THE SUN. 55 



sides are found to be, each about thirty-eight times the 

 length of the base, and the resulting distance of the moon 

 from the earth's centre about thirty diameters of the 

 latter, or more exactly sixty times and a quarter its 

 radius, that is to say, 238,100 (say 240,000) miles, 

 which is rather under a quarter of a million so that, 

 speaking roughly, we may consider the moon's orbit 

 round the earth as a circle about half a million of miles 

 across. In the case of the sun, however, it is otherwise. 

 The sides of our triangle are here what may be called 

 extravagantly out of proportion to its base : and the 

 result of the calculation is found to assign to the sun a 

 distance very little short of four hundred times that 

 already found for the moon being in effect no less than 

 23,984 (in round numbers 24,000) radii, or 12,000 

 diameters of the earth, or in miles 94,880,700 or about 

 95,000,000.* 



(9.) When so vast a disproportion exists between the 

 distance of an object and the base employed to measure 

 it, a very trifling error in the measured angles produces a 

 great one in the result. Happily, however, there exists 

 another and a very much more precise method, though 

 far more refined in principle, by which this most import- 

 ant element can be determined ; viz., by observations of 

 the planet Venus, at the time of its " transit" (or visible 

 passage) across the sun's disc. It would lea'd us too far 

 aside from our purpose to explain this, however, at 



* These numbers and all the subsequent statements in miles are 

 too large by about I mile in 31. See Lecture III. on Comets, 

 9- 



