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Printing designed and executed by W. P. Dunn Company may be found upon the desks of the most fastidious and enterprising business men, because it has that indefinable something about it that attracts and holds until its mission as a salesman has been fulfilled We know from long experience that if your booklet or catalog is dressed up in "Dunn" style it will become an agent from which more results will be obtained than from any other source

Mention The Technical World.

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By PROFESSOR DAVID TODD, Ph. D.
Director, Amherst College Observatory

HAT unique New England poet,
a compound of daring, whimsi-
cality and
genius, once wrote:

"Eclipses are predicted,

And Science bows them in."

True enough at the time Emily Dickinson jotted down these lines, her statement has become increasingly accurate during all the years following. As long ago as the days of Thales, in the sixth century before Christ, a periodicity in the return of eclipses had been discovered, so that their appearance could be roughly foretold. Probably first noted by the Chaldeans, the greatest astronomers of antiquity, it is not unlikely that the Chinese had also found general methods of prediction as early as 2000 B. C., halffabulous incidents of their astrologers perhaps tending to support this theory.

But from the first accurately foretold eclipse by Thales, 585 B. C., so closely as "this very year in which it did actually occur," to that of August 30th, 1905, methods, discoveries, and precision have steadily advanced, until now it is possible to give all the circumstances of coming eclipses—exact locality, duration, and in

stant of occurrence-for many years ahead

Periodic Occurrence

The period or round of eclipses that these early astronomers employed is still useful to us. It is called the Saros, and its length is 6,585 days, or 18 years 11 days. Usually 41 eclipses of the sun will happen in this period, and about ten of them will be total ones. A Saros may be taken as beginning at any time, and the nature of the eclipses occurring in any one period changes but slowly; so that once we have the time and place and circumstances of all the eclipses in one Saros, we can predict all those of the next half-century with confidence.

But not with great accuracy, for there are too many variable conditions entering into the problem of the celestial machine.

Operation of the Solar System

The cosmos of the solar system is but a vast mechanism, and eclipses are but the inevitable phenomena of its perfect working. Compare it with the automatic contrivances of a modern Hoe printing

Copyright, 1905, by The Technical World Company

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