Page:Popular Science Monthly Volume 11.djvu/49

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since its weight has been increased twenty-seven times by the sun's attraction.

We have hitherto considered the mutual attraction of two bodies, but now let a third be introduced, as, for instance, in the case of A and F, let G be placed at equal distances from A and F, and let the relative masses of A and F be as stated before in this paper: then will the force which measures the mutual attraction of F and G be equal to four times the force which measures the mutual attraction of G and A, or, in other words, F will attract G with four times the force that A will attract G. Lastly, let G's mass equal A's mass, and let G be placed at double the distance from F that A has been placed: then, according to the second law of gravitation, the units of force which measure the mutual attraction of A and F will be four times the force which measures the mutual attraction of G and F.



THE anthropoid apes no doubt approach nearer to man in bodily structure than do any other animals; but when we consider the habits of ants, their social organization, their large communities, elaborate habitations, their roadways, their possession of domestic animals, and even in some cases of slaves, it must be admitted that they have a fair claim to rank next to man in the scale of intelligence. They present, moreover, not only a most interesting but also a very extensive field of study. In this country we have nearly thirty species; but ants become more numerous, in species as well as individuals, in warmer countries, and more than seven hundred kinds are known. Even this large number certainly is far short of those actually in existence.

I have kept in captivity nearly half of our British species of ants, and at the present moment have in my room more than thirty nests, belonging to about twenty species, some of which, however, are not English. No two species are identical in habits, and on various accounts their mode of life is far from easy to unravel. In the first place most of their time is passed underground; all the education of the young, for instance, is carried on in the dark. Again, ants are essentially gregarious; it is in some cases difficult to keep a few alive by themselves in captivity, and at any rate their habits under such circumstances are entirely altered. If, on the other hand, a whole community is kept, then the greater number introduces a fresh element of difficulty and complexity. Moreover, within the same species, the individuals seem to differ in character, and even the same individual