1869.] Astronomy. 261 



hemisphere of the earth is turned towards the sun. The transits 

 of 1761 and 1769 took place in June, when the northern hemi- 

 sphere was bowed towards the sun. Hence, principally, arises this 

 important difference between the approaching pair of transits and 

 the pair observed last century. 



Failing observations on the duration of the transit in 1882, 

 the accelerated and retarded ingress, and the accelerated and re- 

 tarded egress, may be respectively observed from the four following 

 sets of stations : — 



1. Kerguelen, Crozet's, Bourbon, Mauritius, and Eodriguez 

 Islands. 



2. Every city near the seaboard of the United States, and every 

 important city of Canada, also Bermuda, Jamaica, and the West 

 Indian Islands. 



3. The stations mentioned under 2, and the coast of South 

 America from the Isthmus of Darien to Eio Janeiro. 



4. Parts '"of the Antarctic Continent, Sydney, Melbourne, and 

 parts of New Zealand, 



If the durations of transits are to be observed, then certainly 

 portions of the Antarctic Continent will have to be selected. Cap- 

 tain Richards, Captain Toynbee, Eear-Admiral Ommanney, and 

 Staft-Commander J. E. Davis, supply some remarks on the geogra- 

 phical difficulties to be encountered in finding stations in high 

 southern latitudes, but the examination of their papers would lead 

 US away from astronomical considerations. 



Mr. De la Eue gives an interesting paper on the possibility of 

 taking photographs of Venus in transit. If this were done at 

 several well-separated stations, it seems clear that a most important 

 auxihary means of estimating the sun's distance would be afforded. 

 Mr. De la Eue points out that the close correspondence between 

 the results obtained by micrometricai measurements applied to his 

 eclipse-photographs in 1860, and the elements calculated by Mr. 

 Farley, of the ' Nautical Almanac ' office, show that a very close 

 approximation to the truth is to be looked for in the case of the 

 transit of Venus. For the difficulty of measuring the solar and 

 lunar discs presented in an eclipse-photograph is very much greater 

 than that attending the corresponding measurements in the case of 

 a transit-photograph. And moreover, the observer of a transit 

 would not be hurried hke the observer of an eclipse, since the 

 former phenomenon is several hours in progress, while the latter 

 lasts but a few minutes. 



Mr. De la Eue deals with the optical and physical corrections 

 which would have to be made, showing how the distortion due to 

 the optical peculiarities of the telescope could be determined before- 

 hand, and suggesting that the experiments which appear to show 

 that the collodion in drying shrinks only in the direction of its 



VOL. VI. T 



