Electricity for Boys | Page 3

100. Section of electric iron 141 101. Thermo-electric couple 143 102. Cutting a magnetic field 146 103. Alternations, first position 148 104. Alternations, second position 148 105. Alternations, third position 148 106. Alternations, fourth position 148 107. Increasing alternations, first view 149 108. Increasing alternations, second view 149 109. Connection of alternating dynamo armature 150 110. Direct current dynamo 151 111. Circuit wires in direct current dynamo 152 112. Alternating polarity lines 154 113. Alternating current dynamo 155 114. Choking coil 157 115. A transformer 158 116. Parallel carbons 164 117. Arc-lighting circuit 165 118. Interrupted conductor 166 119. Incandescent circuit 167 120. Magnetic action in dynamo, 1st 177 121. Magnetic action in dynamo, 2d 177 122. Magnetic action in dynamo, 3d 178 123. Magnetic action in dynamo, 4th 178 124. Magnetic action in motor, 1st 179 125. Magnetic action in motor, 2d 179 126. Magnetic action in motor, 3d 180 127. Magnetic action in motor, 4th 180

INTRODUCTORY
Electricity, like every science, presents two phases to the student, one belonging to a theoretical knowledge, and the other which pertains to the practical application of that knowledge. The boy is directly interested in the practical use which he can make of this wonderful phenomenon in nature.
It is, in reality, the most successful avenue by which he may obtain the theory, for he learns the abstract more readily from concrete examples.
It is an art in which shop practice is a greater educator than can be possible with books. Boys are not, generally, inclined to speculate or theorize on phenomena apart from the work itself; but once put them into contact with the mechanism itself, let them become a living part of it, and they will commence to reason and think for themselves.
It would be a dry, dull and uninteresting thing to tell a boy that electricity can be generated by riveting together two pieces of dissimilar metals, and applying heat to the juncture. But put into his hands the metals, and set him to perform the actual work of riveting the metals together, then wiring up the ends of the metals, heating them, and, with a galvanometer, watching for results, it will at once make him see something in the experiment which never occurred when the abstract theory was propounded.
He will inquire first what metals should be used to get the best results, and finally, he will speculate as to the reasons for the phenomena. When he learns that all metals are positive-negative or negative-positive to each other, he has grasped a new idea in the realm of knowledge, which he unconsciously traces back still further, only to learn that he has entered a field which relates to the constitution of matter itself. As he follows the subject through its various channels he will learn that there is a common source of all things; a manifestation common to all matter, and that all substances in nature are linked together in a most wonderful way.
An impulse must be given to a boy's training. The time is past for the rule-and-rote method. The rule can be learned better by a manual application than by committing a sentence to memory.
In the preparation of this book, therefore, I have made practice and work the predominating factors. It has been my aim to suggest the best form in which to do the things in a practical way, and from that work, as the boy carries it out, to deduce certain laws and develop the principles which underlie them. Wherever it is deemed possible to do so, it is planned to have the boy make these discoveries for himself, so as to encourage him to become a thinker and a reasoner instead of a mere machine.
A boy does not develop into a philosopher or a scientist through being told he must learn the principles of this teaching, or the fundamentals of that school of reasoning. He will unconsciously imbibe the spirit and the willingness if we but place before him the tools by which he may build even the simple machinery that displays the various electrical manifestations.
CHAPTER I
THE STUDY OF ELECTRICITY. HISTORICAL
There is no study so profound as electricity. It is a marvel to the scientist as well as to the novice. It is simple in its manifestations, but most complex in its organization and in its ramifications. It has been shown that light, heat, magnetism and electricity are the same, but that they differ merely in their modes of motion.
FIRST HISTORICAL ACCOUNT.--The first historical account of electricity dates back to 600 years B. C. Thales of Miletus was the first to describe the properties of amber, which, when rubbed, attracted and repelled light bodies. The ancients also described what was probably tourmaline, a mineral which has the same qualities. The torpedo, a fish which has the power of