formed from experience in regard to the one have been transferred to the other, and the properties belonging to one, such as density, elasticity, etc., have been asserted as properties of the other.
There is so considerable a body of knowledge bearing upon the similarities and dissimilarities of these two entities that it will be well to compare them. After such comparison one will be better able to judge of the propriety of assuming them to be subject to identical laws.
1. MATTER IS DISCONTINUOUS.
Matter is made up of atoms having dimensions approximately determined to be in the neighbourhood of the one fifty-millionth of an inch in diameter. These atoms may have various degrees of aggregation;—they may be in practical contact, as in most solid bodies such as metals and rocks; in molecular groupings as in water, and in gases such as hydrogen, oxygen, and so forth, where two, three, or more atoms cohere so strongly as to enable the molecules to act under ordinary circumstances like simple particles. Any or all of these molecules and atoms may be separated by any assignable distance from each other. Thus, in common air the molecules, though rapidly changing their positions, are on the average about two hundred and fifty times their own diameter apart.
This is a distance relatively greater than the distance apart of the earth and the moon, for two hundred and fifty times the diameter of the earth will be 8000 × 250 = 2,000,000 miles, while the distance to the moon is but 240,000 miles. The sun is 93,000,000 miles from the earth, and the most of the bodies of the solar system are still more widely separated, Neptune being nearly 3000 millions of miles from the sun. As for the fixed stars, they are so far separated from us that, at the present rate of motion of the solar system in its drift through space—500 millions of miles in a year—it would take not less than 40,000 years to reach the nearest star among its neighbours, while for the more remote ones millions of years must be reckoned. The huge space separating these masses is practically devoid of matter; it is a vacuum.
THE ETHER IS CONTINUOUS.
The idea of continuity as distinguished from discontinuity may be gained by considering what would be made visible by magnification. Water appears to the eye as if it were without pores, but if sugar or salt be put into it, either will be dissolved and quite disappear among the molecules of the water as steam does in the air, which shows that there are some unoccupied spaces between the molecules.
If a microscope be employed to magnify a minute drop of water it still shows the same lack of structure as that looked at with the unaided eye. If the magnifying power be the highest it may reveal a speck as small as the hundred-thousandth part of an inch, yet the speck looks no different in character. We know that water is composed of two different kinds of atoms, hydrogen and oxygen, for they can be separated by chemical means and kept in separate bottles, and again made to combine to form water having all the qualities that belonged to it before it was decomposed. If a very much higher magnifying power were available, we should ultimately be able to see the individual water molecules, and recognize their hydrogen and oxygen constituents by their difference in size, rate of movements, and we might possibly separate them by mechanical methods. What one would see would be something very different in structure from the water as it appears to our eyes. If the ether were similarly to be examined through higher and still higher magnifying powers, even up to infinity, there is no reason for thinking that the last examination would show anything different in structure or quality from that which was examined with low power or with no microscope at all. This is all expressed by saying that the ether is a continuous substance, without interstices, that it fills space completely,
and, unlike gases, liquids, and solids, is incapable of absorbing or dissolving anything.