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104 with all you have previously seen, to show you how we procure heat. And now for the effects of this power. We need not consider many of them on the present occasion, because when you have seen its power of changing ice into water and water into steam, you have seen the two principal results of the application of heat. I want you now to see how it expands all bodies—all bodies but one, and that under limited circumstances. Mr. Anderson will hold a lamp under that retort, and you will see the moment he does so that the air will issue abundantly from the neck which is under water, because the heat which he applies to the air causes it to expand.

And here is a brass rod (fig. 32) which goes through that hole and fits also accurately into this gauge; but if I make it warm with