3«54 



PHYSIOGRAPHY. 



[chap. 



resembles the earth. One rotation of the sun is accom- 

 plished in about twenty-six of our days.^ 



From the different forms which the same spot appears to 

 assume, in passing across the disc, it may be inferred, that 

 the shape of the sun is spherical ; an inference which has 

 been abundantly corroborated by other observations. A 

 given spot when near to the margin of the disc, is fore- 

 shortened, and presents quite a different appearance from 

 that which it shows when in full view near the centre of 







-~tf / .ffi 





Fio. 119. — The great sun-spot of 1865 as it appeared on Oct. 14. (HowlettJ. 



the disc. Fig. 119 is a central view of a great sun-spot 

 which appeared in 1865. 



If the spots always travelled across the disc in straight 

 lines parallel to the sun's equator, it would obviously indicate 

 that the sun revolved in an upright position ; that is, with 



1 This time differs from the time given above as that at which a spot 

 appears and reappears at the same edge of the disc (about 28 days). The 

 difference is due to the earth's revolution. 



