95. Thus we have two things. In the first place, before the two terminals, or poles, have been brought together, we have them charged with opposite electricities; and, secondly, when once they have been brought together, we have the production of a continuous current of electricity. Now, this current is an energetic agent, in proof of which we shall proceed to consider the various properties which it has,--the various things which it can do. _Its Magnetic Effects._ 96. In the first place, _it can deflect the magnetic needle_. For instance, let a compass needle be swung freely, and let a current of electricity circulate along a wire placed near this needle, and in the direction of its length, then the direction in which the needle points will be immediately altered. This direction will now depend upon that of the current, conveyed by the wire, and the needle will endeavour to place itself at right angles to this wire. In order to remember the connection between the direction of the current and that of the magnet, imagine your body to form part of the positive current, which may be supposed to enter in at your head, and go out at your feet; also imagine that your face is turned towards the magnet. In this case, the pole of the magnet, which points to the north, will always be deflected by the current towards your right hand. The strength of a current may be measured by the amount of the deflection it produces upon a magnetic needle, and the instrument by which this measurement is made is called a _galvanometer_. 97. In the next place, _the current is able_, not merely to deflect a magnet, but also _to render soft iron magnetic_. Let us take, for instance, the wire connected with the one pole of the battery, and cover it with thread, in order to insulate it, and let us wrap this wire round a cylinder of soft iron, as in Fig. 9. If we now make a communication between the other extremity of the wire, and the other pole of the battery, so as to make the current pass, it will be found that our cylinder of soft iron has become a powerful magnet, and that if an iron keeper be attached to it as in the figure, the keeper will be able to sustain a very great weight. [Illustration: Fig. 9.] _Its Heating Effect._ 98. _The electric current has likewise the property of heating a wire through which it passes._ To prove this, let us connect the two poles of a battery by means of a fine platinum wire, when it will be found that the wire will, in a few seconds, become heated to redness. In point of fact, the current will heat a thick wire, but not so much as a thin one, for we may suppose it to rush with great violence through the limited section of the thin wire, producing in its passage great heat. _Its Chemical Effect._