Davis's manual of magnetism : including galvanism, magnetism, electro-magnetism, electro-dynamics, magneto-electricity, and thermo-electricity (1854)
Davis, Daniel · Boston : Palmer and Hall · leaf 130
rotation, by making Fig. 64. use of a copper wheel, thecircumference of which iscut into rays, instead of thewire. The points of thewheel, W (Pig. 64,) dip in-to mercury contained in asmall trough, T, supportedbetween the legs of a U-magnet, fixed in an uprightposition. The axis of thewheel is… … 114 DAVISS MANUAL. 182. If the quantity of mercury is so adjusted thatone ray shall quit its surface before the succeeding onetouches it, a spark will be seen at each rupture ofcontact. When the machine is set in motion in thedark, so that it may be illuminated by the rapid suc-cession of these…
