November 13, 1903.] 



SCIENCE. 



613 



space, and these distant worlds, of course, 

 included the sun, although it is practically 

 our neighbor. 



It was now established that the solar 

 radiation came from the incandescence of 

 metallic vapors and gases in the sun's at- 

 mosphere, the metals and gases being for 

 the most part those with which we are 

 familiar on the earth. Not only was a 

 high temperature demonstrated in this way, 

 but it was furtlier shown that above tho 

 sun's apparent surface there was an ab- 

 sorbing atmosphere, consisting of vapors 

 cooler than those below, but yet hot enough 

 to be composed of the steam of iron and 

 other metals. 



In 1865, De la Rue, Stewart and others, 

 in an attempt to get the periodicity of the 

 solar phenomena still more accurately de- 

 termined, started work at Kew; while the 

 former observations were carried on by 

 Schwabe and Wolf by the eye, photog- 

 raphy, which was then being introduced 

 into astronomical work by the labors of 

 Warren De la Rue, was for the first time 

 now utilized, and a picture of the sun was 

 taken each day. 



In 1866 a new method of observing solar 

 changes, which consisted in throwing an 

 image of the sun on the slit plate of a spec- 

 troscope, revealed the fact that the spectra 

 of spots differed from that of the photo- 

 sphere generally; certain lines were 

 widened in the spot spectrum.* 



In 1867 a connection between changes 

 in .spotted area and in terrestrial tempera- 

 tures was pointed out by Baxendell.f He 

 noticed a distinct and very striking rela- 

 tion between the number of sun spots and 

 the ratio which exists between the differ- 

 ence of the mean maximum temperature 

 of solar radiation and the mean maximum 

 air temperature on the one hand, and that 



• Lockyer, I'roc. Roy. Soc, October 11, 1866. 

 t Memoirs of the Manchester Lit. and Phil. Soc., 

 Third Series, Vol. IV., pp. 128 et seq. 



of the mean temperature of the air and of 

 evaporation on the other. 



In 1868 a spectroscopic method was dis- 

 covered of observing in full daylight the 

 'prominences' or 'red flames' which hith- 

 erto had only been glimpsed during 

 eclipses, and it was established that, closely 

 surrounding the sun ordinarily seen, there 

 was an envelope, named the chromosphere, 

 of incandescent gases and vapors, hydrogen 

 and a new substance named helium chief 

 among them.-"-= 



JIany spectroscopic observations made 

 on the spots and prominences about this 

 time indicated great changes in the .solar 

 temperature in different regions, and pos- " 

 sibly, therefore, changes in the amoimt of 

 heat radiated earthwards. From the 

 changes thus actually seen it was easy to 

 imagine that there might be a cycle of ter- 

 restrial changes depending no longer on 

 the sun's presentation to us in its daily 

 and yearly rounds, but on physical changes 

 in the sun itself, requiring, perhaps, many 

 years to accomplish. 



In 1869, Janssen showed + that by a 

 special arrangement of the spectroscope an 

 image of the sun, showing the prominences 

 both on the disc and surrounding it, might 

 be obtained. 



It was not very long before it was found 

 that the reaction of these solar changes on 

 the earth was not so limited as had formerly 

 been thought. This was an idea started by 

 Dr. Stone of the Royal Observatory at the 

 Cape of Good Hope, Piazzi Smyth of the 

 Royal Observatory of Edinburgh, and 

 others, about the years 1870 and 1871, but 

 the most striking imperial contribution to 

 the matter we owe to the labors of a dis- 

 tinguished meteorologist, Dr. Meldrum, 

 director of the observatory at Mauritius, 

 which has since become the Royal Alfred 



• Lookyer, Proc. Roy. Soc., October 20, 1868. 

 f Comptes Rcndiis, Vol. LXVIII. (1869), pp. 

 367 et seq. 



