infinitely small, and distant from each other." These ideas were nothing more than a brilliant speculation. The atomic theory remained a speculation for over two thousand years, until Dalton discovered the law of mutiple proportions, and deduced therefrom that matter is composed of atoms having weights, and that the atoms are of various kinds. When atoms of the same kind come into juxtaposition, elements are formed, such as oxygen, hydrogen, chlorine, etc. Compounds are formed from the juxtaposition of different kinds of atoms, such as water, ammonia, carbon dioxide, etc.
This is not all: to Dalton's law of multiple proportions, the law of Avogadro is adjoined. The latter law establishes that all gases, temperature and pressure being equal, have the same elastic force. As this force is probably due to the shock of atoms or groups of atoms (molecules) on the sides of vessels which contain the gases, it is evident that equal volumes of all elementary gases contain the same number of molecules or atoms. And, finally, Dulong and Petit proved that the atoms of the elements all possess the same specific heat. All these laws, which were the result of observation and experiment in the early part of the nineteenth century, have converted into a scientific theory the ideas of the philosophers of ancient Greece.
Dalton's laboratory was in the lower rooms of the Manchester Literary and Philosophical Society, and
