File:Davis's manual of magnetism - including galvanism, magnetism, electro-magnetism, electro-dynamics, magneto-electricity, and thermo-electricity (1854) (14589896340).jpg

Identifier: davissmanualofma00davi (find matches)
Title: Davis's manual of magnetism : including galvanism, magnetism, electro-magnetism, electro-dynamics, magneto-electricity, and thermo-electricity
Year: 1854 (1850s)
Authors: Davis, Daniel
Subjects: Magnetism Electricity Electromagnetic Phenomena
Publisher: Boston : Palmer and Hall
Contributing Library: Francis A. Countway Library of Medicine
Digitizing Sponsor: Open Knowledge Commons and Harvard Medical School

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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 supported by twobrass pillars upon the poles,N and S, of the magnet.One of the screw-cups onthe stand is connected withthe magnet, and throughthat with the wheel. The mercury trough, whichis insulated from the magnet, is connected with theother cup. 181. When connection is made with the battery,the current passes from the axis of the wheel to thetrough through any one of the points which happensto touch the mercury. Under these circumstances,the ray through which the current is flowing passesforward between the poles of the magnet, like thevibrating wire in Fig. 62, until it rises out of themercury. At this moment the next succeeding rayenters it, and goes through the same process; andso on. 10*
Text Appearing After Image:
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 sparks, the revolving wheel willappear to be nearly at rest; exhibiting only a quickvibratory movement, in consequence of the sparksnot succeeding each other precisely at the same point.This optical illusion arises from the fact, that theelectric light is so extremely transient in its duration,that the wheel has not time to move to any appre-ciable extent during the electrical discharge; andtherefore each spark shows it in an apparently sta-tionary position. If the sparks occur at one placemore frequently than at the rate of eight in a secondof time, the eye cannot appreciate them separately,and the impression of a continuous light is received.For this reason, the wheel is seen constantly, as i

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