NEBULAE. 



185 



scope. " Astronomers," says the former, " place three stars close to each other in the 

 sword of Orion : and, when I viewed the middlemost with a telescope in the year 1656, 

 there appeared, in the place of that one, twelve other stars ; among these, three that 

 almost touch each other, and four more besides, appeared twinkling as through a cloud, 

 so that the space about them seemed much brighter than the rest of the heavens, which 

 appearing wholly blackish, by reason of the fair weather, was seen as through a certain 

 opening, through which one had a free view into another region which was more 

 enlightened. I have frequently observed the same appearance in the same place without 

 any alteration; so that it is likely that this wonder, whatever it may be in itself, has been 

 there from all time ; but I never took notice of any thing like it among the rest of the 

 fixed stars." This nebula discerned by the naked eye, exhibits an indefinite, foggy 

 appearance, brighter, yet more diffuse and strange when a telescope is used, but the 



whole light and power of Herschel's forty 

 feet reflector could not resolve it into dis- 

 tinct stars. " This highly interesting ob- 

 ject," he states, "engaged my attention in 

 the beginning of the year 1774, when, 

 viewing it with a Newtonian reflector I 

 made a drawing of it ; and, having from 

 time to time reviewed it with my large 

 instruments, it may easily be supposed 

 that it was the very first object to which, 

 in February, 1787, I directed my forty- 

 feet telescope. The superior light of this 

 instrument showed it of such a magnitude 

 and brilliancy, that, judging from these 

 circumstances, we can hardly have a doubt 

 of its being the nearest of all the nebulae 

 in the heavens, and, as such, will afford 

 us much valuable information." It seems 

 composed of little flocky masses, or wisps 



of cloud, adhering to some small stars at its outskirts, and enveloping one with an atmo- 

 sphere of considerable extent. " I know not," says Sir John Herschel, " how to describe 

 it better than by comparing it to a curdling liquid, or a surface strewed over with flocks of 

 wool, or to the breaking up of a mackarel sky, when the clouds of which it consists begin to 

 assume a cirrous appearance. It is not very unlike the mottling of the sun's disk, only, if I 

 may so express myself, the grain is much coarser, and the intervals darker ; and the flocculi, 

 instead of being generally round, are drawn into little wisps. They present, however, no ap- 

 pearance of being composed of stars ; and their aspect is altogether different from that of 

 the resolvable nebulas. In the latter, we fancy, by glimpses, that we see stars, or that, 

 could we strain our sight a little more, we should see them : but the former suggests no 

 idea of stars, but rather of something quite distinct from them." Whatever this filmy 

 substance may be, its dimensions are enormous, for it subtends an angle of nearly 10', 

 and, supposing it at the distance of a star of the eighth magnitude, its size must be at 

 least 3,208,600,000,000,000,000, or more than three trillions of .times that of our sun. 

 Upon comparing the present appearance of this great nebula with former drawings of 

 it, it appears to have undergone some marked changes, at least if the older representations 

 are to be depended upon. The following memorandum was made by Herschel when 

 he viewed it in 1774 : " Its shape is not like that which Dr. Smith has delineated in his 

 ' Optics,' though somewhat resembling it, from this we may infer that there are undoubtedly 



