NEW WA YS OF MEASURING THE SUN'S DISTANCE. 75 



with great zeal and completeness, we may consider that 

 the result affords an excellent test of the qualities of this 

 method, and may supply a satisfactory answer to the ques- 

 tions which were under discussion in 1872-74. Sir George 

 Airy, indeed, considers that the zeal and completeness with 

 which the British operations were carried out suffice to set 

 the result obtained from them above all others. But this 

 opinion is based rather on personal than on strictly scien- 

 tific grounds. It appears to me that the questions to be 

 primarily decided are whether the results are in satisfactory 

 agreement (i) inter se and (ii) with the general tenor of former 

 researches. In other words, while the Astronomer Royal 

 considers that the method and the manner of its application 

 must be considered so satisfactory that the results are to be 

 accepted unquestionably, it appears to me that the results 

 must be carefully questioned (as it were) to see whether the 

 method, and the observations by it, are satisfactory. In 

 the first place, the result obtained from Northern and 

 Southern observations of the commencement ought to agree 

 closely with the result obtained from Northern and Southern 

 observations of the end of transit Unfortunately, they 

 differ rather widely. The sun's distance by the former 

 observations comes out about one million miles greater 

 than the distance determined by the latter observations. 



This should be decisive, one would suppose. But it is 

 not all The mean of the entire series of observations by 

 Delisle's method comes out nearly one million miles greater 

 than the mean deduced by Professor Newcomb from many 

 entire series of observations by six different methods, all of 

 which may fairly be regarded as equal in value to Delisle's, 

 while three are regarded by most astronomers as unques- 

 tionably superior to it Newcomb considers the probable 

 limits of error in his evaluation from so many combined 

 series of observations to be about 100,000 miles. Sir G. 

 Airy will allow no wider limits of error for the result 01 the 

 one series his observers have obtained than 200,000 miles. 

 Thus the greatest value admitted by Newcomb falls short 



