44 



for photographing faint extended objects, such as comets 

 and nebulae; the 2b-in. refractor, for the parallax work. 

 In the 1914 Report it is mentioned that " the method 

 adopted for the parallax observations consists in an exposure 

 of the same plate at two different epochs, approximately 

 six months apart, on the star whose parallax is required, 

 and the surrounding field. During the year the first expos- 

 ure has been given to 292 plates, and a second exposure 

 to 219 plates." 



The largest refractor in the Observatory, and in the British 

 Isles, is mounted in the " South-East Dome." The mounting, 

 which, like the Transit Circle, was constructed by RANSOMES 

 AND MAY, is quite unlike that of any of the other telescopes, 

 being of what is known as the " English " form, the polar 

 axis being supported at both its northern and southern end. 

 The mounting was originally set up for the I2|-in. refractor, 

 now used as the guiding telescope to the 20-in. Thompson 

 telescope, but has proved strong enough to carry the present 

 much larger and heavier instrument, which has been mainly 

 devoted to measures of double stars, and a catalogue of the 

 observations of 3,000 of these, made since the year 1893, is 

 to be published at the first opportunity. 



The Astrographic Equatorial already mentioned and a 

 smaller telescope known as the Six-inch Astrographic Triplet, 

 have been devoted to obtaining standards for the determina- 

 tion of the photographic magnitudes of stars. Thus, in 1914, 

 a catalogue was published giving the photographic magnitudes 

 of 2,329 stars within 15 of the North Pole, and believed to 

 be complete down to magnitude 9. Parallel with this work, 

 and closely associated with it, have been the " counts " of 

 an immense number of stars on plates taken by the late 

 JOHN FRANKLIN-ADAMS (1843-1912), with a triple lens 

 of 10 inches aperture (since purchased by the Royal Observa- 

 tory), made by DENNIS TAYLOR of COOKE AND SONS, of York, 

 the constructors of the mounting of the telescope. Franklin- 

 Adams bequeathed the plates of his photographic chart of 

 the entire heavens to Ureenwich Observatory, which has 

 undertaken their reproduction by photography. From the 

 " counts " of the stars of these plates, formulae have been 

 inferred for deducing the total number of luminous stars 

 in our system, and also their general distribution with respect 

 to the Milky Way. 



As one of the chief purposes for which Greenwich Observa- 

 tory was founded was the " rectifying " "the places of the 

 fixed stars," it has followed that the preparation and issue 



