390 Nebular and Stellar Spectra. 



one whose name must ever stand foremost as the leader of the 

 prismatic analysis of the starry heavens. 



Another eminent observer, Secchi, has been diligently 

 prosecuting spectroscopic, or, as he calls them, " spectro- 

 metries inquiries, and has arrived at conclusions differing in 

 some respects from those of Huggins. He has formed a 

 classification of stellar spectra according to distinctly-marked 

 types : — 1. That of the bluish-white stars, such as Sirius 

 and Wega, with dark bands in the blue and violet, including 

 nearly one-half of the stars examined: — 2. That of the red, 

 or orange stars, with broad zones, such as Betelgeuse and 

 Antares : — 3. That of the yellow stars, comprising Capella, Arc- 

 turus, etc., marked by fine lines, and resembling the spectrum 

 of our sun. To these are added a type the inverse of the first, 

 found only as yet in 7 Cassiopeas and j3 Lyras, and a type pecu- 

 liar to Orion, distinguished by the intensity of the green. He 

 has also observed in other regions the separate and special 

 predominance of some one type of light. All this is certainly 

 very remarkable, but is only given by himself as the result of 

 a few evenings' work preparatory to a more general and 

 detailed research. Before, however, any fully satisfactory con- 

 clusion can be attained, a question will have to be decided as 

 to the nature of many of the bands towards the red end of 

 the solar spectrum, the origin of which, as will be seen in our 

 last number (p. 317), has been largely referred by M. Jansen, 

 of Paris, to the presence of aqueous vapour. As to some of 

 these confessedly delicate and obscure points, further inves- 

 tigation and the labours of many observers are obviously de- 

 sirable. In such stellar spectra as are crossed by numerous 

 dark bands, a difficulty has been pointed out in ascertaining 

 whether certain intervening luminous spaces may not assume 

 the deceptive aspect of bright and gaseous lines from contrast 

 alone, and here the finest instruments will be required for the 

 decision. As to nebulous material, it is frequently so deficient 

 in luminosity as to elude all known means of analysis. Up to 

 the beginning of the present year Secchi had discovered 

 fourteen very feeble nebulas which had escaped all former 

 observers ; and has found occasionally large spaces where the 

 sky has a milky aspect — the " diffused nebulosity/' no doubt, 

 of the Herschels. In the latter case there seems no impos- 

 sibility in the idea of a vicinity to our own system, which, if 

 it could be estimated, might perhaps surprise us. According 

 to the Eoman astronomer the nebula of Orion extends through 

 all the space from £ southwards to 49 and v, two 5 mag. stars 

 nearly on the parallel, and somewhat less than 2° apart, forming 

 the bottom of the sword. 



One of the most curious observations of this nature, for 



