166 ASTRONOMICAL HISTORY. 



ether, of which although the thickness or depth may be 

 supposed considerable, still it is not so great as to create 

 a difference in their incitation or celerity, but only such, 

 that through the whole of each region respectively, all the 

 bodies revolve simultaneously as if fastened with the chain 

 of one common essence, or, at least with such discrepancy 

 as, by reason of the- distance, is not brought within our 

 vision. Now, if the earth moves, the stars may either 

 stand still (as Copernicus thought), or, which is far more 

 probable, and was suggested by Gilbertus, they may re 

 volve each in its place, round its own centre, without any 

 motion of that centre, (as the earth does, if you divide its 

 diurnal motion from those two supposed motions which 

 Copernicus has superadded to it). For whichever of these 

 is the fact, it hinders not that there may be stars ranged 

 one above another, till they escape our vision. 



The fourth question relates to the cohesion of the sys 

 tem, or to the substance connecting it. As to the na 

 ture and essential properties of that body or thing which 

 is thought to be pure ether, and is interfused between 

 the stars, we shall presently inquire. We shall now speak 

 only of the principle of cohesion in the system. There are 

 three modes of viewing this. For we must either grant a va 

 cuum, or a substance whose parts are in contact, or lastly, in 

 continuity. Our first inquiry is, whether there is an extent of 

 absolute vacuity or a vacuum coacervatum in the interstellar 

 space, which Gilbertus ably maintained, and which several 

 of the ancients appear to countenance, who supposed that 

 the various orbs were scattered about without any regular 

 system, especially those who declared the bodies of the 

 stars to be compact masses. Such an opinion amounts to 

 this, that all the globes, as well the stars as the earth, con 

 sist of solid and dense matter. That they are enveloped, 

 next their surface, with a certain description of bodies, 

 which are so far homogeneous to their respective globes, 

 but nevertheless more thin, feeble, and attenuated, and 

 which are nothing but effluvia or emanations from the globes 

 themselves, such as are vapours and exhalations, and air 

 itself, if compared with earth. That these effluvia reach 

 to a distance not considerable round each several globe, 

 and that the rest of the interval between the globes, which 

 is incomparably the largest part, is a void. Which opinion 

 we may be prepared to adopt by the fact, that the bodies 

 of the stars are visible from such a prodigious distance. 

 For were the whole of that space full, especially of bodies 



