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On the mythology of the North American Indians, J. W. POWELL.

Brain-weight and size in relation to the relative capacity of races, D. WILSON. On some fragments of pottery from Vermont, G. H. PERKINS.

On the ancient and modern Pueblo tribes of the Pacific slope of the U. S., E. A. BARBER.

The mood of the verb in conditional clauses, ISAAC B. CHOATE.

The museums of industrial art in Austria, HEINRICH FRAUBERGER.

The archæology of Europe and America compared, S. D. PEET. On the state of society in the Primitive age, id.

3. Geographical Distribution of Plants and Animals; by C. PICKERING, Wilkes' U. S. Exploring Expedition, author of the Races of Man. Part II, Plants in their wild state. 524 pp. 4to, with several colored maps. Salem, Mass. (Naturalist's Agency.) -This work, completing Dr. Pickering's Report on the Geographical Distribution of Plants and Animals, is the result of extensive personal observation about the world as well as of much study. It is a large storehouse of facts, on a subject of general interest, gathered with great labor and fidelity. It gives observations with regard to the characteristic plants and predominant botanical features of all the various islands and continental regions visited by the Exploring Expedition under Captain (now Admiral), Wilkes, and also many collateral facts on climate, topography, scenery, etc., that came under the author's observation. The text is illustrated by maps of the world, presenting by colors the conclusions arrived at by the author.

4. Proceedings of the Davenport Academy of Natural Sciences. Vol. 1, 1-67-1876. 284 pp. 8vo, with 35 plates. Davenport, Iowa, 1876.-This first volume of the Proceedings contains a number of very valuable papers on mounds and mound-builders, by R. J. Farquharson, M.D., W. H. Pratt, A. S. Tiffany, C. Lindsley, and J. D. Putnam, with 34 plates, full of figures representing the structure of mounds, flint and other stone implements, pipes of the form of birds, frogs, and other animals, woven cloth, copper axes, awls, beads, and ear-drops, silver ear-drop, bone knives, pottery, skulls, etc., from different mounds, illustrating a paper by Dr. Farquharson. There are also Zoological articles by J. D. Putnam; Botanical notes by Dr. C. C. Parry; and lists of species of plants, and of land and fresh-water shells, of Coleoptera, Lepidoptera, Hymenoptera, of the vicinity of Davenport, besides other

papers.

OBITUARY.

EBENEZER S. SNELL, of Amherst College, Massachusetts, Professor of Mathematics and Natural Philosophy, died, September 18th, aged seventy-five years.

Prof. CHARLES DAVIES, author of various mathematical works, a graduate of West Point of distinction, and from 1857 to 1867 Professor of Mathematics in Columbia College, died September eighteenth, in his seventy-ninth year.

THE

AMERICAN

JOURNAL OF SCIENCE AND ARTS.

[THIRD SERIES.]

ART. XXXVIII.— Observations on the Displacement of lines in the Solar Spectrum caused by the Sun's rotation; by Professor C. A. YOUNG, of Dartmouth College.

[THE substance of this paper was read at the Buffalo Meeting of the American Association for the Advancement of Science, August 24th, 1876.]

Renewed interest in the question as to the effect of the motion of a luminous body in altering the wave length of the emitted light, has lately been excited by Van der Willigen's mathematical papers upon the subject, and the recent criticisms of Secchi upon the spectroscopic determinations of stellar motions published by Huggins, Vogel, Christie and others. The former, it will be recollected, impugns the received doctrine on mathematical grounds, and it must be acknowledged, that, although his reasoning is not admitted to be conclusive by most astronomers, it has produced a wide-spread distrust, which has been strengthened by the papers of Secchi. The objections of the latter seem however to have been fairly met by the reply of Mr. Christie, recently published in the Monthly Notices, showing the substantial agreement of the results obtained by the different observers after they had learned the delicate precautions essential to success in such observations.

Certainly it seems little short of self-evident that, whenever a point is communicating periodic vibrations to any medium whatever, and, by means of this medium, transmitting them to a second point at a distance, then the frequency, or virtual wave length, of these pulses received at the second point must

AM. JOUR. SCI.-THIRD SERIES, VOL. XII, No. 71.-Nov., 1876.

be affected by any relative motion of approach or recession between it and the source of the vibrations.

It is not difficult to verify this conclusion in the case of sound waves. The beautiful experiments of Vogel, lately published, show as the result of careful quantitative measurements, that the pitch of a locomotive whistle actually undergoes the precise alterations which theory requires, when the engine is either approaching the observer, or receding from him at a known velocity.

Undoubtedly a considerable point would be gained if we could obtain a similar verification in the case of light-if an alteration in the luminous pitch or wave length, produced in a ray of light by some known rate of motion, could actually be made sensible, measured, and shown to coincide with theory within observational limits of error. This verification unfortunately is not easy to obtain, because the velocity of light is so enormous that it is difficult to find an object sufficiently bright, and moving rapidly enough, to make the change of wave length perceptible in our instruments.

I think it was Zöllner who first suggested that the rotation of the sun might furnish the desired test, since its eastern and western limbs have a relative motion of nearly 23 English miles per second along the line of sight. But the displacement of lines in the spectrum due to this velocity is so small (in the case of the D lines about of the distance between them) that the dispersive power of the instruments heretofore employed by most observers, has been insufficient to make it clearly evident. Vogel alone (in 1871) seems to have succeeded in getting any measurements; his results for the sun's equatorial velocity of rotation ranging from 0:35 to 0:42 of a geographical mile, or from 162 to 194 English miles.

By using a diffraction grating, however, combined with a prism in such a way as to separate the overlapping spectra of the higher orders from each other, as described in my recent note on the duplicity of the 1474 line, it is possible to obtain much greater dispersive power, and the displacement then becomes quite sensible.

The apparatus which I have employed consisted of a very fine diffraction grating of 8,640 lines to the inch (for which I am indebted to Mr. Rutherfurd) combined with a telescope and collimator each of 24 inches aperture and sixteen inches focal length, and a prism of 45° inserted between the grating and the object glass of the eye-telescope. The refracting edge of the prism was of course perpendicular to the lines on the grating. The grating, collimator, &c., were mounted on a wooden framework constructed for the purpose, and arranged to be

*This Journal, June, 1876.

attached to the 9 inch Equatorial of the Dartmouth College Observatory, in place of its ordinary spectroscope. Undoubtedly a metallic mounting would have been firmer and better, but with careful manipulation the wooden arrangement answered reasonably well. The eye-telescope and collimator were at a fixed inclination, and the spectra of the different orders were brought into the field of view by turning the grating in the plane of dispersion. This of course made the dispersive power quite different for the spectra of the same order on opposite sides of the image of the slit. The eye-telescope magnified about twenty times and was provided with a micrometer* borrowed from one of the reading microscopes of the meridian circle.

Between the two D lines, the spectra of the sixth and eighth orders usually showed no less than eight other lines, most of which are supposed to be water lines, produced by the vapor in our atmosphere, and therefore of course not subject to displacement by the sun's rotation. I was in hopes to make use of them as reference points, and to determine the displacement of the D lines by simply measuring the intervals with the micrometer. I soon found, however, that the atmospheric lines were too faint and shadowy to admit of sufficient accuracy of bisection, especially by the rather coarse threads with which the micrometer had been provided for the purpose of observing in a feeble light. I was accordingly compelled to make the ob

servations as follows

The grating having been adjusted so as to bring the group of lines to be observed into the center of the field of view, the spectroscope was turned around the optical axis of the telescope until the slit was accurately north and south, so that, if placed tangent to the eastern limb of the sun, a motion of the Right Ascension tangent screw would bring the western limb to tangency. Of course proceeding in this manner the observations were made at points not precisely on the sun's equator, but having a solar latitude ranging from 2° to 15°, according to the date. It was thought better to do this, however, than to risk the disturbance which might be produced by using the Declination tangent screw, which sometimes worked a little jerkily. The slit was then accurately adjusted to the focal plane of the sun's image, and the collimator and the eye telescope were focused carefully for distinct

*The value of one revolution of the micrometer screw (whose head was graduated into 60 divisions,) was about 4′ 9′′; but it was continually varying by a slight amount, since in adjusting for distinct vision of the spectrum no pains was taken to keep the distance between the object glass and the cross hairs strictly constant. This will account for the small variations of the measured intervals between the same lines as determined on different occasions-variations considerably exceeding the probable errors of reading.

vision; after this no adjustment of either telescope or spectroscope was touched in the slightest until the observation was complete. The slit being placed nearly tangent to the limb of the sun, and the driving clock started, a series of micrometer readings was made upon the different lines in the group to be observed, first running the micrometer wires one way and then back, thus obtaining two readings for each line. Then the Right Ascension tangent screw was gently turned until the opposite limb was brought to the slit, and the micrometer readings were repeated, running down and back twice, so as to give four readings of each line; finally, moving the tangent screw so as to bring back the limb first observed, another set of readings was taken, two on each line, which finished the observation. The object of this arrangement of readings is of course to detect any possible disturbance of the instrument during the work, and to eliminate the effect of the earth's rotation, or of any uniformly progressive change in the relative positions of the collimator, grating, and eye-telescope, due to slight alterations of flexure caused by the motion of the telescope. Each reading given in the following tables is therefore the mean of four. The probable error of a single reading (due to inaccuracy of bisection or instrumental disturbance, but not of course including possible constant errors) was found to be about of one micrometer division; so that the probable error of each reading given in the tables is about 0.15 of a division.

It did not occur to me until near the end of the observations that, with the slit tangent to the sun's image, the heat would tend to displace the line of collimation by expanding the slitplate more on one side than the other, and slightly bending the tube to which it is attached. Since, however, the effect would be in opposite directions according as the grating was inclined so as to throw the reflected slit-image to the right or the left, this effect must be nearly eliminated from the final mean. In some of the observations of Aug. 12, it was eliminated by inverting the spectroscope, i. e., rotating the whole spectroscope 180°, around the line of collimation; this, however, in one of the series of readings always brings the eyepiece into an inconvenient position. One set of observations on Aug. 12, was made with the slit radial to the sun's imagein this case the heat of the image has no injurious effect, but it is much more difficult to point the micrometer on the end of a line than on its middle, and the probable errors of reading are more than doubled.

=

The formulæ employed in reducing the observations are as follows: Let U the relative velocity of two opposite points of the sun's equator, and d the corresponding change of wave length of a spectrum-line, whose wave length is A; also let the

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