262 THE POPULAR SCIEXCE MONTHLY. 



noted for the iirst time, so far as I know : this recession is a real phe- 

 nomenon, and is thus spoken of by Sir John Herschel: "The nebula, 

 which is very bright in the parts surrounding the trapezium, seems 

 (whether by the effect of contrast with the dazzling light of these 

 stars, or from a real deficiency in nebulous matter) to have retreated 

 from immediate contact with them, so that they appear in some de- 

 gree insulated and with a darkness about them. This would agree 

 with the idea of a subsidence of the nebula into the stars by gravita- 

 tion ; but it is probably only a deception." 



Nebula Orionis. (Herschel, 1824.) 



Sir John likewise expresses an opinion as to the resolvability of 

 the nebula, and describes its appearance in a very graphic way. He 

 says : " I know not how to describe it better than by comparing it to 

 a curdling liquid, or to a surface strewed over with flocks of wool, or 

 to the breaking up of a mackerel sky when the clouds of which it 

 consists begin to assume a cirrous appearance. ..." It presents, how- 

 ever, " no appearance of being composed of small stars, and its aspect 

 is altogether different from that of resolvable nehuloe. In the latter 

 we fancy by glimpses that we see stars, or that, could we strain our 

 sight a little more, we should see them. But the nebula suggests no 

 idea of stars, but rather of something quite distinct from them." 



In the beginning of 1834 Sir John Herschel went to the Cape 

 of Good Hope for the purpose of completing a survey of the whole 

 heavens, which had been commenced in England : he took with him 

 his 20-foot reflector (aperture 18^ inches), and devoted himself during 



