xxiv GENERAL SUMMARY OF SCIENTIFIC AND 



analyses of the structure of the solar surface, as was ex- 

 plained in the Annual for 1S74, he has now called to his aid 

 photometry and the thermo-electric pile. He finds that the 

 nuclei of the solar spots are cooler than the neighboring bright 

 portions of the sun's surface, but in general warmer than the 

 limb of the sun as seen through the solar atmosphere. He 

 lias, moreover, shown that the light and heat which we re- 

 ceive from the sun emanates from the superficies of the nu- 

 cleus, which is covered by a thin layer of gaseous material, 

 which latter absorbs botli heat and light ; but in so doing- 

 exercises a distinct selective power in that the absorption of 

 the lower or heat rays of the spectrum is to the absorption 

 of the visual rays as one to six. He finds, moreover, that a 

 sensible amount of heat is received from those portions of the 

 lower envelope that are distant thirty seconds of arc from 

 the visible limb of the sun. 



Pickering and Strange have investigated, photometrically, 

 the amount of light absorbed by the solar atmosphere. The 

 probable error of the result is exceedingly small, and shows 

 that the lio-ht at the edo-e is about four tenths of that at the 

 centre. It appears to them that there is a slightly different 

 distribution of the light across the polar and the equatorial 

 diameters. 



Professor Mayer has continued to develop his method of 

 obtaining the isothermals of the solar disk, and is now hav- 

 ing a telescope arranged for the purpose of making continu- 

 ous observations in this novel and interesting field. He sug- 

 gests that the discordance in results obtained by Secchi and 

 Langley may possibly be due to the fact that these observ- 

 ers have thrown the image of the sun upon inclined instead 

 of horizontal disks of paper, thereby introducing superficial 

 currents of air, whose presence lie found extremely deleteri- 

 ous to his own results, and which were almost entirely obvi- 

 ated by employing a perfectly horizontal plane of projection. 



Although our review strictly begins with November, 1874, 

 yet we will not omit to notice the work of Violle, published 

 a little earlier than that date, on the effective temperature of 

 the sun. Assuming that the mean emissive power of the sun 

 is sensibly equal to that of steel in fusion, Violle concludes 

 that the true temperature of the sun is about two thousand 

 decrees. 



