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Page 115 | Volume 1 | Chapter 9 | Magnetism

Solenoids.—A solenoid consists of a spiral of conducting wire wound cylindrically so that, when an electric current passes through it, its turns are nearly equivalent to a succession of parallel circular circuits, and it acquires magnetic properties similar to those of a bar magnet.

Ques. What is the character of the lines of force of a solenoid in which a current is flowing?

Ans. The lines of force must be thought of as closed loops linked with the current. The conductor conveying the current

Fig. 117. - Lines of force of a circular loop.
Fig. 117.—Lines of force of a circular loop. If the loop pass through a piece of cardboard at right angles to its plane, and the current flow as indicated, the dotted lines on the cardboard will represent the direction of the lines of force in the plane of the cardboard. The student should verify the lines of force as here given by applying the corkscrew rule.

passes through all the loops of force, and these are, so to speak, threaded or slung on the current-line of flow, as in fig. 116.

Ques. What is the distribution of the lines of force?

Ans. The lines of force form continuous closed curves running through the interior of the coil; they issue from one end and enter into the other end of the coil, as shown in fig. 117.


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When first published in 1914, these books were intended to explain the scientific principles of electricity (which at the time was a new and exciting technology) with "the aid of a very large number of illustrations, together with specific explanations, worded in concise and simple language".

What really makes this collection of books special today is the detailed documentation of most of the earliest inventions in electrical history including telegraphs, motors, switchboards, and high power distribution systems.

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