1894.] on the Astronomical Telescope. 305 



this international work we have the independent surveys of Dr. Gill 

 and Professor Pickering, taken photographically with short focus 

 lenses on a small scale. 



We have also the recording by the aid of photography of specially 

 interesting objects, star clusters and groups, comets, &c, and more 

 particularly very faint objects such as nebulas, which require long 

 exposure. The results in this field of work demonstrate perhaps 

 more than any other the powerful agent that photography becomes in 

 the hands of the astronomer. It is not necessary to go into any 

 detail in considering this work, the results of which are tolerably 

 familiar to you. It is only necessary to mention the names of Draper, 

 Common, Gill, the Brothers Henry, Roberts, Gothard, Barnard 

 Russell and Dr. Max Wolf, to indicate how much we owe to long 

 exposure photography on these objects. 



Of new minor planets, 33 were discovered by photography in 

 1893, and several lost planets were rediscovered. 



We have also the study of the parallax of fixed stars and of nebulas 

 by this means, as carried out by Rutherford and Jacoby in America, 

 Professor Pritchard at Oxford, Sir Robert Ball and Professor 

 Rambaut at Dunsink and Dr. Wilsing at Potsdam. 



Turning to spectroscopy, we find again the enormous importance 

 of the photographic method. The development of Fraunhofer's 

 original idea of a slitless spectroscope has given us the objective 

 prism of to-day, and with this instrument we are able to simulta- 

 neously photograph the spectra of several hundreds of stars on a 

 single plate, these spectra being available for study at leisure, so that 

 they can be classified and selected for future work and more crucial 

 examination and investigation. The results from a single plate are 

 more accurate than could possibly be given by months of very close 

 observation by the older method. The Draper Catalogue, which we 

 owe to Professor E. C. Pickering, of Cambridge, Mass., gives the 

 spectra of over 10,000 northern stars obtained in this manner. In 

 addition to this he has in preparation a similar catalogue of the 

 southern stars. The beautiful photographs obtained by Professor 

 Lockyer at South Kensington, in which the detail is so fine that tho 

 spectra can be enlarged to a length of five feet, show the great 

 value of this method for complete study of the spectra after the first 

 rough cataloguing. With the slit spectroscope equally important 

 work has been done in the "New Astronomy." Not only can we get 

 the spectra of celestial objects with comparison spectra of terrestrial 

 substances on the same plate, and thus investigate the chemical nnd 

 physical constitution of these bodies, but by the adaptation of the 

 beautiful discovery of Dr. Huggins we can detect and measure the 

 motion in the line of sight, the photographic method giving far more 

 accurate results than can be obtained by visual means. In the hands 

 of Dr. Yogel, of Potsdam, this spectrograph^ method has been used 

 for nearly fifty stars, and he is only waiting for a larger instrument 

 to further extend this work. We have also in this connection the 



Vol. XIV. (No. 88.) y 



