652 THE POPULAR SCIENCE MONTHLY. 



and perhaps also its incandescence, may be simple consequences of 

 the processes of aggregation. 



The lecturer proceeded to show that if we suppose the great nebu- 

 lous mass to have been a continuous gas or fluid, symmetrical in form, 

 and either homogeneous or heterogeneous in structure, provided the 

 component strata were homogeneous in themselves " the fundamental 

 principles of mechanics assure us that the process of cooling and con- 

 densation by contraction, would not generate a motion of rotation." 

 Nay, more ; he thought it was very difficult to conceive the mechan- 

 ical possibility of a continuous gaseous or liquid mass of any form 

 whether homogeneous or otherwise acquiring a motion of rotation by 

 the internal motions of its several parts. The mass being isolated, and 

 out of the sphere of external forces all of its parts being in inter- 

 communication through fluid continuity how can we reconcile a gen- 

 eration of rotation in the whole mass, with the fundamental principles 

 of the equality of action and reaction ? Any force, that begins and 

 ends in a body whose parts are in continuous material connection 

 cannot impart motion to the whole mass whatever relative move- 

 ments might be communicated to portions of it. 



The lecturer was disposed to look for the origin of the primitive 

 rotation of the nebulous mass in the discontinuous structure of the 

 primordial nebulous matter. Adopting Sir John Herschel's idea, that 

 the nebulous condition indicates not the gaseous, but the cloudy form 

 of matter, we must look upon nebulous masses as consisting of dis- 

 crete portions of matter of various density and bulk aggregated into 

 special forms, under the influence of mutual attraction. By the gradual 

 subsidence and condensation of these discrete particles by the effect 

 of gravity, a central aggregation or nucleus would be formed the 

 germ of our sun. Let us hasten to see what light this view throws 

 upon the physical cause of the rotation of the primitive solar nebula. 

 It is obvious that a crowd of aggregating bodies, animated by inde- 

 pendent and partially-opposing impulses, must produce collision, de- 

 struction of velocity, and a subsidence toward the centre of attrac- 

 tion. It is also evident that those impulses which conspire or remain 

 outstanding after such conflicts, must ultimately give rise to circulation 

 or rotation of a permanent character about some axis. It will be ob- 

 served that the causes imparting motion to the central mass are, in 

 this view, entirely exterior to it. For the subsiding and conflicting 

 bodies, being discrete and independent of each other, act like the im- 

 pinging of a comet, or any cosmical mass, on the central nucleus. Un- 

 der this aspect, the Nebular Hypothesis becomes identical with Sir 

 John Herschel's " Theory of Sidereal Aggregation ; " the only differ- 

 ence consisting in the magnitudes of the agGregating bodies. 



Instead of supposing that the primitive or chaotic condition of 

 matter was intensely hot, is it not more rational to suppose that it was 

 originally deficient in heat or cold, and that the high temperature was 



