344 AKXCAL OF SOreXTIFIC DISCOVERT. 



tlic nclmlir!. A circular portion of the sun's disk subtcndinjif 1' 

 Miulil <x\\i' a li;rlit ('(jiial to 7.^0 full moons; yet many of tlie ni'l)U- 

 la', tlioui;h they subtend a mueh lar^^er angle, are invisible to the 

 naked eye. 



2. If these enormous masses of gas are luminous throughout, 

 the light from tlie jjortions of gas I)eyond tlie surl'aee visil)le to us 

 Avould be in a great mcasin-e extinguished by the absorption of the 

 gas through which it wouhl have to jiass. These gaseous ni'l)uhB 

 would, therefore, present to us little more than a luminous surface. 



3. It is probalile that two of tlie constituents of thes(? nel)idaj 

 are tlie elements iiydrogen and nitrogen, unless the alisence of 

 tiie other lines of the spectrum of nilrog(!n indicates a form of 

 matter more elementary than nitrogen. The third gaseous sub- 

 stance is at present unreeognized. 



4. The uniformity and extreme simplicity of the spectra of all 

 these nebuhu opjiose the opinion that this gaseous matter repre- 

 Bents the ** neliulous lluid "^ suggested In' Sir William llm'schel, 

 out of which stars an* elal)orati'd by a process of subsidence and 

 condensation. In such a primordial lluid, all the elemmits enter- 

 ing into the composition of the stars should i)e found. If tliese 

 existed in these nel)nlae, the sp(!ctra of their light wouM be as 

 crowded with bright lines as the stellar spectra are with dark 

 lines. 



o. A progi'CPsive formation of some character is suggested by 

 the presence of more condensed portions, and, in some nebulaj, of 

 a nucleus. NcIjuLtc which give a continuous spectrum, and 3'et 

 show l)Ut little indication of resolvabilit}', such as the great neljula 

 in Andromeda, are not necessarily clusters of stars. They may be 

 gaseous nebuhe, which. In' tlie loss of heat or the influence of other 

 forces, have become crowded with portions of matter in a more 

 condensed and opaque condition. 



6. If the ol)servations of Lord llosse. Prof. Bond, and others, are 

 accepted in favor of the partial resolution of the annular nelxda in 

 Lyra, and the great nel)ula in Orion, into discrete briglit points, 

 these nebulas must be n-garded not as simple masses of gas, but as 

 systems formed by the aggregation of gaseous masses. 



7. The opinion of the enormous distance of the nebula) from our 

 system, since it has been founded upon the supposed extent of re- 

 moteness at which stars of consideral)le brightness would cease to 

 be separately visilde in our telescopes, has no longer an}' found;i- 

 tion on which to rest, in reference at least to those of tlie nebula3 

 ■which give a spectrum of briglit lines. It may lie that some of 

 tliese are not more distant from us than the Ijrigliter stars. 



8. As far as his observations extend, they a2)pear to be in favor 

 of the opinion that these nebula) arc gaseous systems possessing a 

 structure and a iiurpose in relation to the universe, altogether dis- 

 tinct from the great cosmical masses to wliich tlie sun and the lixed 

 .stars belong. — Lecture before the Eoyal Institution. 



