Despite its egoism and the obvious marks of haste and imperfection it displays, the work may still be read with interest by the chemical student. We would recommend him before perusing it to study Dalton’s “New System of Chemical Philosophy,” and he will gain a vivid impression of the extraordinary strides which the science had made during the four years which intervened between the publication of these memorable books. Each work, too, is strongly typical of its author, and reflects in the most striking manner the range and limitations of his powers and the characteristics of his genius. Towards the middle of October Davy returned to town. In a letter written to his friend Children, from Edinburgh, he says:-- “I have received a very interesting letter from Ampère. He says that a combination of chlorine and azote has been discovered at Paris, which is a fluid, and explodes by the heat of the hand; the discovery of which cost an eye and a finger to the author. He gives no details as to the mode of combining them. I have tried in my little apparatus with ammonia cooled very low, and chlorine, but without success.” The substance here referred to is nitrogen chloride, one of the most formidable explosives known to chemists, and which seriously maimed Dulong, its discoverer, as stated. The “little apparatus” refers to a portable chemical chest which accompanied Davy on all his travels. Any new combination of nitrogen was certain to attract his immediate attention. He seems to have remained to the last convinced that nitrogen would turn out to be a non-elementary substance, and it is remarkable how eagerly he caught at any hint or surmise which appeared likely to afford support to his conjecture. He at once repeated Dulong’s experiments in Children’s laboratory at Tunbridge, and succeeded in obtaining considerable information concerning the chemical and physical properties of this extraordinary substance, when he was wounded in the eye by its explosion. He thus breaks the news of his accident to Lady Davy:-- “... Yesterday I began some new experiments to which a very interesting discovery and a slight accident put an end. I made use of a compound more powerful than gunpowder destined perhaps at some time to change the nature of war and influence the state of society. An explosion took place which has done me no other harm than that of preventing me from working this day [Sunday] and the effects of which will be gone to-morrow and which I should not mention at all, except that you may hear some foolish exaggerated account of it, for it really is not worth mentioning....” In reality the accident was more serious than he would have Lady Davy believe, and the injury prevented him from resuming his work for some time. In a letter written about the middle of January, 1813, from Wimpole, where he was staying with Lord Hardwicke, he says:--