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LII. On the Application of Electro-magnetism as a Motive 

 Power: in a Letter from Prof. P. Forbes of Aberdeen, to 

 Michael Faraday, D.C.L., Sfc. S^c* 



« King's College, Aberdeen, Oct. 7, 1839. 

 " My dear Sir, 

 " TJTAVING seen a notice from Mr. Jacobi sent by you 



^-*- to the London and Edinburgh Philosophical Maga- 

 zinef, regarding the success of his experiments on the produc- 

 tion of a moving power by electro-magnetism, I am sure it 

 will give you pleasure to know that a countryman of our own, 

 Mr. Robert Davidson, of this place, has been eminently suc- 

 cessful in his labours in the same field of discovery. For in 

 the first place, he has an arrangement by which with only 

 two electro-magnets and less than one square foot of zinc- 

 surface (the negative metal being copper) a lathe is driven 

 with such velocity as to be capable of turning small articles. 

 Secondly, he has another arrangement, by which, with the 

 same small extent of galvanic power, a small carriage is driven 

 on which two persons were carried along a very coarse wooden 

 floor of a room. And he has a third arrangement, not yet 

 completed, by which, from the imperfect experiments he has 

 made, he expects to gain very considerably more force from the 

 same extent of gal vanic power than from either of the other two. 



" The first two of these arrangements were seen in opera- 

 tion by Dr. Fleming, Professor of Natural Philosophy in this 

 University, and myself, some days ago ; and there remains no 

 doubt on our minds that Mr. Davidson's arrangements will, 

 when finished, be found available as a highly useful, efficient, 

 and exceedingly simple moving power. He has been busily 

 employed for the last two years in his attempts to perfect his 

 machines, during all which time I have been acquainted with 

 his progress, and can bear testimony to the great ingenuity 

 he has shown in overcoming the numberless difficulties he has 

 had to encounter. So far as 1 know, he was the first who 

 employed the electro-magnetic power in producing motion 

 by simply suspending the magnetism without a change of 

 the poles. This he accomplished about two years ago. About 

 the same time he also constructed galvanic batteries on Pro- 

 fessor Daniell's plan by substituting a particular sort of canvas 

 instead of gut, which substitution answers perfectly, is very 

 durable, and can be made of any form or size. And lastly, he 

 has ascertained the kind of iron, and the motJe of working it into 

 the beststaie for producing the strongest magnets with certainty. 



" The first two machines, seen in operation by Dr. Fleming 

 and myself, are exceedingly simple, without indeed the least 



• Communicated by Dr. Faraday. f See our number for Sept., p. 164. 



