of Wires of different Qualities and Dimensions. 3 



feet of copper, compressed within a small compass and acting 

 as single plates. 



With this power at my disposal I was anxious if possible 

 to make the experiments upon such a scale as should leave 

 nothing doubtful in the results. I accordingly procured about 

 900 feet of small copper bell wire, in one length. This was 

 arranged in the manner hereafter described, and experiments 

 carefully made upon it with three compasses at twenty different 

 lengths, varying from 838 feet to 98 feet, and the results care- 

 fully read and registered. The three compasses were placed, 

 one at each extremity of the wire and the other exactly in the 

 middle of its length. 



Before I proceed to state these results it may be well to 

 refer to one marked peculiarity in them which is independent 

 of the laws in question, viz. that with very trifling anomalies 

 the three compasses placed as above were instantaneously and 

 equally deflected, proving that the whole wire was in the same 

 state of electric tension, and that the diminished effect by 

 lengthening the wire was not, as I had at first supposed, due 

 to dissipation during its transmission. The same result was 

 afterwards independently obtained by M. Becquerel and com- 

 municated to the Royal Academy of Sciences of Paris, and is 

 now I believe considered as an established law of electro-mag- 

 netic action. 



M. Becquerel also pursued a similar inquiry into the laws 

 of conduction as depending on the lengths and diameters of 

 the conductors; and here unfortunately are found discrepancies 

 between the two results, which it is necessary to examine, par- 

 ticularly as Professor Cumming seems to have obtained re- 

 sults in many cases at variance with both. 



Confining ourselves at present to that law which relates to 

 diameter, Professor Cumming in different comparisons found 

 it to vary from the simple first power of the diameter to nearly 

 the cube of the same. M. Becquerel finds it to vary as the 

 square of the diameter ; while in my experiments, beyond very 

 small limits, I found the deflections wholly independent of the 

 diameter. Indeed if the deflection depended upon the square 

 or any power of the diameter, it would follow that we might in 

 any case supply a deficiency of galvanic power by only enlar- 

 ging the diameter of our conductor, a doctrine which will not 

 be maintained ; and yet this is a necessary consequence if we 

 admit the deflections to be a measure of the conducting power 

 without limits ; and if it has limits, on what do they depend? — 

 is it absolute dimension, or has it reference to the intensity of 

 the battery? This is certainly a question which requires in- 

 vestigation; for whatever it may be that establishes thes 



B 2 



