XVI 



President's Address 



and furnish ample food for speculation, even if it does not 

 add considerably to our definite knowledge of these myste- 

 rious occupants of space. 



The exact distance of the sun from the earth is yet an 

 unsolved problem, and although a large addition to our 

 knowledge upon this subject has been anticipated from the 

 very successful observations of the late Transit of Yenus, I 

 am sorry to say the results are not yet arrived at. Success 

 having attended so many of the numerous observing parties, 

 the necessary calculations have assumed almost stupendous 

 proportions, and it yet remains doubtful how much longer 

 the final results will be delayed. Another favourable oppor- 

 tunity for determining the solar parallax is now about to 

 occur in the opposition of the planet Mars, which takes 

 place on September 5th, on which occasion its distance from 

 the earth will be almost a minimum. You will remember 

 that all our methods of determining the sun's distance 

 depend on the determination first of the distance of any 

 planet from the earthy when Kepler's famous law (that the 

 distances of the planets from the sun are proportional to the 

 times in which they complete their revolution about the sun) 

 furnishes the rest of the required data ; so that in the transit 

 of Yenus what is actually determined is the distance of 

 Yenus from us, and hence by Kepler's third law the distance 

 of the sun ; and the observation consists in the measurement 

 of the displacement of the planet upon the sun's disc as seen 

 from various parts of the earth's surface. In the case of Mars, 

 its displacement with regard to certain selected fixed stars 

 near it, is measured at widely different points of the earth's 

 surface, instead of with respect to the solar disc, as in the 

 case of Yenus. The opportunity which is now about to occur 

 will not be lost sight of, and arrangements have already been 

 made by which the co-operation of various Observatories in 

 both hemispheres will be secured, and we have already com- 



