374 RECORD OF SCIENCE FOR 1886. 



2. Electric Generators. 



Dorn has proved that wbeu tourtnaline is electrified by heating it, the 

 amount of positive electricity produced is precisely similar to the 

 amount of negative electricity. The proof comes from the fact that if 

 the tourmaline, after being heated, is brought inside a conducting but in- 

 sulated hollow body, an electrometer connected with this body should 

 show no signs of electricity as the crystal cools. No deflection was ever 

 obtained which exceeded the uncertainty of the instrument employed. 

 (Wied. Ann., November, 10, 1885; Phil. Mag., January, 1886, V,xxi, 78). 



Hilliaret has described and discussed the action of an influence ma- 

 chine of the Wimshurst type constructed by Br^guet. If the charge of 

 the machine is maintained from an external source the charge is theo- 

 retically limited ; but if the machine is self-exciting, the charge dimin- 

 ishes in geometical progression as the operations increase in arithmetical 

 progression, and the excitation falls rapidly to zero. This is readily 

 seen by putting the combs of the machine in contact. For practical 

 use the author thinks this type of machine preferable to any other 

 form. (,^p Phys., May, 1886, II, v, 208.) 



Budd/ has calculated the quantity of electricity carried by a chem- 

 ical atom. Faraday showed that the quantity of electricity carried to 

 the electrode by an atom of any electrolyte is directly proportional to 

 its combining power or valence ; and therefore that the quotient of this 

 quantity divided by the valence is constant for all atoms. The authors 

 therefore considers that this quotient, since it is the smallest quantity 

 of electricity which can be set free from any chemical decomposition, 

 represents an elementary electrical particle. To calculate it we must 

 know: (1) the electro-chemical equivalent of an electrolyte, and (2) 

 the absolute number of molecules contained in a unit mass of this sub- 

 stance. In the case of hydrogen, which is univalent, the electromag- 

 netic value of the current which evolves 1 milligram of hydrogen per 

 second is 957, and its electrostatic value 957 v, or 957 x (3x 10"). One- 

 half this sets free 14x10'^ molecules or twice this number of atoms; 

 these values being given in milligram-millimeter-second units. Divid- 

 ing, we get for the value carried by any univalent atom 0.00000051 elec- 

 trostatic unit. (Wied. Ann., xxv, 562; J. Phys., November, 1886, II, v, 

 523.) 



Lodge's paper on the seat of the electromotive forces in the voltaic 

 cell has called forth several re])lies. In one of these, Ayrton and 

 Perry object to the assumption which he tacitly makes that there is 

 a, prima facie absurdity in acknowledging a considerable difference of 

 potentials between two metals such as zinc and copper in contact 

 with each other. Taking Lodge's definition of electromotive force, as 

 already given by Maxwell, " the seat of the E. M. F. in any circuit is 

 the place at which the circuit receives or gives up energy as distinct from 

 heat due to resistance, and the amount of the E. M. F. is measured as 



