Marsh Olefiant | Carbonic Carbonic Gas Gas | Oxide Acid Carbon 6 6 | Carbon 5 6 Hydrogen 1 2 | Oxygen 8 16 Thus the first compound, marsh gas, was regarded by Dalton as composed of an atom of carbon in union with an atom of hydrogen; or, to reproduce his symbols, as ⊜◉; while the second, olefiant gas, on this hypothesis, was a compound of two atoms of hydrogen with one of carbon, or ◉◍◉. Similarly the symbols ◍○, and ○◍○ were given to the two compounds of carbon with oxygen. So water was assigned the symbol ◉○, for Dalton imagined it to be a compound of one atom of hydrogen with one of oxygen. Compounds containing only two atoms were termed by him “binary”; those containing three, “ternary”; four, “quaternary,” and so on. The weight of an atom of oxygen was eight times that of an atom of hydrogen; while that of an atom of carbon was six times as great as the unit. By assigning symbols to the elements, consisting of the initial letters of their names, or of the first two letters, formulas were developed, indicating the composition of the compound, the atomic weights of the elements being assured. Thus, NaO signified a compound of an atom of sodium (natrium), weighing twenty-three times as much as a similar atom of hydrogen, with an atom of oxygen, possessing eight times the weight of an atom of hydrogen. Therefore, thirty-one pounds of soda should consist of twenty-three pounds of sodium in combination with eight pounds of oxygen, for, according to Dalton, each smallest particle of soda contains an atom of each element, and the proportion is not changed, however many particles be considered. It has been pointed out by Judge Stallo, of Philadelphia, in his _Concepts of Physics_, that such a hypothesis as that of Dalton is no explanation; that a fact of nature, as, for example, the fact of simple and multiple proportions, is not _explained_ by being minified. Allowing the general truth of this statement, it is, nevertheless, undoubted that chemistry owes much to Dalton’s hypothesis—a lucky guess at first, it represents one of the fundamental truths of nature, although its form must be somewhat modified from that in which Dalton conceived it. Dalton’s work was first expounded by Thomas Thomson, professor at Glasgow, in his _System of Chemistry_, published in 1805; and subsequently in Dalton’s own _New System of Chemical Philosophy_, the three volumes of which were published in 1808, in 1810, and in 1827.