60 ROUGH WAYS MADE SMOOTH. 



greater number of those made by the best methods, and 

 under the most favourable conditions, lie between 91 and 94 

 millions of miles. All the very best cluster closely around 

 a distance of 92^ millions of miles. We are not for the 

 moment, however, concerned with the question of the exact 

 distance, but with the question whether astronomy has ob- 

 tained satisfactory evidence that the sun's distance lies in 

 the neighbourhood of the distances deduced by the various 

 methods lately employed. Putting the matter as one of 

 probabilities, as all scientific statements must be, it may be 

 said as confidently that the sun's distance lies between 85. 

 millions and 100 millions of miles as that the sun will rise to- 

 morrow ; and the probability that the sun's distance is less 

 than 90 millions, or greater than 95 millions of miles, is so 

 small that it may in effect be counted almost as nothing. 

 Thirdly, the possibility that the earth may be drawing nearer 

 to the sun by three or four millions of miles in a century may 

 be dismissed entirely from consideration. For, one of the 

 inevitable consequences of such a change of distance would 

 be a change in the length of the year by about three weeks ; 

 and so far from the year diminishing by twenty days or so 

 in length during a century, it has not diminished ten seconds 

 in length during the last two thousand years. If there has 

 been any change year by year in the earth's distance from 

 the sun, it is one to be measured by yards rather than by 

 miles. Astronomers would be well content if their 'probable 

 error ' in estimating the sun's distance could be measured 

 by thousands of miles ; so that any possible approach of the 

 earth towards the sun would go but a very little way 

 towards accounting for the discrepancies between the 

 different estimates of the distance, even if these estimates 

 grew always smaller as time passed, which is assuredly not 

 the case. 



But in truth, if we consider the nature of the task under- 

 taken by astronomers in this case, we can only too readily 

 understand that their measurements should differ somewhat 

 widely from each other, Let us picture to ourselves for a 



