1886.] on Photographj as an Aid to Astronomy. 369 



the publication of Daguerre's process, tlie negative statement that 

 Daguerre had failed where Draper had succeeded, is strange ; and the 

 allusion to the distinct representation of the moon's surface rather 

 implies that other representations existecl. It is, however, the earliest 

 record I can find, and we may consider it the starting-point. 



Beyond experimental work little seems to have been done with the 

 daguerreotype. 



Some astronomers, notably G. P. Bond in America, assisted by 

 two skilful photographers, with the 15-inch refractor of the Harvard 

 College Observatory, obtained photographs of some of the brighter 

 stars, and also some very fair pictures of the moon, that were 

 exhibited at the 1851 Exhibition in London, and also at a meeting of 

 the R.A.S. in May of that year ; and some solar and spectroscoj^ic 

 work was also done in Europe. 



The important fact of the possibility of thus getting pictures of 

 the heavenly bodies was established, so that with the introduction 

 of the collodion process in 1851, with its great advantages over 

 the difficult and costly daguerreotype, astronomical photography 

 was taken up and soon became firmly established. From this 

 time its history became a record of continual advance, delayed, it is 

 true, from time to time by the want of improvement in instrument or 

 method, when further extensions of the art were attempted, in every 

 case with ultimate success. 



Of the early workers with the collodion process, and the more 

 recent workers with the modern gelatine or dry plate process, and the ' 

 persevering and skilful way they have dealt with the difficulties that 

 always surround a new art, I do not propose to speak, excej)t inci- 

 dentally. Time would not allow me to do so here, nor is it part of 

 my purpose ; my object being rather to deal with the results obtained, 

 to speak of this new art or method of astronomical observation and 

 record, than to give an account of the labours of those who have made 

 it what it now is. I propose to exhibit by the electric lantern such 

 specimens of early and recent work as I have been able to obtain for 

 this purpose,* and from which I think you may form an idea as to the 

 present value of photography as an aid to astronomy, and the probable 

 greater aid it may in future become. 



Before doing so, however, although the art of photography is now 

 known to almost every one, I should like to say a few words about the 

 three processes I have mentioned, the daguerreotype, the collodion, 

 and the gelatine or dry plate process, and also to give very shortly 

 a general idea of the instruments and methods in use by the astrono- 

 mical photographer. 



For an account of the daguerreotype one has to refer to the text 

 w^orks, as it is not now in general use. Shortly it may be described 



* For the loan of some of the photographs exhibited I ata indebted to the 

 kindness of Mr. Crookes, Dr. de la Rue, Mr. Lockyer, and Caj^tain Abney, and 

 also to tlie Brothers Henry of Paris for specimens of their recent work. 



2 B 2 



