The next circumstance recorded in the history of Harrison's invention is his reception of the annual gold medal of the Royal Society, in 1749, on which occasion the president, Martin Folkes, made the speech to which we are indebted for an account of the construction of the earliest machines. Harrison was recommended to the Royal Society on this occasion by Sir Hans Sloane. At that time Folkes stated that the third time-piece was finished, and was being regulated, in order to being taken to sea, and that Harrison expected to be able, "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," continued the president, "that is astonishing, and even stupendous, considering the immense number of difficulties, and those of very different sorts," which had to be overcome.

Respecting Harrison's progress during the next nine years we find no information, but the pamphlet before quoted, and said to be attributed to Mr. Short, but which appears to have been founded on information communicated by the inventor himself, states that about 1758 he finished the third time-keeper above alluded to (in which, perhaps, he had made some alterations since Folkes mentioned it as being nearly ready for use), and that he then had in hand a fourth, of much smaller size, which is commonly, although this writer says improperly, called a watch. Believing, however, that the third was sufficiently accurate to obtain the highest parliamentary reward, he sought permission to have it tried in a voyage to the West Indies, and, in March, 1761, received orders to send it, under the care of his son William, to Portsmouth, for that purpose. Circumstances having occurred to prevent his sailing as intended, he did not leave England until the 18th of November, when he went in His Majesty's ship Deptford, taking with him the fourth time-keeper, which, in the Admiralty instructions for the voyage, is called a watch.

The Deptford arrived at Jamaica on the 19th of January, 1762, the chronometer repeatedly correcting her reckoning, which, during the voyage, frequently erred as much as a degree and a half. The Deptford had 43 ships in convoy, 20 of which arrived at the Madeiras three days before His Majesty's ship Beaver, which had sailed ten days before them, but had lost her reckoning. Between Portsmouth and Madeira the time-piece corrected the log of the Deptford to the extent of three degrees of longitude; and those of several ships in the fleet as much as five degrees! On its arrival at Port Royal, Jamaica, after allowing for a losing rate* of 2·66 seconds a day, which had been de

It may be well here to explain that the keeping of absolutely correct time, which is almost impossible, is by no means essential to the value of a chronometer. Before taking it to sea the degree in which it either gains or loses should be ascertained by very careful observation, and this variation is called its rate. In making observations with the instrument, the amount of this ascertained variation must be added to or subtracted from the time indicated by the chronometer, and the result will be the same as if it had kept time perfectly.,

termined before leaving Portsmouth, the chronometer indicated the longitude within 5.1 seconds of the result of astronomical observation; or within little more than a geographical mile. It was brought back to England in the Merlin, and was, owing to tempestuous weather, exposed to violent agitation during the voyage; being frequently placed on the counter, in order to avoid continual exposure to the sea-water. This circumstance retarded the motion of the time-keeper; yet, on its arrival at Portsmouth, it was found that its total error in going and returning was only 1 minute and 54.5 seconds; which is equal to 28.5 minutes of longitude; or, in the latitude of Portsmouth, about 18 geographical miles. The Act of Parliament, be it remembered, offered the maximum prize if the longitude were shown within thirty miles, and specified an outward voyage only. The Merlin arrived at Portsmouth on the 26th of March, 1762.

It might be supposed that, after this success, the persevering efforts of Harrison would have met with a suitable reward; but, instead of this, he was subjected to most vexatious delays and disappointments. Several objections were started, as, for instance, that there was no proof of the chronometer having maintained a uniform rate during the voyage. It was also pleaded that the previous determination of the longitude of Jamaica by astronomical observation was not satisfactory; although this could hardly have affected the justice of his claim, since the return of the chronometer to the port from which it had set out proved, it might have been thought beyond all dispute, the fact of its having kept time greatly within the stipulated limits. Still it appears, from the minutes of a meeting of the Commissioners of Longitude on August 17, 1762, that they "were of opinion that the experiments made of the watch had not been sufficient to determine the longitude at sea," but passed a resolution to the effect" that it appears to them that the said watch, though not yet found to be of such great use for discovering the longitude at sea as required by the Act of the 12th of Queen Anne, is nevertheless an invention of considerable utility to the public.' They therefore voted Harrison 25007.; of which only 1500/, should be paid before a second voyage to the West Indies had been made; such sum to be considered as a part of the great reward, in case it should be subsequently awarded.* The backwardness shown by the Commissioners to do justice to Harrison according to the terms of the parliamentary offer, elicited the pamphlet from which most of the preceding facts are taken. It was published in 1763, and appeals to parliament for interposition on Harrison's behalf; pleading that twenty-one years had been spent in perfecting his time-keepers, after the certificate of the greatest mathematicians then living had declared their opinion that he had attained as high a degree of accuracy as was required by the Act; and that during that time

From statements in the Annual Register,' it appears that the sum of 15001. was paid immediately, and the subsequent 10007. on the 18th of September, 1764.

many lamentable shipwrecks had occurred, which might probably have been prevented had they been brought into use.*

At the latter end of 1762 a proposal was made to the Commissioners for a further trial of the chronometer without the risk and inconvenience of a second voyage to the West Indies. This proposal was founded on a suggestion, made many years previously by Dr. Halley, that the chronometer should be placed for some months on board the guard-ship in the Downs, and should be considered to have fulfilled the intentions of the Act if found correct, within the assigned limits, after such trial. Such a trial was now recommended, an arrangement being proposed by which the time-keeper might be compared daily, by signal, with an astronomical clock in Deal Castle, and exposed for any required time to a degree of heat greater than any experienced in Jamaica. The highest reward was to be given if the chronometer kept time within one minute a month; or the smaller rewards in proportion; allowing four minutes of time to correspond to one degree of longitude. This proposal, however, was not acted upon; but an Act of Parliament‡ was passed in March, 1763, to carry into effect the resolution passed by the Commissioners in the preceding month of August, and authorizing further the payment of 50007. upon the principles of construction being so divulged that other persons might make similar chronometers, and of the remainder of the reward so soon as the merits of the invention should be fully proved.

A second voyage to the West Indies being determined on, the chronometer, under the care of William Harrison, as before, was placed on board the Tartar, and sailed with it from Spithead to Barbadoes, setting off on the 28th of March, and arriving at Barbadoes on the 13th of May, 1764. This experiment proved satisfactory.§ and elicited from the Commissioners, on the 19th of February, 1765, an admission that the chronometer had kept time with sufficient exactness. But even then, instead of paying the reward for which Harrison had been toiling during the greater part of his life, an Act was passed (5 Geo. III. cap. 20) awarding him, upon a full discovery of the principles of his time-keeper (such discovery not having been made under the provisions of the Act of 1763), the payment of such a sum as, with the 25007. he had already received, would make one-half of the reward; the remaining 10,000l. to be paid when other chro

* The writer alludes especially to the then recent wrecks of the Litchfield, Ramilies, and Humber, men-of-war, and the Doddington East-Indiaman. In the latter case alone about 250 lives were lost.

Dr. Halley is also said to have told the Commissioners, soon after Harrison's arrival in London, that, if his time-keeper were sent a voyage of some months from any port, and were to return to the same port, and be then found to have varied no more than the allowed degree, he should consider the test as quite satisfactory, and that "he should look upon a time keeper which did not alter, one way nor the other, more than four seconds a day, as sufficiently accurate for all the purposes of determining the lon gitude at sea."

3 George III., cap. 14.

The preamble of the Act 5 George III., cap. 20, states that the watch did not lose the longitude beyond ten geographical miles.

nometers had been made, and their capabilities fully proved. Harrison was also required, by this Act, to give up his three time-keepers and his watch for the use of the public. A

It is by no means surprising that these conditions, imposing a yet further and an indefinite delay, and requiring that which the original Longitude Act of 1714 did not specify, should have been unsatisfactory to Harrison, who was now an old man, and had so long laboured without any adequate remuneration. He has been accused of displaying a bad spirit on the occasion, and possibly he was irritated by repeated disappointments into the use of language that is to be regretted; yet a letter addressed by him to the Commissioners, dated May 30, 1765, and printed in the Annual Register for that year, can hardly fail to excite sympathy. Our space will only admit of an extract. "I cannot help thinking," he writes, "but I am extremely ill-used by gentlemen who I might have expected a different treatment from; for if the Act of the 12th of Queen Anne be deficient, why have I so long been encouraged under it, in order to bring my invention to perfection? And after the completion, why was my son sent twice to the West Indies? Had it been said to my son, when he received the last instruction, 'There will, in case you succeed, be a new Act at your return, in order to lay you under new restrictions, which were not thought of in the Act of the 12th of Queen Anne,' I say, had this been the case, I might have expected some such treatment as I now meet with. It must be owned that my case is very hard; but I hope I am the first, and for my country's sake shall be the last, that suffers by pinning my faith on an English Act of Parliament. Had I received my just reward, for certainly it may be so called after forty years' close application in the improvement of that talent which it had pleased God to give me, then my invention would have taken the course which all improvements in this world do; that is, I must have instructed workmen in its principles and execution, which I should have been glad to have had an opportunity of doing. But how widely this is different to what is now proposed; viz. for me to instruct people that I know nothing of, and such as may know nothing of mechanics; and if I do not make them understand to their satisfaction, I may then have nothing!" He probably misconceived in some degree what was required of him, but after a time the misunderstanding between him and the Commissioners was compromised, and he gave a full explanation of the principles of his chronometer to Dr. Maskelyne, the astronomer royal, and six other gentlemen, who had been appointed to receive it. Assigning all the time-keepers to the use of the Commissioners, he received, on the 28th of October, their certificate for 7500%.

The Annual Register for 1765 contains a “Short View of the Improvements made or attempted in Mr. Harrison's Watch," addressed to the Commissioners by the Rev. W. Ludlam, one of the persons to whom it was explained; and in 1767 a minute description, with engravings of all its parts, was published by the

Commissioners. In the latter it is stated that "the grand principle of the watch is that of giving the greatest possible motion to the balance with a given force." The machine had four springs1st. The mainspring, by which the whole apparatus was propelled; 2nd. The maintaining spring in the fusee, for continuing the motion during winding up; 3rd. A delicate spring, which acted upon the balance by the intervention of only one wheel, was, to maintain equality of force, never allowed to unroll itself more than one-eighth of a turn, and was wound up by the mainspring eight times in a minute; and 4th. The balancespring. The pivot-holes were in rubies, with diamonds at the ends; and diamond pallets were used. The balance was about 22 inches in diameter; being three times the diameter, and much more than three times the weight, of that of a common watch; and therefore, when at rest, the power of the wheels was as insufficient to move it, as those of a clock are to set the pendulum in motion. By the increased size of the balance it was made to move through about 24 inches in a second, whereas that of an ordinary watch moves through about 6 inches in the same time. A contrivance was added to render the vibrations of the balance isochronal, notwithstanding its liability to vibrate to a greater or less extent according to accidental circumstances. The means of applying compensation for temperature resembled that formerly described as adopted in the second and third of Harrison's time-keepers. With regard to the plan of using secondary springs wound up at short intervals by the mainspring, Mr. Ludlam observes that he believes it to be an improvement, though not a very considerable one; and that, probably, if the other errors to which a common watch is liable were overcome, those arising from changes of force in the mainspring would not be sufficient to render them useless at sea. By some notes in reply to Mr. Ludlam's paper, it appears that Harrison himself doubted the continued use of this arrangement. The increased size and weight of the balance, and consequent inability of the wheels to set it in motion, was considered to be liable to the inconvenience of the watch stopping if subjected to a quick motion in the same direction that the balance vibrated; but such a motion it was not likely to receive with proper usage. The means of affording compensation for heat and cold Mr. Ludlam pronounced ingenious and useful, although he doubted whether it could be made to answer the purpose with precision. In the notes upon Mr. Ludlam's paper it is stated that it was not until 1757 that Harrison thought of reducing his improved mechanism into a very small compass; although this machine, popularly termed his watch, was ready for sea early in 1761. It resembles a pocket-watch in form, and is mounted in a silver case, about six inches in diameter.

The trials and disappointments of Harrison were not even yet at an end. From May 6, 1766, to March 4, 1767, his watch underwent a rigid course of trial at the Royal Observatory, under the eye of Dr. Maskelyne, who was charged, and apparently with

« ElőzőTovább »