instruments are made of very light materials; and, as already mentioned, they are attached to a light framework called a "spider," consisting of three bamboo rods tied together, at their middle points, and set each one at right angles to the other two. To keep them in this position their ends are joined up by thin strings, the whole forming a framework which is very strong for its weight, and which may fall on any part of itself without much damage. The precious apparatus is securely fixed to the very centre of this framework, so that when the balloon drops, it falls always on its feet so to speak. You know how a cat prevents its body being hurt when it falls by twisting in a remarkable way so as to fall on its springy feet? Well, we cannot provide the apparatus with the agility of a cat, so as to make its feet twist under it; but the "spider" has feet in all directions, which acts just as well. Make a "spider" for yourselves when you get home, and see how strong and light it is. Here is a miniature "spider" which Mr. Bellamy has kindly made out of three bits of straw and some thread; and it is so light that even a toy balloon will carry it up if properly filled with hydrogen. We will make the experiment. There! you see; up it goes! It cannot rise high enough to burst in the proper way because the roof stops it; but fortunately Galileo is still up there in the roof, or has gone back again, and he can arrange the bursting for us; and down come the case and spider and all! One very important thing I had nearly forgotten. The spider may fall anywhere—perhaps far away from any town or people. Who is to find it, and send it home? It stands well above the
