We read in Malpighi’s journal that in July he made his great discoveries in the suprarenal glands. It is curious to observe how some one month predominates in certain years: for example, January in 1788 and 1790, and June in 1771, during which he made thirteen discoveries.[214] The first idea of the barometer came to Torricelli in May, 1645, as may be seen by his letters to Ricci; in March, 1644, he had made the discovery, of great moment at that time, of the best way of making glasses for spectacles. The first experiments of Pascal on the equilibrium of fluids were made in September, 1645.[215] In March, 1752, Franklin began his experiments with lightning conductors, and concluded them in September. Goethe declared that it was in May that his original ideas on the theory of colours arose, and in June that he made his fine observations on the metamorphoses of plants.[216] Hamilton discovered the calculus of Quaternions on the 16th of October, 1843. Volta invented the electric pile in the beginning of winter, 1799-1800. In the spring of 1775 he invented the electrophore. In the first days of November, 1784, he discovered the production of hydrogen in organic fermentations. His invention of the eudiometer took place in the spring, about May. In April of the same year (1777) Volta wrote to Barletta the famous letter in which he divined the electric telegraph. In the spring of 1788 he constructed his great conductor. Luigi Brugnatelli found out galvanoplasty in November, 1806, as is shown by a letter which the advocate Zanino Volta found in the correspondence of his grandfather. Nicholson discovered the oxydation of metals by means of the Voltaic pile, in the summer of 1800. From the examination of Galvani’s manuscripts it appears that his studies on intestinal gases began in December, 1713. His first studies on the action of atmospheric electricity on the nerves of cold-blooded animals were undertaken, as he himself writes, “at the 20th hour of the 26th of April, 1776.” In September, 1786, he began his experiments on the contractions of frogs, whence the origin of galvanism. In November, 1780, he stated his experiments on the contractions of frogs by artificial electricity.[217] 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]