450 Mr. Carrington on the Evidence of the 



parent centre of the disc, S a spot, SM its parallel, CS = p, 



j^ / \ • no-MT m — l. sin CM , 



d\=(p) . sin CSM= ^ r- . tan t ^ , nearly : 



sin 1" sin p *' 



or dX varies nearly as —. — ; since CM is constant. 

 •' sin p 



I have given the values of this ratio for convenience in the 

 last column of Table I. for h = ^, by which it appears that they 

 may be considered constant in connexion with the unavoidable 

 errors of observation, and absolutely vary very slowly for most 

 values of p. 



We are compelled to recur again to longitudes. If a pair of 

 well-defined spots could be found differing little in latitude and 

 about 30^ in longitude, which had twice crossed the disc to- 

 gether under favourable circumstances of observation, I should 

 select them for our next discussion ; but the conditions are such 

 as are not satisfied by any series I have yet succeeded in ob- 

 taining. 



Accordingly, that the conclusions of this paper may not rest 

 on a single series of observations, although satisfactory in them - 

 selves, I will, lastly, take another series of deduced longitudes 

 for examination, which were obtained at nearly the same time 

 in the same year, 1854. During its first passage, the spot ex- 

 hibited a circular and well-defined nucleus, which appeared to 

 attain its greatest actual expansion about the time it first passed 

 the centre. At its reappearance, all trace of penumbra was 

 gone, the nucleus was much reduced, and was an exceedingly 

 sharp object for observation. After Sept. 1 it was no longer 

 to be seen. 



