S68 Mr. J. Walsh on the Circle. 



accelerated nor retarded the galvanic influence — and it made 

 no difference whether the needle was placed near the portion 

 of the wire which moved from the positive pole to the nega- 

 tive, or the portion which moved in the opposite direction. 



If a jet of mercury, in communication with one pole of a 

 very large calorimotor, is made to fall on the poles of a horse- 

 shoe magnet communicating with the other, the metallic 

 stream will be curved outwards or inwards, accordingly as 

 one or the other side of the magnet may be exposed to the 

 jet — or as the pole communicating with the mercury may be 

 positive or negative. When the jet of mercury is made to 

 fall just within the interstice, formed by a series of horse-shoe 

 magnets mounted together in the usual way, the stream will 

 be bent in the direction of the interstice, and inwards or out- 

 wards, accordingly as the sides of the magnet, or the com- 

 munication with the galvanic poles, may be exchanged. This 

 result is analogous to those obtained by Messrs. Barlow and 

 Marsh* with wires or wheels. 



It is well known that a galvanic pair, which will, on immer- 

 sion in an acid, intensely ignite a wire connecting the zinc and 

 copper surfaces, will cease to do so after the acid has acted 

 on the pair for some moments — and that ignition cannot be 

 reproduced by the same apparatus, without a temporary re- 

 moval from the exciting fluid. 



I have ascertained that this recovery of igniting power does 

 not take place — if, during the removal from the acid, the 

 galvanic surfaces be surrounded either by hydrogen gas, nitric 

 oxide gas, or carbonic acid gas. When surrounded by chlo- 

 rine, or by oxygen gas, the surfaces regain their igniting 

 power in nearly the same time as when exposed to the air. 



The magnetic needle is, nevertheless, much more powerfully 

 affected by the galvanic circuit, when the plates have been 

 allowed repose, whether it take place in the air or in any of 

 the gases above mentioned. 



I have not as yet had time, agreeably to my intention, to 

 examine the effect of other gases, or of a vacuum. 



LX. On the Circle. By John Walsh, Esq. 



¥ N my last paper in your Journal f, I alluded to a proposition 

 -*• demonstrated by the binomial calculus. I shall state, in 

 this paper, the nature of that demonstration. By the principles 

 of the binomial calculus, the part of the tangent between y 

 and y is the dinomial of u, whatever may be dx, u being 



* See Philosophical Magazine, vol. lxii. p. 321. f p. 2J\. 



the 



