SOME REFLECTIONS SUGGESTED BY THE APPLICA- 

 TION OF PHOTOGRAPHY TO ASTRONOMICAL RE- 

 SEARCH." 



By H. H. Turner, D. Sc, F. U. S. 



It is a familiar fact that there are epochs in the history of a 

 science when it acqnires new vigor; when new branches are |)ut forth 

 and ohl branches bud afresli or bh)ssom morc^ plenteonsly. The vivi- 

 fying cause is generally to be found either in the majestic form of the 

 discovery of a new law of nature oi* in the humbler guise of the 

 invention of a new instrument of research. The history of astron- 

 omy has been rich in such epochs, notable among them jjeing that 

 when Newton announced to the world the great law of gi-avitation. 

 and that wh(>n Galileo first turned his telescope to the skies. 



We have within the last half centui'y been fortunate enough to 

 include another great epoch in astronomical history, characterized 

 by the birth, almost a twin bii'th. of two new scientific weai)ons — the 

 spectroscope and the sensitive film. It is, of course, somewhat diffi- 

 cult and scarcely necessary to assign an exact date for the origin of 

 either of these. The spectroscope was perhaps fir^t systematically 

 used on the heavenly bodies by Huggins, Rutherfurd, and Secchi in 

 the fifties, but we may trace it back to the early work of Fi-aunhofer, 

 who described the spectrum of Sirius in 1817. or further back to tlie 

 experiments of Newton with a prism; and the dry plate, which in 

 particular has conferred such benefits on our science, had of course 

 its precursors in the collodion })late or the daguerreoty])e. But the 

 greater part of the influence on asti'onomy of both the spectroscope 

 and the photographic method dates from the time when the dry i)late 

 was first used successfully, not unich more than a cpiarter of a cen- 

 tury ago; and in that quartei- of a century there have been compressed 

 new advances in our knowledge which })erha])s will compare favor- 



a Address delivered by II. II. Turner, I). Sc F. li. S., Savilian professor of 

 astronomy in tlie University of Oxford, in tlie section of nstropliysics at tli(^ 

 Congress of Arls4 and Scienct s at St. Louis, on Wednesday, Sei»teniI)(M- lil, I'.KM. 

 Reprinted from the Ol»esra\ tory. London, Novenil)er-I)ec(>ml)ei-. 1904. 



171 



