28 SECTIONAL ADDRESSES. 
been published by the British Association and by the National Academy 
of Washington. Another minor suggestion is the publication each 
month of the titles (without any abstracts) of the physical papers published 
in scientific periodicals and the Proceedings of Scientific Societies during 
the preceding month. This used to be a feature of Wiedemann’s Beiblatter 
and I found it very useful. 
In addition to the advances we have been considering, the instruments 
and appliances in laboratories are very much better and more convenient 
than they used to be. The most vivid impression I have of my early 
work in the laboratory is that of Groves Cells, these had platinum foil 
immersed in nitric acid for one electrode, zinc in dilute sulphuric for 
the other, and what with the fumes which assailed one’s throat and the 
acid which destroyed one’s clothes, the assemblage of a battery of cells 
was a most disagreeable business. I have not seen a Groves Cell for 
forty years and do not want to see another. Now instead of making up a 
battery we just put a plug into a hole. Another instrument which was 
exasperating to work with was the old quadrant electrometer, this not 
infrequently refused to hold its charge and neither prayers nor imprecations 
would induce it to do so, it has, fortunately, been replaced by more 
sensitive and convenient instruments. With regard to galvanometers, 
I have the authority of Mr. Whipple in saying that one suitably selected 
for the purpose for which it is required may be at least ten thousand 
times more efficient than the instruments available fifty or sixty years ago. 
The extensive use of electrical instruments in connection with electrical 
lighting and engineering has caused a great deal of attention to be paid 
to their design with the result that they are far more convenient and 
reliable than they used to be. The improvement of instruments is of 
first rate importance for the progress of Physics, a considerable increase 
in the efficiency of an instrument may open up a new region of physical 
phenomena. The most striking example of this is the effect produced by 
improvements in the methods of producing high vacua. Roughly speak- 
ing, we may say that modern physics depends on our power of studying 
individual atoms and electrons and not merely large crowds of these 
particles. To do this, one atom must not be hit by another while under 
observation, as it would make more than ten thousand collisions in a 
centimetre if the pressure were atmospheric; a very high vacuum is 
required. Until early in this century this had to be got by Sprengel 
pumps, which involved one raising and lowering a vessel filled with 
mercury for hours on end and getting what would now be considered a 
very poor result, but a vivid appreciation of the intensity with which 
Nature abhors a vacuum. All this was changed after Sir James Dewar 
introduced the method of producing high vacua by means of charcoal 
cooled by liquid air. This was not only much more rapid and convenient 
but produced very much higher vacua and made it possible to make 
experiments and measurements which could not have been made before 
the introduction of this method and which have revolutionised our 
ideas of the structure of matter. If Science helps the industries they in 
return help Science. An illustration is that the need of a high vacuum for 
hot wire valves and electric lamps made its production a matter of com- 
mercial importance with the result that the physicist has now at his 
