In 1844, the use of nitrous oxide gas (laughing gas) as an anæsthetic was introduced by Dr. Wells. It cannot be said that this invention has had any direct influence on history itself, though it has had a great deal of influence on the history of some individuals. It contributed a new and distinct part to the Machine, however, and certainly helped to ameliorate the conditions of living. Besides, it seems to be one of the lessons of history that most new and distinct creations, even if no use has been found for them for a long while, have ultimately found a field of usefulness. Furthermore, every new and useful thing, like nitrous oxide gas, attracts the attention of men to the advantages that the study of physical sciences and the prosecution of invention offer, and gives inspiration for further study and endeavor. In the same year, Léon Foucault invented the first practical electric arc-light. Davy had made the basic invention of the Voltaic arc in 1808; but his invention was in the class just spoken of, in that it was not utilized for many years. Even the arc-light that Foucault produced in 1844 was not utilized then. In both cases, the cause of slowness of utilization did not rest so much in the invention as in the stage of civilization at the time. The world was not yet ready for the arc-light. In fact, it did not become ready, and it could not become ready, to use the arc-light in real service, until a cheaper means of producing electric current had been invented. This did not happen until the dynamo-electric machine had been invented and had been brought to such a point of practical development that it could supply electric current, not only adequately and economically, but reliably. A necessary step toward the utilization of the arc-light was made in 1845, however, by Thomas Wright, who invented a means whereby the carbons could be kept automatically at the correct distance apart for maintaining a continuous and uniform light. In 1845, Robert Hoe made an important contribution in his double-cylinder printing press. In the same year, R. W. Thompson invented the pneumatic tire. This invention belongs distinctly in the class just spoken of, for the pneumatic tire did not come into general use until the bicycle did, about 1890. It may be asked if there is any use in inventing appliances long before they are needed. So far as the inventor is then concerned--no: so far as the public is eventually concerned, yes. All inventions made and patented are described and illustrated in the Patent Office Gazette; and many of them are described and illustrated in magazines and newspapers, even if they are not used in actual practice. These records form part of the general knowledge of mankind, just as much as do the facts of geography and history and arithmetic; and they can be drawn upon by investigators and inventors, and made to assist them in their work.