NEBULA. 23 



«riew, as well in his opening address before the British Asso- 

 ciation at Cambridge in 1845, as in the Outlines ofAstroU' 

 omyy 1849, where he expresses himself as follows : " The 

 magnificent reflecting telescope constructed by Lord E-osse, 

 six feet in aperture, has resolved or rendered resolvable mul- 

 titudes of nebulas which had resisted all inferior powers. . . . 

 Although, therefore, nebulae do exist which, even in this pow- 

 erful telescope, appear as nebulae, without any sign of resolu- 

 tion, it may very reasonably be doubted whether there be 

 really any essential physical distinction between nebulae and 

 clusters of stars*."* 



The constructor of the powerful optical apparatus at Par- 

 sonstown, who always discriminates between the result of act- 

 ual observation and the promises of a knowledge to which 

 we hope to attain, expresses himself with much caution re- 

 garding the nebula in Orion, in a letter to Professor Nichol, 

 of Glasgow,! dated Parsonstown, 19th of March, 1846 : "In 

 accordance with my promise of communicating to you the 

 result qf our examination of Orion, I think I may safely say, 

 that there can be little, if any, doubt of the resolvability of 

 the nebula. Since you left us, there was not a single night 

 when, in absence of the moon, the air was fine enough to ad- 

 mit of our using more than half the magnifying power the 

 speculum bears ; still we could plainly see that all about the 



town telescope, and that a great number of nebulae appeared like clus- 

 ters or groups of stars, while others, at least to his sight, presented no 

 appearance of resolution." 



* See Outlines, p. 597, 598; also the Report of the Fifteenth Meeting 

 of the British Association held at Cambridge in June, 1845, p. xxxvi. : 

 " By far the major part," says Sir John Herschel, *' probably, at least, 

 nine tenths of the nebulous contents of the heavens, consist of nebulae 

 of spherical or elliptical forms, presenting every variety of elongation 

 and central condensation. Of these a great number have been resolved 

 into distant stars (by the reflector of the Earl of Rosse), and a vast mul- 

 titude more have been found to present that mottled appearance which 

 renders it almost a matter of certainty that an increase of optical pow- 

 er would show them to be similarly composed. A not unnatural or un- 

 fair induction would therefore seem to be, that those which resist such 

 resolution do so only in consequence of the smallness and closeness of 

 the stars of which they consist; that, in short, they are only optically, 

 and not physically nebulous. Although nebula? do exist which, even 

 in this powerful telescope (of Lord Rosse), appear as nebula?, without 

 any sign of resolution, it may very reasonably be doubted whether there 

 be really any essentiil physical distinction between nebula) and clus- 

 ters of 8tar§." 



t Dr. Nichol, Professor of Astronomy at Glasgow, published the let- 

 ter above referred to in his Thoughts of some Important Points relating 

 to the Syttem of the World, 1846, p. 55. 



