more prominent men in science. The various papers are quite largely devoted to statements of the unsolved practical and theoretical problems, in so far as they are capable of statement.
In the line of theory and research the most promising field seems to be the development of the electron theory which has been in the past mainly built up on experimental studies of the electrical discharge in gases. This theory is an attempt to represent all electrical phenomena in terms of the conception of the electron, an excessively minute charged particle, a thousand times smaller than an atom. This theory has already given a remarkably clear insight into the electrical properties of gases, and tentative explanations of the most promising kind of the ultimate constitution of matter, and of the nature of gravitation, two of the most stupendous problems of the present day in physics.
Among the purely practical problems, purely practical because the scientist has, one might almost say, given it up in despair, is the production of electrical energy direct from coal. One can say almost to a certainty that if one is to transform a large percentage of the latent energy of coal into electrical energy the coal must not be burned. The mischievous waste at present endured seems to be inherent in the burning process, but the wildest dreamer has never imagined that coal can be of any use other than for feeding a fire! There does seem to be a difficulty here, and perhaps the example of the scientist who revels in thermodynamics might just as well be followed by the inventive practical man. One thing, however, is certain and that is that the solution of this problem depends upon the invention of a new kind of fire which can be stopped in mid air, as it were, by a turn of the hand, each atom of carbon and each atom of oxygen stopping its mad whirl to begin it again at our pleasure, standing in the meantime in a state of quiet expectancy. Such a fire the physicist would call a reversible fire. The burning of zinc in a voltaic cell is indeed such a fire, and most of the attempts to transform the latent energy of coal into electrical energy efficiently have been attempts to construct a voltaic cell which will burn coal. Another kind of reversible fire might be realized in the gas engine if we had materials, to build a gas engine of, which would stand excessively high temperatures and excessively high pressures. In such a gas engine a mixture of gas and air could be enormously compressed and made so hot that it could not burn, then by expanding the mixture combustion would slowly take place and in such a way that to stop expanding would be to stop the combustion. Such combustion would be reversible, for to recompress the mixture would literally unburn it. Such a gas engine would have a very high efficiency if one could keep the cylinder from being cooled by the surrounding air.
The burning of food in the body of a work horse is a case in which an unusually large percentage of the latent energy of the fuel, or food, is converted into useful work, and thermodynamics tells us beyond peradventure that this high efficiency must be due to a state of affairs something like the following: Let us imagine the muscles built up of enormously complicated molecules, like the molecules of albumin for example, and let us imagine that as a muscle contracts these complicated molecules are distorted slowly, and that as they become distorted some of the atoms of carbon and hydrogen are slowly bulged out of the molecular structure and gingerly allowed to approach the atoms of oxygen in the blood in such a way that the process would be arrested at any moment by a cessation of the contraction. If such a process could be completely realized and if the atoms of oxygen could also be kept at bay by being themselves involved in some fashion in the bulging process of the muscular structure, then the efficiency of muscular action would be one hundred per cent. It is in fact much less
