20 



POPULAR SCIENCE MONTHLY 



is the so-called Trapezium, already described. That these four stars 

 form a system by themselves cannot be doubted. The darkness of the 

 nebula immediately around them suggests that they were formed at 

 the expense of the nebulous mass. 



Great interest has recently been excited in the spiral form of cer- 

 tain nebulas The great spiral nebula M. 51 in Canes Venatici has long 

 been known . We reproduce a photograph of this object and another. 

 It is found by recent studies at the Lick Observatory that a spiral form 

 can be detected in a great number of these objects by careful examina- 

 tion. 



Fig. 10. The Great Spiral Nebula M. 51, as Photographed with the 

 Crossley Reflector at the Lick Observatory. 



Another striking feature of numerous nebulas is their varied and 

 fantastic forms, of which we give a number of examples. The Triphid 

 nebula' is a noted one in this respect. 



The great nebula of Andromeda is second only to that of Orion. 

 It also is plainly visible to the naked eye and can be more readily 

 recognized as a nebula than can the other. It has frequently been 

 mistaken for a comet. Seen through a telescope of high power, its 

 aspect is singular, as if a concealed light were seen shining through 

 horn or semi-transparent glass. It is somewhat elliptical in form, as 

 will be seen from a photograph by Sir William Roberts, F.E.S., which 

 we reproduce (page 19). 



