C. GENERAL PHYSICS. 161 



resistance of the bodies penetrated by it. The study of the 

 failure of Ohm's formula in this ease has been the subject of 

 an investigation by Rossetti, who, among many other con- 

 clusions, establishes the following principles : In one and the 

 same series of experiments, conducted under identical cir- 

 cumstances with reference to atmospheric humidity, the in- 

 tensity of the current excited by the electric machine is 

 nearly, but not exactly, proportional to the velocity of the 

 revolving disk. The relation between the velocity of the 

 disk and the intensity of the current is not independent of 

 the moisture in the air, but varies sensibly therewith, the 

 number of turns the disk must make in a second, in order 

 that a current of constant intensity may be developed, is 

 greater on moist than on dry days. The work required to 

 make the electric machine active is exactly proportional to 

 the intensity of the current, assuming that the humidity re- 

 mains the same. The ratio between the work and the in- 

 tensity of the current diminishes with increasing moisture, 

 so that in order, on a moist day, to obtain a current of given 

 intensity, there may indeed be required a greater velocity 

 of rotation ; but equally is it true that a less amount of work 

 would be expended, so that the electric machine is more 

 economical on moist days than on dry. 19 C, VIII., 140. 



XEW MODIFICATION OF THE LECLANCHE BATTERY. 



M. Kern, of St. Petersburg, after detailing several grave 

 objectionable qualities of the Leclanche cell, at present very 

 popular for telegraphic and other uses, recommends the fol- 

 lowing modification, which he claims will act very constant- 

 ly. Two parts of well-washed coke and one of manganese 

 dioxide, in the state of powder, are well mixed together with 

 a small quantity of water acidulated with some drops of 

 nitric acid, and the mixture is then pressed into a cylindrical 

 mould of suitable size. The resulting coke-manganese cylin- 

 ders are dried in a warm place, but not over a fire, as a strong 

 heat will decompose the peroxide. The dried cylinders are 

 placed in glass jars containing concentrated solution of am- 

 monium chloride, and surrounded with zinc plates curved in 

 the usual manner. By this arrangement the use of porous 

 cells is avoided, and a battery of such elements acts more 

 constantly, besides which the construction is materially cheap- 



