254 THE NEBULAE HfVOTIIESIS. 



Ami, referring to this same order of objects, M. Arago 

 says : &quot; The forms of very large diffuse ncbuhe do 

 not appear to admit of definition ; they have no regular 

 outline.&quot; 



Xow this coexistence of largeness, irrcsolvability, 

 irregularity, ami indetinitcness of outline, is extremely 

 si-mif Scant. The fact that the largest nebulie arc either 



O C3 



irresolvable or very difficult to resolve, might have been 

 inferred a ^ luri ; seeing that irrcsolvability, implying that 

 the aggregation of precipitated matter has gone on to but 

 a small extent, will be found in nebuhe of wide diffusion. 

 Again, the irregularity of these large, irresolvable nebulie, 

 might also have been expected ; seeing that their out 

 lines, compared by Arago to &quot; the fantastic figures which 

 characterize clouds carried away and tossed about by 

 violent and often contrary winds,&quot; are similarly charac 

 teristic of a mass not yet gathered together by the 

 mutual attraction of its parts. And once more, the fact 

 that these large, irregular, irresolvable nebula? have 

 indefinite outlines outlines that fade off insensibly into 

 surrounding darkness is one of like meaning. 



Speaking generally (and of course differences of dis 

 tance negative anything beyond an average statement), the 

 spiral nebuhe arc smaller than the irregular nebula?, and 

 more resolvable ; at the same time that they are not so 

 small as the regular nebuhe, and not so resolvable. This is 

 as, according to the hypothesis, it should be. The degree of 

 condensation causing spiral movement, is a degree of con 

 densation also implying masses of flocculi that arc larger, 

 and therefore more visible, than those existing in an earlier 

 stage. Moreover, the forms of these spiral nebula) are 

 quite in harmony with the explanation given. The curves 

 of luminous matter which they exhibit, are nut such aa 

 would be described by more or less discrete masses start- 

 in ; from a state of rest, and moving through a rcsistinp 



