186 Prof. Henry on Electrical Induction 



by those (of whom " Shadow " seems one) who deny the cor- 

 rectness of the assumption upon which the argument depends ; 

 the agreement of my results with well-known formulas would 

 be merely an additional argument in favour of the new mode 

 of regardinij imaginaries. 



Opposed as his views appear to be to this manner of inter- 

 preting impossible quantities, it seems to me (unless I have 

 mistaken the sense in which he uses the term ^^ incongnious" 

 which is the case perhaps) that they in reality support it. 



Tims, incongruity in geometrical problems (and of course 

 in those only can we consider \/ — la symbol of perpendicu- 

 larity) can only affect the length or the direction of a line : if 

 it affiscted the length of a line, this would be evidenced by our 

 obtaining such a result as the coexistence of the two equations 

 A=B, A>B. 



When the incongruity affected the direction, it would be 

 evidenced by the appearance of \/— 1 . It being once admitted 

 that v' — 1 marks an error in estimating direction, it is easy 

 to show that this error is one of a right angle ; for the error 

 shown by v/ — 1 being twice repeated, gives — a in place of 

 H-ff, or an incongruity of two right angles ; hence the incon- 

 gruity represented by \/ —\ must be half of two right angles, 

 that is, one right angle. 

 Port of Spain, Trinidad, 

 Oct. 3, 1846. 



XXXIV. On the Induction of Atmospheric Electricity on the 

 Wires of the Electric Telegraph. By Prof. Joseph Henry*. 



'T'HE action of the electricity of the atmosphere on the wires 

 of the electrical telegraph is at the present time a subject 

 of much importance, both on account oi its practical bearing, 

 and the number of purely scientific questions which it involves. 

 I have accordingly given due attention to the letter referred 

 to me, and have succeeded in collecting a number of liicts in 

 reference to the action in question. Some of these are from 

 the observations of different persons along the principal lines, 

 and others !"rom my own investigations during a thunder-storm 

 on the 19th of June, when I was so fortunate as to be present 

 in the office of the telegraph in Philadelphia, while a series of 

 very interesting electrical phoenomena was exhibited. In con- 

 nexion with the facts derived from these sources, I must ask 

 the indulgence of the Society in frequently referring, in the 

 course of this communication, to the results of my previous 



* From the Proceedings of the American Philosophical Society, vol. iv. 

 p. 260. 



