426 THE CHEMISTRY OF THE SUN. [CHAP. 



his work, and also to Sporer's, we owe very much of our present 

 knowledge on this subject. 



Carrington, from the observation of some thousand spots, 

 came to the conclusion that the photosphere in which these spots 

 are supposed to float, really moves more rapidly at the equator 

 than it does away from it, in the manner that Schemer had 

 suggested, in such a way that the movement at the equator 

 really takes place in, as near as may be, twenty-five days, per- 

 haps a little less ; but that in latitude 30 there is a slackening 

 off of a day and a half, so that it takes a spot in latitude 30 

 north or south not twenty-five days, but twenty-six and a 

 half days to make its movement right round ; if we go as 

 high as latitude 45, we have to add on still another day, 

 and then we find that the rotation takes twenty-seven and a 

 half days. 



Several distinguished men have endeavoured to formulate a 

 law, a mathematical statement, by which, given the rate of spot 

 movement in one latitude, we may determine it for all other 

 latitudes, and several of them have very nearly succeeded in 

 doing it; but most confess that it does not amount to much 

 at the end of the chapter ; by which I mean that the formula 

 after all contains no physical basis. 



The formulaB to which I have referred may be given in this 

 place. In them all x = daily motion in minutes of solar 

 longitude, and / = latitude. They are as follows: 



Carrington , . . x = 865' 166' sin J I 



Faye x = 862' 186' sin 2 I 



Sporer . . . . x = 1011' 203' sin (41 13' + 1) 

 863' 619' sin 3 I. 



Zollner 



cos I 



The second of these four expressions deserves particular 

 attention, since it professes to be, not like the rest, merely 

 empirical, but to convey a " law " in the true sense that is, a 



