Lessons in elementary physics / by Balfour Stewart.

  • Balfour Stewart
Date:
1895
Catalogue details

Licence: Public Domain Mark

Credit: Lessons in elementary physics / by Balfour Stewart. Source: Wellcome Collection.

    478/502 page 458
    exhatistecl of air by niean.s of pumps, capable of producimj a very g:ood vacuum, and then hermetically sealed. It remains now only to provide a convenient method of connection of the lamp to the supply of electrical energ'v. This is usually done by soklering' copper wires a and h, terminating in brass plates, to the ends of the platinum wires. By means of plaster of Paris the terminal plates are held in place. The positive and negative leads are connected to a lampholder having two brass studs c and i7, which are held against the brass plates by springs when the lamp is in position. 1 he ordinary lamp in use is of i6 candle power, and at lOO volts t.akes o’6 amperes. 4-47. The Arc Lamp.—When two pieces of carbon arc con- nected with a battery of about 20 Bun.sen cells or other source of 40 volts of pressure, and the carbons are made to touch and then separated a short distance, a globe ot intensely luminous carbon vapour is produced. The carbon connected \\ith the positive pole becomes the hottest and a hollow or crater is formed (sec Fig. 155), whereas the carbon connected with the negative pole becomes pointed. Most light is emitted from
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