208 M. J. M. Gaugain on an Electrical Apparatus 



ourselves to the description of an apparatus wherewith M. Gau- 

 gain has obtained results much more satisfactory than with any 

 other, and which is founded upon an observed fact which he 

 believes to be new. 



Let an ordinary electric egg"^ be taken, and let the upper knob 

 be coated with an insulating substance, the stem which supports 

 the knob being similarly coated, leaving naked only an exces- 

 sively small portion of the surface of the knob : let the egg thus 

 prepared be placed in the circuit of a RuhmkorfF's coil : intro- 

 ducing a galvanometer also into the same circuit, the following 

 facts may be observed : — When the induced cuiTcnts which cor- 

 respond to the interruption of the inducing current (the only 

 ones which traverse the vacuum of the egg) pass from the covered 

 to the naked knob, the intensity of the current indicated by the 

 galvanometer goes on increasing as the air within the egg is 

 more and more rarefied ; but this is not the case when the 

 induced currents pass through the egg from the naked to the 

 covered knob. In this case the intensity of the current goes on, 

 at first advancing as the pressure is diminished; but when this 

 pressure descends below a certain limit, the deviation of the gal- 

 vanometer diminishes ; for a certain pressure it becomes zero, 

 and tiually changes the sign when the vacuum is as perfect as 

 can be obtained with a good air-pump. M. Gaugain limited 

 himself to the establishment of this fact without seeking an in- 

 terpretation; this sufficed for the object he had in view, namely, to 

 show that the cui-rents traversed the egg freely when they passed 

 from the covered knob to the naked one, and could not pass in 

 the opposite direction, when the vacuum was suitably made. 

 From this it follows that the electric egg, disposed as indicated, 

 can act, in relation to certain currents, the part of a valve with 

 respect to liquids. 



M. Gaugain believes that this electric valve may be useful in 

 a certain number of researches, and he has already applied it to 

 the solution of a question raised by M. du Monccl in one of the 

 last comumnications made by the latter to the Academy of 

 Sciences. When a condenser is interposed in the induced cir- 

 cuit of the apparatus of RuhmkorfF, the motion of the electricity 

 continues, as is proved by the physiological and luminous effects 

 produced on the circuit : but two different hypotheses may be 

 made as to the nature of this movement. It might be supposed 

 that the electricity propagates itself across the insulating film of 

 the condenser in the same manner as it passes through a con- 

 ducting body, and in this case its direction would be constantly 

 the same; it might, on the contrary, be supposed that the two 



* A glass receiver shaded like an cg^. 



