The Rev. Prof. Callan in reply to Dr. Ritchie. 461 



who has substituted the indefinite article an for the definite 

 article the. In my paper it is not affirmed than an electro-mag- 

 net, but that the electro-magnet, (that is, the electro-magnet 

 of which I was speaking, or which was formerly used in the 

 apparatus for continued rotation,) when its magnetism is in- 

 duced by a battery of 200 pairs of small plates, will have a 

 greater power of inducing magnetism at a distance than any 

 permanent magnet ;" that is, than any permanent magnet sub- 

 stituted for the electro-magnet the use of which has been 

 abandoned. Dr. Ritchie asks, " does the author mean to say 

 that a small electro- magnet when connected with a battery of 

 200 pairs of plates induces more magnetism on soft iron at a 

 distance than any permanent magnet?" I mean to say, what 

 my words clearly imply, that the electro-miagnet formerly used 

 in the apparatus for continued rotation, when rendered mag- 

 netical by the voltaic current from a battery of 200 pairs of 

 plates, will have a greater power of inducing magnetism on 

 soft iron at a distance than any permanent magnet substituted 

 for the electro-magnet, or than any permanent magnet of 

 equal or nearly equal size. And this position Dr. Ritchie has 

 not disproved, nor will he be ever able to disprove. 



But is there the slightest foundation for Dr. Ritchie's as- 

 sertion that the only thing new in my paper is the affirmation 

 that the " electro-magnet, when its magnetism is induced by a 

 compound battery of 200 small pairs of plates, will have a 

 greater power of inducing magnetism at a distance than any 

 permanent magnet?" I answer that this assertion is utterly 

 destitute of foundation. 



In my paper it is proved, first, that the magnetic power given 

 to an electro-magnet by the voltaic current, and the distance at 

 which that power is exerted, increase nearly in proportion to 

 the number of plates employed ; secondly, that the shock given 

 by the helix of an electro-magnet, when battery communica- 

 tion is broken, increases nearly in proportion to the number 

 of plates employed ; thirdly, that the shock given by a long 

 wire, on breaking communication with the battery, increases 

 with the number of plates in the battery ; and fourthly, that 

 with the aid of an electro-magnet, and of a small instrument 

 for rapidly breaking communication between the battery and 

 magnetic helix, a battery containing but 20 voltaic circles 

 may be made to produce effects of decomposition equal to 

 those of a battery containing 1000 or 2000 voltaic circles. 

 Surely, were it in his power. Dr. Ritchie would not have failed 

 to show by reference to some published works, that I was not 

 the discoverer of the three above-stated facts, or of the means 

 of rendering a battery of 20 pairs of plates as efiective in pro- 



