210 ASTRONOMY. 



the photographs at the followiug uortheru stations, Wladiwastok (13), 

 Nagasaki (45), Peking (2G), and from those at southern stations, Ker- 

 guelen (S), Hobartown (37), Campbelltown (32), Queenstown (45), 

 Chatham Island (7), Mr. Todd finds the solar parallax from measured an- 

 gles of position on the photographs of the Sun and Venus, n= 8".873 i 

 0".0G0; from measured distances, 7r = 8".88S± 0".040; and finally, hav- 

 ing regard to the weights, 7r= 8".883± 0".034. 



Velocity of light. — An experimeDtal determination of the velocity of 

 white and colored light formed the subject of a memoir, the joint pro- 

 duction of Dr. J. Young and Prof. G. Forbes, read before the Eoyal 

 Society, London, lately. The official summary states that the method 

 employed was that of Fizeau, but instead of using one distant reflector 

 and observing the total eclipse of the reflected ray by a toothed revolv- 

 ing wheel, two reflectors nearly in the same line with the observing tel- 

 'Cscope and one a quarter of a mile behind the other were used, and the 

 rays were viewed when brought to equal brightness by means of the 

 r adjustment ©f the speed of the wheel. The general result was that the 

 ■velocity of the light of an electric lamp is 187,200 miles per second. 

 Conui found that of the light of a petroleum lamp to be 186,700 miles 

 ,per second, and Michelson that of the sun to be 180,500 miles i)er sec- 

 ond. The higher number of Young and Forbes is possibly due to the 

 bluer light of electricity, for further experiments made with colored 

 lights and the spectrum tended to jjrove that the blue light probably 

 travels faster by 1 per cent, than the red light. The experiments were 

 made at Wemyss Bay, Scotland. 



The results of Forbes and Young have, we believe, not been accepted 

 as yet by physicists. From theoretical considerations. Lord Eayleigh 

 and Mr. Michelson, among others, have shown the improbability of 

 these figures for the velocity of light of different colors. 



Transit of Venus December 6, 1882. — In view of the fact that many of 

 the readers of this report will have an opportunity to observe the next 

 transit of Venus we present the instructions issued by the International 

 Conference for the observation of the transit of Venus of 1862. 



''-Article 1. It is desirable, from a theoretical stand-point, that the 

 telescope used should be of as large aperture as possible. In practice, 

 the difficulty of transportation on the one hand, and the necessity of 

 observers at different stations having similar instruments, limits the 

 apertures to from 0.12 meter to 0.15 meter (about 4.J to inches.) 



In all cases the objectives should be as perfect as possible. Observ- 

 ers should give an exact description of the quality and defects of the 

 objecti ve, as also the eye-jiiece employed. Towards this end they should 

 determine : 



1. The form of the image of a star in focus, as also the image of the 

 same star at a point before and after coming into focus. 



2. The separating power of the objective for double stars. 



