CHAPTER XV.
THE CONSTITUTION OF GASES.
F late years the attention of those who study the mysteries of nature has specially tended in the direction of examining the very smallest particles into which the chemical elements can be divided. It is true that these particles or molecules, as we generally call them, are too minute to be appreciated by our senses; they cannot be detected even by the most potent microscope. Indeed, if we will but think of it, we could hardly expect our nerves to disclose the character of objects so minute as molecules. Like all the rest of matter, nerves are constituted of molecular particles, and the structure of the most sensitive fibre is far too coarse to transmit indications of the special characteristics of the molecules, of which matter in general is composed. The little objects about which we are to write are things which we can never see, which we can never feel severally. They require to be brought together in clustering myriads where individual peculiarities are merged in general properties before they can make any successful appeal to our organs of sense.
How then, it may well be asked, are we able to learn
