PRESIDENTIAL ADDRESS — SECTION A. 23 



cation between distant bodies. It can take place — (1) by direct 

 contact, or by means of some medium that is continuous be- 

 tween the bodies and connects them ; (2) by one body send- 

 ing a projectile to the other; 



This is so well illustrated by Mr. Oliver Lodge that I can- 

 not do better than quote from his work : "To call the atten- 

 tion of a dog, there are several methods : one plan is to prod 

 him with a stick, another is to heave a stone at him, a third is 

 to whistle or call, while a fourth is to beckon him by gesture or, 

 what is essentially the same process, to flash sunlight into his 

 eye with a mirror. In the first two of these methods the media 

 of communication are perfectly obvious — the stick and the 

 stone. In the third, the whistle, the medium is not so obvious, 

 and this case might easily seem to a savage like action at a 

 distance, but we know of course that it is the air, and that if 

 the air between be taken away all communication by sound is 

 interrupted. But the fourth or optical method is not so inter- 

 rupted : the dog can see through a vacuum perfectly well, 

 though he cannot hear through it ; but what the medium now 

 is which conveys the impression is not so well known. The 

 sun's light is conveyed to the earth by such a medium as this 

 across the emptiness of planetary space. The only remaining 

 typical plans of acting on the dog would be either by electric 

 or by magnetic attraction, or by mesmerism ; and I would have 

 you seek for the medium which conveys these impressions with 

 just as great a certainty that there is one as you feel in the 

 other cases." 



Every possible means of communication — namely, either by 

 continuous medium or by projectile — are fully illustrated by the 

 two simplest methods quoted above : by " the stick and the 

 stone." 



Explanations of the phenomena of light and gravitation 

 have been given, making them simply cases of the projectile 

 method of communication. These corpuscular theories, as 

 they are called, of light and gravitation are however exploded 

 nowadays. The phenomena connected with the sense of smell 

 and the transmission of pressure by gases are true examples 

 of the projectile method. 



Cutting the matter short, I may say that we are as certain 

 of the existence of the ether filling all space and interpene- 

 trating the grosser matter of all bodies as we are of the exist- 

 ence of the bodies themselves. The evidence in favour of the 

 existence of the one is as strong as that in favour of the exist- 

 ence of the other. If the existence of the one be denied, so 

 must that of the other. 



The constitution of the ether, as far as it is at present 

 known to us, is that of a continuous, frictionless medium, pos- 

 sessing inertia, density, and rigidity. It pervades all space, 



