Electro Magnetism. 



351 



supported by wood, as every piece of metal of any kind surround- 

 ing a magnet, detracts from its action, by reason of closed cur- 

 rents excited by the disturbance of magnetic forces. For the ac- 

 tion of closed currents see Vol. xxxv. No. 2, pages 254 and 5. 

 The armature «, is mounted upon a brass shaft e, as I have here- 

 tofore shown by experiment that an iron or steel shaft detracts 

 greatly from the inductibility of the armature. At e, firmly secur- 

 ed to the shaft is the electrotome or cut-oflf, the black portions 

 representing the intersections of ivory or other non conducting 

 material. Two pairs of plates (compound series) are connected 

 by their poles with the cups p p. By the revolution of the arma- 

 ture the two magnets are charged in succession, and thus the 

 action is maintained during the entire revolution. 



Fiff. 2. 



Figure 2, exhibits a machine of more simple construction than 

 the last, or perhaps than any other. It possesses also the advan- 

 tage of straight magnets much preferable to the U magnet, h h 

 are wooden frames or braces supporting the straight magnets m m. 

 a a are the two armatures upon the brass shaft e. The electro- 

 tome constructed upon the same principle as that of figure 1 may 



