CELESTIAL CUEMISTRY. 259 



but the cylindrical lens was generally removed, since the nebulas pre- 

 sent a visible disc instead of a point when in focus. The first object 

 attacked was 37 II. IV. Draconis, which is described by Sir J. Iler- 

 schel in his latest catalogue as " very bright ; pretty small ; with a 

 very small nucleus." Its color is greenish blue. Looked at with the 

 telescope and spectrum apparatus, Mr. Hnggins was astonished to find 

 no spectrum visible, but only one short line of light in the direction 

 which the dark lines always occupy in the spectrum. At first he sus- 

 pected derangement of the apparatus, but this being found in good 

 order, it became apparent that this celestial body differed from all 

 others that have been examined, not in degree, but absolutely in kind ; 

 for its light was not composed of rays of different refrangibilities, but 

 mostly of one monochromatic light only. Careful examination with 

 a narrower slit detected a more refrangible, but much fainter bright 

 line, and at about three times the distance another still fainter was 

 seen. The direct comparison of these lines with those of the solar 

 spectrum viewed through the atmosphere * was then made, and it was 

 found that the brightest line corresponded with the strongest line due 

 to nitrogen, and the faintest with one of the hydrogen lines, while the 

 intermediate one was nearly, but not quite, coincident with a barium 

 line. An excessively faint spectrum was also detected on both sides 

 of the bright lines, which is, doubtless, due to the minute solid or 

 liquid nucleus, and perhaps is crossed by both lines. 



The significance of this discovery is invaluable. Terrestrial physics 

 show us that only liquid and solid bodies give a continuous spectrum, 

 while gases alone, when rendered luminous by heat, give out light which, 

 after dispersion by the prism, is found to consist of certain degrees of 

 refrangibility only, which appear as bright lines on a dark ground. 

 Here there was clear and unimpeachable evidence, according to the 

 present state of our knowledge, that large masses of gas exist ; and 

 these may be the nebulous matter of Herschel and Laplace, which then 

 is no fiction, and that we may yet fairly speculate on the process 

 of the origin of worlds from such a primal form. But other nebulas 

 were to be tested. A very similar planetary nebula (^ 6), in Taurus 

 Poniatowski, when examined, gave precisely the same bright lines, 

 with the merest suspicion of a faint spectrum. 7o H. IV. Cygni gave 

 the same three bright lines, with a stronger continuous spectrum than 

 the nebula in Draco. This nebula has a distinct llth magnitude star 

 in the middle, which evidently produces the continuous spectrum ; and 

 this opinion was confirmed by a most crucial experiment. The cylin- 

 drical lens being removed from the apparatus, it was found that the 

 three bright lines still remained of considerable length, corresponding 

 to the diameter of the telescopic image of the nebula, while the faint 

 spectrum became a narrow line, showing that the object producing it 

 was a point in the focus of the object-glass. 51 H. IV. Sagitarii is a 

 fainter planetary nebula, and the two brighter lines were seen, and 

 the third by glimpses. 1 H. IV. Acquarii had the three bright lines 

 distinct and sharp, but the indications of the faint spectrum were mere 



*It should here be noted, that some of the lines crossing the solar-spectrum are 

 due undoubtedly to the elements of our atmosphere, as oxygen, nitrogen, hydro- 

 gen, &c. It was with the lines produced by these atmospheric gaseous elements 

 that the nebula lines were compared. 



