/lis Magnetic Electrical Machine. 265 



of the magnetic electrical machine, either rotatory or recipro- 

 cating motion can be produced at pleasure of the wires dd. 



Sixth. In apaper of mine (see Phil. Mag., March 1835: vol.vi. 

 p. 169.) I gave a diagram of that part of the magnetic electrical 



machine called the mercury cup, in which a copper disk B' re- 

 volves, (being in connexion with one end of the copper wire 

 coils by the wire A',) and a double-bladed or pointed piece of 

 copper B also dips, it being connected with the other ends of 

 the copper wire coils by the wire A. It is obvious that by 

 this arrangement, when the point and disk are put into rapid 

 motion, the mercury must be scattered about, which is not 

 the only evil, for as you require a very accurate adjustment of 

 the surface of mercury, so that the pointed piece B will leave 

 the mercury at a particular period twice during each revolu- 

 tion, each succeeding rotation tends to destroy that adjustment, 

 consequently the effect produced is constantly on the decrease, 

 and ultimately ceases altogether unless you stop and renew the 

 level you previously had. By my arrangement the mercury 

 is inclosed in a wooden box, and the steel spring I, and the 

 hollow brass cylinder z, do the duty of B' A' C' of the old ar- 

 rangement, and kg also do the duty of B A C, so that the mer- 

 cury is not directly acted upon as formerly. Whatever adjust- 

 ment yoti make is permanent, and, come isohen you 'will, you are 

 sure of a uniform and steady stipply of electricity. This is a 

 most important point for medical practitioners, as the uncer- 

 tainty of action of all electrical machines, both magnetical and 

 Third Scries. Vol.9. No. 5i. Oc/. 1836. 2 11 



