October 19, 1900.] 



SCIENCE. 



595 



raphy ; but no real progress seems to have 

 been made until after the introduction of 

 the collodion process. Sir John Herschel 

 in 1847 suggested the daily self-registration 

 of the sun-spots to supersede drawings ; and 

 in 1867 the de la Rue photo-heliograph was 

 installed at Kew. From 1858-72 a daily 

 record was maintained by the Kew photo- 

 heliograph, when the work was discon- 

 tinued. Since 1873 the Kew series has 

 been continued at Greenwich, which is sup- 

 plemented by pictures from Dehra Dun in 

 India and from Mauritius. The standard 

 size of the sun's disc on these photographs 

 has now been for many years 8 inches, 

 though for some time a 12-inch series was 

 kept up. 



The first recorded endeavor to employ 

 photography for eclipse work dates back to 

 1851, when Berowsky obtained a daguerreo- 

 type of the solar prominences during the 

 total eclipse. From that date nearly every 

 total eclipse of the sun has been studied by 

 the aid of photography. 



In 1860 the first regularly planned attack 

 on the problem by means of photography 

 was made, when de la Rue and Secchi suc- 

 cessfully photographed the prominences and 

 traces of the corona, but it was not until 

 1869 that Professor Stephen Alexander ob- 

 tained the first good photograph of the 

 corona. 



In recent years, from 1893 up to the 

 total eclipse which occurred last May, 

 photography has been employed to secure 

 large-scale pictures of the corona. These 

 were inaugurated in 1893 by Professor 

 Schaeberle, who secured a 4-inch picture of 

 the eclipsed sun in Chili ; these have been 

 exceeded by Professor Langley, who ob- 

 tained a 15-inch picture of the corona in 

 North Carolina during the eclipse of May, 

 1900. 



Photography also supplied the key to the 

 question of the prominences and corona be- 

 ing solar appendages, for pictures of the 



eclipsed sun taken in Spain in 1860 termi- 

 nated this dispute with regard to the prom- 

 inences, and finally to the corona in 1871. 



In 1875, in addition to photographing the 

 corona, attempts were made to photograph 

 its spectrum, and at every eclipse since then 

 the sensitized plate has been used to record 

 both the spectrum of the chromosphere and 

 the corona. The spectrum of the lower 

 layers of the chromosphere was first suc- 

 cessfully photographed during the total 

 eclipse of 1896 in Nova Zembla by Mr. 

 Shackleton, though seen by Young as early 

 as 1870, and a new value was given to the 

 wave-length of the coronal line (wrongly 

 mapped by Young in 1869) from photo- 

 graphs taken by Mr. Fowler during the 

 eclipse of 1898 (India). 



Lunar photography has occupied the at- 

 tention of various physicists from time to 

 time, and when Daguerre's process was 

 first enunciated, Arago proposed that the 

 lunar surface should be studied by means 

 of the photographically produced images. 



In 1840 Dr. Draper succeeded in impress- 

 ing a daguerreotype plate with a lunar im- 

 age by the aid of a 5-inch refractor. The 

 earliest lunar photographs, however, shown 

 in England were due to Professor Bond, of 

 the United States. These he exhibited at 

 the Great Exhibition in 1851. Dancer, the 

 optician, of Manchester, was perhaps the 

 first Englishman who secured lunar images, 

 but they were of small size.* 



Another skillful observer was Crookes, 

 who obtained images of 2 inches diameter 

 with an 8-inch refractor of the Liverpool 

 Observatory. In 1852 de la Eue began ex- 

 perimenting in lunar photography. He em- 

 ployed a reflector of some 10 feet focal 

 length and about 13 inches diameter. A 

 very complete account of his methods is 

 given in a paper read before the British As- 

 sociation. Mr. Rutherfurd at a later date 

 having tried an llj-inch refractor, and also 



*Abiiey (Photography). 



