126 MM. van Breda and Logcman on Amperian Repulsion. 



precipitates the basic salt, 



CuON0 5 3CuOHO, 

 while the hypochlorites throw down 



3CuO, CuCl,4HO. 



"When potash in the cold is added in excess to any of the 

 soluble salts of copper, the pale-blue hydrated oxide is precipi- 

 tated, which blackens slightly at 120° F., and becomes quite 

 dehydrated at 212°. It is very singular that when metallic 

 copper is dissolved by means of hydrochloric acid and chlorate 

 of potash in the cold, and potash added to the liquid still hold- 

 ing the oxides of chlorine in solution, the oxide of copper is pre- 

 cipitated as a black powder, even at the ordinary temperature. 



XVII. On Amperian Repulsion. 

 By MM. J. G. S. van Breda and W. M. Logeman. 



To Dr. Tyndall, F.R.S. 

 Sir, 



WE take advantage of the opportunity afforded by the 

 sending of the accompanying letter, to address, through 

 your kindness, to the readers of the Philosophical Magazine a 

 few lines in answer to the remarks published by Mr. Croll 

 of Glasgow, in the Number of that Journal for this month, 

 pp. 365 et seq. t in reference to our experiments on Amperian 

 repulsion. 



There must be, either in the description of our experiments, or 

 in the figure which accompanies them, some want of accuracy or 

 of clearness ; otherwise we are at a loss to understand how 

 Mr. Croll could say that the currents in the mercury ought to 

 repel the horizontal parts, while they attract the vertical parts of 

 our moveable conductor. This seems to us to contradict all the 

 received ideas of electric currents. We would willingly take 

 trouble to make our description more clear or more accurate, 

 but the remainder of Mr. CrolPs article induces us to think that 

 such an attempt would be quite useless. 



In fact, Mr. Croll first admits that "our experiments with 

 the reversed conductor, and some others detailed by us, certainly 

 prove that the molecules of a conductor, while the current is 

 passing, do repel each other ; 9i and then goes on to discuss the 

 question from a point of view which is new to us, adding that 

 this repulsion of the molecules of a conductor proves nothing as 

 to the repulsion of the contiguous parts of the current itself. 

 Now we will not follow Mr. Croll into the arguments upon which 

 he bases his opinion concerning the mutual action of the parts of 



