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Page:Popular Science Monthly Volume 21.djvu/476

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462
THE POPULAR SCIENCE MONTHLY.

when the focus is so distant that a strong echo is returned from the opposite wall. Their object is rather to control such rays of sound as would otherwise go up to the roof and be retained as a disagreeable echo. A perfectly flat surface placed over the pulpit and not too far from the speaker's head, will often do this; but it is better to have the wall back of the pulpit gradually curve forward until it completely overhangs the speaker's head. The speaker must be near to this wall, so that the direct and reflected sounds may be as nearly as possible identical.

There is a belief, prevalent among some architects, that a hall, in order to be acoustically good, must have its length, breadth, and height in harmonic proportion. There seems to be no good foundation for this belief, and the author, after careful experimental inquiry, has failed to find that this is the case.

It frequently happens that, in a building in which there is considerable resonance, the speaker, by timing his syllables so that the resonance of one shall have disappeared before the next is uttered, may make himself understood to a large audience with comparative ease. This is recognized by most public speakers, and it is not uncommon to hear them speak of the "key-note" of any particular hall.

The act of striking the "key-note" consists not so much in pitching the voice at any particular key as in carefully timing the rate at which the syllables succeed each other.

 

PROGRESS OF THE GERM THEORY OF DISEASE.[1]
By JOHN TYNDALL, F. R. S., LL. D. (M. D., TÜBINGEN).

THE virtual triumph of the antiseptic system of surgery, based as that system is on the recognition of living contagia as the agents of putrefaction, is of good augury as regards the receptivity of the public mind to new views respecting the nature of contagia generally.

To the credit of English surgeons it stands recorded that, guided by their practical sagacity, they had adopted in their hospitals measures of amelioration which reduced, almost to a minimum, the rate of mortality arising from the "mortification" of wounds. They had discovered the evils incident to "dirt"; and, by keeping dirt far away from them, they had saved innumerable lives, which would undoubtedly have succumbed under conditions prevalent in many of the hospitals of Continental Europe.

In thus acting, English surgeons were, for the most part, "wiser than they knew." Their knowledge, however momentous in its prac-

  1. Introductory Note reprinted from Professor Tyndall's "Essays on the Floating Matter of the Air, in Relation to Putrefaction and Infection."