276 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1910. 



tained in equal volumes the same number of molecules, and that the 

 definite proportions in which they combined represented the invari- 

 able relation between the weights of the atoms which were in juxta- 

 position. 



The theory is that in the interior of bodies the constituent mole- 

 cules are perpetually animated by a movement which becomes cor- 

 respondingly greater as the temperature becomes higher. If the 

 swiftness of these thermic movements could be gradually reduced to 

 zero, temperatures would be obtained which would approach more 

 and more closely to the limit of temperature found at about — 273° C. 

 This temperature, the lowest conceivable, since it corresponds to a 

 state of repose of the molecules, is called absolute zero. 



The principles of mechanics which apply to this conception of 

 molecules in movement takes account of all these laws to which 

 gases and dissolved bodies are subjected. I can not enlarge here on 

 the methods which have made it possible to count in a cubic centi- 

 meter of gas at ordinary temperature and pressure, thirty billion 

 billions of molecules, and to evaluate the dimensions of one of 

 these molecules. The diameter of a molecule of oxjgen, for example, 

 is a few ten-millionths of a millimeter. These figures give some 

 idea, however, of the extreme divisibility of matter. In connection 

 Avith this divisibility of matter it is interesting to recall that accord- 

 ing to Berthelot the odor of one hundred-thousand-millionth of a 

 gram of iodoform per cubic centimeter of air is perceptible to the 

 sense of smell. 



You are all aware that matter attracts matter, in accordance with 

 the universal law of gravitation which rules the movements even of 

 the stars. The invariability of the constant of gravitation has sug- 

 gested the idea that the atoms of all bodies can be formed by the 

 unequal condensation of a single principle and the relations dis- 

 covered by chemists between the different elements lend themselves 

 favorably to this hypothesis. 



The idea of a single principle as the ultimate constituent of all 

 things, dates in reality from the most ancient times. Twenty-five 

 centuries ago, Thales propounded the existence of a primordial fluid 

 to which he attributed a sort of soul and a power of attraction. 

 Anaximander, Anaximines. and Herodotus spoke of a universal prin- 

 ciple, and Pythagoras located above the air "ether, a celestial sub- 

 stance free from all perceptible matter." Five hundred years before 

 our era Leucippus and Democritus had conceived of atoms indi- 

 visible and eternal which moved about in infinite space; Lucretius 

 a little later expounded similar doctrines. Finally Descartes and 

 Leibnitz developed for themselves an idea of matter which led them 

 to similar conclusions. 



