398 



KNOWLEDGE. 



October, 1910. 



more closelv to accuracy new difficulties appear. The 



^e 



The Altazimuth Huilding. 



hori/on recedes with the stature of the Observatory. 

 The most ob\'ious adxance which has been made 

 in Sir W'ilham Christie's time has been in the 

 multiphcation of telescopes and in their increas- 

 ing size. When Sir George .\ir\-. the preceding 

 Astronomer Ro\al. mounted a thirteen-inch telescope 

 at Greenwich in the fifties, he did so, says Professor 

 H. H. Turner", in the earnest hope that its use 

 should not interfere with the proper work of the 

 Observatory, which was to be done with instruments 

 distinguished for their steadiness rather than their 

 size. But since .\ir\"s da\' a twent\-eight inch 

 telescope has been set up where the old telescope 

 stood : and is. indeed, economicalh' attached to the 

 old mounting. The thirteen-inch is now used as a 

 sighting telescope. In addition to the twenty-eight 

 inch refractor there is the Thompson Equatorial. 

 Sir Henry Thompson presented to the Observatory 

 a large photographic refractor of twentv-six inches 

 aperture ; and attached to the same mounting, like 

 the second prong of a two - pronged fork, is a 

 beautiful reflecting telescope which was made b\- 

 Dr. Common, of Ealing. Sir Henry Thompson, 

 seeing how much this addition would enhance the 

 .value of his own gift, hastened to increase his original 

 estimate of the mounting, and thanks to his gener- 

 osity and that of Dr. Common, Greenwich Observa- 

 tory possesses one of the most serviceable "large" 



telescopes in the world. The thanks are due. it will 

 be noted, to private benefactors, not to the ta.\pa\er. 

 The mention of the Thompson twiti telescope 

 directs attention to the implement of research in 

 astronomy — the use of photograph\- — which is 

 perhaps more important than an\- other which has 

 been devised since the time of .^irw .-Xs long ago as 

 1873 a beginning was made with photographing the 

 Sun b\' means of a photo-heliograph at Kew — in the 

 Obser\-atory which now stands in the middle of the 

 Mid-Surre\- Golf Course — and these photographs 

 were studied and measured at once, so that the 

 Greenwich Observations are in this, as in other 

 fundamental work, the standard reference for records 

 of Sun-spots. .\ larger instrument for solar work 

 has since been presented to Greenwich Observatorv, ' 

 and is under the charge of Mr. W. E. Maunder; and 

 bv arrangement with the Observatories of India and 

 the Cape (and fornicrh- of Mauritius) a complete 

 dailv photographic record of the Sun is now kept. 

 But the photographic plate subserves many other 

 astronomical purposes. In 1887 the International 

 Conference on the Photographic Star Map of the 

 Hea\ens met at Paris, and the great [iroject (.)f 

 mapping the skies by photography, which owed its 

 inception to Sir David Gill and the late .-\dmiral 

 Mouchez, Director of the Paris Observatory, was 

 entered upon. One of the most important reso- 

 lutions of the Conference decided the pattern of 



' " Modern -Astronomy, 



28 iConbtable). 



Also by Sir Henry Thompson. 



