13 REPORT 1864. 



salts, m-anous salts, permanganates, blue salts of cobalt, ferric sulpbocyanide, 

 siilphindigotic acid, litmus, azuliue, chinoliue blue, bleu de Paris, ceruleine, acid 

 nitrosonaphtbaline, cochuieal, chloropliyll, and the pm-jjle colom- produced by the 

 action of a sidphide on a nitroprasside. These solutions were exhibited ; and two 

 of them, litmus and chinoline blue, being placed in the hollow glass wedges, 

 showed the phenomena of dichromatism — that is, the thin part of the wedge of liquid 

 was blue, the middle part pm-ple, while the thick part was red. This is due to the 

 fi-ee transmission of the red ray, while the other parts of the spectrum are more 

 qiuckly absorbed. Several of the other liquids are dichromatic from the same cause ; 

 for instance, the salts of chromium, which are either gi-een or red, according to the 

 quantity seen through. No probable cause was assigned for this double peculiarity 

 — the very fr-ee transmission of the red ray, and the speedy absoiirtion of the neigh- 

 bouring nxy ; nor did the author see any chemical relationship between the sub- 

 stances that exhibit it. 



On ilie Spectra of some of tJie Heavenhj Bodies. 

 By Professor "W. A. Hixiee, V.P.R.S., and W.'Hfggins, F.B.A.S. 



The fii-st part of the commimication related to observations on planetaiy spectra. 

 It was necessary to compare these spectra side by side with that of the sun ; but 

 liere arose a difficulty, for a planet is not usually visible until simset. Ultimately 

 the plan adopted was to compare the light of the planet with that of the sim 

 reflected from the sky in the immediate vicinity of the planet, just after the sim 

 had sunk below the horizon. The object of this comparison was chiefly to ascertain 

 whether the sun's light, after being reflected from a planet, and having passed 

 through a portion of its atmosphere, contains any of those lines of absorption which 

 are produced in the solar spectrum when the rays of the sun traverse a large extent 

 of om- earth's atmosphere. This was found to bo the case, and one line in particular 

 was much more powerfully developed by the atmosphere of Jupiter than by that 

 of our earth. The colour of the light of Mars was in like manner foimd to be due 

 to absoi-ption exercised by something in the atmosphere of that planet. 



The second part of the communication refen-ed to the spectra of binary stars. 

 These are most difficult of observation, as the two members of the system are so 

 very near one another that it is difficvdt to obtain the spectrum of one without the 

 other. This difficidty was, however, overcome in some cases, where the stars were 

 not extremely close, by rotating the spectroscope in the tube of the telescope until 

 the slit for admitting the light was at right angles to the line joining the two stars ; 

 the coloiu-ed appearance presented by some of these interestiag bodies was foimd 

 to be produced by peculiar absorption of certain parts of the spectinmi, similar to 

 that which, on a small scale, is produced by the atmosphere of our liuninary. 



The third and most remarkable part of this communication was that which re- 

 fen-ed to the spectra of nebulae ; and the observations in this field were stated to 

 have been conducted solely by Mr. Huggins. The nebidaj examined were chiefly 

 those denominated planetary nebulae. It was scarcely expected that the extremely 

 faint light of these bodies would be sufficient to produce any spectrum at all ; nor 

 would it have done so had theii- construction been that which has been usually 

 assigned to them. But to the sui-prise of the observer he beheld, not a continuous 

 spectrum such as that which proceeds from a solid body interspersed with dark 

 lines due to atmospheric absoi-ption, but a specti'um consisting of a few bright lines 

 such as that which proceeds from an intensely heated gas. It was, indeed, the 

 smallness in number of these component lines that enabled any success to be ob- 

 tained ; and the result fr-om three or four of these nebulffi revealed the fact that 

 thev were in each case composed of glowing gas, probably hydrogen and nitrogen, 

 without any solid nucleus whatever. But what can be the origin of this high 

 temperature, since, iipon the principle of the conservation of energy, some other form 

 of motion must be destroyed in order to produce the luminosity ? The origin of the 

 light of the heavenly bodies thus becomes more pei-plexing than ever, and seems to 

 point to some law regarding which we are jot in the dark. 



