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-off, the black portions 
representing the intersections of ivory or other non conducting 
material. . 'T'wo 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. 
Fig. 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. 506 
ate wooden frames or braces supporting the straight magnets m m. 
@ a are the two armatures upon the brass shaft e. The electro- 
tome constructed upon the same principle as that of figure 1 may 
