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78 105. Thus we see that whether we keep both coils stationary, and suddenly produce a current in the right-hand coil, or whether, keeping this current constantly going, we suddenly bring it near the other coil, the inductive effect will be precisely the same, for in both cases the left-hand coil is suddenly brought into the presence of a current. And again, it is the same, whether we suddenly break the right-hand current, or suddenly remove it from the left-hand coil, for in both cases this coil is virtually removed from the presence of a current.

106. We are now in a position to enumerate the various kinds of energy which occur in nature; but, before doing so, we must warn our readers that this enumeration has nothing absolute or complete about it, representing, as it does, not so much the present state of our knowledge as of our want of knowledge, or rather profound ignorance, of the ultimate constitution of matter. It is, in truth, only a convenient- classification, and nothing more.

107. To begin, then, with visible energy. We have first of all—

(A.) Visible energy of actual motion—in the planets, in meteors, in the cannon ball, in the storm, in the running stream, and in other instances of