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Page:Popular Science Monthly Volume 38.djvu/662

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THE POPULAR SCIENCE MONTHLY.

independent concepts. But if cowardice and slavishness gave the true and only explanation, still more pointed would be the lesson taught by the modern general exchange of the same courteous action between strong and weak, rich and poor.

The history of salutations does not directly show the contest of good and evil or of any principles, but it illustrates the transition from egoism to altruism. Whatever was a custom, men considered to be right, while it lasted. Men have not at any time chosen between industrialism and militarism, but an evolution has proceeded in industrialism and militarism themselves as also in peoples, who have advanced, though slowly and with stumbles, from lower to higher planes of culture. Differing environments affected their earliest conceptions and practices, and expedited or delayed their march. Those peoples who have reached civilization and enlightenment can still find the representatives of their early greetings among remote savages, and perhaps trace some of the salutations above mentioned to subhuman ancestors. Ages before the great poet wrote, the human race obeyed the precept, to

"Move upward, working out the beast,
And let the ape and tiger die."

Note.—A similar study of verbal salutations, inculcating the same lessons as the present article on gestural greetings, has been published by the same author in the American Anthropologist for July, 1890, under the title of Customs of Courtesy.

[Concluded.]

 

NON-CONDUCTORS OF HEAT.
By JOHN M. ORDWAY,

PROFESSOR OF APPLIED CHEMISTRY IN TULANE UNIVERSITY OF LOUISIANA.

IT is a matter of common observation that a hot body continually gives off its heat to things around it, until at length the giver and the receivers all come to a common temperature. This gradual equalization may be brought about in three different ways: In the first place, heat is thrown off in every possible direction from every point of a heated body by what we call radiation. Secondly, when air, water, or any other fluid is in contact with a hot surface that is not directly over it, the touching particles become warm and light, and move away to give place to others. This carrying away heat by the successive particles of a fluid is called convection. In the third place, when a solid substance is placed against anything of a higher temperature, its nearest parts are warmed and give up a portion of the heat received to those parts lying next to them; and these, again, share their gain with those next in order; and so on, till