We see by Lagrange’s manuscripts, published by Boncompagni, that he had the first idea of the Calculus of Variations on the 12th of June, 1755; on the 19th of May (1756) he conceived the idea of the Mécanique Analitique; in November, 1759, he found a solution of the problem of vibrating cords.[218]
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]
The reader who has had the patience to follow this wearisome catalogue to the end, may convince himself that many men of genius have, as it were, a specific chronology; that is to say, a tendency to make their most numerous observations, to accomplish their finest discoveries, or their best æsthetic productions, at a special season or in one month rather than another: Spallanzani in the spring, Giusti and Arcangeli in March, Lamartine in August, Carcano, Byron, and Alfieri in September, Malpighi and Schiller in June and July, Hugo in May, Béranger in January, Belli in November, Melli in April, Volta in November and December, Galvani in April, Gambart in July, Peters in August, Luther in March and April, Watson in September.
A more general kind of specific chronology, a sort of intellectual calendar, is presented when we sum up various intellectual creations—poetry, music, sculpture, natural discoveries—of which the date of conception can be precisely fixed. This may be seen from the following table:—
| Month. | Literary and Artistic Works. | Astronomical Discoveries.[224] | Physical, Chemical, and Mathematical Discoveries. | Total. |
| January | 101 | 37 | — | 138 |
| February | 82 | 21 | 1 | 104 |
| March | 104 | 45 | 5 | 154 |
| April | 135 | 52 | 5 | 192 |
| May | 149 | 35 | 9 | 193 |
| June | 125 | 24 | 5 | 154 |
| July | 105 | 52 | 5 | 162 |
| August | 113 | 42 | — | 155 |
| September | 138 | 47 | 5 | 190 |
| October | 83 | 45 | 4 | 132 |
| November | 103 | 42 | 5 | 150 |
| December | 86 | 27 | 2 | 115 |
One observes at once that the most favourable month for æsthetic creations is May; then come September and April; the minimum is presented by the months of February, October, and December. The same may be observed partially with astronomical discoveries; but here April and July predominate, while for physical discoveries as well as for æsthetic creations, the months of May, April, and September stand first. Thus the advantage belongs to the months of early heat more than to the months of
