YEAR-BOOK

OF

NATURE

AND

POPULAR SCIENCE

FOR 1872.

EDITED BY

JOHN C. DRAPER, M. D.,

PROFESSOR OF NATURAL HISTORY AND PHYSIOLOGY IN THE COLLEGE OF
THE CITY OF NEW YORK, AND OF CHEMISTRY IN THE

UNIVERSITY MEDICAL COLLEGE.

NEW YORK:

SCRIBNER, ARMSTRONG & Co.

1873.

Entered according to Act of Congress, in the year 1873, by

SCRIBNER, ARMSTRONG & CO.,

In the Office of the Librarian of Congress, at Washington.

Stereotyped at the
WOMEN'S PRINTING HOUSE,

56, 58 and 60 Park Street,

New York.

PREFACE.

THE presentation of a complete record of the investigations in Nature and Science, for a year, would require a library of many volumes; the editor has, therefore, selected only such subjects as appeared to be of general interest, the object in view being to reach the largest number of readers, and diffuse among these a knowledge of the more important results obtained and opinions advanced during the year.

It will be found that in many instances different opinions are given regarding the same subject. This arises from the character of the work, and the editor in no way assumes responsibility for any opinions, except in those instances in which it is expressly stated. The endeavor has been made in all cases to give credit to those to whom it belongs. In a few instances the authorities have been accidentally omitted. For these omissions it is hoped indulgence will be granted. In

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