at different places where the parties were encamped, and diagrams ou sixteen plates giving the ĥorary and diurnal barometric curves, temperature, mean differences of wet and dry thermometers, diurnal force of vapor, and relative humidity.

4. Die Vereinigten Staaten von Nord Amerika, von Dr. FRIEDR. RATZEL. Erster Band. Physikalische Geographie und Naturcharakter, mit 12 Holzschn. u. 5 Kart. in Farbendruck. 668 pp. large 8vo. Munich, 1878.-This very large and beautifully printed work is the first of two volumes on the United States, and treats of the physical geography and natural features of the country. The work has been prepared by one who has well mastered his subject, through the writings of the various American contributions to it-those of the earlier and later exploring expeditions, the principal State Geological Reports, the works of Lyell, Fremont, J. D. Whitney, Guyot, Humphreys and Abbott, Walker's Statistical Atlas, Schott's table and results of Precipitation, and others; and he has presented the facts in a judicious and systematic manner. The maps are handsomely colored and illustrate the geology (from Blake and Hitchcock's map), surface relief, forest-distribution, and other characteristics.

The volume opens with a general sketch of the Continent, and of the outlines of the country. Then follow-a brief review of the geology of the United States; an account of the surface reliefs, occupying 115 pages; of the rivers, lakes, hot springs, etc.; the climate; and the distribution of plants and animals. The second part of the volume occupying the following 200 pages, contains special descriptious of different natural sections of the country— for example, forest regions, prairies, New England, the Atlantic coast, the Florida Keys, Cypress swamps, the Western plains, the Bad Lands, "California natur;" the Sierra Nevada, the Great Lakes, and other topics. The second volume will be occupied with the "culturgeographie" of the United States; and will give the facts with fulness like the first, and with reference to the practical rather than the theoretical.

5. Report upon Forestry; by FRANKLIN B. HOUGH. 650 pp. Washington, 1878.-This report by Mr. Hough was prepared under the direction of the Commissioner of Agriculture, in pursuance of an act of Congress, of August, 1876. It is a practical, comprehensive work, embracing a wide range of topics bearing on forest waste; forest growth; forest lands and reservations; forest distribution; forest culture as affected by legislation, climate, treatment; methods of tree planting and effects of the various kinds of soils and exposures; the cultivation of special kinds of trees; uses of woods, charcoal, the resins and other products of trees; insect ravages and the consequences of other enemies, with the modes of prevention; a general detailed discussion of climate in this and other countries, in its bearing on the subject, with the experiences and experiments of the nations of Europe and elsewhere; effects of forests on climate; forest legislation over the world; forest resources and culture in different

United States; lumber statistics; and various other topics, on all of which the author has brought forward a great amount of valuable facts, and in a manner to enlighten and benefit every part of the country.

6. Bulletin of the Bussey Institution, vol. ii, Part iii, 1878.This number of the Bussey bulletin contains the following papers: on the hybridization of Lilies by F. PARKMAN; on the composition of Equisetum arvense by F. H. STORER; composition of shells of crabs and lobsters, and those of oysters, clams, mussels, etc., id.; prominence of carbonate of lime as a constituent of solutions obtained by percolating dry cultivable soils with water, id.; Supplementary note to an article on the composition of pumpkins, id.; a list of Fungi found in the vicinity of Boston, with remarks, by W. G. FARLOW.

7. The Speaking Telephone, Talking Phonograph, and other Novelties; by GEORGE B. PRESCOTT. 432 pp. 8vo, with numerous illustrations. New York. 1878. (D. Appleton & Co.).—This volume contains a complete account of the Telephone and Phonograph, in their various forms, with a large number of excellent figures illustrating their construction and mode of use, and also diagrams of the vibrations or "logographic records" of the phonograph. It also treats of Quadruplex telegraphy at much length, giving many detailed figures in the course of the chapter.

8. The Naturalist's Directory for 1878. Edited by S. E. Cassino. 184 pp. 12mo. Salem, Mass., 1878.-This well arranged catalogue of the names and addresses of all "naturalists of America north of Mexico," and of all Scientific Societies, is a very useful and convenient work to those who are interested in any way in science, even if not doing more than collecting a cabinet. The new edition, just published, appears to be very complete. The editor states in his preface that he will be thankful for corrections and additions.

9. Fownes's Elementary Chemistry, revised and corrected by Henry Watts, B.A., F.R.S., a new American from the 12th English edition, edited by ROBERT BRIDGES, M.D., Professor of Chemistry, Philadelphia College of Pharmacy. 1026 pp. 8vo. Philadelphia, 1878. (Henry C. Lea).—A new and improved edition of this very convenient manual.

10. Journal of the Cincinnati Society of Natural History. Vol. I, No. i, April, 1878. 52 pp. 8vo, with two plates.-Contains contributions to paleontology by S. A. Miller and C. B. Dyer, describing various Silurian fossils, figures of which are given on the plates; also a paper on a new species of Pupa by C. R. Judge; and another on the tongue of some Hymenoptera by V. T. Chambers.

11. Glaciers of the Western Himalayas.-The glaciers of the Western Himalayas, according to measurements recently given in the Tour de Monde, far surpass in extent any hitherto examined outside of the polar regions. In the Mustagh range, two glaciers immediately adjoining one another possess a united length of sixty-five miles. Another glacier in the neighborhood is twenty

one miles in length, and from one to two miles in width. Its upper portion is at a height of 24,000 feet above the level of the sea, and its lower portion terminating in masses of ice 250 feet in height, and three miles in breadth, is 16,000 feet above the sea.— Nature, July 4.

12. Instructions for observing the Total Solar Eclipse of July 29, 1878. Prepared by Professor WM. HARKNESS and issued by the United States Naval Observatory. 30 pp. 4to. Washington, 1878.

Elements of Dynamic: an Introduction to the study of motion and rest in solid and fluid Bodies; by W. K. CLIFFORD, F.R.S.-Part I, Kinematic. 222 pp. 12mo. London. 1878. (Macmillan & Co.).

OBITUARY.

WILLIAM M. GABB died, of consumption, on the 30th of May last, at Philadelphia, where he was born on the 20th of January, 1839. In 1862, Mr. Gabb entered upon the duties of paleontologist of the Geological Survey of California, under Professor J. D. Whitney. The larger part of the first volume on the paleontology and the whole of the second, are occupied with his reports on the Cretaceous and Tertiary fossils of the State; the two illustrated by sixty plates of fossils. In 1868 he undertook a survey in Santo Domingo for the Santo Domingo Land and Mining Company; and in 1873 published an extended memoir on the Topography and Geology of that islaud in the Transactions of the American Philosophical Society (vol. xv). In 1873 Mr. Gabb went to Costa Rica, under an appointment from the government of the State, and engaged in a topographical and geological survey of the territory, in which he made also extensive ethnological and natural history collections for the Smithsonian Institution. A memoir on the topography of the country, with a map, was published in Petermann's Mittheilungen; and another, on ethnology, in the Transactions of the American Philosophical Society. But an extensive report on Costa Rica geology and paleontology remains to be published. Various papers of his have appeared also in the Proceedings of the Philadelphia and Philosophical Society; and several in this Journal, the last in the number for March of the current year. Mr. Gabb was a man of vast energy, and an earnest and careful investigator. His various contributions to science are a great honor to the country-and eminently so to the State of California, for which a large share of his work was done.

BARON VON BIBRA died on June 5th at Nuremberg, in his seventy-second year. He was the author of various chemical, zoological, physiological, archæological and literary works and memoirs. He explored Brazil, Chili and some other parts of South America, and published accounts of his observations and his discoveries in natural history. He is the author also of many popular works of fiction, the scenes of several of which were laid in South America.

ANDREAS VON ETTINGSHAUSEN, Professor of Physics at Vienna, died on the 25th of May, having been born in Heidelberg, Nov. 25, 1796.

THE

AMERICAN

JOURNAL OF SCIENCE AND ARTS.

[THIRD SERIES.]

ART. XV.-On the Origin of Comets; by H. A. NEWTON.

1. KANT in the exposition of his theory of the development of the solar system treats the comets as formed from the matter of the condensing solar nebula. To him they were planets, in fact, but somehow thrown out of their normal circular orbits. Although he gave for this origin of the comets no reasons which astronomers can respect, yet it is proper to call the hypothesis by his name. On the other hand, Laplace in his exposition of the nebular hypothesis considered that the comets were made from the matter that is scattered through the stellar spaces, and that in their origin they have no relations with the solar nebula. Have we in our accumulation of facts since the times of Kant and Laplace learned any thing which helps us to decide between these two hypotheses? I propose to consider what peculiarities each of them requires in the shape and distribution of the cometic orbits, and then compare with the theories the observed facts.

2. For convenience I shall assume that the solar system has been brought into its present condition by some process of development. Hence the comets have not through all past time moved, even approximately, in their present orbits. After the comets became separate parcels of matter two kinds of forces could alter the forms of their orbits, resistance of a medium (if such exists), and the attraction of gravitation of the sun and planets.

3. Nearly all the comets that we have seen, and have computed the orbits of, come nearer to the sun than the planet Mars. The exceptions are only about five per cent of the AM. JOUR. SCI.-THIRD SERIES, VOL. XVI, No. 93.—SEPT., 1878.

whole number. We may therefore assume that comets to become visible to us ought, in general, to come nearer to the sun than that planet. All others may be regarded as permanently invisible. There is, however, no reason to doubt that many such unseen comets exist. Even those which we see become invisible at a moderate distance from the earth and sun.

4. The orbits of most comets are so near to a parabolic form that it is only when they are very well observed that we can detect any deviation therefrom. They pass to a great distance from the sun, and it is reasonable to suppose that their origin, even on Kant's hypothesis, was remote from the sun. We must interpret that hypothesis as meaning that some of the parcels of matter that would normally have gone to make up distant planets became scattered into comet masses.

5. Consider such a parcel, or comet mass, A, at a point such that the line AS from A to the sun S is large; for example, 1,000 times the distance from the earth to the sun. Now if the velocity of A exceeds the small velocity acquired by a body falling by attraction from an infinite distance down to A, that is, exceeds the velocity in a parabolic orbit, then by the law of gravitation the orbit of A around S must be an hyperbola. The more the velocity of A is in excess of the parabolic velocity the more manifestly will the hyperbola differ from a parabola. But, since the known comet orbits, if any of them are hyperbolas, differ little from parabolas, we are permitted to assume for them a velocity at the distance AS not largely in excess of the parabolic velocity. All other orbits we have nothing to do with. Laplace proves satisfactorily that we ought, by the theory of probabilities, rarely to see such comets.

6. Let now the velocity of A be resolved into two parts by the parallelogram of motions, one component along AS, and one at right angles to AS. The part at right angles to AS will be very small compared with the parabolic velocity for the point A. Otherwise the comet, whatever is the curve it is describing, would go around the sun at a great distance, and would belong to the class of comets that are always invisible to us and with which we have, therefore, nothing to do.

7. Consider a large number of comets passing through the point A, or rather shot from the point A. Through S draw a plane perpendicular to AS, and on that plane draw a circle whose radius is twice the radius of Mars' orbit. That plane and circle we may regard as a target at which the several cometic masses may be regarded as launched. Only those whose velocities perpendicular to AS are small will strike within the circle, and so coming nearer to the sun than Mars will form part of the group of comets which we know any. thing about.