of The Rev. J.W. MacGauley and The Rev. N.J. Callan. 61 



to its neutral state tend to induce electricity on the coil in the 

 same direction with the returning current in the coil, the effecf: 

 will be increased; on the contrary, diminished, which seems to 

 be the case which presented itself to Mr. MacGauley's obser- 

 vation. His fourth position has been known so long that I 

 scarcely know its discoverer. 8ir H. Davy knew it well, and 

 endeavoured to investigate the law of diminution in the effect 

 of the battery depending on the length of the wire connecting 

 its poles. The only thing new in this paper is the statement 

 of a fact which is not correct. It is said that if two persons put 

 their hands in salt water, and if they are placed in the electric 

 circuit, eac/i receives a more powerful shock than when only 

 one person was placed in the circuit. That this is not the case 

 every one who possesses a magneto-electric machine may easily 

 satisfy himself. ( 



The paper in page 472, by the Rev. N. T. Callan, is equally 

 destitute of originality. Tlie battery which he describes has 

 been known for a long time. 1 had one exactly the same, 

 made by Mr. Newman six or seven years ago, and frequently 

 used at my public lectures in the Royal Institution. The au- 

 thor talks of the "enormous quantity of electricity circulated 

 by this battery." The quantity is simply, as I have shown in 

 the Philosophical Transactions, directly as the surface, and 

 when used as a compound battery, as the square root of the 

 number of plates. The author speaks of a shock as if it were 

 a quantity, and institutes a comparison between the size of the 

 shock and the number of plates. " When two pair of plates 

 were used the shock appeared to be doubled ; with three vol- 

 taic circles it appeared to be trebled." This, 1 believe, is the 

 first attempt to bring sensations under the power o^ analysis. 

 It is needless to dwell on this paper. The only thing new in 

 it is the affirmation that an " electro-magnet, when its magnet- 

 ism 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." The very looseness 

 of this statement is a proof of its fallacy. 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 ani/ permanent magnet? Though he 

 says so he cannot seriously mean what he says. His meaning 

 then must be this, that if an electro- horseshoe-magnet have the 

 same lifting power with a permanent one when the keeper is in 

 contact with it, it will lift a small piece of soft iron at n greater 

 distance than the electro magnet. That this is not the case every 

 person may satisfy himself by the sin^plest experiment. I have 

 shown it to be so in the Phil. Mag. for last August, (vol. ix. 



