380 Professir G. H. Danrin [Jau. 25, 



It appears, then, to be probable that the immediately antecedent 

 state of the sun and planets was not a continuous gas, but was a 

 swarm of loose stones. Here, then, there arises a dilemma ; for on 

 the one hand the meteoric theory denies the continuity of the matter 

 forming nebulae, whilst on the other hand the nebular hypothesis 

 demands such continuity. 



The object of this lecture was to show that there is, however, a 

 wav in which these two apparently conflicting ideas may be reconciled. 



In order to prepare the way for the suggested reconciliation, a 

 sketch was then given of the Kinetic Theory of Gases, according to 

 which a gas consists of a great number of elastic molecules, moving 

 at high speed in all directions at hazard, and continually coming 

 into collision with one another by chance. 



According to this theory a pigmy, of a size comparable with the 

 average distance between adjacent molecules, would be conscious of 

 the blows he received from individual molecules, and he would have 

 lost the sense of gaseous pressure, which arises from impacts too 

 numerous and too rapid for discrimination. Thus, what is called 

 gaseous pressure is a question of the magnitude of the observer. 



The suggestion, then, of this lecture was that celestial nebulae are 

 of such large dimensions, that meteorites might be treated as mcdecules 

 and that their collisions might impart to a nebula, as a whole, the quasi- 

 gaseous mechanical properties demanded by the nebular hypothesis. 



But if such a suggestion is to rise above the level of mere con- 

 jecture, it demands a careful examination in detail. It is accordingly 

 necessary not only to consider the details of an individual collision, 

 but also to examine whether a meteoric medium is of sufficiently fine 

 texture to fulfil the conditions imputed to it. 



The kinetic theory of gases requires that the molecules of gas 

 should be perfectly elastic, and, although meteorites are certainly not 

 perfectly elastic, it was maintained that the sudden volatilisation of 

 gas, at the point of contact of two of them at the moment of collision, 

 would act as a violent explosive between them, and would impart to 

 them a virtual elasticity of considerable perfection. 



The investigation of the degree of fineness of grain necessary to 

 admit the applicability of the theory involved numerical calculation, 

 and the requisite data had necessarily to be derived from the solar 

 system. 



If the sun's mass were broken up into iron meteorites, each 

 weighing say a pound, the dimensions of each meteorite would be 

 known, and their number would be four followed by thirty zeros. 



These iron stones were then supposed to be distributed in a swarm 

 extending beyond the present orbit of the planet Xeptune. To give 

 numerical precision, the swarm was taken to extend as far beyond 

 Neptune as Saturn now is from the Sun. 



These supposed conditions were adopted merely by way of an 

 example which should represent a nebula of extreme tenuity ; fur if 

 the meteorites were not too sparsely distributed to impart quasi-gaseous 



