THE LAST RIDDLE 455 



water, attract each other and tend to approach. In the sup- 

 position of a light-bearing ether we have something of such an 

 incompressible medium, supra-sensible to our present methods 

 of observation ; if we could conceive of every ultimate particle 

 of matter as a pulsating sphere, then we might have here an 

 explanation of attraction. But it was pointed out by Arago, 

 and doubtless by many another before him, that such pulsa- 

 tions would require a definite time for their propagation. The 

 theory stumbles over the fact that no finite speed for gravitation 

 can be detected. 



This order of ideas has recently found an ingenious extension 

 at the hands of two Swedish investigators, C. A. and Victor 

 Bjerknes, father and son. Their work has given emphasis to 

 the idea that it is to such a hypothetical ether that we must 

 look for the ultimate explanation of the interaction of all forces. 

 By means of such an assumption we may do away with the 

 utterly unthinkable notion of action at a distance ; but it must 

 be said that the various attributes framed for this highly useful 

 ethereal medium are as absolutely incongruous as the incon- 

 gruous conceptions it is designed to avoid. There never was 

 folly more sheer than to suppose that we can think of con- 

 tinuous extended substance in which matter or material bodies 

 may move. Perhaps this is no worse than our endeavours to 

 conceive of an atom which cannot be divided. We have here 

 passed the limit of experimental proof and stepped into a realm 

 where we are offered the choice of fancy or metaphysics. The 

 one is undoubtedly of as much value as the other, with the 

 difference perhaps that where ingenious fancy has sometimes, 

 if rarely, pointed to new paths of discovery, metaphysic has 

 never. It is a fatal anodyne to physical inquiry, the relaxation, 

 sometimes, in summer moods, for healthy minds ; their staple 

 diet never. It is the predilection, the writer has long been 

 convinced, only of cobweb brains, lost in the phantasies of a 

 mild distemper. 



In such a summer mood, amid serene days when the mind 

 refuses to be vexed with difficulties, even the most obvious and 

 insuperable, let us turn the last page. Above me, as I look high 

 over the hills, the azure is entrancing in its beauty, boundless, 

 so far as I can ever know. For the spacious abstraction we call 

 the universe we can imagine no end ; its annihilation is unthink- 



