36 



ASTRONOMICAL PROGRESS AND PHENOMENA. 



curity which they afforded against the images 

 being disturbed by slipping of the film. The 

 daguerreotype process was made public in 1839, 

 and in March, 1840, prior to the introduction 

 of bromine for increasing the sensitiveness of 

 the plates, Dr. John W. Draper, of New York, 

 took some daguerreotypes of the moon about 

 one inch in diameter, with an exposure of 

 twenty minutes. Daguerreotypes were taken 

 of the total solar eclipse of July 8, 1842, by 

 Prof. Majocchi, at Milan, and of the total solar 

 eclipse of July 28, 1851, by Father Secchi, at 

 Rome, and by Dr. Busch, at Konigsberg, Dr. 

 Busch's pictures being the first that showed the 

 corona. The first eclipse photographed on col- 

 lodion plates was that of Sept. 7, 1858, some 

 negatives of the partial phases being made by 

 Liais in South America. All the pictures thus 

 far mentioned were made with ordinary astro- 

 nomical telescopes, corrected for visual rays, 

 and it was not till the total eclipse of July 18, 

 1860, that De la Rue introduced the use of 

 equatorial cameras, having lenses specially cor- 

 rected for photography, the particular instru- 

 ment employed being one that had been con- 

 structed under his direction in 1 855-'56 for the 

 Kew Observatory. Since then all solar eclipses 

 have been observed with what may be called 

 modern instruments. The first daguerreotype 

 of the uneclipsed sun was made in 1845 by 

 Fizeauand Foucault. After Draper's daguerre- 

 otypes of the moon, it is not known that 

 any more were made until 1850, when the 

 Bonds took up the subject, and with the Cam- 

 bridge 15-inch telescope produced daguerreo- 

 types of such excellence that they attracted 

 marked attention in the Great Exposition held 

 in London in 1851. These pictures incited De 

 la Rue to take up photography, and toward the 

 end of 1852 he made some beautiful negatives 

 of the moon, which were remarkable as being 

 the first astronomical pictures taken on collo- 

 dion. Since that time photographs of the 

 moon have been made by many persons, but 

 those produced by Lewis M. Rutherfurd and 

 Dr. Henry Draper are unrivaled. On July 17, 

 1850, the Bonds, aided by Messrs. "Whipple and 

 Black, of Boston, daguerreotyped a Lyne by 

 means of the Cambridge 15-inch telescope, and 

 this was the first stellar photograph ever made. 

 The double star Castor was subsequently da- 

 guerreotyped, but the experiments were soon 

 abandoned on account of the length of the ex- 

 posures indeed, for some reason hard to com- 

 prehend at the present day, they were unable 

 to obtain any impression whatever from Po- 

 laris, no matter how long the exposures were 

 continued. In 1857 the Bonds again reverted 

 to the subject, and on April 27 of that year, 

 they made collodion negatives of f and g Urs89 

 Majoris; and the former being a double star, they 

 measured the position, angle, and distance of 

 its components from the negatives, in the man- 

 ner now in vogue. During 1857 they succeeded 

 in photographing stars of the sixth to seventh 

 magnitudes in less than a hundred seconds, 



and they inferred that stars of the ninth mag- 

 nitude could be photographed in ten miuutes. 

 At that time they also made some negatives of 

 Saturn. The next person to take up the subject 

 was Lewis M. Rutherfurd, of New York. In 

 1857-'5S he worked with an ordinary achromatic 

 telescope; in 1859-'60 he used the snme tele- 

 scope with correcting lenses applied between 

 the objective and the eye-piece; in 1861 he 

 used a silver-on-glass reflector; and having 

 found all these unsatisfactory, in 1864 he con- 

 structed a telescopic objective of 11 J inches 

 aperture, specially corrected for photography. 

 With that instrument he obtained photographs 

 of ninth magnitude stars upon wet collodion 

 plates, after an exposure of about three min- 

 utes; and thus modern stellar photography came 

 into being. Nevertheless, for twenty years it 

 made little progress, and it is only recently that 

 astronomers seem to have realized its impor- 

 tance. As frequently happens with new pro- 

 cesses, there is now a tendency to exaggerate 

 its capabilities, but in due time that will be cor- 

 rected, and much of the secondary work hith- 

 erto done by meridian circles will fall to the 

 photographic camera. The adoption of the 

 new method will doubtless be hastened by the 

 action of the Paris International Congress, an 

 account of which is given below. Photography 

 affords special facilities for the detection of 

 small planets or stars having large proper mo- 

 tion, and it has been successfully used for both 

 these purposes during the past year. By its 

 aid Mr. Roberts determined the position of the 

 asteroid Sappho (80), which is not known to 

 have been observed since 1872, except by Dr. 

 Gill in 1882. The asteroid was of about the 

 eleventh magnitude, and with an exposure of 

 an hour it showed a distinct trail upon the 

 plate. As an instance of the detection of a 

 star's proper motion by the aid of photography, 

 the case reported by Herr von Gothard, in the 

 " Astronomische Nachrichten," may be cited. 

 On examining a photograph of the cluster No. 

 4440, Herschel's " General Catalogue," taken at 

 the Hereny Observatory, he found that a small 

 star of the eleventh magnitude had changed its 

 position relatively to the other stars since Vo- 

 gel's measurement of the cluster in 1867-'69. 

 The proper motion thus detected amounts to 

 about 2'3" per annum. Prof. Pritchard, of the 

 Oxford University Observatory, has published 

 some results, which he regards as provisional 

 only, of his photographic investigation of the 

 parallax of the well-known double star 61 

 Cygni. The measurement of 330 plates, ob- 

 tained on 89 nights, gives : 



Parallax of 61 1 Cygni - 042SO" 

 Parallax of 61 3 Cygni = 0-4358 



For comparison we may cite the following 

 results obtained by other astronomers working 

 with equatorials and heliometers in the usual 

 way: 



I5essolinl840 ... .. 0-84S" 



Auwersinl863 0-564 



Ball in 1878 0-468 



Hall in 1880 . . , . . 0'261 



