1887.] on the Applications of Photography in Astronomy. 171 



Miss Gierke tells the story most admirably and suggestively in 

 the last edition of her ' History of Astronomy,' to which work I 

 would refer those of my hearers in whom these beautiful photographs 

 may excite a sufficient interest. 



To enter fully into the matter would demand a lecture to itself — 

 and the minute hand of that inexorable clock warns me that I must 

 move on. 



Here are some photographs of Saturn, which illustrate the remark- 

 able progress of celestial photograj)hy. 



Here are some photographs of double stars : one of these, a photo- 

 graph of y Virginis, taken at Greenwich, is probably the finest 

 photograph of a double star in existence. The star discs measure 

 less than 1" in diameter. 



Last of all I come to the most recent revelations of the power of 

 photography as an aid to astronomy. Dr. Henry Draper, in 1872, 

 was the first to photograph the lines in the spectrum of a star, but his 

 admirable investigations were interrupted by death in 1882. In 

 1886, his widow placed in the hands of Professor Pickering, of 

 Harvard College Observatory, in America, not only an ample sum of 

 money for the purchase of costly apparatus, but also made a liberal 

 provision for carrying on the work of photographic spectroscopy as a 

 memorial to her husband. So noble a gift, and the execution of 

 so pious a purpose, could not have been placed in abler or more 

 active hands. 



Within the past few weeks we have received the first-fruits of tho 

 Henry Draper Memorial Fund. 



When I began prej)aration of this lecture, I cabled to Professor 

 Pickering a request for some glass copies of his original negatives. 

 He kindly complied, and they arrived this morning. Time only 

 permits me to show them rapidly, but those who remember Dr. 

 Huggins's lectures on stellar spectra in this theatre, will recognise 

 the enormous importance of such pictures as these. 



The ingenuity of the adopted methods, the extraordinary success 

 attained, the promise of rich harvest, exceeding our highest previous 

 expectations, which the results afford, are themes upon which one 

 could dilate for hours. 



Here we have the spectra of the distant stars whose actual discs 

 we can never hope to see, registering in these rhythmical lines the 

 story of their constitution and temperature, with an accuracy and 

 precision which not many years ago we should have been glad to 

 obtain in the records of the spectrum of our own sun. 



And this is not all ; not only have we such results for a few stars, 

 but we are promised " that the complete work will include a catalogue 

 of the spectra of all the stars of the 6th magnitude and brighter, a 

 more extensive catalogue of spectra of stars brighter than the 8th 

 magnitude, and a detailed study of the sj)ectra of the bright stars." 

 These are Prof. Pickering's own words. 



What Prof. Pickering promises, we know from long experience, 



