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four sections, whereof the first treats of heat, the second of steam-engines and boilers, the third of locomotives, and the fourth of marine-engines.

Bulletin of the Minnesota Academy of Natural Sciences for 1874. Pp. 108. Price, 50 cents.

It is gratifying to receive so substantial an evidence as this of the progress of science in the more recently-settled portions of our country. The titles of the papers in the present number are: "Birds of Minnesota," by Dr. P. L. Hatch; "Mammalia of Minnesota," by Dr. A. E. Ames; "Report of the Curator of the Museum;" "Prerequisites to a Proper Study of Science," by Dr. Charles Simpson; "Minnesota Geological Notes," by N. H. Winchell; "Antiquity of Man," by Dr. A. E. Johnson; "Astronomy—Scientific and Unscientific," by G. W. Tinsley.

Archives of Dermatology: a Quarterly Journal of Skin and Venereal Diseases. Edited by L. Duncan Bulkley, M. D. New York: Putnams. $3.00 a year.

This is anew periodical, and as a "first number" the specimen before us is excellent. The Archives has no rival on this side of the Atlantic, and this circumstance, taken in connection with its intrinsic worth, ought to insure its success. Besides original communications, of which the present number contains six, the Archives will contain the Transactions of the New York Dermatological Society, clinical records, a digest of the current literature of dermatology, reviews and bibliography, and editorials.

The Protoplasm Theory. By Edward Curtis, A. M., M. D. Pp. 23.

Dr. Curtis is Professor of Materia Medica and Therapeutics in the New York College of Physicians and Surgeons, and this is his introductory lecture for the winter course of 1873. It is an able argument for the oneness of the physical basis of life throughout the organic world. Though the lecture was originally addressed to medical students, it nevertheless may be read understandingly and with profit by the lay public.

Organic Chemistry. By W. Marshall Watts, D.Sc, F.C.S. New York: Putnams. Pp. 130. Price, 75 cents.

The primary aim of this little manual appears to be, to fit students for passing the examinations of the English "Science and Art Department." In so far as the book discusses its subject-matter proper, viz., the chemistry of the carbon compounds, it is as full and explicit as could be expected, considering its size.

Report upon Ornithological Specimens collected in the Years 1871, 1872, and 1873. Pp. 148.

Catalogue of Plants collected in the Years 1871, 1872, and 1873. Washington: Government Printing-Office. Pp. 62.

These valuable Reports form a part of the published work of the geographical and geological explorations under the charge of Lieutenant Wheeler. The Ornithological Report is by Dr. H. C. Yarrow, and has been revised and corrected by Robert Ridgway, of the Smithsonian Institution. The Catalogue of Plants is by Mr. Sereno Watson and Dr. J. T. Rothrock.


The Cause of "Cold Snaps."—In a paper read before the American Academy of Science, Prof. Loomis offered a new theory to account for sudden falls of temperature, or "cold snaps," as they are called. The usual mode of accounting for these is by supposing that a current of cold air sets in from the north. A laborious investigation of the subject has led Prof. Loomis to the conclusion that these low temperatures, which occur at irregular intervals in every month, and particularly during the winter, are due mainly to the descent of cold air in the neighborhood, and that this descent of air results from the outward movement, which generally takes place from the centre of an area of high barometer. The theory is fully sustained by observations. As for the opposite theory, if the cold comes to us from the north, "whence does it come," asks Prof. Loomis, "to these colder known points on the earth's surface?" In summer, during a thunder-storm, the temperature often