THE ETHER OF SPACE 303 



everywhere, without break or intermittance of any kind; 

 while the latter has gaps in it it is here, and there, but 

 not everywhere. 



Indeed, this very argument was used long ago by that 

 notable genius, Robert Hooke ; and I quote a passage which 

 Professor Poynting has discovered in his collected posthu- 

 mous works, and kindly copied out for me : 



As for matter, that I conceive in its essence to be immutable, and 

 its essence being expatiation determinate, it cannot be altered in its 

 quantity, either by condensation or rarefaction; that is, there cannot 

 be more or less of that power or reality, whatever it be, within the 

 same expatiation or content; but every equal expatiation contains, is 

 filled, or is an equal quantity of materia; and the densest or heaviest, 

 or most powerful body in the world contains no more materia than that 

 which we conceive to be the rarest, thinnest, lightest, or least powerful 

 body of all ; as gold for instance, and (Ether, or the substance that fills 

 the cavity of an exhausted vessel, or cavity of the glass of a barom- 

 eter above the quicksilver. Nay, as I shall afterwards prove, this 

 cavity is more full, or a more dense body of asther, in the common 

 sense or acception of the word, than gold is of gold, bulk for bulk; 

 and that because the one, viz., the mass of aether, is all aether : but the 

 mass of gold, which we conceive, is not all gold; but there is an 

 intermixture, and that vastly more than is commonly supposed, of 

 aether with it; so that vacuity, as it is commonly thought, or errone- 

 ously supposed, is a more dense body than the gold as gold. But if 

 we consider the whole content of the one with that of the other, 

 within the same or equal quantity of expatiation, then are they both 

 equally containing the materia or body. From the Posthumous 

 Works of Robert HooTce, H.D., F.E.S., 1705, pages 171 and 172 (as 

 copied in "Memoir of Dalton," ~by Angus Smith). 



Newton's contemporaries do not shine in facility and 

 clearness of expression, as he himself did, but Professor 

 Poynting interprets the above singular attempt at utter- 

 ance thus: 



All space is filled with equally dense materia. Gold fills only a 

 small fraction of the space assigned to it, and yet has a big mass. 

 How much greater must be the total mass filling that space! 



The tacit assumption here made is that the particles of 

 the aggregate are all composed of one and the same con- 

 tinuous substance practically that matter is made of 



