600 



SCIENCE. 



[N. S. Vol. XII. No. 303. 



between the English and German forms of 

 mountings, and Airy's preference for the 

 English form. The general feeling amongst 

 astronomers has, however, been largely in 

 favor of the Grerman mounting for refract- 

 ors, due, no doubt, to a great extent, to the 

 enormous advance in engineering skill. We 

 have many examples of this form of mount- 

 ing. A list of the principal large refract- 

 ing and reflecting telescopes now existing is 

 given. All the refractors in this list, with 



List of Large Telescopes in Existence in 1900. 



Refractors 15 inches and upwards. 



Paris (Exhibition). 



Yerkes 



Lick 



Pulkowa 



Nice 



Paris 



Greenwich 



Vienna 



Washington, TJ. S 



Leander, McCormiok Observatory, Vir. 



Greenwich 



Newall's, Cambridge 



Cape of Good Hope 



Harvard 



Princeton, N. J., U. S 



Mount Etna 



Straasburg 



Milan , .. 



(Dearborn) Chicago 



Warner Observatory, Rochester, TJ. S.... 

 Washburn Observatory, Madison, Wis.. 



Edinburgh 



Brussels 



Madrid 



Rio Janeiro 



Paris 



Sir William Huggins 



Paris 



50 



40 



36 



30 



29.9 



28.9 



28.0 



27.0 



26.0 



26.0 



26.0 



25.0 



24.0 



24.0 



23.0 



21.8 



19.1 



19.1 



18.5 



16.0 



15.5 



15.1 



15.1 



15.0 



15.0 



15.0 



15.0 



15.0 



the exception of the Paris telescope of 50 

 inches and the Greenwich telescope of 28 

 inches, are mounted on the German foi-m. 



Some of these carry a reflector as well as, 

 for instance, the telescope lately presented 

 to the Greenwich Observatory by Sir Henry 

 Thompson, which, in addition to a 26-inch 

 refractor, carries a 30-inch reflector at the 

 other end of the declination axis, such as 

 had been previously used by Sir William 

 Huggins and Dr. Roberts ; the last, and 

 perhaps the finest, example of the German 

 form being the Yerkes telescope at Chicago. 



The small reflector made by Sir Isaac 

 Newton, probably the first ever made, and 

 now at the Eoyal Society, is mounted on a 

 ball, gripped by two curved pieces attached 

 to the body of the telescope, which allows 

 the telescope to be pointed in any direction. 

 We have not much information as to the 

 mounting of early reflectors. Sir William 

 Herschel mounted his 4-foot telescope on a 

 rough but admirably planned open-work 

 mounting, capable of being turned round 

 and with means to tilt the telescope to any 

 required angle. This form was not very 

 suitable for picking up objects or determin- 

 ing their position, except indirectly ; but 

 for the way it was used by Sir William 

 Herschel it was most admirably adapted : 

 the telescope being elevated to the required 

 angle, it was left in that position, and be- 

 came practically a transit instrument. All 

 the objects passing through the field of 

 view (which was of considerable extent, as 

 the eye-piece could be moved in declina- 

 tion) were observed, and their places in 

 time and declination noted, so that the po- 

 sitions of all these objects in the zone ob- 

 served were obtained with a considerable 

 degree of accuracy. It was on this plan 

 that Sir John Herschel made his general 

 catalogue of nebulae, embracing all the 

 nebulse he could see in both hemispheres ; 

 a complete work bj^ one man that is almost 

 unique in the history of astronomy. 



Sir William Herschel's mounting of his 

 4-foot reflector differs in almost every par- 

 ticular from the mountings of the long- 



