A text-book on chemistry : for the use of schools and colleges . Fig. 122,through which a cur-rent is made to flow,all the portions of thewire conspire to movethe needle in the same direction. The effect, thereforebecomes much greater than in the case of a single con-tinuous wire. On the same principle, if, instead of a single turn, thewire is repeatedly coiled upon it- Fig. 123. self, so as to make a great many gturns, the effect upon the needle may ,_be greatly increased; and when the n-c needle is made nearly astatic, that ? is to say, its tendency to point north Sc nearly destroyed by arra
A text-book on chemistry : for the use of schools and colleges . Fig. 122,through which a cur-rent is made to flow,all the portions of thewire conspire to movethe needle in the same direction. The effect, thereforebecomes much greater than in the case of a single con-tinuous wire. On the same principle, if, instead of a single turn, thewire is repeatedly coiled upon it- Fig. 123. self, so as to make a great many gturns, the effect upon the needle may ,_be greatly increased; and when the n-c needle is made nearly astatic, that ? is to say, its tendency to point north Sc nearly destroyed by arranging it upon an axis with another needle, similar to it in all respects, but with its poles reversed, as N S, S N, Figure 123, the directive tendency of the one needle neutralizing How does the intensity of magnetic action vary? In what does CEr-steds discovery consist ? What is the direction which the needle movesin the four positions round the wire ? What is the effect on a needle inthe interior of a rectangle ? What is the principle of the galvanometer ?. 3N lD> 3N 136 ELECTRO-MAGNETIC ROTATION. Fig. 121. the other, but both tending to turn in the same directionby the current in the coil of wire, inasmuch as one is with-in the coil and the other above it, the arrangement formsa most delicate means of discovering and measuring anelectric current. It is called a galvanometer. As action and reaction are always equal and contrary,it is obvious that, if a conducting wire be movable andthe magnet stationary, the latter can be made to impressmotions on the former. Conducting wires can be made to revolve round thepoles of a magnet, or the pole of a mag-net round a conducting wire; thus, in aglass cup, Fig. 124, let a magnet, n, befixed vertically, and the cup filled withmercury; by means of a loop, a, let aconducting wire, b, be suspended, havingperfect freedom of motion. If an electriccurrent is made to pass down this wirethrough the mercury, and escape by thepath d, the wire r
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