ASTRONOMICAL HISTORY. 167 



extremely unequal in their degrees of density and rarity, 

 so great would be the refraction of their rays that they could 

 not be propagated to our vision, which, if by far the greatest 

 portion of this space were unoccupied, it is consistent to 

 believe they might be. And, indeed, this question seems 

 to depend, in a great measure, on the question which we 

 shall immediately bring forward respecting the substance 

 of the stars, whether it be dense, or subtle, or expanded? 

 For if their substance be solid, it should certainly seem as 

 if nature were only occupied and in action about these 

 globes, and their boundaries, and had neglected, and as 

 it were left fallow, the interposed spaces. Wherefore it 

 is not improbable that the globes are, towards their cen 

 tres, more compact, towards their surface more lax, in their 

 circumambient substances and effluvia grow less substan 

 tial still, and finally terminate in a vacuum. On the other 

 hand, if the essence of the stars is subtle and igneous, it 

 will be manifest that the nature of rare is not merely pri 

 vative, but of itself a powerful and primary element, not 

 less than the nature of solid, and that it exists in force or 

 prevails in the stars, in ether, and in the atmosphere, so 

 that there is need of the hypothesis of a vacuum coacer 

 vatum. That question, too, about a vacuum in the inter 

 stellar fields will depend upon another connected with the 

 great principles of nature : whether we must admit a vacuum 

 at all? And this not without modifying it by a distinction : 

 for it is one thing to deny a vacuum absolutely, and another 

 to deny a vacuum coacervatum. For much more solid 

 reasons may be alleged for a vacuum intermistum being in 

 terposed to keep bodies in a certain degree of laxity, than for 

 maintaining a vacuum coacervatum (or large vacant spaces). 

 And not only was that ingenious man, and great mechanician 

 Hero sensible of this, but also Democritus and Leucippus, 

 the inventors of the theory of a vacuum, which Aristotle 

 attempts to attack and overthrow by certain logical subtle 

 ties. These two most acute and famous philosophers admit 

 a vacuum intermistum in such a manner as to exclude a 

 vacuum coacervatum. For according to the opinion of De 

 mocritus every vacuum is so limited and circumscribed as 

 not to admit of the separation or disruption of bodies beyond 

 certain limits, no more than it does of their contraction and 

 consolidation. Though in what has been preserved of the 

 writings of Democritus, this is no where propounded expli 

 citly, yet he seems to say this, that bodies, as well as spaces, 

 are infinite, that otherwise (that is, if there were in fact 



