The question of the discovery of the longitude had been considered of national importance since the year 1714, when an Act was passed offering 10,000_l._, 15,000_l._, and 20,000_l._ for any method of discovering the longitude within 60, 40, or 30 miles respectively. In 1735 Harrison arrived in London with his time-piece, and showed it to several members of the Royal Society. He obtained a certificate of its goodness, signed by Halley, Smith, Bradley, Machin, and Graham, in consequence of which he was allowed to proceed with it to Lisbon, in a king’s ship, in 1736. The watch was found to correct the ship’s reckoning a degree and a half; and the commissioners thereupon gave Harrison 500_l._, to enable him to proceed. He finished a second time-piece in 1739, and a third in 1758, each nearer to perfection than the former, and both abounding in ingenious contrivances to overcome the effects of temperature, and of the motion of a vessel at sea. In 1741 he obtained another certificate, signed by almost every name of eminence in English science of the time. In 1749 the gold medal of the Royal Society was awarded to him. In 1761, having then a fourth time-piece in hand, but being convinced that the third was sufficiently correct to come within the limits of the act of parliament, he applied to the Commissioners for a trial of it. Accordingly, in 1761 (Nov. 18), his son, William Harrison, was sent in a king’s ship to Jamaica with the watch, and returned to Portsmouth, March 26, 1762. On arrival at Port Royal, Jan. 19, 1762, the watch was found wrong only 5⅒ seconds; and at its return, only 1 minute 54½ seconds. This was sufficient to determine the longitude within 18 miles; and Harrison accordingly claimed 20,000_l._, in a petition to the House of Commons, presented early in 1763. The Commissioners had awarded him 1,500_l._, and promised 1,000_l._ more after another voyage. Owing to some doubt as to the method of equal altitudes employed in finding the time at Port Royal, they do not appear to have been of opinion that the first voyage was conclusive. In 1763 an act passed, by which, firstly, no other person could become entitled to the reward until Harrison’s claim was settled; and, secondly, 5,000_l._ was awarded to him on his discovery of the structure of the instrument. But the Commissioners not agreeing about the payment, another voyage was resolved on, and Mr. William Harrison sailed again for Barbadoes, with Dr. Maskelyne, afterwards the Astronomer Royal. The result was yet more satisfactory than before; and in 1765 a new act was passed, awarding to Harrison the whole sum of 20,000_l._: the first moiety upon the discovery of his construction; the second, so soon as it should be found that others could be made like it. In this act it is stated that the watch did not lose more than ten miles of the longitude. But Harrison had by this time been rendered unduly suspicious of the intentions of the Commissioners. He imagined that Dr.