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 232
te are threepointers, which mark the revo-lutions up to 1000. The timeoccupied by any known numberof revolutions at once enables uslo ascertain the speed of the ro-tating bar. Though very great,it is necessarily somewhat lessthan when the bar carries nomachinery. 343. Electro-Magnet revolving by… … 216 DAVISS MANUAL. Fiff. 149. t>* constructed with some delicacy. A small electro-magnet, (Fig. 149,) is so supported as to have freedomof motion in a vertical plane, like the dipping needle,a pole-changer being secured on its axis of motion.The springs which press upon the pole-changershould be…
