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XXVll. On certain Imiirovcments in the Comtruction of Mag- 

 neto-electrical Machines, and on the Use oj Caoutchouc for 

 Insulation in Voltaic Batteries. By Fred. W. Mullins, 

 Esq., M.P., F.S.S. 



To the Editors of the Philosophical Magazine and Journal. 



Gentlemen, 

 T THINK it important to call the attention of the scientific 

 ■■- readers of your valuable Journal, to some improvements 

 recently made by me in the construction of the magneto-elec- 

 tric machine, which go far to demonstrate the still very im- 

 perfect state of these instruments, and form a foundation for 

 alterations infinitely more important both in their mode of 

 construction and application. 



The machine whose power I had an opportunity of testing 

 was constructed on the most approved principle, and consists 

 of two sets of bar-magnets arranged vertically, each set con- 

 sisting of a dozen bars, and the upper poles of one set being- 

 unconnected with those of the othei". I had previously seen 

 and examined horizontal horse-shoe machines, and so far as 

 1 was enabled to institute a comparison considered the other 

 mode of construction to be preferable. After trial, however, 

 it struck me that the power of all magneto-electric machines 

 was very imperfectly developed, and that it might be possible 

 to obtain considerably greater effects from the same number 

 of magnetic bars by establishing a magnetic connexion be- 

 tween the poles of the latter, and this without much difficulty 

 or increased expense. With this view I procured two mag- 

 netized arcs of the shape given in the an- ,, 



nexed figure, and of the same width and /'' ,, ^.^ \ 



thickness as the bars of the machine. I / / \ \ 



then applied them, one to the opposite s n 



poles of the outside pair of bars, and one to those of the inside, 

 and on giving the shock to a gentleman who was present, and 

 who had tried the power of the instrument when the poles 

 were unconnected, the effect was so much increased that he 

 refused to repeat it, and on trying it on myself I found the 

 power to be fully double what it had previously been. I was 

 aware that connecting pieces of soft iron were sometimes used, 

 but that their utility was said to be very questionable, and 

 having myself ti-ied them, I can safely say tliat soft iron as a 

 mode of connexion is useless; it is evident, therefore, that the 

 increase of power does not de|)end upon connexion, unless 

 when the substance forming the connexion is in a peculiar 

 slate, and therehj capable (f exerting a certain influence on the 



