To the student these essays have no other interest than is due to the fact that they are Davy’s first contribution to the literature of science. No beginning could be more inauspicious. It is the first step that costs, and Davy’s first step had well nigh cost him all that he lived for. As additions to knowledge they are worthless; indeed, a stern critic might with justice characterise them in much stronger language. Nowadays such writings would hopelessly damn the reputation of any young aspirant for scientific fame, for it is indeed difficult to believe, as we read paragraph after paragraph, that their author had any real conception of science, or that he was capable of understanding the need or appreciating the value of scientific evidence. The essays are partly experimental, partly speculative, and the author apparently would have us believe that the speculations are entirely subservient to and dependent on the experiments. Precisely the opposite is the case. Davy’s work had its origin in Lavoisier’s “Traité Elémentaire,” almost the only text-book of chemistry he possessed. Lavoisier taught, in conformity with the doctrine of his time, that heat was a material substance, and that oxygen was essentially a compound body, composed of a simple substance associated with the matter of heat, or caloric. The young novitiate puts on his metaphysical shield and buckler; and with the same jaunty self-confidence that he assailed Locke and criticised Berkeley, enters the lists against this doctrine, determined, as he told Gregory Watt, “to demolish the French theory in half an hour.”