« ПредыдущаяПродолжить »
Grammar, Criticism of Mr. Waters's Ar-
In the spirit, T. S. Lowden.
Lesson Story, Ruric N. Roark..
Lightning, A Stroke of, J. A. Culler.. 454
Machine, A, J. A. Culler..
Minutes of Department of Superintendence 428
Normal Schools, Emerson E. White.. 223
Opening Exercises, Some Plans for, Mar-
........171, 215, 269
166, 206, 265, 310, 418, 463, 503, 543, 590
School Curriculum, Limitations of, Arthur
Self-Training of the Teacher, The, Mary
Taught in the Country Schools? George
Suggestion in Life and Society, Daniel
By FRANK G. CARPENTER, author of "ASIA” and “NORTH AMERICA.” Traveler and newspaper correspondent. A fascinating book of travel, profusely illustrated, with photographs by the author.
“SOUTH AMERICA," just issued, contains
Across the Isthmus of Panama..
In Lima, the Capital ....
On the Roof of South America
A Visit to a Chileau Farm
At the End of the Continent.
Life on the Pampas.
A Trip to the Interior
In the Land of Coffee..
Up the Amazon
8 15 17
7 62 10 12 15 9
Single copies of any of our publications witl be sent by mail, postpaid, on
AMERICAN BOOK COMPANY,
317 Walnut Street, Cincinnati, Ohio.
Pipelir berary, JAN 8/1900 Who JUL
THE PROBABLE AGE OF THE EARTH, AND HOW
IT IS DETERMINED.
BY J. A. BOWNOCKER.
Aside from the origin of the rocks (sandstones, limestones, earth there is perhaps no question shales, etc.); while Sir Alfred R. relating to our planet of more gen- Wallace thought 28,000,000 years eral interest than its age. At the sufficient time to allow. Some outset let it be understood that we years ago Professor Alexander can not hope to make anything like Winchell announced 3,000,000 an exact statement of this, and that years as the time required, this bewe must content ourselves with a ing the lowest geological estimate rough approximation.
of 'which the writer has knowTo determine this estimate we ledge. In 1893 Mr. C. D. Walcott, have at present two methods, one the director of the United States of these may be styled the Geo- geological survey, announced 45,logical, since it is based on data 000,000 as the time necessary for pertaining to that science; and the the formation of the sedimentary other the Physical, because it uses rocks; and in the same year Mr. the principles of Physics. How W. J. McGee stated that in his these estimates are actually made opinion, 6,000,000,000 years are will be stated later in this paper.
These figures show Let us first examine the estimates two things: (1) That geologists themselves, as made by the follow- themselves vary greatly in their esers of these two sciences.
timates of the age of the earth;
and (2) that our planet is very old, THE GEOLOGISTS' ESTIMATES.
for if the smallest of the above James Croll thought 72,000,000 figures should be adopted even years have elapsed since the depo- then our planet would have an ansition of the first sedimentary tiquity greater than would have
been thought possible a few gener- examined, it will be found that ations ago.
those of the former are generally THE PHYSICISTS' ESTIMATES. much larger than those of the latLord Kelvin, who has taken the
In fact until comparatively lead in this mode of computations,
recent years geologists were announced in 1862 that the crust of
customed to deal with time as of
unlimited extent. If 100,000,COO the earth could not have been formed less than 20,000,000 years
years sufficed for the production of ago nor more than 400,000,000
a certain phenomenon, very good; years ago. At the same time he but if it did not, then this period
trebled. stated that 100,000,000 would be might be doubled sufficient to include the total geo
Thus it happened that the geolological history of our planet. But
gist became accustomed to dealing later, after reviewing the evidence,
with vast periods, and time became he announced that only about 20,
to him an important item of his
stock in trade. 000,000 years could be granted. Professor Tait still further restricts
But in the sixties the physicist geological time, and can not allow began to call a halt to these heavy more than 10,000,000 years. Pro
demands on the “bank of time." fessor Simon Newcomb, the emi
Instead of geological time being of nent American astronomer, states
unlimited extent it was declared to that owing to the great heat of the be just the reverse; and while it is early crust water in the liquid doubtless very long when judged form has not existed on our planet by human standards, it is nevermore than 10,000,000 years, and he
theless short when compared to estimates the age of the solar sys
the periods demanded by the geoltem at about 20,000,000. Profes- ogists. Not
content, however, sor George Darwin has computed with this general restriction, the that the moon separated from the physicist has made reduction after earth about 57,000,000 years ago,
reduction in his estimates, until and since this happened while the
the time allowed for the evolution planet was still in a liquid condi- of our planet appears altogether intion it was long before the begin- adequate to the geologist. ning of geological time, which, we While these restrictions may say, dates from the formation hardly be accepted by the geoloof a solid crust.
gist, it must be admitted that they HOW THE PHYSICIST HAS CHECKED
have performed a useful service in THE GEOLOGIST.
restraining him from the use of If the estimates of the geolo- vast ages for which there is neither gists and physicists just named be authority nor necessity.