LOCAL PARTICLLARS OF THE TRANSIT OF YENUS 



IN J 874. 



Ey H. C. Eussell, Esq , B.A., Grovernment Astronomer. 



\^Sead before the Royal Society, September 3, 1873.] 



It 13 uot my intention in the following paper to enter at all into 

 tbe general question of the Transit of Venus ; so much has been 

 written on this subject, both in regard to the method of observing 

 it and the best stations, that it would seem nothing of further 

 interest can be said. But I propose to give such an account of 

 the methods of observing and the best stations in the Colony as 

 will enable us to make the best use of the circumstances in which' 

 we are placed. A few preliminary considerations will, however, 

 enable us to apprehend more easily the methods of observation 

 which are possible, and the difficulties which present themselves 

 to the observer. The Transit will occur on the 9th December, 

 1874, and the first contact will take place at llh. 52m. a.m. 

 Sydney mean time. The sun will then be in the zenith of the 

 place whose longitude is 151° 36' E., and 22° 57' S. latitude, or near 

 Rockhampton, in Queensland. If we could at that time be at 

 Rockhampton, and, -turning to the north, look up at the sun, we 

 should not see Venus on the sun's limb, for the planet would then 

 be a little to the right, or north-east, of our line of sight — to us, 

 of course, invisible, owing to the superior brilliance of the sun ; 

 but if we could at that same moment move to the north-east, and 

 take our station at the point of first contact, we should see Venus 

 just beginning to encroach on the sun's limb. Our point of 

 observation at that time would be on the mail steamer route from 

 San Erancisco to Honolulu, and about one-third of the distance 

 from the former city. 



If from this point a series of curves were described, increasing 

 the radius each time, they would indicate, at least sq far 

 as they were on that part of the earth from which the sun was 

 visible, sections of Venus's shadow cone, or all those parts of 

 the earth from which Venus in transit would be visible ; and the 

 time which this shadow cone will take to include the whole earth 

 is twenty-one minutes, or, from the time that Venus is first visible 

 on the earth's surface until it will be visible all over the earth 

 will be twenty-one minutes, the last point on the earth to see the 

 first contact from will be a place near Prince Edward's Island. 

 Unfortunately, both first and last contact points are on the ocean, 



