METEOROLOGY OF THE SUN AND EARTH. 77 



of colder matter from the atmosphere of the sun, while the upward 

 rush of heated matter was supposed to accouut for the facula^ or bright 

 patches which almost invariably accompany spots. In the next place 

 the Kew observers, making use not only of the Kew series but of those 

 of Schwabe and Carrington, which were generously placed at their dis- 

 posal, have discovered traces of the influence of tlie nearer planets 

 upon the behavior of sun-spots. This influence appears to be of such 

 a nature that spots attain their maximum size when carried by rota- 

 tion into positions as far as possible remote from the influencing planet 

 that is to say, into positions where the body of the sun is between 

 them and the planet. There is also evidence of an excess of solar ac- 

 tion when two influential planets come near together. But, although 

 considerable light has thus been thrown on the periodicity of sun- 

 spots, it ought to be borne in mind that the cause of the remarkable 

 period of eleven years and a quarter, originally discovered by Schwabe, 

 has not yet been properly explained. The Kew observers have like- 

 wise discovered traces of a peculiar oscillation of spots between the 

 two hemispheres of the sun, and finally their researches will place at 

 the command of the observers the data for ascertaining whether cen- 

 tres of greater and lesser solar activity are connected with certain 

 heliocentric positions. 



While the sun's surface was thus being examined both telescopi- 

 cally and photographically, the spectroscope came to be employed as 

 an instrument of research. It had already been surmised by Prof. 

 Stokes, that the vapor of sodium at a comparatively low temperature 

 forms one of the constituents of the solar atmosphere, inasmuch as the 

 dark line D in the spectrum of the sun coincides in position with the 

 bright line given out by incandescent sodium-vapor. 



This method of research was greatly extended by Kirchhoflf, who 

 soon found that many of the dark lines in the solar spectrum were co- 

 incident with the bright lines of sundry incandescent metallic vapors, 

 and a good beginning was thus made toward ascertaining the chemi- 

 cal constitution of the sun. 



The new method soon brought forth further fruit when applied in 

 the hands of Huggins, Miller, Secchi, and others, to the more distant 

 heavenly bodies. It was speedily found that the fixed stars had con- 

 stitutions very similar to that of the sun. But a peculiar and unex- 

 pected success was attained when some of the nebula? were examined 

 spectroscopically. To-day it seems (so rapidly has knowledge pro- 

 gressed) very much like recalling an old superstition to remind you 

 that until the advent of the spectroscope the irresolvable nebulae were 

 considered to be gigantic and remote clusters of stars, the individual 

 members of which were too distant to be separated from each other 

 even with a telescope like that of Lord Rossc. But Mr. Huggins, by 

 means of the spectroscope, soon found that this was not the case, and 

 that most of the nebulae which had defied the telescope gave indica- 



