360 Obituary Notices of Fellows deceased. 



photographs were taken with the 20-inch mirror, which had been 

 recently re-silvered, and the length of exposure was generally 1J hours. 

 In this year, as in others, the principal comets which appeared were 

 .also photographed. 



The last of these notable lists, dated February, 1904, contains a 

 magnificent record of work. There are upwards of ninety entries. 

 The great majority of the objects photographed are nebulae, as in the 

 former lists, but a good many clusters, or parts of the milky way, are 

 included, and occasionally some other objects, such as the famous 

 .star (1830) Groombridge, and the comet of Borelly, in 1903. 



In the words of Roberts himself he " has contributed to the Royal 

 Astronomical Society and to 'Knowledge,' between the years 1886 arid 

 1903, upwards of 150 photographs taken with his 20-inch reflector, 

 each of which showed structural and other details of objects in the sky, 

 that were previously unknown to astronomers." The last words make 

 a great claim, but its complete justice will be admitted. 



Much labour was devoted by Dr. Roberts to the design and con 

 struction of an instrument which he called the Pantograver. The 

 object of this instrument was to transfer, as it were, the images of 

 stars, both in size and position, from a perishable gelatine film to an 

 imperishable record, by engraving them on a copper plate. But this 

 machine originated in the early years of Dr. Roberts' astronomical 

 work, and before the time when he had fortunately decided to devote 

 himself to the photography of nebulae. It was at first Dr. Roberts' 

 intention to prepare a photographic chart of the heavens on a scale 

 twice the size of Argilander's, and with an exposure of 15 minutes 

 for each plate, and several specimen plates were sent to the Royal 

 Astronomical Society in 1886. After the international scheme had 

 been formed by the Convention in Paris for the preparation of the 

 photographic chart of the heavens on a vast scale, Roberts saw that 

 his energies could be most effectively employed in some other direction 

 than that of charting stars, and thus the Pantograver has had but little 

 relation to his later work. For a description of this machine reference 

 may be made to his paper * On an instrument for measuring the 

 positions and magnitudes of stars in photographs, and for engraving 

 them upon metal plates, with illustrations of the method of using the 

 instrument.' " Monthly Notices," vol. xlix., p. 5. 



The Gold Medal of the Royal Astronomical Society was awarded to 

 Dr. Isaac Roberts in 1895 for his photographs of star clusters and 

 nebulas. The address on the presentation of the medal was delivered 

 by the President, Sir W. de W. Abney, whose profound acquaintance 

 with the photographic arts, made the occasion one of exceptional 

 interest. In this address Sir W. Abney says : 



