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SYDNEY CHAl'MAN^ B.A., D.SC._, F.R.A.S., ON 



one half can be seen at any one time, as only ono hemisphere 

 of the sky can be seen at any moment from a given station. 

 Thus oh the clearest night a person with good eyesight can only 

 see distinctly some 3,000 stars. Of course he can" see the Milky 

 Way, which is composed of millions of very faint stars, but he 

 cannot isolate their images or see the stars individually. 



Down Co the 9th magnitude, which is about the limit of 

 visibility in a telescope of l)etween two or three inches aperture, 

 there are just about 100,000 stars, so that quite a small tele- 

 scope enables us to see more than a dozen times as many stars 

 as can be seen by the naked eye alone, a fact which indicates 

 the tremendous increase in the power of vision which even a 

 small telescope gives as compared with the naked eye. As the 

 table is followed down to the fainter and yet fainter stars, by 

 steps of one magnitude at a time, the number is seen to increase 

 rapidly. Down to the 14th magnitude, the total amounts to 

 over eight millions, or eighty times as many as were registered 

 down to the 9th magnitude. The 14th magnitude is the limit 

 chosen for the great International scheme for photographing 

 the entire heavens in which this country, in conjunction with 

 many others, has taken part, and for a large section of the 

 heavens the stars have already been photographed on this plan, 

 and partly catalogued. 



The table shows that if still fainter stars are embraced, and 

 the survey is extended to the 17th magnitude, the total number 

 is increased to 55,000,000, and this is the limit adopted for a 

 series of photographs taken by the enterprise of the late 

 Mr. Franklin-Adams. This remarkable work owed its origin 

 to a suggestion by the late Sir David Gill, pointing out the 

 desirability of a photographic research into the structure of the 

 Milky Way. Mr. Franklin-Adams subsequently extended the 

 programme to embrace the photography of the entire sky. 

 With this end in view, he obtained in 1898 from Messrs. Cooke 

 and Sons a 6-inch photographic lens, designed by Mr. Dennis 

 Taylor to give good definition over a large field. This lens was 

 so successful that a larger one of similar type was ordered ; it 

 was delivered in 1903, and was of 10 inches aperture, and 45 

 inches focal length, giving good images over a field 15 degrees 

 in diameter. 



Mr. Franklin-Adams and his assistant Mr. Kennedy used 

 this lens at the Cape Observatory in the years 1903 to 1904, 

 and the southern sky was photographed with exposures of two 

 hours for each plate. After his return to England, Mr. Franklin- 

 Adams built an observatory adjoining his house at Mervel Hill, 



