250 Mr. S. Bidwell's Experiments illustrating 



between electricity and light. Under the circumstances, it is 

 reasonable that such a theory should not be abandoned with- 

 out the exercise of very considerable caution. 



I propose therefore in this paper to treat the subject in 

 greater detail than at first seemed necessary. Attention will 

 be directed to facts and arguments which in my former paper 

 were left altogether unnoticed ; and those points which, as I 

 have gathered from conversation and correspondence, seem to 

 present the greatest difficulty, will be considered at some 

 length. With regard to the experiments upon which I rely, 

 such of them as are new are of a very simple character, and 

 can easily be repeated by an}- one possessing a reflecting gal- 

 vanometer. They are of course of a somewhat delicate nature, 

 and more suitable for the laboratory than for public demon- 

 stration ; but I shall be bold enough to attempt the perform- 

 ance of most of them in the presence of the members of the 

 Physical Society. 



Mr. Hall's first paper on the subject appeared in Silliman's 

 Journal in 1879, and is reproduced in the i Philosophical 

 Magazine ' for March 1880. After stating that his object was 

 to prove that the current of electricity in a fixed conductor is 

 acted upon by a magnet, he describes the following experi- 

 ment : — A strip of gold-leaf, forming part of a circuit, was 

 placed between the poles of an electromagnet, cutting the lines 

 of force perpendicularly. The terminals of a galvanometer 

 were applied to opposite edges of the gold-leaf, and moved 

 about until two equipotential points were found. The magnet 

 was then excited, and a galvanometer-deflection immediately 

 occurred. This deflection was too large to be attributed to 

 the direct action of the magnet upon the galvanometer-needle. 

 It was permanent, and so not due to induction. It was 

 reversed when the magnet was reversed. " In short," says 

 Mr. Hall, "the phenomena observed were just such as we 

 should expect to see if the electric current were pressed, but 

 not moved, toward one side of the conductor. In regard to 

 the direction of this pressure, as dependent on the direction of 

 the current in the gold-leaf and the direction of the lines of 

 magnetic force, the following statement may be made : — If 

 we regard an electric current as a single stream flowing from 

 the carbon pole of the battery through the circuit to the zinc 

 pole, the phenomena indicate that two currents in the same 

 direction tend to repel each other. But if we regard the cur- 

 rent as a stream flowing from negative to positive, then the 

 phenomena indicate that two currents in the same direction 

 attract each other/' The meaning of this is, as appears from 

 subsequent papers, that the direction of the transverse current 



