as a Measure Jor Elect ricilj/. 257 



or a vertical needle. — The same effects were manifested what- 

 ever were the forms of the surfaces intei-posed between the 

 galvanic plates. — On varying the experiment by connecting 

 both extremities of the plates with each other, by means of 

 small wires, so that there was a metallic circuit throughout, 

 (in which case it is generally conceived that all galvanic effect 

 ceases), I found that every part of this circuit aflected the 

 magnetic needle. 



The magnetism of ihe connecting wires was examined in the 

 usual mode ; that of the plates themselves by inmiersing in the 

 exciting fluid a small compass in a glass case, made imj^ervious 

 to the water. It is perhaps premature to form any theoretical 

 opinions upon these few facts, which seem to me adverse to 

 the received opinion, that the galvanic effects are produced by 

 the decomposition of an electric fluid circulating between the 

 positive and negative plates ; yet, if ever the mysterious agency 

 of galvanism is to be detected, it must be by examining it in 

 its simplest form ; and this, the discovery of the connexion 

 l)etween galvanism and magnetism, and the delicacy of the in- 

 struments it enables us to a})ply, seems to promise, more readily 

 than any modes A'et tried, the means of accomplishing. 



Since this paper was read to the Society, I have had an op- 

 portunity, with the assistance of Dr. Clarke and Mr. Lunn, of 

 trying the magnetic effects of atmospherical electricity. — A wire 

 of about 100 yards in length, connected with a kite, readily 

 magnetised a steel needle inclosed in a spiral wire, but caused 

 no deviation in a compass placed beneath it. — I have obtained 

 the same, results in repeating Sir TI. Davy's experiments both 

 with the Leyden jar and with sparks taken from the conductor 

 of an electrical machine. — It seems that the galvanic mag- 

 netism is most readily made sensible by the deviation it causes 

 in the compass needle ; but the electrical by its power of com- 

 municating permanent magnetism. 



The experiment on atmosplicrical electricity suggests an 

 easy method of ascertaining, from time to time, the prevalent 

 electricity of the air; by inclosing small steel bars in a s])iral 

 wire connected with a conducting rod, and examining the 

 magnetism induced in them. 



XLVm. Report of a Committee of the House of Commons on 

 Steam-Boats. 

 [(Joncliitlfil from p. 1.32.] 

 A List of all the Steam-Boats built since 181 1: showing their 

 Tonnag(!, and the Power of their Kngines; (he Names of 

 the liiiilders and oi'the I'jigine-IMakers; the Dates ofllieir 

 being laiinelied, and also the Stations wlure lluy ply. [I'lom 

 the Appendix nli'rn d to, siipia^ p. I if.*.] 

 Vol. (JO. No. L"J1-. Ocl.Wl'l. Kk 



