Knowledofe. 



With which is incorporated Hardwickc's Science Gossip, and thi- Illustrated Scientific News. 



A Monthly Record of Science. 



Conducted by Wilfred Mark Webb, F.L.S., and E. S. Grew, M.A. 

 NOVHMBEK, 1912. 



THE SPIRAL NEBULAE. 



r.v F. W. HEXKEL, 15. A., I'.R.A.S. 



Probably no other announcement e.xcited so much 

 interest in the astronomical world about twenty 

 years ago, as that a photograph bv Dr. Isaac 

 Roberts of the well-known lenticular nebula in 

 Andromeda (see "Knowledge," Volume XXXI V, 

 l-'rontispiece), described by its original discoverer, 

 Simon Marius, as " like a candle shining through 

 horn," and since so often mistaken for a comet, had 

 revealed the fact of its essentialh' spiral nature. 

 Some there were who thought they saw in this 

 photograph something like a proof of the substantial 

 truthof theLaplacian nebularhypothesis(e.^. Darwin's 

 " Mechanical Conditions of a Swarm of Meteorites," 



1889). The name nebula. i.'<]ui\'alent to the Greek 

 i'e<peX>], a cloud, was given to cloud-like masses in 

 the heavens, some of which have been resolved into 

 stars, but others are of a totally different character. 

 Xext after the nebula in .\ndromeda, the great 

 nebula in Orion, perhaps the most remarkable of all 

 these objects, was detected by Huygens in 1656. 

 Hallev, in 1714, gave an account of si.x, including the 

 two just mentioned, the nebula in Sagittarius (see 

 Figure 441). the cluster o' ("entauri, discovered by 

 himself in 1677. and the cluster in Hercules 

 detected in 1714 (see Figure 440), and tinalh' 

 another in Antinous. 



FlGURli 43J. 

 M. 11730 frsae Majoris 



1 IGURE 434. 

 H.\'. 43 Ursae Majoris. 



Spiral Nebulae photographed at Lick Observatory. 



ri:'/,s.<,'>- r. J. y. Sc. 



I'IGI'KE 435. 



M. lOl) Comae Berenices. 



409 



