PROGRESS OF ASTRONOMY FOR I8iU AND lS!t2. 707 



let), iiiid t lie expeiiiiiciital (Ictt'iiiiiiiatioiis have Ikhmi siUlicit'iitly coii- 

 coidant in themselves, the diveruoiicies aiisinu lV(»iii the diflereiit laws 

 ad()i)t"d to eoiiiieet tlie radiation of incaiKh^sceui bodies \\itli their tem- 

 perature. Newton's hiw, w hii'li hohls only tor an intcrx al ol' a lew 

 deji'rees. ^ixcs for the temperature of tin- sun millions of dej^rees. 

 Dniou'i's, wliicli is only exact o\er a ran.ue of l.'iO'' at most, g'ives 

 1,5()()"J. Rosetti's law. established by cxpi'riments nnule iietween O"^ and 

 300°, uives l().0(tO . A nn>re recent series of experiments has been 

 made by M. 11. Le < 'imtelier. and is published in the Citmjitts h'eii(li(s for 

 Mareh 28, 1S92, in w liich the temi»eratures eiujiloyed coxci' a ran^e of 

 1J0(P (700° to l.Sixr ). Tlie -n'tfeetive'' temperature tliat he finds for 

 the sun is 7.00(P. wiiich he tliiidcs nmy be subJiM-t to an uncertainty, on 

 account of errors which nmy effect the law of radiation, not ureater 

 tliaii 1.000°, the '• effective "^ temi»erature bein.ii- that temperature which 

 a body of endssive power ecpud to unity nnist liav<' in order to send us 

 radiations of the same intensity as the sun. The actual tein])eiature 

 of the photosphere is hij;her, for a part of its radiations are absorbed 

 by the less hii;hly heated solar atmosphere, ami ])erhaps also (altlioniili 

 this seems hardly probabh') because the endssive power of the sun may 

 be less than unity. 



Solar act ir it 1/ in is'J.'J. — The development of the solar activity during- 

 LS02 was no less marked with regard to prominenees than with regard 

 to sun spots. On April (! Trouvelot reported au arched jn'ominenee 

 extending some 90,000 miles along the limb of the sun and attaining a 

 height of over r>7,oOO miles. Two days later an enormous i)rotuberance 

 rose to a height of 71,!>70 nnles, extending in a little over half an hour 

 to 10.),550, and a week later another extending over 2.-)r),00(> mih'S along 

 the circuniferenc<'. 



Tlie great Sim sjxtt (fro up of lsi):j. — It appears that the original I'orma- 

 tion of the group took place on the farther side of the sun, and it lirst 

 came under obseivation on No^('nd)er 15, 1801. when it was seen as a 

 si)ot of considerable size close to the east limb. On November \i\ 

 the group consisted of thi'ee spots, and by]Srovend>er 18 it had assunu'd 

 the appearance so tyi)ical of tliemoi-e important disturbances, of a long 

 procession of spots of \arious sizes, the s]»ot in the van and that in 

 the rear being the largest. During tlie I)ecend)er apjx'arance (De- 

 cember 12-24) it was throughout one well-deUiu'd circulai' spot. 



One spot, roughly circular in shape, ah)ne appeared on .January 7. 

 it is not (piitc clear whether it represented the |)riiici|)al groui> of the 

 November appearance or the little group whicli formed in ad\ance of 

 it and which b<icame prominent during Decembei-. It seemed to oc- 

 cupy a position nearly midway between the two. though the two are 

 practically to be regarded as one disturbance'. 



Befoi-e its a]t])earance at the east lind> <»n March 4 a gieat change 

 had taken place. 'IMie group, which on l''el)rnary l.'i liad co\-ei-ed more 



