ASTRONOMICAL PROGRESS IN 1899. 



53 



radial, and tangential) though very bright, can 

 not be seen except when the Sun is totally eclipsed 

 and the observer near the center of the Moon's 

 shadow. The making of long journeys, often of 

 many thousand miles, to observe a total eclipse 

 is not for observing the Sun itself, which would 

 be impossible, as it is entirely covered by the 

 Moon, but to study, with telescope, spectroscope, 

 and photographic camera, the Sun's immediate 

 surroundings. 



On Jan. 22, 1898, a large party from several 

 countries visited India to observe a total solar 

 eclipse, which at every station selected was suc- 

 cessfully observed. The result of all the observa- 

 tions has just been published in book form, with 

 many elaborate illustrations, by the British As- 

 tronomical Association of London. It appears 

 that the observations were almost exclusively 

 photographic, and were a great success. On sev- 

 eral of the plates the flash-light spectrum, and 

 on others the corona spectrum, are clearly seen, 

 and also on plates exposed during partial phase 

 the Fraunhofer dark spectrum bordered with 

 dark lines. On some of the plates the flash-spec- 

 trum lines in the ultra-violet are beautifully de- 

 nned, and can be traced as far as wave length 

 3242. In this region from H more than 218 

 lines can be counted, and the wave lengths of all 

 measured. A great many of the lines were due 

 to iron, calcium, and magnesium. Three of the 

 strongest lines have been identified by Mr. Jew- 

 ell, at Johns Hopkins University, as due to the 

 rare element titanium, which, instead of being 

 confined to the flash layer, extended as high in 

 the chromosphere as hydrogen, and also in the 

 prominences, which are eruptions from the 

 chromosphere, extending to a height of 100,000 

 miles, and were plainly visible to the naked eye 

 during the totality of the eclipse of 1869. The 

 coronium line, to produce which no substance 

 has yet been found on the Earth, was traced to 

 a height of 160,000 miles. This eclipse has con- 

 firmed what several previous ones have shown 

 that the corona, chromosphere, prominences, etc., 

 belong to the Sun, and not to the Moon. 



The grandest problem in astronomy is to meas- 

 ure the Sun's distance from the Earth. It was 

 formerly thought that the problem was solved 

 over one hundred years ago, and that the dis- 

 tance was 95,000,000 miles, but is now thought 

 to be about 93,000,000. Millions of dollars were 

 spent to observe the transits of Venus of 1874 

 and 1878 for this purpose, but the discussion of 

 the observations still left a possible error of 

 200,000 miles. Now, thanks to the discovery of 

 an insignificant asteroid, by the first day of the 

 twentieth century (Jan. 1, 1901) the doubt will 

 be reduced 75 per cent., as described under 

 Asteroids. 



The month of September, 1898, was rendered 

 memorable to solar physicists by the sudden 

 appearance of one of the largest Sun spots on 

 record. As it appeared during the period of mini- 

 mum Sun-spot activity, it created far greater in- 

 terest than if it had occurred during the maxi- 

 mum period, and has created a distrust as to 

 the existence of the eleven-year period of Sun 

 spots. It first appeared on the east limb of the 

 Sun on Sept. 2, and on the following day it as- 

 sumed gigantic proportions, equal to 1,400,000,- 

 000 square miles. On the 10th the spot covered 

 an area of only 24,000,000 square miles. During 

 its passage across the central meridian of the 

 solar disk the northern regions of the Earth were 

 treated to one of the most magnificent auroral 

 displays seen for many years. The simultane- 

 ousness of the two phenomena goes far to estab- 



lish the truth of the theory long entertained that 

 there is a connection between them. At the same 

 time there was a sharp disturbance of the mag- 

 netic needle in various countries, and of the tele- 

 graph wires, lasting four hours. The movement 

 of the needle in declination extended through an 

 arc of more than a degree. When it is consid- 

 ered that Sun spots last many days, and often 

 weeks, it seems to militate against the truth of 

 the above-mentioned theory that the aurora 

 should last but a day, and often much less, and 

 magnetic intensity but four hours. 



Photographic Astronomy. Ur. E. E. Bar- 

 nard, of the Yerkes Observatory, Williams Bay, 

 Wisconsin, has published two papers, the first 

 being a description of one of his photographs of 

 the Milky Way, near Theta Ophiuchi, accompa- 

 nied by a print of it, which reveals much of the 

 intricate structure of that portion of the starry 

 girdle. Certain appearances in the photograph 

 appear to justify the belief that in this portion of 

 the galaxy a substratum of a dual nebulosity 

 exists, while huge dark rifts and black lines sug- 

 gest the idea that the photograph actually pierced 

 through the luminous girdle into the blackness 

 and starless space beyond. These peculiarities, 

 he says, strongly remind one of the appearances 

 often seen in the umbra of Sun spots, where a 

 dark halo lies in the dark central spot, as if the 

 cavity was partly veiled with some sort of medi- 

 um, with apertures in it. His second paper can 

 be found in the March number of the Astro- 

 Physical Journal. 



Prof. E. C. Pickering, of Harvard Observatory, 

 has lately received from its station at Arequipa, 

 Peru, a series of the most successful photographs 

 of the heavens yet taken. One plate especially, 

 14 X 18 inches, taken with the Bruce photo- 

 graphic telescope, shows with marvelous clear- 

 ness and exactness as to magnitudes and position 

 the enormous number of 400,000 stars, all de- 

 picted by a single exposure of probably several 

 hours' duration. Miss Catharine Bruce, of New 

 York, gave the professor $50,000 for the construc- 

 tion of this celebrated photographic telescope of 

 unique construction. The object glass corrected 

 for actinism (thus being useless for visual work) 

 is 24 inches in diameter, and has only a 12-foot 

 focus. The professor is now constructing a tele- 

 scope, going to the other extreme as to focal 

 length, to be about 175 feet, to lie horizontal and 

 immovable. The light from objects to be ob- 

 served is to be reflected from a plane mirror 

 driven by clockwork, equatorially mounted, and 

 regulated to sidereal time; or the photographic 

 plate itself may be moved by clockwork, to coun- 

 teract the rotational velocity of the Earth, that 

 a star may be held during exposure on the meridi- 

 onal wire in the eyepiece. The great Yerkes tele- 

 scope, with a 40-inch object glass, is 67 feet long, 

 while this new instrument, with an objective 

 only 13 inches in diameter, will be more than 

 100 feet longer. One advantage possessed by the 

 long telescope will be the immense size of the 

 photographed Moon and planets; that of the 

 former will be about 15 inches in diameter, while 

 with ordinary telescopes 3 inches is about the 

 limit. The great telescope building in Paris for 

 the Exposition is to have an object glass 50 

 inches in diameter, and to be about 100 feet in 

 length. Enlarging photographs, especially of the 

 Moon, is often done, but always at the expense 

 of distinctness; but as the Moon taken with the 

 long telescope will be 15 inches in diameter, no 

 further details of value would be gained by en- 

 larging. 



It has been known for many years that in 



