Intelligence and Miscellaneous Articles. 443 



experiment — and that if I get any credit for it whatever, it is 

 merely in the way of carrying out Helmholtz's ideas, instead of all 

 the credit for ideas, design of apparatus, the carrying out of the 

 experiment, the calculation of results, and every thing which gives 

 the experiment its value. 



Unfortunately for me, Helmholtz had already experimented on 

 the subject with negative results ; and I found, in travelling through 

 Germany, that others had done the same. The idea occurred in 

 nearly the same form to me eleven years ago ; but as I recognized 

 that the experiment would be an extremely delicate one, I did not 

 attempt it until I could have every facility, which Helmholtz kindly 

 gave me. 



Helmholtz kindly suggested a more simple form of commutator 

 than I was about to use, and also that I should extend my experi- 

 ments so as to include an uncoated glass disk as well as my gilded 

 vulcanite ones ; but all else I claim as my own, the method of experi- 

 ment in all its details, the laboratory work, the method of calculation — 

 indeed every thing connected with the experiment in any way, as com- 

 pletely as if it had been carried out in my own laboratory 4000 miles 

 from the Berlin laboratory. 



Tours truly, 



H. A. BOWLAND. 



ON ELECTBIC BOUNDARY LAYEBS. BY PBOE. HELMHOLTZ. 



In all cases in which two contiguous bodies have different values 

 of the electric-potential function, there must be along the common 

 boundary between them a double layer of positive and negative 

 electricity, the moment of which (taking this expression in the 

 same sense as in the phrase "magnetic moment"), multiplied by 

 4tt, calculated for unit surface, is equal to the difference of poten- 

 tial-function on the one side and on the other of the double layer. 

 Now, as the value of the moment is equal to the electric density of 

 the positive E multiplied by the mean value of the distance between 

 the two layers, this distance cannot become vanishingly small with- 

 out the density with a given difference of potential becoming infi- 

 nitely great. But the work done, in the formation of such a double 

 layer, against the electrostatic forces is =PE, if E denotes the 

 amount of positive electricity on the unit of surface, and P the dif- 

 ference of potential on the two sides of the double layer. Since, 

 with the distance h between the two layers, 



47rEA=P, 

 the value of the work is 



and would therefore become infinite for vanishing h. From this 

 Sir William Thomson has already calculated a limit for the distance 

 between, the double layer at the galvanic tension between copper 



