250 



KNOWLEDGE. 



[NOMSMBER 1, 1900. 



The great light-grasping power of the Paris refractor 

 next proved, as was natui-ally to be anticipated, wonder- 

 fully efficient on nebulae. Though these delicate objects 



^w 



Fia. 



7. — The Planet Venus, as seen in the Great Siderostat on 1900, 

 September, 15(1. llh. 40m, G.C.M.T. 



require, in order to be advantageously scrutinized, (a) 

 a minimum of luminous absoqjtion on the pai-t of the 

 refracting medium, (b) a maximum of darkness of the 

 sky, and (c) a good definition ; and though, on account 

 of the dust, smoke, illumination, and perpetual mixture 

 of air masses of different dersities, none of these con 



Tia. 8.— Annular Xebula y IV. 13 Cygni, lf««), Julv 17. 



ditions was fulfilled at the Exhibiticn, the results already 

 secured in this line are very satisfactory indeed. 



Thus in the annular nebula W lY. 13 Cygni the sidero- 

 stat showed, probably for the first time visital/y, the faint 

 central condensation visible on Dr. Isaac Roberts' bea^i- 

 tiful negatives, and which is not shown on the drawing 

 published by Lord Rosse II. in his " Observations of 

 Nebulas and Clusters of Stars made with the 6 foot and 

 3 foot Reflectors at Birr Castle, from 1848 to 187S," 

 Part III.,' Plate V. The annulus is, moreover, distinctly 

 elliptical from north-east to south-west, and not round 

 as has been shown heretofore. A faint haziness fills the 

 interior of the ring (Fig. 8). 



The spiral structure of I^ TV. 16 Sagittce was easily 

 detected with the siderostat, though it was rather hard 

 to say whether the object was a right or left-handed 

 spiral (Fig. 9). 



No less interesting was the appearance of the Saturn- 

 like planetary nebula Ijl IV. 1 Aquarii (Fig. 10). In a 

 paper read before the Royal Society on June 20, 1850, 

 Lord Rosse I. described this object thus : — " It has ansae, 

 which probably indicate a suiTOunding nebulous ring 



Fig. 9.— ^Jpiral \ebula ^ IV. 16 Sagittse, 1900, Julv 26. 



seen edgeways. "§ His drawing of ^ TV. I is very- 

 remarkable, as showing the nebula in the form of the 

 planet Saturn, flatt-ened at the poles and with a scarcely 

 opened ring — which is aho its appearance in the Paris 

 refractor. But the rows of dots shown by Lord Rosse 

 in the body of the nebula, and the rays shooting from 

 it are invisible in the siderostat, and the writer fears 

 that these details are not of an objective character. 



We append, in conclusion, a drawing of the central 

 regions of the Andromeda nebula, as seen with the 



Fig. 10.— Planetary Nebula y IV. 1 Aquarii, 1900, July. 



siderostat on September 1 last (Fig. 11), and in which 

 flashed in 1885 the well-known bright temporary star. 

 It will be seen that the nucleus is nebulous at present, 

 and that there is not the slightest indication here of a 

 stellar condensation. It is, moreover, strongly elliptical 

 and not circular, following in this the form of the great 

 nebula itself. 



Such are a few of the results obtained with the new 

 siderostat in the midst of Paris in 1900. But it is not 

 in the dust and smoke of gi-eat cities that large telescopes 

 show their full power, so that the day when we hear that 

 the huge refractor has been remounted, fully prepared 



§ Philosophical Transactions, MDCCCL., p. 507. 



