At length he combined his philosophical views into a connected system, which he published in 1789, under the title of ‘Elements of Chemistry:’ a beautiful model of scientific composition, clear and logical in its arrangement, perspicuous and even elegant in its style and manner. These perfections are rarely to be found in elementary works written by original discoverers. The genius which qualifies a man for enlarging the boundaries of science by his own inventions and researches is of a very different class from that which confers the ability to elucidate, in a simple and systematic course, the order and connexion of elementary truths. But in Lavoisier these different species of talent were most happily blended. He not only added profound truths to science, but succeeded in adapting them to the apprehension of students, and was able to render them attractive by his eloquence. In 1791 he entered upon extensive researches, having for their object the application of pneumatic chemistry to the advancement of medicine, in reference to the process of respiration. With this view he examined in great detail the changes which the air undergoes, and the products generated in that process of the animal economy. He had previously, however, as far back as 1780, detailed a series of experiments to determine the quantity of oxygen consumed and carbonic acid generated by respiration, in a given time, in the Memoirs of the French Academy. In the twenty volumes of the Academy of Sciences, from 1772 to 1793, are not less than forty memoirs by Lavoisier, replete with all the grand phenomena of the science:—the doctrine of combustion in all its bearings; the nature and analysis of atmospheric air; the generation and combinations of elastic fluids; the properties of heat; the composition of acids; the decomposition and recomposition of water; the solutions of metals; and the phenomena of vegetation, fermentation, and animalization. These are some of the most important subjects of his papers; and during the whole of this period he advanced steadily in the course which was pointed out to him by the unerring rules of inductive inquiry, to which his original genius supplied the commentary. So well did he secure every point of the results to which he ascended, that he never made a false step. It was only in one subject, before alluded to, that he may be said to have gone a few steps too far. Nor did he ever suffer himself to be discouraged, or his ardour to be damped by the difficulties and obstacles which perpetually impeded his progress. He traced new paths for investigation, and founded a new school of science; and his successors had ample employment in following out the inquiries which he had indicated, and exploring those recesses to which he had opened the way.