Gambar halaman
PDF
ePub

eclipse-observations indicated a change in the color and appearance of the corona. The gaseous elements were much less conspicuous than in the eclipses of 1869, 1870, and 1871, near the epoch of sun-spot maximum. In short, the conclusion of most astronomers is that the non-gaseous matter of the corona is cosmical, while the gaseous elements so conspicuous in eclipses at the epochs of spot maxima are strictly solar, consisting of torrents thrown out to great distances by the sun's eruptive force. "In spot-maximum years," says Mr. Lockyer, we have violent up-rushes of gas from the sun's interior, and the corona is mainly built up of such gas. Further, we have spots, and, if these are not evidences of the return convection currents, we have none other. In spot-minimum years, such as the present, we have no up-rushes, and the corona contains no gas, and there are no spots. Spots, then, are only observed when we have a right to look for the return of the upward current, about which there is no doubt, and the rate of which we have measured."

66

The serrations known as Baily's beads remained visible, according to Mr. Colbert, for two and a half seconds, indicating that the mountains around the moon's disk are one and a half mile high.

The Relation between Sun-spot Frequency and Changes in the Earth's Atmosphere.-The "American Journal of Science" for June, 1878, contains a letter from Dr. B. A. Gould, Director of the Cordoba (S. A.) Observatory, announcing the probable discovery of a mutual relation between the number of sun-spots and the condition of the earth's atmosphere. During the first two or three years of Dr. Gould's residence at Cordoba-at the epoch of sunspot maximum-the state of the atmosphere was eminently favorable for astronomical observations. With the change, however, in the condition of the sun's surface, a simultaneous variation occurred in the atmosphere and mean temperature of Buenos Ayres and the Argentine Republic. In 1877 there were but ten clear nights at Cordoba during the months of March and April, while in July and August the number was still less; and from January 1 to March 20, 1878, there was but one clear night. In Dr. Gould's view these strong contrasts indicate periodic fluctuations, and an elaborate discussion of the facts at his disposal sustains the theory of a mutual relation. It is manifest," Dr. Gould remarks, "that if the variations of the terrestrial temperature follow those of the sun-spots, and are thus adequate to account for the correspondence observed between these and the variations of the magnetic declination, all necessity for assuming any direct and transcendental connection between this latter and the disturbance of the solar surface disappears."

[ocr errors]

The Transit of Mercury.-A transit of Mercury occurred on the 6th of May, 1878, the passage occupying 7. 33m.. The phenomenon was

generally observed under favorable conditions. Prof. S. P. Langley of Allegheny, Pa., saw the entire disk of Mercury outside the sun at least half a minute before the first external contact. This visibility was regarded as due to the brightness of the coronal background. A remarkable difference was noticed between the apparent size of the planet before and after its entrance upon the sun; the former being greater than the latter in the ratio of five to four. Prof. Langley saw no "black drop" nor "ligament." He failed also to see the central bright spot, as well as the aureola around the planet-phenomena observed by several other astronomers.

A comparison of the best contact-observations obtained at different stations gave new evidence in favor of Leverrier's theory of the motion of Mercury's perihelion, and of the existence of a cause of perturbation between Mercury and the sun.

Relative Brightness of Venus and Mercury. -On September 26, 1878, Mercury and Venus were so close together that they were telescopically in the same field of view. Mr. James Nasmyth of Kent, England, improved this favorable circumstance by making careful comparisons of the relative brightness of the two planets. The result of the observation was that Mercury has less than half the brightness of Venus, or, in other words, less than half the reflective power. This relative deficiency is the more remarkable when it is considered that, in consequence of Mercury's nearness to the sun, its brightness ought to be nearly four times greater than that of Venus. The fact seems to indicate an important difference between the atmospheres of the two planets.

The

The Satellites of Mars.-In a memoir recently published by the Washington Observatory, Prof. Asaph Hall has discussed all the observations of the satellites of Mars, and has determined the elements of their orbits within very narrow limits of probable error. name Phobos has been adopted by Prof. Hall for the inner satellite, and that of Deimos for the outer. In brightness the former is rated by the discoverer as an 113-magnitude star; the latter as of the 12th. The diameter of Deimos is estimated by Prof. Pickering of Harvard Observatory at six miles, that of Phobos at seven. At Washington alone 43 observations of Phobos and 52 of Deimos were obtained up to October 25th, when they could no longer be detected by the 26-inch equatorial. The periods and eccentricities derived from these observations are as follows:

[blocks in formation]
[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][ocr errors][ocr errors][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][ocr errors][merged small]

The following minor planets, discovered in 1877, have been named since the issue of our last volume: No. 171, Ophelia; 172, Baucis; and 178, Belisana.

The Mass of Saturn's Rings. In the "Comptes Rendus," vol. lxxxv., No. 16, M. Tisserand has given a new determination of the mass of Saturn's rings. Bessel's value of the mass was found from its disturbing effect on Titan, the largest satellite. M. Tisserand includes in his discussion the motions of the other satellites, and finds that the change in the position of their orbits is not so much due to the attraction of the ring as to that of the protuberant matter about Saturn's equator. M. Tisserand's value of the mass is, the mass of Saturn being 1. This is less than one fifth of the value obtained by Bessel.

Comets.-The first comet of 1878 was discovered by Mr. Lewis Swift of Rochester, N. Y., on the 7th of July. It had a perceptible central condensation, but neither tail nor nucleus. Its motion is direct; its inclination, 78 degrees; and its perihelion distance was 128,000,000 miles.

The second comet of 1873 was detected on its first predicted return by M. Tempel of Arcetri, near Florence, on the 19th of July, 1878. It had the appearance of a nebula three or four minutes in diameter, with several nuclei. With the aid of Dr. Von Asten's ephemeris Mr. John Tebbut of Windsor, New South Wales, detected Encke's comet on the evening of August 3d. This is the eighteenth perihelion passage since its periodicity was discovered by Encke, and the comet has been observed at each successive return. Its appearance in 1878 was that of an extremely faint nebulosity. Mr. J. D. Hirst, writing from Sydney, New South Wales, under date of August 21st, says:

The comet is a very inconspicuous object, even with a low power and the full aperture of the 11inch Sydney refractor. It appears as a circular nebulous body, showing signs of condensation in the center, but no distinct nucleus. On the evening of the 20th of August two tenth-magnitude stars wero observed in the field with the comet, the motion of the latter rendering it apparent that it must pass very close to, if not immediately over, one of them. This actually took place just before the comet set, the center of the comet passing directly over the

star. It is interesting to record that this faint tenthmagnitude star was not even dimmed, much less obliterated, by the interposition of the densest part of the comet; it shone right through the center and most condensed part as bright as it had before appeared against the dark background of the sky. The other star of the same magnitude in the field formed an accurate standard of comparison by which to determine any diminution of light in the former.

The Origin of Comets.-The "American Journal of Science" for September, 1878, contains an elaborate article on the origin of comets, by Prof. H. A. Newton of Yale College. In the theory of Kant comets as well as planets were originally parts of the nebulous mass from which the solar system was formed. Laplace, on the other hand, regarded them as of extraneous origin. Prof. Newton discusses such cometary phenomena as have an obvious bearing on this interesting question, and finds a decided preponderance of evidence in favor of a foreign origin. He grants, however, that the group of comets with periods corresponding with those of the minor planets may have originated in the solar nebula.

Meteoric Showers.-The meteors of January 1st-3d-called Quadrantids from the fact that their radiant is in Quadrans-were observed in unusual numbers by Prof. Herschel at Hawkhurst, England, on the morning of January 2, 1878. In thirty minutes Prof. Herschel counted twenty meteors, of which seventeen were Quadrantids. Two were as bright as Jupiter, five equal to first-magnitude, six equal to second-, and the rest about equal to third-magnitude

stars.

The Meteors of April 19th-23d. - The "Monthly Notices" for May, 1878, give the results of Mr. W. F. Denning's watch for and 22d of the month. Twelve meteors were meteors of the April shower on the 20th, 21st, seen which belonged, undoubtedly, to the group of Lyraids. The radiant, very exactly determined, was in R. A. 272°, N. decl. 32°.

The August Meteors.-The meteors of August 8th-12th were observed in 1878 under unfavorable circumstances; cloudy weather in many places, as well as bright moonlight, interfering with the observations. In "The Observatory" for September, Mr. H. Corder of sults of his observations: During four hours Chelmsford, England, gives the following reon the night of the 10th he counted 113 meteors, of which 97 were Perseids. Of these,

60 had visible streaks and 20 were colored.

The

One

The maximum was from 2h 15m. to 3h 15m. during which hour he saw 44 meteors. radiant was in R. A. 43°, N. decl. 56°. 47°, N. decl. 58°. On the same night Mr. W. meteor was seen absolutely stationary at R. A. F. Denning, watching at Bristol, England, saw 130 meteors in four hours and a half. During the half hour ending at 3 o'clock, when the moon had set, he counted 33.

Meteoric Fire-balls.-In "The Observatory" for February and March, 1878, Capt. G. L. Tupman discusses the observations of a great

fire-ball seen in England, Ireland, and Wales, on the evening of November 23, 1877, at 8h. 24TM, G. M. T. The radiant of this meteor was in R. A. 62°, N. decl. 21°; height when first seen, 96 miles; first explosion at mid-course, exactly over Liverpool, at a height of 46 miles; length of visible path, 183 miles; time of flight, 8 seconds nearly; velocity, 17 miles per second; final explosion over the Irish Sea, at an elevation of 14 miles. A bright streak 40 miles in length and nearly half a mile in diameter remained visible for several seconds over the latter part of the path. "All that was left after the explosion settled slowly downward, perhaps for a mile, before becoming invisible, which would indicate that it was of the nature of an impalpable powder." The plane of the meteor's motion was nearly coincident with that of the ecliptic. Capt. Tupman remarks that this fireball undoubtedly belonged to a meteor stream previously known, whose radiant is in Taurus, and that the orbit is near that of the comet of 1702.

The disappearance of the meteor was followed by the most violent detonation. "The explosion of a 13-inch bomb-shell, consisting of some 200 pounds of iron, would not have produced a sound of one hundredth part of the intensity of the meteor explosion. This proves that it was of considerable mass compared to an ordinary shell. A difficult question remains to be answered. How is it conceivable that such a mass of heavy matter can be reduced to impalpable powder in five or six seconds? All these bodies must be heavy to retain their planetary velocities after impact with the atinosphere in the way they do."

Several other large meteors were seen on the same evening, their paths, or at least some of them, radiating from the same point in the constellation Taurus. Capt. Tupian thus concludes his interesting paper:

The frequency of large detonating meteors about November 21st-23d was long ago pointed out by Mr. R. P. Greg and Prot. A. S. Herschel, but the exact determination of the radiant point or of their real heights has seldom been possible. It is satisfactory to have secured one of them so well. From the investigations of Prof. H. A. Newton of Yale University, the great detonating meteor of November 20, 1877, in the United States, proceeded from the radiant near Gamma Cassiopeia, found by Prof. Herschel for a detonating meteor on the same night in 1864. It is evident, therefore, that there are two streams, perfectly distinct, crossing the earth's orbit in the place it occupies about November 20th-28d, and both yielding very large detonating meteors.

In "Nature" for February 28, 1878, Mr. H. Hatfield describes a meteor seen by himself on the morning of February 18th, at 12" 47".. Its brilliancy surpassed that of the moon then full.

third that of the moon. The same fire-ball was seen at Everett, Mass., by Mr. William F. Delany.

A daylight meteor was seen in full sunshine near Hawick, England, by Mr. James Elliott and others, at 10h 20m on the morning of March 25th.

A large detonating fire-ball was observed at several points in England on the evening of April 2d, at 7h 55m.. It appeared in Ursa Major, passed between Sirius and the belt of Orion, and thence at a slow rate and in a direct line to the horizon. Its diameter was about half that of the moon.

A meteor whose apparent magnitude was estimated at one third that of the moon was seen at Pultney, England, by Mr. James L. McCance, on the evening of April 20th. In about two seconds it moved from R. A. 42°, N. decl. 30°, to R. A. 47°, N. decl. 20°.

A very bright meteor was observed by Mr. Trouvelot of Cambridge, Mass., on the evening of June 6th, at 9h 25m.. It occulted Omicron Ursa Majoris, and moved nearly due west. When about the middle point of its visible path it burst into several parts, but the explosion was followed by no detonation.

On the evening of August 22d, at 10h. 2m., a brilliant meteor was simultaneously seen by Mr. Seth C. Chandler, Jr., at Marlboro, N. H., and Mr. E. F. Sawyer, at Cambridge, Mass.

At 7 o'clock P, M., November 12, 1878, a very brilliant meteor was seen in southern Indiana. Prof. D. E. Hunter of Washington, Davies County, describes it as presenting a clearly defined disk with a diameter equal to two thirds that of the full moon. It appeared in Lyra, very close to Vega, passed in a southerly direction through the Milky Way, and disappeared about 20° N. W. of Jupiter. It was visible ten seconds.

Binary Stars.-In Christie's "Observatory" Doberck of Markree, Ireland, has a valuable for August and the following months Dr. memoir on binary stars. The following are his latest determinations of the periods of seventeen systems, together with the true eccentricities of their orbits:

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small]

402.62 66

0.7890

845.86 1001.21

66

0.7515

66 0.3292

XI Boōtis... Tau Ophiuchi.. Eta Cassiopeia Lambda Ophiuchi... 44 Bootis.... 1938 Struve.. 86 Andromeda. Gamma Leonis. Sigma Coronæ.. Alpha Geminorum

In the "Science Observer" for April, Mr. E. F. Sawyer describes a meteor observed at Boston on the 31st of March, at 7 54m. It moved very slowly over an arc of eight de- The average eccentricity of the binaries grees, and its apparent diameter was one whose periods are less than 200 years is

0.4306; of those whose periods exceed 200 years, 0.6055.

New Double Stars.-A new companion of Aldebaran has been discovered by Mr. S. W. Burnham of Chicago, at the distance of only 30" from the large star. It is very faint, being about equal in apparent magnitude to the outer satellite of Mars. In February, 1878, the same distinguished observer discovered the companion of Rigel to be undoubtedly double. The instrument used in his observations was the 18-inch Clark equatorial of the Chicago Observatory. Mr. Burnham calls attention also to the star 99 Herculis, whose duplicity was discovered by Mr. Alvan Clark in 1859. The companion, since the date of its discovery, has undergone a change of 42° in its angular position. The components, therefore, in all probability, constitute a binary system.

Birmingham on Red Stars.—Mr. Birmingham of England has been engaged for several years on the observations of red stars, and has recently published some interesting results and speculations in the "Transactions of the Royal Irish Academy." His catalogue contains 658 of these objects, with descriptions by himself or references to the observations of other astronomers. According to Mr. Birmingham, red stars are to be found chiefly in a particular part of the heavens, viz., that part of the Milky Way extending through the constellations Aquila, Lyra, and Cygnus. It is noticed, moreover, that a large proportion of the red stars are variable, and that the intensity of their color varies inversely with the apparent magnitude. Mr. Birmingham refers these phenomena to the existence of nebulous rings with an accumulation of matter on one side, and more or less absorption of some of the colored rays, according to the densities of the different sections. The color of the red stars which are not variable may be due, he supposes, to a permanent atmosphere. Mr. Birmingham's memoir contains a collection and discussion of the spectroscopic observations of Huggins, Secchi, Vogel, and D'Arrest.

Belation between the Colors and Periods of Variable Stars.-The "Science Observer" for July, 1878, contains a paper by Mr. Seth C. Chandler of Boston on the relation between the colors of variable stars and the lengths of their periods. In Schönfeld's catalogue of 138 variable stars he finds 26 whose colors are not given, or whose periods are irregular. Deducting these, he arranges the remaining 112 in classes according to the length of their periods, separating the red or reddish from those noted as white, yellow, or of no decided color. The result is as follows:

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

It is seen at a glance that the number of rea stars increases with the length of the period, while that of white or colorless stars de

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][ocr errors]

"The progressive increase in the value of the average period from the white stars at the one end of the scale to the intense red at the other end is very remarkable."

The Origin of Nebula.-The "Philosophical Magazine" for July, 1878, contains an article on the origin of nebulæ by Dr. James Croll of Scotland. Laplace and other writers on Cosmogony had assumed the existence of matter in a state of gaseous diffusion, and had shown how the solar and sidereal systems may have been formed by the process of condensation, and how future systems may be evolved in like manner from existing nebulæ ; but what the previous condition of a nebula was, or what physical cause had produced its present gaseous state, they had never inquired. The object of Dr. Croll's memoir is "to examine the bearings of the modern science of energy on the question of the origin of nebulæ, and in particular to consider the physical cause of the dispersion of matter into stellar space in the nebular form."

A brief view of Dr. Croll's hypothesis may be presented as follows: The so-called fixed stars are well known to have a proper motion in space. Reasons are not wanting for believing that non-luminous bodies also exist, in indefinite numbers, moving in all possible directions, and with various degrees of velocity. The occasional impact of these opaque stars would be a necessary consequence. With great velocity at the moment of collision, sufficient heat might be developed to reduce the united mass to the form of a gaseous nebula. is supposed to have been the origin of the thousands of nebulae revealed by the telescope. The fixed stars have been produced by the condensation of ancient nebula. These as they cool down must gradually become extinct, to continue their motion as non-luminous bodies until a new encounter, in the distant future, shall reconvert them into nebula.

Such

The process by which opaque stars are supposed to have been transformed into nebulæ is thus given in Dr. Croll's very interesting memoir:

Take the case of the origin of the nebulous mass out of which our sun is believed to have been formed. Suppose two bodies, each one half the mass of the sun, approaching each other directly at the rate of

0

476 miles per second (and there is nothing at all improbable in such a supposition), their collision would transform the whole of the motion into heat, affording an amount sufficient to supply the present rate of radiation for 50,000,000 years. Each pound of the mass would, by the stoppage of the motion, possess not less than 100,000,000,000 foot-pounds of energy transformed into heat, or as much heat as would suffice to melt 90 tons of iron or raise 264,000 tons 1° C. The whole mass would be converted into an incandescent gas, with a temperature of which we can form no adequate conception. If we assume the specific heat of the gaseous mass to be equal to that of air (viz., 2374), the mass would have a temperature of about 300,000,000° C., or more than 140,000 times that of the voltaic arc. It may be objected that, enormous as would be such a temperature, it would nevertheless be insufficient to expand the mass against gravity so as to occupy the entire space included within the orbit of Neptune. To this objection it might be replied that, if the temperature in question were not sufficient to produce the required expansion, it might readily have been so if the two bodies before encounter be assumed to possess a higher velocity, which of course might have been the case. But without making any such assumption, the necessary expansion of the mass can be accounted for on very simple principles. It follows in fact from the theory that the expansion of the gaseous mass must have been far greater than could have resulted simply from the temperature produced by the concussion. This will be obvious by considering what must take place inmediately after the encounter of the two bodies, and before the mass has had sufficient time to pass completely into the gaseous condition. The two bodies coming into collision with such enormous velocities would not rebound like two elastic balls, neither would they instantly be converted into vapor by the encounter. The first effect of the blow would be to shiver them into fragments, small indeed as compared with the size of the bodies themselves, but still into what might be called in ordinary language immense blocks. Before the motion of the two bodies could be stopped, they would undoubtedly interpenetrate each other; and this of course would break them up into fragments. But this would only be the work of a few minutes. Here, then, we should have all the energy of the lost motion existing in these blocks as heat (molecular motion), while they were still in the solid state; for as yet they would not have had sufficient time to assume the gaseous condition. It is obvious, however, that the greater part of the heat would exist on the surface of the blocks (the place receiving the greatest concussion), and would continue there while the blocks retained their solid condition. It is difficult in imagination to realize what the temperature of the surfaces would be at this moment. For, supposing the heat were uniformly distributed through the entire mass, each pound, as we have already seen, would possess 100,000,000,000 footpounds of heat. But as the greater part of the heat would at this instant be concentrated on the outer layers of the blocks, these layers would be at once transformed into the gaseous condition, thus envelop ing the blocks and filling the interspaces. The temperature of the incandescent gas, owing to this enormous concentration of heat, would be excessive, and its expansive force inconceivably great. As a consequence, the blocks would be separated from each other, and driven in all directions with a velocity far more than sufficient to carry them to an infinite distance against the force of gravity were no opposing obstacle in their way. The blocks by their mutual impact would be shivered into smaller fragments, each of which would consequently become enveloped in incandescent gas. These smaller frag; ments would in a similar manner break up into still smaller pieces, and so on until the whole came to assume the gaseous state. The general effect of the

explosion, however, would be to disperse the blocks in all directions, radiating from the center of the mass. Those toward the outer circumference of the mass, meeting with little or no obstruction to their outward progress, would pass outward into space to indefinite distances, leaving in this manner a free path for the layers of blocks behind them to follow in their track. Thus eventually a space, perhaps twice or even thrice that included within the orbit of Neptune, might be filled with fragments by the time the whole had assumed the gaseous condition. It would be the suddenness and almost instantaneity with which the mass would receive the entire store of energy, before it had time even to assume the molten, far less the gaseous condition, which would lead to such fearful explosions and dispersion of the materials. If the heat had been gradually applied, no explosions, and consequently no dispersion, of the materials would have taken place. There would first have been a gradual melting; and then the mass would pass by slow degrees into vapor, after which the vapor would rise in temperature as the heat continued until it became possessed of the entire amount. But the space thus occupied by the gaseous mass would necessarily be very much smaller than in the case we have been considering, where the shattered materials were first dispersed into space before the gaseous condition was assumed.

Researches of Prof. Chase.-Recent volumes of the "Proceedings of the American Philosophical Society" contain papers of great interest by Prof. Pliny E. Chase of Haverford College, Pa., on "Centers of Aggregation and Dissociation, ""Illustrations of Central Force," "Results of Wave Interferences," "Criteria of the Nebular Hypothesis," "Radiation and Rotation," etc., etc. The numerous harmonies of the solar system pointed out in these papers attention of astronomers and physicists. are very remarkable, and must command the

Gold Medal of the Royal Astronomical Society.-The gold medal of the Royal Astronomical Society of London was awarded in 1878 to Baron Dembowsky of Gallarate, for his observations of double stars, communicated from time to time during the last quarter of a century to the "Astronomische Nachrichten."

Prizes of the French Academy of Sciences.— The prizes of the French Academy, in the section of Astronomy, have been awarded as follows: the Lalande prize to Prof. Asaph Hall of Washington, for his discovery of the satellites of Mars; the Vaillant prize to Dr. Schulhof, for his researches which led to the rediscovery of three of the lost asteroids; and the Valz prize to the brothers Paul and Prosper Henry of the Paris Observatory, for their continuation of Chacornac's ecliptic charts.

Gold Medal of the Vienna Academy of Sciences. -The gold medal of the Vienna Academy has been awarded to Mr. Lewis Swift of Rochester, N. Y., for his discovery of the first comet of 1878. The observations of Mr. Swift have hitherto been made under unfavorable circumstances. He now proposes, however, the immediate erection of an observatory, to be furnished with a 9-4-inch refractor by Messrs. Clark & Sons, the distinguished opticians of Cambridgeport, Massachusetts.

« SebelumnyaLanjutkan »