A.—_MATHEMATICAL AND PHYSICAL SCIENCES. 29 
command pumps so powerful that they can maintain an exceedingly high 
vacuum in spite of the influx into the vessel of a stream of the particles 
we wish to study; this is exceedingly important when investigating 
charged atoms and electrons. 
The hot wire valve is another instrument which has helped greatly 
research in physics ; the immense magnification of weak effects which can 
be produced by it enables us to detect with certainty phenomena which 
before its introduction were almost beyond our ken. Those who like 
myself repeated, more than forty years ago, Hertz’s experiments will 
contrast the difficulty we had in detecting electrical waves even when the 
source was only a few yards away with the ease with which modern 
methods using hot wire valves detect waves which have travelled thousands 
of miles. 
I have alluded to advances in the efficiency of the instruments. There 
is another advance in them which ‘is not so gratifying, that is the advance 
in price. The cost of research in physics is much greater than it used to 
be. Before the war when about thirty research students were working 
at the Cavendish Laboratory, the cost of their researches was about £300 
per annum, now it would be at least five times that amount. To balance 
this there are now far greater sums available for research than there were 
in those days. 
I have in this address confined myself to what may be called the 
machinery of research in physics. I will now say a word or two about 
another point. The additions to our knowledge of physical phenomena 
and to physical conceptions made in the last sixty years have not been 
excelled by those made in any period of the history of the science, 
and yet I remember that at the beginning of this period the view was 
prevalent that all the fundamental principles of physics had been 
discovered and that the work of the future would be to develop and 
co-ordinate those principles and to measure more and more accurately 
the value of known physical constants. This view seems ludicrous when we 
Inow that within a few years Réntgen rays, the electron and radio- 
activity were discovered. The existence of these was quite unexpected, 
and no hint of the possibility of their existence was given by any of the 
physical theories then extant ; this view was, however, to my knowledge, 
held by some eminent physicists. The great generalisations expressed 
by the first and second Laws of Thermodynamics loomed so large in 
those days that it was thought that nothing was beyond their purview. 
This state of mind is apt to occur after a great discovery ; it occurred 
after that of universal gravitation; there are signs that it exists now. 
Yet it has always been falsified by experience, and I think always 
will be. There are no signs that physics is approaching an asymptotic 
state in which the progress gets slower and slower as time goes on. The 
additions to our knowledge of physics made by our generation do not get 
smaller and smaller as one generation succeeds another, each great 
discovery is not a terminus but an avenue leading to new knowledge. An 
improvement in technique may, as we have seen, lead to fundamental 
changes in our views of the nature of matter and of physical processes. 
There is far more in physics than is dreamt of in our theories ; and Nature 
herself, if we observe her carefully, is more suggestive of ideas than the 
