4f60 The Rev. Prof. Callan in reply to Dr. Ritchie. 



the battery described by me, though it contains but 20 pairs 

 of plates, is capable of producing in the space of one minute 

 3000 or 4000 electric currents, each equal in point of intensity 

 to that of a battery containing 1000 or 2000 voltaic circles. 

 That the helix of an electro-magnet is capable of giving a 

 shock at the moment when battery communication is broken, 

 was discovered only about two years ago (Phil. Mag. for No- 

 vember 1834, p. 351); that the shock given by the magnetic 

 helix increases with the -number of plates employed was not 

 known till discovered by me within the last year. Surely, 

 then, Dr. Ritchie had not a battery six or seven years ago, 

 which, though containing only a small number of plates, was 

 capable of producing in the space of one minute 3000 or 4000 

 electric currents, each equal in point of intensity to that of a 

 battery containing 1000 or 2000 voltaic circles. 



Again, Dr. Ritchie says, " the author speaks of a shock as 

 if it were a quantity^ and institutes a comparison between the 

 she of the shock and the number of plates." That I speak 

 of the shock as if it were a quantity, and that I institute a 

 comparison between the size of the shock and the number of 

 plates, Dr. Ritchie infers from my saying that " with one pair 

 of plates the shock from the helix of the electro-magnet was 

 equal to that of a battery containing 20 pairs of plates; when 

 two pairs of plates were used, the shock appeared to be doubled; 

 with three voltaic circles it appeared to be treble ; and with 

 every increase in the number of voltaic circles, there appeared 

 to be a proportional increase of the shock." Had Dr. Ritchie 

 read the remainder of the paragraph from which these words 

 are taken, he could not but see that his inference is most un- 

 just. For in the following line I speak of the shock as strong, 

 and never speak of it as if it were large or had size. The 

 obvious meaning then of my words is, that the shock increases 

 with the number of plates, not in size, but in strength or in- 

 tensity. My language may be inaccurate ; but it is the lan- 

 guage of Mr. Singer, who, in his treatise on galvanism, 

 speaks of the shock as increasing : it is also the language of 

 Dr. Ritchie himself, who says that " the physiological effects 

 (among which he of course includes the shock) continued to 

 increase'' (Phil. Mag., June 1836, p. 455.) 



Lastly, Dr. Ritchie says, that " the only thing new in my 

 paper is the affirmation that an electro-magnet, when its mag- 

 netism 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." Dr. Ritchie adds, 

 " the very looseness of this statement is a proof of its fallacy." 

 The looseness of this statement is due to Dr. Ritchie himself, 



