308 ANNUAL. KEPORT SMITHSONIAN INSTITUTION, 1910. 



In the Nineteenth Century Keview for June, 1897, Sir William 

 has given an interesting account of his entry into the spectroscopic 

 field: 



I soon became a little dissatisfied with the routine character of ordinary 

 astronomical work, and in a vague way sought about in my mind for the 

 possibility of research upon the heavens in a new direction or by new methods. 

 It was just at this time, when a vague longing after newer methods of observa- 

 tion for attacking many of the problems of the heavenly bodies filled my mind, 

 that the news reached me of Kirchhoff's great discovery of the true nature and 

 the chemical constitution of the sun from his interpretation of the Fraunhofer 

 lines. 



This news was to me like the coming upon a spring of water in a dry and 

 thirsty land. Here at last presented itself the very order of work for which 

 in an indefinite way I was looking — namely, to extend his novel methods of re- 

 search upon the sun to the other heavenly bodies. A feeling as of inspiration 

 seized me. I felt as if I had it now in my power ta lift a veil which had never 

 before been lifted ; as if a key had been put into my hands which would unlock 

 a door which had been regarded as forever closed to man — the veil and door 

 behind which lay the unknown mystery of the true nature of the heavenly 

 bodies. This was especially work for which I was to a great extent prepared, 

 from being already familiar with the chief methods of chemical and physical 

 research. 



It was just at this time that I happened to meet at a soiree of the pharma-' 

 ceutical society, where spectroscopes were shown, my friend and neighbor, Dr. 

 W. Allen Miller, professor of chemistry at King's College, who had already 

 worked much on chemical spectroscopy. A sudden impulse seized me to suggest 

 to him that we should return home together. On our way home I told him of 

 what was in my mind and asked him to join me in the attempt I was about to 

 make, to apply Kirchhofii's methods to the stars. At first, from consideration of 

 the great relative faintness of the stars, and the great delicacy of the work 

 from the earth's motion, even with the aid of a clockwork, he hesitated as to 

 the i)robability of our success. Finally he agreed to come to my observatory 

 on the first fine evening for some preliminary experiments as to what we might 

 expect to do upon the stars. 



* * * From the sun, with which the Heidelberg professors had to do — 

 which, even bright as it is, for some parts of the spectrum has no light to 

 spare — to the brightest stars is a very far cry. The light received at the 

 earth from a first magnitude star, as Vega, is only about the one-forty- 

 thousand-millionth part of that received from the sun. 



Fortunately, as the stars are too far off to show a true disk, it is possible 

 to concentrate all the light received from the star upon a large mirror or 

 object glass, into the telescopic image, and so increase its brightness. 



We could not make use of the easy method adopted by Fraunhofer of plac- 

 ing a prism before the object glass, for we needed a terrestrial spectrum, 

 taken under the same conditions, for the interpretation, by a simultaneous 

 comparison with it of the star's spectrum. KirchhofC's method required that 

 the image of a star should be thrown upon a narrow slit simultaneously with 

 the light from a flame or from an electric spark. 



These conditions made it necessary to attach a spectroscope to the eye end 

 of the telescope, so that it would be carried with it, with its slit in the focal 

 plane. Then, by means of a small reflecting prism placed before one half of 

 the slit, light from a terrestrial source at the side of the telescope could be 



