OCTOBEE 19, 1900.] 



SCIENCE. 



591 



branches in South America, all the photo- 

 graphic and specti-oscopic work carried out 

 by many different astronomers, and the 

 new lines of research initiated show an 

 amount of enthusiasm not excelled by any 

 other country. A greater portion of the 

 astronomical work in America has been on 

 the lines of the new astronomy, but the old 

 astronomy has not been at all neglected. 

 In this branch pace has been kept with 

 other countries. 



From this report we gather that the 

 mural quadrant at most of the observa- 

 tories was about to be replaced by the di- 

 vided circle. Troughton had perfected a 

 method of dividing circles, which, as the 

 author says, 'may be considered as the 

 greatest improvement ever made in the art 

 of instrument making. ' 



Two refractors of 11 and 12 inches aper- 

 ture had just been imported into this coun- 

 try ; clockwork for driving had been ap- 

 plied to the Dorpat and Paris equatorials, 

 but the author had not seen either in a state 

 of action . 



The method of mounting instruments 

 adopted by the Germans was rather se- 

 verely criticised by the author, the general 

 principle of their mounting being ' tele- 

 scopes are always supported at the middle, 

 not at the ends.' 



" Every part is, if possible, supported by 

 counterpoises." 



" To these principles everything is sacri- 

 ficed. For instance, in an equatorial the 

 polar axis is to be supported in the middle 

 by a counterpoise. This not only makes 

 the instrument weak (as the axis must be 

 single), but also introduces some inconveni- 

 ence into the use of it. The telescope is on 

 one side of the axis ; on the other side is a 

 counterpoise. Each end of the telescope 

 has a counterpoise. A telescope thus 

 mounted must, I should think, be very 

 liable to tremor. If a person who is no 

 mechanic and who has not used one of 



these instruments may presume to give an 

 opinion, I should say that the Germans 

 have made no improvement in instruments 

 except in the excellence of workmanship." 



I have no doubt that this question had 

 often occupied Airy's mind, for in the 

 N"orthumberland Equatorial Telescope 

 which he designed shortly after for Cam- 

 bridge he adopted what has been called 

 the English form of mounting, where the 

 telescope is supported by a pivot at each 

 side, and a long polar axis is supported at 

 each end. This telescope is in working 

 order at the present time at Cambridge. 



When he became Astronomer Royal he 

 used the same design for what was for 

 many years the great equatorial at Green- 

 wich, though the wooden uprights forming 

 the polar axis were in the Greenwich tele- 

 scope replaced by iron. It says much for 

 the excellence of the design and workman- 

 ship of this mounting, designed as it was for 

 an object glass of about 13 inches diameter, 

 when we find the present Astronomer Eoyal, 

 Mr. Christie, has used it to carry a tele- 

 scope of 28 inches aperture, and that it does 

 this perfectly. 



Notwithstanding the greater steadiness 

 of the English form of mounting, the Ger- 

 man form has been adopted generally for the 

 mounting of the large refractors recently 

 made. 



There is much interesting matter in this 

 report of an historical character. 



As I have already said, the new as- 

 tronomy, as we know it, did not exist, but 

 in a report * on optics, in the same volume, 

 by Sir David Brewster, we find that spec- 

 trum analysis was then occupying atten- 

 tion, and the last paragraph of this report 

 is well worth quoting : " But whatever 

 hypothesis be destined to embrace and ex- 

 plain this class of phenomena, the fact 

 which I have mentioned opens an extensive 

 field of inquiry. By the aid of the gaseous 



* Brit. Assoc. Rep., 1831-32, p. 308. 



