really and truly electrical phenomena. [Illustration: Fig. 46. and Fig. 47.] Now, let us consider what is this spark. I take these two ends and bring them together, and there I get this glorious spark, like the sunlight in the heavens above us. What is this? It is the same thing which you saw when I discharged the large electrical machine, when you saw one single bright flash; it is the same thing, only _continued_, because here we have a more effective arrangement. Instead of having a machine which we are obliged to turn for a long time together, we have here a _chemical_ power which sends forth the spark; and it is wonderful and beautiful to see how this spark is carried about through these wires. I want you to perceive, if possible, that this very spark and the heat it produces (for there is heat) is neither more nor less than the chemical force of the zinc--its _very_ force carried along wires and conveyed to this place. I am about to take a portion of the zinc and burn it in oxygen gas, for the sake of shewing you the kind of light produced by the actual combustion in oxygen gas of some of this metal. [A tassel of zinc-foil was ignited at a spirit-lamp, and introduced into a jar of oxygen, when it burnt with a brilliant light.] That shews you what the affinity is when we come to consider it in its energy and power. And the zinc is being burned in the battery behind me at a much more rapid rate than you see in that jar, because the zinc is there dissolving and _burning_, and produces here this great electric light. That very same power, which in that jar you saw evolved from the actual combustion of the zinc in oxygen, is carried along these wires and made evident here; and you may, if you please, consider that the zinc is burning in those cells, and that _this_ is the light of that burning [bringing the two poles in contact, and shewing the electric light]; and we might so arrange our apparatus as to shew that the amounts of power evolved in either case are identical. Having thus obtained power over the chemical force, how wonderfully we are able to convey it from place to place! When we use gunpowder for explosive purposes, we can send into the mine chemical affinity by means of this electricity; not having provided fire beforehand, we can send it in at the moment we require it. Now, here (fig. 47) is a vessel containing two charcoal points, and I bring it forward as an illustration of the wonderful power of conveying this force from place to place. I have merely to connect these by means of wires to the opposite ends of the battery, and bring the points in contact. See what an exhibition of force we have! We have exhausted the air so that the charcoal cannot burn; and, therefore, the light you see is really the burning of the zinc in the cells behind me--there is no disappearance of the carbon, although we have that glorious electric light; and the moment I cut off the connection, it stops. Here is a better instance to enable some of