72 The. Ether of Space. [Feb. 21, 



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 expatia- 

 tion, then are they both equally containing the materia or body." 



[_From the Posthumous Works of Robert Hooke, M.D., F.B.S., 1705, 

 2)}?. 171-2 (as copied in Memoir of Dalton, by Angus Smith). 



Newton's contemporaries did not excel in power of clear expression, 

 as he himself did, but Professor Pojnting interprets this singular 

 attempt at utterance 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 mast be the total mass 

 filling that space." 



The tacit assumption here made is that tne particles of the aggre- 

 gate are all composed of one and the same continuous substance, 

 practically that matter is made of ether ; and that assumption, in 

 Hooke's day, must have been only a speculation. But it is the kind 

 of speculation which time is justifying, it is the kind of truth which 

 we all feel to be in process of establishment now. 



AYe do not depend on that sort of argument however ; what we 

 depend on is experimental measure of the mass, and mathematical 

 estimate of the volume, of the electron. For calculation shows that 

 however the mass be accounted for, whether electrostatically or mag- 

 netically, or hydrodynamically, the estimate of ratio of mass to effect- 

 ive volume can differ only in a numerical coefficient, and cannot differ 

 as regards order of magnitude. The only way out of this conclusion 

 would be the discovery that the negative electron is not the real or 

 the main matter-unit, but is only a subsidiary ingredient, whereas 

 the main mass is the more bulky positive charge. That last hypo- 

 thesis however is at present too vague to be useful. Moreover, the 

 mass of such a charge would in that case be unexplained, and would 

 need a further step, which would probably land us in much the same 

 sort of etherial density as is involved in the estimate which I have 

 based on the more familiar and tractable negative electron. 



It may be said why assume any finite density for the ether at all- ? 

 Why not assume that, as it is infinitely continuous, so it is infinitely 

 dense — whatever that may mean — and that all its properties are 

 infinite ? This might be possible were it not for the velocity of 

 light. By transmitting waves at a finite and measurable speed, the 

 ether has given itself away, and has let in all the possibilities of 

 calculation and numerical statement. Its properties are thereby 

 exhibited as essentially finite — however infinite the whole extent of 

 it may turn out to be. 



[O. L.] 



