File:A text-book on chemistry - for the use of schools and colleges (1846) (14595409620).jpg

Identifier: 04510130R.nlm.nih.gov
Title: A text-book on chemistry : for the use of schools and colleges
Year: 1846 (1840s)
Authors: Draper, John William, 1811-1882
Subjects: Chemical Phenomena
Publisher: New York : Harper & Bros.
Contributing Library: U.S. National Library of Medicine
Digitizing Sponsor: Open Knowledge Commons, U.S. National Library of Medicine

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Some mechanism, such as a winch, is required toturn the glass on its axis; and when it is desired to bringthe machine into activity, all the parts of it having beenmade thoroughly clean and dry by rubbing with a pieceof warm silk or flannel, a little Mosaic gold or amalgamof zinc being spread on the rubber, as soon as the winchis turned the instrument becomes excited. One of the most striking manifestations of electricaldevelopment is the spark; this, which must have beenoften seen when the back of the domestic cat is rubbed ona frosty night, was first discovered in the case of glass orsulphur, by Otto Guericke, and by him referred to itsproper source, electric excitement. On presenting a brassball or the finger to the prime conductor of the machine,the spark passes, attended with a slight report. It may be What varieties of electrical machines have we ? What are the threeessential parts of these machines 7 What is the rubber? What is theprime conductor ? How is the machine excited ?
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ELECTRICAL LIGHT AND REPULSION. 99 Fig. 74. I.IHI I.Hiilliili,M,ll MMIimiM - : ■■—tnini un,i,ii;.ii,ini ll.lllil^IM very beautifully shown by pasting Fis-73- small pieces of tin foil round a glass #N,.-v-, .,.•■•.. .,-■..,.■■, ,\ jt-tp*^tube in a spiral form, as shown in a b *^f Fig. 73, a b c, distances of the twentieth of an inch inter-vening between each piece, and the ends of the tube ter-minated by balls. On presenting one of these balls to theprime conductor, and holding the other in the hand, asthe spark passes, it has to leap over each interstice be-tween the spangles of tin foil, and exhibits a beautifulspiral line of light. By pasting the tin foil on a pane of glass in such away as to direct the sparkproperly, words may be writtenin electric light, as shown inFig. 74. As the electric spark canscarcely be confounded with any other physical phenom-enon whatever, its presence is always indubitable evi-dence of electric excitement. Thus, we can prove thatelectr

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