.127 



scope with a lower one. The " sweejiing power" was only 

 157, and though it was the best for finding nebulae, it was 

 much too low to give the utmost range of vision. 



But far the most singular objects which he has seen are 

 the nebulte which exhibit a spiral arrangement. He re-exa- 

 mined 51 Messier, Herschel's fig. 25, in which Lord Rosse 

 had first seen it, and fully verified it : he could not, however, 

 satisfy himself that it was to be traced in the three feet. On 

 the night of March 1 1 (the only fine one, by the way, which 

 occurred during his stay), he found several others, of which, 

 however, it is difficult to give an idea without drawings.* In 

 99 Messier the centre is a globular cluster, surrounded by 

 spirals, in the brighter parts of which stars are seen with 470 : 

 these have the same direction as in Messier 51, namely, from 

 east to west, in receding from the centre. But these are 

 combined with traces of another system in a reverse direction. 

 h 604 is also spiral, but without any other peculiarity. 97 

 Messier is a strange object. With the finding eye-piece it 

 looks like a figure of 8 with a star at the intersection, but 

 with 470 it is spiral with two centres. The principal one still 

 looks like a star, but with 830 gives a suspicion that it is a 

 very small cluster.! The spirals related to this have the same 

 direction as the former ; but the other centre, which also looks 

 like a minute star, has a smaller set in the opposite direction. 

 Lastly, h 731, his fig. 43, in which the stars seem larger 

 than the preceding, but in which no central cluster was observed, 

 has curved dark bands across it, looking so like the section of 

 a turbinated shell as to induce a suspicion that this has a 

 similar arrangement, but is seen edgewise. 



On the dynamical condition of such systems it would at 



* Drawings of M 51, M 99, M 97, and h 731, were exhibited. 



f The next power is 1530, but it was impossible to use it effectually 

 without a clock movement. This is also the case with single lenses, which 

 are particularly effective on such objects. 



