and using a red glass to diminish the glare of the light, admitted by the slit, the prominence being seen by means of the C line in the red. Mr. Lockyer had a design for seeing the prominences as a whole by giving the slit a rapid motion of small extent, but this proved to be superfluous, and they are now habitually seen with their actual forms. Nor is our power of observing them restricted to those which are so situated that they are seen by projection outside the sun's limb; such is the power of the spectroscopic method of observation, that it has enabled Mr. Lockyer and others to observe them right on the disc of the sun, an important step for connecting them with other solar phenomena. One of the most striking results of the habitual study of these prominences is the evidence they afford of the stupendous changes which are going on in the central body of our system. Prominences, the heights of which are to be measured by thousands and tens of thousands of miles, appear and disappear in the course of some minutes. And a study of certain minute changes of position in the bright line F, which receive a simple and natural explanation by referring them to proper motion in the glowing gas by which that line is produced, and which we see no other way of accounting for, have led Mr. Lockyer to conclude that the gas in question is sometimes travelling with velocities comparable with that of the earth in its orbit. Moreover, these exhibitions of intense action are frequently found to be intimately connected with the spots, and can hardly fail to throw light on the disputed question of their formation. Nor are chemical composition and proper motion the only physical conditions of the gas which are accessible to spectral analysis. By comparing the breadth of the bright bands (for though narrow they are not mere lines) seen in the prominences, with those observed in the spectrum of hydrogen, rendered incandescent under different physical conditions, Dr. Frankland and Mr. Lockyer have deduced conclusions respecting the pressure to which the gas is subject in the neighborhood of the sun."

Since the discovery of Lockyer's, Janssen's, and Huggins' method of viewing the prominences, Zöllner has discovered a way of seeing them as a whole. His method will be found on page 322; Prof. Young's method will be also found in detail on page 315. He makes use also of the Cline, and likens it to looking at the sunset sky through a chink in the window. It is thought that this method may be used to advantage in the coming transit of Venus. The total eclipse of August 7th, 1869, was very fully observed.

The "American Journal of Arts and Sciences" thus speaks of the arrangements made for observing the phenomenon:—

“Few astronomical phenomena have probably ever called out a more thoroughly organized system of observation than that arranged for the recent eclipse. The line of total obscuration crossed the North American continent diagonally, entering the territory of the United States at Behring's Straits, in about the 65th degree of latitude, and longitude 90° west of Washington, while it left our shore at the latitude of 34° and the meridian of Washington itself. It traversed a central belt of well-populated territory, yet there seems to have been scarcely a town of any considerable magnitude along the entire line which was not garrisoned by observers having some special astronomical problem in view.

An appropriation was made by Congress, at its last session, for carrying out a series of observations under the direction of the Superintendent of the Nautical Almanac, and Prof. Coffin has succeeded, by the liberal aid of the Navy Department, and the very generous and extensive facilities contributed by some of the principal railroads, in providing for an amount of work which for magnitude, variety, and thoroughness, seems large beyond all proportion to the sum placed at his disposal. Three cities in Iowa, Burlington, Mount Pleasant, and Ottumwa, were occupied by astronomical, photographic, and physical observers under his direction, and special observers, provided with telescopes and instruments for determining geographical position, were sent by him to the North and South, to fix the limits of the belt of total obscuration.

The Navy Department, besides making other provisions, sent observers to the western shore of Behring's Straits; and the War Department detailed Dr. Curtis to make special photographic observations at Des Moines, Iowa.

The Coast Survey established parties on the Yaken River, in Alaska, at Des Moines in Iowa, Springfield in Illinois, and Abingdon in West Virginia, and perhaps at still other stations, that at Springfield being amply provided with photographic observers and apparatus. Most of the principal observatories likewise organized expeditions of greater or less magnitude. From Washington, the several observers arranged independent series of investigations, stellar, spectroscopic, physical, and meteorological. From Cambridge, a large party went to Shelbyville, Ky., with large photographic outfit, and spectroscopic equipments.

From Albany, a similar party went to Mattoon, Illinois; others, from Clinton and Chicago, went to Des Moines, from Cincinnati to Sioux City; and the number of private astronomers who established themselves along the central line with telescopes and other apparatus of investigation must have been exceedingly large.

The beginning and end of the eclipse seem to have been observed a few seconds later, and the beginning and end of the totality about fifteen seconds later than the predictions of the American Nautical Almanac. As regards the exact position of the central line, and of the limits of the total belt, we have as yet insufficient information to determine the degree of accordance with computation. There can be no doubt that materials have been collected capable of improving the adopted values of the moon's diameter and horizontal parallax. One of the most interesting results is the introduction of a new and accurate method of determining the time of first contact, by observing with a spectroscope the gradual occultation of the bright lines of the chromosphere. This we owe to Prof. Young, of Dartmouth College, who formed one of Prof. Coffin's Nautical Almanac party at Burlington. By keeping the centre of the slit directed to the point at which the contact is to take place, the observer is forewarned of the approach of the moon's limb, by the shortening of the bright lines belonging to the chromosphere. The line C is well adapted to this purpose, and is seen to grow steadily shorter, until it is totally extinguished. The moment of disappearance of the last bright ray is of course that of the first contact, which is thus observed with the same care and accuracy as any other appulsive phenomenon. Although the first contact, as determined in this way by Prof. Young, was noted some five seconds before its recognition by any other observer, it was subsequently found by Prof. Mayer to accord within a small fraction of a second with the time as determined by measurement of a series of photographs taken during the first minute.

Prof. Harkness, of Washington Observatory, observed at Des Moines the spectra of five protuberances, no two of which gave the same lines. In the corona spectrum he found no absorptive lines, and but one bright line. Measures of the protuberances were made by Prof. Rogers, at Des Moines, who found the largest to be nearly a minute and a half high, and observed a peculiar honeycombed or cellular appearance in all of them. Special search was made for intra-mercurial planets by Prof. Newcomb, at Des Moines, according to the plan suggested by

him in the April number of the "American Journal of Science and Arts," with two 6-inch object-glasses, having a field of about 20° each, and previously clamped to the desired position. A similar scrutiny of the ecliptic near the sun was made by Dr. Gould, at Burlington, in connection with Prof. Coffin's party, using a Tolles' telescope of five inches' aperture and a field of nearly 2°, provided with occulting discs at the focus. But neither of these observers, nor any others engaged in similar research, found any indications of planets nearer than Mercury. Dr. Gould says in a letter to Prof. Morton: "An examination of the beautiful photographs made at Burlington and Ottumwa, by the section of your party in charge of Professors Mayer and Himes, and a comparison of them with my sketches of the corona, have led me to the conviction that the radiance around the moon, in the pictures made during totality, is not the corona at all, but is actually the image of what Lockyer has called the chromosphere."

Prof. Pickering, of the Massachusetts Institute of Technology, who observed at Mt. Pleasant, Iowa, concludes his report as follows:

"An increase of heat and actinic power is observed in the beginning of the eclipse, caused by an increased brightness of the sun's disc near the moon's limb. The spectrum of the corona appears to be free from dark lines, but may contain two or three bright ones. Its striæ are spiral rather than radial, and its light is unpolarized. The sky adjoining it, however, reflecting light from the earth, shows strong signs of polarization.”

From Prof. Winlock's report we learn that "The chromosphere was carefully examined both before and after the eclipse. Only three lines could be seen, C, one near D, and F. During totality only, the brightest protuberance on the lower limb of the sun was examined carefully. In the short time occupied in getting into this, nothing was seen but a faint continuous spectrum; but since the observing telescope took in only a small part of the spectrum at once, nothing conclusive can be inferred from the observation as to the non-existence of bright lines in the corona. During totality, eleven bright lines were seen. Besides the three described above, there was a short line at or very near E; the three lines of B were bright and very sharp, and there were four lines above F. Although these lines were very bright on a dark ground, all of them but the three seen before the eclipse disappeared instantly on the first burst of sunlight, and the same

66

point in the sun's disc was examined with great care after totality without finding any of the lines but those above described.

"The photograph of the corona, taken at Shelbyville, shows a flattening at the extremities of the sun's axis, and an elevation about the equatorial region. The appearance can be explained by the hypothesis that it is a photographic view of the sun's atmosphere, and the form is that which it would assume from the sun's rotation about its axis with its upper surface disturbed by the protuberances or planes below, and by large waves which are to be expected in such an atmosphere."

The report of Com. B. F. Sands, U. S. N., Superintendent of the U. S. Naval Observatory, on the late eclipse, just published, is an exhaustive one, and compares favorably with the best efforts of a similar nature on the other side of the Atlantic.

Prof. Kirkwood, of Bloomington, Indiana, has lately published two able papers; one upon the periodicity of the solar spots, and another on comets and meteors. In the first-named paper he discusses the disturbing action of the planets on the sun's envelope, and suggests the hypothesis that a particular portion of the sun's surface is more favorable to spot formation than other portions. From his discussions he concludes: :

1. A connection between the behavior of sun-spots and the configuration of certain planets has been placed beyond reasonable doubt.

2. The theory, however, of spot formation by planetary influence is encumbered with anomalies and even inconsistencies, unless we admit the co-operation of a modifying cause.

3. The hypothesis that a particular part of the solar surface is more susceptible than others to planetary disturbance is rendered probable by the observations of different astronomers.

4. The 11-year cycle of spot variation is mainly dependent on the influence of Mercury.

5. The marked irregularity of this period from 1822 to 1867 is in a great measure due to the disturbing action of Venus.

6. Wolf's 56-year cycle is determined by the joint action of Mercury and the earth; and, finally, the hypothesis proposed accounts for all the well-defined cycles of spot-variations.

In the paper on comets and meteors, Prof. Kirkwood considers the probable consequences of the sun's motion through regions of space in which cosmical matter is widely diffused, and compares these theoretical deductions with the observed phenomena of comets, aerolites, and falling stars.