01! 



INTRODUCTORY. 



Distance and Dimensions of the Sun. 



From the " Sun," by Professor C. A. Young. 



The problem of finding the distance of the sun is 

 one of the most important and difficult presented by as- 

 tronomy. Its importance lies in this, that this distance — 

 the radius of the earth's orbit — is the base line by means of 

 which we measure every other celestial distance, excepting 

 only that of the moon ; so that error in this base propagates 

 itself in all directions, through all space, affecting with a 

 corresponding proportion of falsehood every measured line, 

 the distance of every star, the radius of every orbit, the 

 diameter of every planet. 



Our estimates of the masses of the heavenly bodies 

 also depends upon a knowledge of the sun's distance from 

 the earth. The quantity of matter in a star or planet is de- 

 termined by calculations whose fundamental data include 

 the distance between the investigated body, and some 

 other body whose motion is controlled or modified by it; so 

 that any error in it involves a more than three-fold error in 

 the resulting mass. An uncertainty of one per cent, in the 

 sun's distance implies an uncertainty of more than three 

 per cent, in every celestial mass and every cosmical force. 



Error in this fundamental element propagates itself 

 in time also, as well as in space and mass. That is to say, 



