to time, by 

 rubbing it with a piece of cloth or linen, so as to remove the oxyde. 

 Finally, in order to diminish the oxydation of the platinum, I have 

 increased the contact surface, giving to it from two to three milli- 

 metres of transverse diameter. 



2 LeEoiix, Be'termi nation expe'rimentale 

 de la Vitesse de propagation d'un ^branle- 

 ment sonore dans un tuyau cylindrique 

 {AnnaU de Cliimie et de Physique, # serie, 

 tome xii. p. 345). 



^ F. P. Le Eoux, De I'induction et des 

 appareils electro-me'dicaux, p. 46. Tliese 

 presentee a I'Ecole Superieure de pharmacie 

 pour V aggregation des Sciences physique. 



