From the manuscripts of Spallanzani, which I have been able to examine in the Communal Library at Reggio, it appears that his observations on moulds began on the 26th of September, 1770. On the 8th of May, 1780, Spallanzani started, to use his own words, “the study of animals which are torpid through the action of cold;” in April and May, 1776, he discovered the parthenogenesis of certain animals. The 2nd of April, 1780, was the richest day in experiments, or rather deductions, on the subject of ovulation. “It becomes clear,” he wrote on this same day, after having made forty-three observations, “that the ova are not fecundated in the womb; that the sperm cells after emission remain apt for fecundation for a certain time, that the vesicular fluid fecundates as well as the seminal, that wine and vinegar are opposed to fecundation.” “Impatience,” adds this curious manuscript, which enables us to assist at the incubation of these wonderful experiments, “will not allow me to draw any more corollaries.” On the 7th of May, 1780, he discovered that an infinitely small amount of semen sufficed for fecundation. A letter to Bonnet shows that Spallanzani had, during the spring of 1771, the idea of studying the action of the heart on the circulation. In March, 1773, he undertook his studies on rotifera, and in his manuscripts for May, 1781, may be found a plan of 161 new experiments on the artificial fecundation of frogs. Géoffroy Saint-Hilaire had his first ideas on the homologies of organisms in February. Davy discovered iodine in December. Humboldt made his first observations on the magnetic needle in November, 1796; in March, 1793, he observed the irritability of organic fibres.[219] The prolegomena of the _Cosmos_ was dictated in October.[220] In July, 1801, Gay-Lussac discovered fluoric acid in fish-bones; he completed the analysis of alum in July.[221] In September, 1846, Morton used sulphuric ether as an anæsthetic in surgery. In October, 1840, Armstrong invented the first hydro-electric machine.[222] Matteucci made his experiments with the galvanoscope in July, 1830; on torpedoes in the spring of 1836; on electro-motor muscles in July, 1837; on the decomposition of acids in May, 1835, he determined in May, 1837, the influence of electricity on the weather; in June, 1833, he concluded his experiments on heat and magnetism.[223]