(These figures are those of the solar spectrum, measured for the first time by Frauenhofer a century ago.) Those are waves in the ether, which is in perpetual movement. If we multiply 300,000 million millimetres by 1,666, we find the number 500 billion. That is the number of waves which enter our eye in one second when we look at red light. It requires 2,230 waves of violet light to fill up a millimetre and 700 billion shocks per second to give the sensation of that colour. Between the red and the violet all the other colours range themselves. The vibrations which give the impression of red are the slowest and their waves are the longest. This subtle substance, ether, penetrates all the bodies; it surrounds the most minute atoms of objects and beings, solids and liquids. Studies in molecular physics have led to this conclusion, that in a cubic centimetre of air the molecules which compose it only occupy a third of a cubic millimetre, that is to say, the 3/1,000 part of the total volume. It is like a cathedral in which children’s balloons might float, the remaining space being empty. All these molecules, all these systems of atoms, are in perpetual motion like the worlds in space, and the structure of bodies is organised by invisible force. In hydrogen, at ordinary temperature and pressure, every molecule is endowed with a speed of translation, vibration, and circulation, of more than a mile per second. Every body, organic or inorganic, air, water, plant, animal, man, is thus formed of molecules in movement. The analysis of bodies, both organic and inorganic, therefore brings us into the presence of movements of atoms controlled by forces, and the infinitely small speaks to us the same language as the infinitely great. The powerful microscopes of to-day and instruments of projection show in these microbian movements in these cells a fantastic life such as that of organisms which circulate by the thousand million in our own blood. The molecule, intangible and invisible, and hardly imaginable by our minds accustomed to superficial judgments, constitutes the only true matter, and what we call matter is, singularly enough, the effect produced upon our senses by the movements of molecules, constituting as it were an incessant possibility of sensation. It follows that matter, like the manifestations of energy, is only a mode of motion. At the temperature of absolute zero, matter, as we know it, would cease to exist. * * * * *