of metal, and bring it against the knob at the top and the metallic coating at the bottom, you will see the electricity passing through the air as a brilliant spark. It takes no sensible time to pass through this; and if I were to take a long metallic wire, no matter what the length--at least as far as we are concerned--and if I make one end of it touch the outside, and the other touch the knob at the top, see how the electricity passes!--it has flashed instantaneously through the whole length of this wire. Is not this different from the transmission of heat through this copper bar (fig. 42), which has taken a quarter of an hour or more to reach the first ball? [Illustration: Fig. 43.] Here is another experiment, for the purpose of shewing the conductibility of this power through some bodies, and not through others. Why do I have this arrangement made of brass? [pointing to the brass work of the electrical machine, fig. 41]. Because it conducts electricity. And why do I have these columns made of glass? Because they obstruct the passage of electricity. And why do I put that paper tassel (fig. 43) at the top of the pole, upon a glass rod, and connect it with this machine by means of a wire? You see at once that as soon as the handle of the machine is turned, the electricity which is evolved travels along this wire and up the wooden rod, and goes to the tassel at the top, and you see the power of repulsion with which it has endowed these strips of paper, each spreading outwards to the ceiling and sides of the room. The outside of that wire is covered with gutta-percha. It would not serve to keep the force from you when touching it with your hands, because it would burst through; but it answers our purpose for the present. And so you perceive how easily I can manage to send this power of electricity from place to place, by choosing the materials which can conduct the power. Suppose I want to fire a portion of gunpowder, I can readily do it by this transferable power of electricity. I will take a Leyden jar, or any other arrangement which gives us this power, and arrange wires so that they may carry the power to the place I wish; and then placing a little gunpowder on the extremities of the wires, the moment I make the connection by this discharging rod, I shall fire the gunpowder. [The connection was made, and the gunpowder ignited.] And if I were to shew you a stool like this, and were to explain to you its construction, you could easily understand that we use glass legs, because these are capable of preventing the electricity from going away to the earth. If, therefore, I were to stand on this stool, and receive the electricity through this conductor, I could give it to anything that I touched. [The Lecturer stood upon the insulating stool, and placed himself in connection with the conductor of the machine.] Now, I am electrified--I can feel my hair rising up as the paper tassel did just now. Let us