Intelligence and Miscellaneous Articles. 315 



order could not be distinguished from the current which produced it, 

 or from that which it had produced ; but there was a difference 

 when a series of observations were made by gradually altering the 

 pressure in the valve. The experiments gave the following rule : — 

 If the secondary current in the same direction as the principal one 

 first starts from the disc, the deflections slowly diminish and retain 

 the same direction as currents of even order, if the pressure in the 

 valve is increased ; a rapid decrease and change in direction when 

 the pressure is increased are characteristic of currents of uneven 

 order. If the secondary current first starts from the point of the 

 valve, the rule prevails, changing both kinds of currents. 



The designation " electrical valve" might lead to the assumption 

 that the instrument only transmits those currents, of whatever den- 

 sity and whatever origin, which follow a given direction from the 

 disc to the point of the valve. The author adverts to the marked 

 opposition in which all his experiments stand to the first experiments 

 made with the valve. M. Gaugain has shown that the opening 

 currents of the magneto-induction apparatus only deflect the mag- 

 netic needle when they proceed from the point to the disc of the 

 valve. The valve might perhaps be a means of investigating the 

 current of the induction apparatus, the most complicated of all elec- 

 trical currents. 



The magnetic deflection by the extra current in the wire itself which 

 discharges the battery furnishes a surprising experiment, which M. 

 Feddersen has described, but, in explaining it, has entirely over- 

 looked the extra current. Two coils of wire are used as galvanometers, 

 between which the magnetic needle oscillates. The coils are joined 

 with each other at opposite ends, and from both wires connexions are 

 led to the coatings of the batten'. Hence the discharge divides into the 

 two branches formed by the battery, and traverses them in opposite 

 directions : the mirror can only show the difference of the deflections 

 which the coils would individually have imparted. By moving one 

 coil, the mirror is made motionless when the discharge passes. If 

 now a valve is brought into each coil, and the valves have opposite 

 directions as regards the discharge, a deflection of the mirror is ob- 

 tained, and of any magnitude by modifying the charge of the bat- 

 tery, and, by the position of the valve, of any direction. The author 

 altered the experiment by uniting the coils at similar ends, but only 

 left one coil near the mirror, the other being at such a distance that 

 it was without direct action on the deflection. When a deflection of the 

 needle was produced by a discharge through the outer metallic circuit, 

 by repeating the experiment and introducing two valves into the 

 branches a twenty-fold deflection was obtained in any direction. 

 The direction could be predicted by means of the above rule. The 

 mirror is deflected by a secondary current which arises from two 

 sources, the two coils of Mire. One source, the coil distant from 

 the mirror, was omitted and replaced by a short platinum wire of 

 the same conducting value : the deflection of the mirror with an 

 entire metallic circuit was the same as before, but, after introducing 

 both valves, much less than in the absence of both coils. These 



