OCTOBEE 19, 1900.] 



SCIENCE. 



593 



Michelson has also recently invented a 

 new form of spectroscope called the ' Eche- 

 lon,'* in which a grating with a relatively 

 small number of lines is employed, the dis- 

 persion necessary for modern work being 

 obtained by using a high order (say the 

 hundredth) into which most of the light 

 has been concentrated. 



Besides lines recorded in the visual and 

 ultra-violet portions of the solar spec- 

 trum, maps have been made of the lines in 

 the infra-red, the most important being that 

 of Langley's, published in 1894, prepared 

 by the use of his ' bolometer.' Good work 

 had, however, been done in this direction 

 previously by Becquerel, Lamansky and 

 Abney ; the last, indeed, succeeded even in 

 photographing a part of it. 



The recording of the Fraunhofer lines in 

 the solar spectrum is not all, however. The 

 application of the spectroscope to the sun 

 has several epoch-marking events attached 

 to it, notably those of proving the solar 

 character of the prominences and corona, 

 the rendering visible of the prominences 

 without the aid of an eclipse by the dis- 

 covery of Lockyer and Janssen in 1868, the 

 photography of the prominences both round 

 the limb and those projected on the solar 

 disc by the invention of the spectro-helio- 

 graph by Hale and Deslandres in 1890. 



Success has not yet favored the many at- 

 tempts to photograph the corona without 

 an eclipse by spectroscopic means ; but even 

 now this problem is being attacked by Des- 

 landres with the employment of the calorific 

 rays. 



Spectroscopic work on the sun has led to 

 the discovery of many hundreds of dark 

 lines, the counterparts of which it has not 

 yet been possible to produce on the earth. 



But besides those unknown substances 

 which reveal their presence by dark lines, 

 there were two others discovered, which 

 showed themselves only by bright lines, the 



*Ast. Phys. Journ., Vol. VIII., 1898, p. 37. 



one in the chromosphere, to which the name 

 of Helium was given, and the other in the 

 corona, to which the name of Coronium waa 

 applied. 



The former was, however, identified ter- 

 restrially by Eamsay in 1895, though the 

 latter is still undetermined. The revision 

 of its wave-length, brought about by the 

 observations of the eclipse of 1898, may, 

 however, result in this element being trans- 

 ferred from the unknown to the known in 

 the near future. 



The study of stellar spectra was taken up 

 by Huggins, Eutherfurd and Secchi. Ruth- 

 erfurd* published in 1862 his results upon 

 a number of stars, and suggested a rough 

 classification of the white and yellow stars ; 

 but Secchi deserves the high credit of in- 

 troducing the first systematic system of dif- 

 ferentiation of the stars according to their 

 spectra, he having begun a spectroscopic 

 survey of the heavens for the purpose of 

 classifi cation, t whilst Huggins devoted him- 

 self to the thorough analysis of the spectra 

 of a few stars. 



The introduction of photography marks 

 another epoch in the study of stellar spectra. 

 Sir William Huggins applied photography as 

 early as 1863, J and secured an impression of 

 the spectrum of Sirius, but nearly another 

 decade elapsed before Professor H. Draper § 

 took a photograph of the spectrum of Vega 

 in 1872, which was the first to record any 

 lines. With the introduction of dry plates 

 this branch of the new astronomy received 

 another impetus, and the catalogues of 

 stellar spectra have now become numerous. 

 Among them may be mentioned those of 

 Harvard College, Potsdam, Lockyer, Mc- 

 Clean, and Huggins. The ' Draper Cata- 

 logue' II of the Harvai'd College, which is a 



*Am. Journ., Vol. XXXV., 1862, p. 77. 



t CompiesBendus, T. LVII,, 1853. 



t PMl. Trans., 1864, p. 428. 



I Am. Journ. of Sc. and Arts, Vol. XVIII., 1879, 

 p. 421. 



II Amuds Harvard Coll., Vol. XXVII., 1890. 



