RESULTS OF BRITISH TRANSIT EXPEDITIONS. 71 



only that the mean of the various times indicated by the 

 clocks at this last- visited place differed thus widely from the 

 tune which we had every reason to consider very nearly 

 exact, but that the different clocks here differed as widely from 

 each other, it would be absurd to rely upon their evidence. 

 The circumstance that there was a range of difference of fully 

 half a minute in their indications would of itself suffice to 

 show how untrustworthy they were, at least for the use of any 

 one who wished to obtain the time with great accuracy. 

 Combined with the observed difference between their mean 

 time and that before obtained, this circumstance would prove 

 the inaccuracy of the clocks beyond all possibility of doubt 

 or question. 



Now the case here imagined corresponds very closely 

 with the circumstances of the recent attempt to correct our 

 estimate of the sun's distance by Delisle's method. Our 

 Government astronomers bethought themselves of this method 

 as likely to give the best possible means for correcting, by 

 observations of Venus in transit, the estimate of the sun's 

 distance which had been deduced by Newcomb, and con- 

 firmed by Leverrier. While as yet their plans were not 

 finally decided upon, reasons for questioning this con- 

 clus on were indicated to those officials by unofficial astro- 

 nomers entertaining very friendly feelings towards them. 

 Retaining, however, their reliance on the method thus called 

 in question, they carried out their purpose, though fortunately 

 making provision, very nearlv sufficient, for the use of another 

 method. Now, instead of the estimate of the sun's distance 

 obtained from the observations by Delisle's method agreeing 

 closely with Newcomb's mean value, about 92,350,000 

 miles, it exceeds this value by about a millipn miles. (See, 

 however, note on the last page of this article.) According 

 to various ways of considering the results sent in by his ob- 

 servers, the chief official astronomer obtains a mean value 

 ranging from about 93,300,000 miles to about 93,375,000 

 m'les. The last named estimate seems preferred on the 

 whole ; but if we take 93,350,000 miles, we shall probably 



