THE PRESIDENTIAL ADDRESS 7 
and slow decay of mountain range after mountain range, each built 
out of, and in some cases upon, the ruins of its predecessor ; the 
chain of slowly evolving organisms, vast in numbers and infinite in 
variety ; told plainly of long zons of time. And the duration of 
these aeons can be dimly realised when it is recalled that, within 
a small fraction of the latest of them, man, with the most primitive 
of implements and the most rudimentary culture, has succeeded 
in penetrating to the uttermost corners of the world, and developed 
his innumerable languages and civilisations. 
Huxley, as our representative, took up the challenge in his address 
to the Geological Society in 1869, and asked the pertinent question 
‘but is the earth nothing but a cooling mass “‘ like a hot water jar 
such as is used in carriages ”’ or ‘“‘ a globe of sandstone”? ?’ And he 
was able to point out at least some agencies which might regenerate 
the earth’s heat or delay its loss. 
So it is only fitting that the great physicist, who imposed a narrow 
limit to geological time, should have prepared the way for those who 
have proved that the earth possesses in its radioactive substances 
a ‘ hidden reserve ’ capable of supplying a continuous recrudescence 
of the energy wasted by radiation, thus lengthening out the time 
required to complete its total loss. These later physicists have given 
us time without stint ; and, though this time is the merest fraction 
of that envisaged by cosmogonists and astronomers, we are now so 
much richer than our original estimates that we are embarrassed by 
the wealth poured into our hands. So far from the last century’s 
urge to ‘hurry up our phenomena,’ we are almost at a loss for 
phenomena enough to fill up the time. 
The far-sighted genius of Lord Rutherford and Lord Rayleigh 
first saw the bearing of the rate of disintegration of radioactive 
substances in the minerals of rocks on the age of the parts of the 
earth-crust built of them. The extension and supplementing of 
this work by Joly, Holmes, and others, has now enabled us to look 
to the disintegration of uranium, thorium, and potassium, as the 
most promising of many methods that have been used in the 
endeavour to ascertain the age of those parts of the earth-crust 
that are accessible to observation. These methods also promise 
a means of dating the geological succession of Eras and Periods in 
terms of millions if not hundreds of thousands of years. 
The decline and early death to which Lord Kelvin’s dictum had 
condemned the earth, according so little with the vigour displayed 
in its geological story, is now transformed into a history of prolonged 
though not perennial youth. It was for Joly, of whose work the 
extent, variety, and fruitfulness are hardly yet fully appreciated, 
to take the next step and see in the release of radioactive energy 
a mechanism which could drive the pulse that geologists had so 
