1865.] Mr. Huggins Spectrum of Nebula in Orion. 39 



their accompanying faculse for all the Kew pictures available for this 

 purpose. 



From this it appeared that out of 1137 cases 584 have their faculse 

 entirely or mostly on the left side, 508 have it nearly equal on both sides, 

 while only 45 have it mostly to the right. It would thus appear as if 

 the luminous matter being thrown up into a region of greater absolute 

 velocity of rotation fell behind to the left ; and we have thus reason to sup- 

 pose that the faculous matter which accompanies a spot is abstracted from 

 that very portion of the sun's surface which contains the spot, and which 

 has in this manner been robbed of its luminosity. 



Again, there are a good many cases in which a spot breaks up in the 

 following manner. A bridge of luminous matter of the same apparent 

 luminosity as the surrounding photosphere appears to cross over the 

 umbra of a spot unaccompanied by any penumbra. There is good reason 

 to think that this bridge is above the spot ; for were the umbra an opaque 

 cloud and the penumbra a semi-opaque cloud, both being above the sun's 

 photosphere, it is unlikely that the spot would break up in such a manner 

 that the observer should not perceive some penumbra accompanying the 

 luminous bridge. Finally, detached portions of luminous matter sometimes 

 appear to move across a spot without producing any permanent alteration. 



From all this it was inferred that the luminous photosphere is not to 

 be viewed as composed of heavy solid, or liquid matter, but is rather of 

 the nature either of a gas or cloud, and also that a spot is a phenomenon 

 existing below the level of the sun's photosphere. 



The paper concluded with theoretical considerations more or less pro- 

 bable. Since the central or bottom part of a spot is much less luminous 

 than the sun's photosphere, it may perhaps be concluded that the spot 

 is of a lower temperature than the photosphere ; and if it be supposed 

 that all the sun's mass" at this level is of a lower temperature than the 

 photosphere, then we must conclude that the heat of our luminary is 

 derived from without. 



II. " On the Spectrum of the Great Nebula in the Sword-handle of 

 Orion." By WILLIAM HUGGINS, F.R.A.S. Communicated by 

 the Treasurer. Received January 11, 1865. 



In a paper recently presented to the Royal Society *, I gave the results 

 of the application of prismatic analysis to some of the objects in the hea- 

 vens known as nebulae. Eight of the nebulae examined gave a spectrum 

 indicating gaseity, and, of these, six belong to the class of small and com- 

 paratively bright objects which it is convenient to distinguish still by the 

 name of planetary. These nebulae present little indication of probable 

 resolvability into discrete points, even with the greatest optical power 

 which has yet been brought to bear upon them. 



The other two nebulas which gave a spectrum indicative of matter in the 

 * On the Spectra of some of the Nebulae, Phil. Trans. 18G4, p. 437. 



