Optic projection : principles, installation and use of the magic lantern, projection microscope, reflecting lantern, moving picture machine, fully illustrated with plates and with over 400 text-figures (1914)

Record Details:

Title:
Optic projection : principles, installation and use of the magic lantern, projection microscope, reflecting lantern, moving picture machine, fully illustrated with plates and with over 400 text-figures
Date:
1914
Author:
Gage, Simon Henry, 1851-1946
Publisher:
Ithaca, N.Y. : Comstock Publishing Co.
Volume:
Optic projection : principles, installation and use of the magic lantern, projection microscope, reflecting lantern, moving picture machine, fully illustrated with plates and with over 400 text-figures
Leaf #:
000512
Language:
English
Format:
Books
Contributor:
Gerstein - University of Toronto
Sponsor:
MSN
Coordinator:
Media History Digital Library
Description:
Bibliography: p. 693-703
Date Added:
July 19, 2022
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CH. XIII] WIRING FOR AN ELECTRIC CURRENT 497 current must travel to get back to the dynamo. In figure 265 if a wire were put across the circuit at the points s. c. instead of the current extending entirely around the circuit, it would take the shorter course. Short circuits are undesirable for two reasons : (i) the current is not available where wanted; (2) it may be dangerous. § 689. Ground. — With many electric circuits such as with street railway circuits, one terminal of the dynamo is permanently connected with the earth. If now the wire connected to the other FIG. 266. AN ELECTRIC CIRCUIT WITH A SINGLE GROUND. C D The two poles of the dynamo. G Generator (dynamo). BI A conductor extending from the electric circuit to the ground (g1). If all the rest of the circuit is insulated this will do no harm, but see fig. 267. g1 The earth into which the conductor, B , extends. A Arc lamp. R Rheostat. terminal of the dynamo should also become connected with the earth, as through a water or a gas pipe, current would wholly or in part take that path back to the dynamo. When any part of the circuit is connected with the earth it is called a "ground." In case the dynamo and circuit are entirely insulated from the earth, a single ground will result in no flow of current outside the wire. If, however, two points in a circuit are connected to the earth the effect will be the same as if the two points of the circuit were connected to each other, by an additional wire (fig. 266, 267). § 690. Insulation of wires. — To avoid short circuits and the consequent danger to men and animals and also the danger from