you to see the certainty with which we can convey this force, where, under ordinary circumstances, chemical affinity would not act. We may absolutely take these two charcoal poles down under water, and get our electric light there;--there they are in the water, and you observe, when I bring them into connection, we have the same light as we had in that glass vessel. Now, besides this production of light, we have all the other effects and powers of burning zinc. I have a few wires here which are not combustible, and I am going to take one of them, a small platinum wire, and suspend it between these two rods, which are connected with the battery; and, when contact is made at the battery, see what heat we get (fig. 48). Is not that beautiful?--it is a complete bridge of power. There is metallic connection all the way round in this arrangement; and where I have inserted the platinum, which offers some resistance to the passage of the force, you see what an amount of heat is evolved,--this is the heat which the zinc would give if burnt in oxygen; but as it is being burnt in the voltaic battery, it is giving it out at this spot. I will now shorten this wire for the sake of shewing you, that the shorter the obstructing wire is, the more and more intense is the heat, until at last our platinum is fused and falls down, breaking off the circuit. [Illustration: Fig. 48.] [Illustration: Fig. 49.] Here is another instance. I will take a piece of the metal silver, and place it on charcoal, connected with one end of the battery, and lower the other charcoal pole on to it. See how brilliantly it burns (fig. 49). Here is a piece of iron on the charcoal--see what a combustion is going on; and we might go on in this way, burning almost everything we place between the poles. Now, I want to shew you that this power is still chemical affinity--that if we call the power which is evolved at this point _heat_, or _electricity_, or any other name referring to its source, or the way in which it travels, we still shall find it to be chemical action. Here is a coloured liquid which can shew by its change of colour the effects of chemical action. I will pour part of it into this glass, and you will find that these wires have a very strong action. I am not going to shew you any effects of combustion or heat; but I will take these two platinum plates, and fasten one to the one pole, and the other to the other end, and place them in this solution, and in a very short time you will see the blue colour will be entirely destroyed. See, it is colourless now!--I have merely brought the end of the wires into the solution of indigo, and the power of electricity has come through these wires, and made itself evident by its chemical action. There is also another curious thing to be noticed, now we are dealing with the chemistry of electricity, which is, that the chemical power which destroys the colour is only due to the action on one side.