Royal Society, 307 



nature, seen more or less perfectly, and variously placed with refer- 

 ence to the line of sight. The author adverts to the description of 

 this nebula by Mesier, Sir William Herscbel and Sir John Herschel, 

 and remarks, that taking the figure given by Sir John, and placing 

 it as it would be seen with a Newtonian telescope, we shall at once 

 recognize the bright convolutions of the spiral which were seen by 

 him as a divided ring : thus with each increase of optical power the 

 structure has become more complicated, and more unlike any thing 

 which we could picture to ourselves as the result of any form of 

 dynamical law of which we find a counterpart in our system. After 

 pointing out the importance of measurements and the difficulty of 

 taking them satisfactorily, the author states, that of a few of the 

 stars with which the nebula is pretty well studded, measurements 

 with reference to the principal nucleus were taken by his assistant 

 Mr. Stoney in the spring of 1849, and that these have been repeated 

 this year during the months of April and May, and also some mea- 

 sures taken from the centre of the principal nucleus to the apparent 

 boundary of the spiral coils in different angles of position. A hope 

 is then expressed that, as several of these stars are no doubt within 

 reach of the great instruments at Pulkova and at Cambridge, U.S., 

 the distinguished astronomers who have charge of them will consider 

 the subject worthy of their attention. 



The spiral arrangement of 51 Mesier was detected in the spring 

 of 1845, and in the following spring an arrangement, also spiral, 

 but of a different character, was detected in 99 Mesier. The author 

 considers that 3239 and 2370 of Herschel's ' Southern Catalogue ' 

 are very probably objects of a similar character ; and as the same 

 instrument does not appear to have revealed any trace of the form 

 of 99 Mesier, he does not doubt that they are much more conspicu- 

 ous, and therefore entertains the hope that, whenever the southern 

 hemisphere shall be re-examined with instruments of great power, 

 these two remarkable nebulae will yield some interesting result. 



The author briefly refers to the other spiral nebulae discovered 

 up to the present time, which are more difficult to be seen, and to 

 clusters in the exterior stars of which there appears to be a tendency 

 to an arrangement in curved branches. He then passes to the re- 

 gular cumular nebulae, in which, although they are perceived at once 

 to be objects of a very different character, there still seems to be 

 something like a connecting link. 



Among the nebulous stars two objects are stated to be well 

 worthy of especial notice — No. 450 of Sir John Herschel's Catalogue, 

 and i Orionis. A representation of No. 450, as seen with the six 

 feet telescope, is given. It has been several times examined, but as 

 yet not the slightest indication of resolvability has been seen. The 

 annular form of this object was detected by Mr. Stoney when ob- 

 serving alone, but Lord Rosse has since had ample opportunities of 

 satisfying himself that the object has been accurately represented. 

 A representation of i Orionis is likewise given. The remarkable 

 feature in this object, the dark cavity not symmetrical with the star, 

 Wf s also discovered by Mr. Stoney when observing alone with the 



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