46 



the sun's 360 radii beyond the earth's orbit to the concave ce- 

 lestial sphere, *' the firmament of heaven," would divide the whole 

 visible universe into 360 apparently equal parts ; and were any 

 globe or mass of matter whatever to revolve in any one of the 

 infinite multitude of orbits that might be drawn round the sun 

 in the centre, and to rotate on its axis 360 times during each 

 complete orbital revolution, then most assuredly each of its ro- 

 tations would be complete only when the same points of its cir- 

 cumference, 180° distant from each other, or diametrically op- 

 posite, respectively returned to their places on each of the pro- 

 tracted radii, with their connecting diameter in one with the 

 radius for the time; the same point facing the sun always at the 

 end of each rotation, and the same opposite point always facing 

 the corresponding point marked on the face of heaven by the 

 protracted radius. On the contrary, every star on the ecliptic 

 would be passed in its turn, and, in consequence of the angular 

 distance continually gained by the revolving body, would fall 

 proportionally short of the true measure of the body's rotation, 

 making 361 transits when there were only 360 rotations. 



What seems to have confounded the ideas of the writer from 

 whose book I am quoting, and of all other astronomers, is that 

 the sun turns round on his own axis in 25 days 10 hours, but 

 it requires 27 days and upwards to bring back the same point 

 of his circumference to the earth's radius-vector ; because, while 

 he is turning round from east to west, the earth is advancing in 

 her orbit in the same direction^ and, consequently, is always gain- 

 ing upon the sun, who remains in his place, and is obliged to 

 take more than a complete turn before the same point of his 

 circumference can overtake the advancing earth's radius-vector. 

 But this has nothing whatever to do with the earth's rotation, it 

 being a matter of perfect indifference what part of the sun's cir- 

 cumference may present itself to the earth's meridian. Whether 

 he rotate or not, the result, so far as the earth and her noons 

 are concerned, will be the same ; for it is the radius-vector di- 

 rected to the sun's centre, and not a particular point of his cir- 

 cumference, that marks the moment of transit. But, owing to 

 the movement of the two bodies (sun and earth) in the same 

 direction, the earth will see the sun's whole circumference one 

 time less than the number of complete rotations which he makes 

 in a year, his rotations as a fixed body being measured and in- 

 dicated, not by the flitting earth's radius-vector, but by his pre- 

 senting the same point of his circumference again to the same 

 equally j^^ef^ point of the heavens; that is to say, for every four- 

 teen complete rotations on his axis, the sun makes only thirteen 

 transits of the earth's meridians, not through any fault of his 

 own, but owing entirely to the earth's moving away from the 



