1498,[204] the design of the Libreria in December, the model in wood of the tomb of Pope Julius in August.[205] Leonardo da Vinci conceived the equestrian statue of the Sforza and began his book _Della luce e delle Ombre_ in April; for we find in his autograph manuscript these words: “On April the 23rd, 1492, I commenced this book and recommenced the horse.” On the 2nd of July, 1491, he designed the pavilion of the Duchess’s Bath; on the 3rd of March, 1509, St. Christopher’s Canal.[206] The first idea of the discovery of America came to Columbus between May and June, in 1474, in the form of a search for the western passage to India.[207] Galileo discovered the sun’s spots contemporaneously with, or before, Scheiner in April, 1611;[208] in December, 1610, and even in September (since he speaks of his observation having been made three months previously), he discovered the analogy between the phases of Venus and those of the moon; in May, 1609, he invented the telescope;[209] in July, 1610, he discovered two stars, afterwards found to be the most luminous points of Saturn’s ring, a discovery which, according to his custom, he expressed in verse:-- “_Altissimum planetam tergeminum observavi._” In January he found Jupiter’s satellites; in November, 1602, the isochronism of the oscillations of the pendulum.[210] Kepler discovered the law which bears his name in May, 1618; the discovery of Zucchi regarding Jupiter took place in May; that of Tycho Brahe in November. Fabricius discovered the first changing star in August, 1546. Cassini discovered the spots which indicate the rotation of Venus in October and April (1666-67), and in October, December, and March (1671, 1672, 1684) four satellites of Saturn. Herschel discovered two in March, 1789. In June, 1631, Hevelius conceived the first ideas of selenography.[211] A satellite of Saturn was discovered by Huygens on the 25th of March, 1665; another by Dawes and Bond on the night of the 19th of September, 1848. Two satellites of Uranus were discovered by Herschel in 1787; one of them, considered as doubtful by Herschel, was again discovered by Struve and Lassel in October, 1847; the last, Ariel, was discovered by Lassel on the 14th of September, 1847; on the 8th of July in the same year he had also seen Neptune’s satellite for the first time.[212] Uranus was discovered by Herschel in March, 1781. The same astronomer observed the moon’s volcanoes in April. Bradley discovered in September (1728) the aberration of light, Enke’s and Vico’s fine observations on Saturn took place in March and April (1735-38). Of the comets discovered by Gambart, three were in July, two in March and in May, one in January, April, June, August, October, December.[213] The last three comets discovered in 1877 were perceived in October, February, and September; in August Hall observed the satellites of Mars. Schiaparelli’s discovery on falling stars dates from August, 1866.