deal in addition to the mere circumstance that particles attract each other. But you must not now suppose that because they are liquid they have lost their attraction of cohesion; for here is the fluid mercury, and if I pour it from one vessel into another, I find that it will form a stream from the bottle down to the glass--a continuous rod of fluid mercury, the particles of which have attraction sufficient to make them hold together all the way through the air down to the glass itself; and if I pour water quietly from a jug, I can cause it to run in a continuous stream in the same manner. Again, let me put a little water on this piece of plate-glass, and then take another plate of glass and put it on the water; there! the upper plate is quite free to move, gliding about on the lower one from side to side; and yet, if I take hold of the upper plate and lift it up straight, the cohesion is so great that the lower one is held up by it. See how it runs about as I move the upper one! and this is all owing to the strong attraction of the particles of the water. Let me shew you another experiment. If I take a little soap and water--not that the soap makes the particles of the water more adhesive one for the other but it certainly has the power of continuing in a better manner the attraction of the particles (and let me advise you, when about to experiment with soap-bubbles, to take care to have everything clean and soapy). I will now blow a bubble; and that I may be able to talk and blow a bubble too, I will take a plate with a little of the soapsuds in it, and will just soap the edges of the pipe, and blow a bubble on to the plate. Now, there is our bubble. Why does it hold together in this manner? Why, because the water of which it is composed has an attraction of particle for particle,--so great, indeed, that it gives to this bubble the very power of an india-rubber ball; for you see, if I introduce one end of this glass tube into the bubble, that it has the power of contracting so powerfully as to force enough air through the tube to blow out a light (fig. 22)--the light is blown out. And look! see how the bubble is disappearing, see how it is getting smaller and smaller. [Illustration: Fig. 22. and Fig. 23.]