THE SUN. 53 



aim at is to convey to their minds, as matters of fact, 

 what those results are in the case of the sun, and to en- 

 able them to form a conception of it as a reality. Still it 

 is reasonable for any one to ask how it is possible to 

 prove such a statement, for instance, as that just made : 

 and as the kind of process by which our conclusions as 

 to the size and mass of the sun are arrived at may be 

 put in a few words, it will not be amiss to give a sketch 

 of it. 



(7.) The first step towards ascertaining the real size of 

 the sun is to determine its distance. Now, the simplest 

 way to find the distance of an object which cannot be 

 got at, is to measure what is called a base line from the 

 two ends of which it can be seen at one and the same 

 moment, and then to measure with proper instruments 

 the angles at the base of the triangle formed by the dis- 

 tant object and the two ends of the base. Geography 

 and surveying in modern times have arrived at such 'per- 

 fection, that we know the size and form of the earth we 

 stand upon to an extreme nicety. It is a globe a little 

 flattened in the direction of the poles, the longer dia- 

 meter, that across the equator, being 7925 miles and five 

 furlongs, and the shorter, or polar axis, 7899 miles and 

 one furlong ; and in these measures it is pretty certain 

 that there is not an error of a quarter of a mile. And 

 knowing this, it is possible to calculate with quite as much 

 exactness as if it could be measured, the distance /;/ a 

 straight line between any two places whose geographical 

 positions on the earth's surface are known. Now there 

 are two astronomical observatories very remote from one 



