Consequently scientific progress is a quite orderly advance, not a spasmodic collection of facts, and in the truest sense of the word it has a history.  In order that opportunities for this steady progress may be provided it is very important that this point should be fully appreciated.  Every one, for example, is vaguely conscious that science played a great part in the War.  As a consequence the number of students of science has greatly increased; manufacturing firms are awakening to the fact that they must pay more attention to scientific development and are founding research laboratories.  It is very important that this awakened attention should be well informed, and for that reason it cannot be pointed out too often that the scientific work which has been the basis of all material progress can only be turned to definite material ends in the last stages of its development.  Fundamentally everything rests on the pure attempt to gain knowledge without any idea of the use to which it may subsequently be put.  Without pure science there is no applied science at all.  It is quite right in my opinion that the researcher in pure science should have with him the hope that what he does may one day be of direct benefit to others.  But it is probable that he does not in his own mind confine the idea of possible uses to such material matters as I have mentioned above and as are so prominent at present.  He believes that his work has a less material side whose value need not be explained to the present audience.

In the general line of progress it is natural to find that there are certain broad roads along which the main advance has been directed.  Students of physics and chemistry and the subjects which are allied to them find that they are in general considering either matter, or electricity, or energy.  I make this classification, not from any philosophical point of view, but simply for present convenience.  The first important principle to which I would like to draw your attention is that each of these things can be measured quantitatively.  If we accept the weight of a substance as an indirect measure of the amount of matter present, then we all know we can express the amount of matter in any given body in terms of a fundamental unit, like a pound or a gramme; and the idea has been put to immemorial use.  In later years we have learnt that electricity itself is also a quantity and that the amount of electricity which stands on an electrified body, or flows past a given point in an electric conductor, as for example the wire connected to an electric light, can be expressed arithmetically in terms of some unit.  Instruments are made for the purpose of measuring quantities of electricity in terms of the legal standard.  It is one of the functions of a Government Institution, like the National Physical Laboratory, to test such instruments and report on their accuracy.  International conferences have been held for the purpose of reducing these units to as small a number as possible so that