RESULTS OF BRITISH TRANSIT EXPEDITIONS. 69 



between their several mean times. If this were observed, 

 we should not hesitate to place entire reliance on these 

 special sets of clocks ; and we should feel certain that if we 

 took the mean of all their means as the true time (perhaps 

 slightly modifying this mean in order to give due weight to 

 the known superiority of one or other of these clock-shops), 

 we should not be in error by more than five or six seconds, 

 while most probably we should have the time true within 

 two or three seconds. 



So far the illustration corresponds well with what had 

 been done during a quarter of a century or so before the last 

 transit of Venus. Several different methods of determining 

 the sun's distance had been applied to correct a value which 

 for many reasons had come to be looked upon with suspicion. 

 This value 95,365,000 miles was known to be certainly 

 too large. The methods used to test it gave results varying 

 between about 90 million miles and about 96 million miles. 

 But all the methods worthy of any real reliance gave results 

 lying between 91 million miles and 94 million miles. Not 

 to enter more fully into details than would here be suitable, 

 we may pass on at once to say that those most experienced 

 in the matter recognised seven methods of determining the 

 distance, on which chief reliance must be placed. Of these 

 seven methods, six each applied, of course, by many 

 different observers were dealt with exhaustively by Pro- 

 fessor Newcomb, of the Washington Observatory, a mathe- 

 matician who has undoubtedly given closer attention to the 

 general problem of determining the sun's distance than any 

 living astronomer. The six methods give six several results 

 ranging from about 92,250,000 miles to about 92,850,000 

 miles ; but when due weight is given to those of the six 

 methods which are undoubtedly the best, the most probable 

 mean value is found to be about 92,350,000 miles. The 

 seventh method, conceived by Leverrier, the astronomer to 

 whom, with our own Adams, the discovery of Neptune was 

 due, and applied by him as he only could have applied it (he 

 alone possessing at once the necessary material and the neces- 



