Not satisfied with his two machines, Harrison proceeded to make a third. This was of an improved construction, and occupied still less space, the whole of the machine and its apparatus standing upon an area of only four square feet. It was in such forwardness in January, 1741, that it was exhibited before the Royal Society, and twelve of the most prominent members signed a certificate of "its great and excellent use, as well for determining the longitude at sea as for correcting the charts of the coasts." The testimonial concluded: "We do recommend Mr.
Harrison to the favour of the Commissioners appointed by Act of Parliament as a person highly deserving of such further encouragement and assistance as they shall judge proper and sufficient to finish his third machine." The Commissioners granted him a further sum of 500L. Harrison was already reduced to necessitous circumstances by his continuous application to the improvement of the timekeepers. He had also got into debt, and required further assistance to enable him to proceed with their construction; but the Commissioners would only help him by driblets.
Although Harrison had promised that the third machine would be ready for trial on August 1, 1743, it was not finished for some years later. In June, 1746, we find him again appearing before the Board, asking for further assistance. While proceeding with his work he found it necessary to add a new spring, "having spent much time and thought in tempering them." Another 500L. was voted to enable him to pay his debts, to maintain himself and family, and to complete his chronometer.
Three years later he exhibited his third machine to the Royal Society, and on the 30th of November, 1749, he was awarded the Gold Medal for the year. In presenting it, Mr. Folkes, the President, said to Mr. Harrison, "I do here, by the authority and in the name of the Royal Society of London for the improving of natural knowledge, present you with this small but faithful token of their regard and esteem. I do, in their name congratulate you upon the successes you have already had, and I most sincerely wish that all your future trials may in every way prove answerable to these beginnings, and that the full accomplishment of your great undertaking may at last be crowned with all the reputation and advantage to yourself that your warmest wishes may suggest, and to which so many years so laudably and so diligently spent in the improvement of those talents which God Almighty has bestowed upon you, will so justly entitle your constant and unwearied perseverance."Mr. Folkes, in his speech, spoke of Mr. Harrison as "one of the most modest persons he had ever known. In speaking," he continued, "of his own performances, he has assured me that, from the immense number of diligent and accurate experiments he has made, and from the severe tests to which he has in many ways put his instrument, he expects he shall be able with sufficient certainty, through all the greatest variety of seasons and the most irregular motions of the sea, to keep time constantly, without the variation of so much as three seconds in a week, --a degree of exactness that is astonishing and even stupendous, considering the immense number of difficulties, and those of very different sorts, which the author of these inventions must have had to encounter and struggle withal."Although it is common enough now to make first-rate chronometers-- sufficient to determine the longitude with almost perfect accuracy in every clime of the world--it was very different at that time, when Harrison was occupied with his laborious experiments. Although he considered his third machine to be the ne plus ultra of scientific mechanism, he nevertheless proceeded to construct a fourth timepiece, in the form of a pocket watch about five inches in diameter. He found the principles which he had adopted in his larger machines applied equally well in the smaller, and the performances of the last surpassed his utmost expectations. But in the meantime, as his third timekeeper was, in his opinion, sufficient to supply the requirements of the Board of Longitude as respected the highest reward offered, he applied to the Commissioners for leave to try that instrument on board a royal ship to some port in the West Indies, as directed by the statute of Queen Anne.
Though Harrison's third timekeeper was finished about the year 1758, it was not until March 12, 1761, that he received orders for his son William to proceed to Portsmouth, and go on board the Dorsetshire man-of-war, to proceed to Jamaica. But another tedious delay occurred. The ship was ordered elsewhere, and William Harrison, after remaining five months at Portsmouth, returned to London. By this time, John Harrison had finished his fourth timepiece--the small one, in the form of a watch. At length William Harrison set sail with this timekeeper from Portsmouth for Jamaica, on November 18th, 1761, in the Deptford man-of-war. The Deptford had forty-three ships in convoy, and arrived at Jamaica on the l9th of January, 1762, three days before the Beaver, another of His Majesty's ships-of-war, which had sailed from Portsmouth ten days before the Deptford, but had lost her reckoning and been deceived in her longitude, having trusted entirely to the log. Harrison's timepiece had corrected the log of the Deptford to the extent of three degrees of longitude, whilst several of the ships in the fleet lost as much as five degrees! This shows the haphazard way in which navigation was conducted previous to the invention of the marine chronometer.
