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THE VARIOUS FORCES OF NATURE.
do. There is no hydrogen in this jar at present, but I will gently turn this jar of hydrogen up under this other jar (fig. 28), and then we will examine the two. We shall see, on applying a light, that the hydrogen has left the 
Fig. 28.jar in which it was at first, and has poured upwards into the other, and there we shall find it.
You now understand that we can have particles of very different kinds, and that they can have different bulks and weights; and there are two or three very interesting experiments which serve to illustrate this. For instance, if I blow soap bubbles with the breath from my mouth, you will see them fall, because I fill them with common air, and the water which forms the bubble carries it down. But now, if I inhale
