4 THE PRESIDENTIAL ADDRESS 
mathematics and mathematical formule—all else is man-made 
decoration. 
For instance, when the undulatory theory had made it clear that 
light was of the nature of waves, the scientists of the day elaborated 
this by saying that light consisted of waves in a rigid, homogeneous 
ether which filled all space. ‘The whole content of ascertained fact 
in this description is the one word ‘ wave’ in its strictly mathe- 
matical sense ; all the rest is pictorial detail, introduced to help out 
the inherited limitations of our minds. 
Then scientists took the pictorial details of the parable literally, 
and so fellinto error. For instance, light-waves travel in space and 
time jointly, but by filling space and space alone with ether, the 
parable seemed to make a clear-cut distinction between space and 
time. It even suggested that they could be separated out in practice 
—by performing a Michelson-Morley experiment. Yet, as we all 
know, the experiment when performed only showed that such a 
separation is impossible ; the space and time of the parable are 
found not to be true to the facts—they are revealed as mere stage- 
scenery. Neither is found to exist in its own right, but only as a way 
of cutting up something more comprehensive—the space-time 
continuum. 
Thus we find that space and time cannot be classified as 
realities of nature, and the generalised theory of relativity shows 
that the same is true of their product, the space-time continuum. 
This can be crumpled and twisted and warped as much as we please 
without becoming one whit less true to nature—which, of course, 
can only mean that it is not itself part of nature. 
In this way space and time, and also their space-time product, 
fall into their places as mere mental frameworks of our own con- 
struction. ‘They are of course very important frameworks, being 
nothing less than the frameworks along which our minds receive 
their whole knowledge of the outer world. This knowledge comes 
to our minds in the form of messages passed on from our senses ; 
these in turn have received them as impacts or transfers of electro- 
magnetic momentum or energy. Now Clerk Maxwell showed that 
electromagnetic activity of all kinds could be depicted perfectly as 
travelling in space and time—this was the essential content of his 
electromagnetic theory of light. Thus space and time are of pre- 
ponderating importance to our minds as the media through which 
the messages from the outer world enter the ‘ gateways of know- 
ledge,’ our senses, and in terms of which they are classified. Just 
as the messages which enter a telephone exchange are classified by 
the wires along which they arrive, so the messages which strike our 
senses are classified by their arrival along the space-time framework. 
Physical science, assuming that each message must have had a 
