The Royal Society, in London, was begun in 1659, but did not assume a regular form till 1662. Its transactions were first published in 1665. The Academy of Sciences, at Paris, was founded in 1686, by Louis XIV., who invited to it Rœmer, from Denmark, Huygens and Cassini from Italy. Cassini was born at Perinaldo, in the county of Nice, on the 8th of June, 1625, and was appointed first professor in the Royal Observatory at Paris, where he prosecuted his discoveries till his death, in 1712, and was succeeded by his son. He was assisted by Picard, Auzoul, and La Hire. By the direction of the Academy of Sciences at Paris, a voyage was undertaken by Riecher and Meurisse, at the king’s expense, to the island of Caienne, in South America, almost under the equator, in 1672, to ascertain several philosophical facts;--the refraction of light, the parallax of Mars, and of the Sun, the distance of the tropics, the variation in the motion of the pendulum, &c. The parallax of the sun is the angle under which an observer at the sun would see the earth: this Cassini fixed at 9½ seconds, and the angle under which we see the sun, at 16 minutes and 6 seconds, or 966 seconds; hence he concluded that these semi-diameters, are as 9½ to 966, or as 10 to 1932. So that, according to Cassini, the semi-diameter of the earth is one hundred times less than that of the sun; and consequently the sun is a million times larger than the earth. The parallax of the sun has since, from the transit of Venus, 6th of June, 1761, and 3rd of June, 1769, been discovered to be but about 8 seconds, consequently his comparative bulk to that of the earth, and his distance from it, to be proportionably greater. The method of finding the distance of the earth from the sun, and consequently of the other planets, was first proposed by Dr. Halley, who had never seen, and was morally certain he would never see, this appearance. Meurisse died during the voyage. Riecher returned in 1676. His answer to the parallax of Mars was not satisfactory. Cassini calculated it at 15 seconds. The distance of the tropics was found to be 46 degrees, 57 minutes, 4 seconds. The chief advantage resulting from the voyage was ascertaining the vibration of the pendulum. In 1669, Placard remarked that clocks went slower in summer than in winter, owing to, as since ascertained, that it is the property of heat to dilate bodies, which consequently lengthens the pendulum; that cold produces an opposite effect. Riecher found that the pendulum made forty-eight vibrations less at Caienne than at Paris; that it went two minutes and twenty seconds a day slower; hence, to adjust, he was obliged to shorten the pendulum.