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had no need of very accurate observations; and who, if they ever transiently observed any deviations from the meridian, either ascribed them to some extrinsick and accidental cause, or willingly neglected what it was not necessary to understand.

But when the discovery of the new world turned the attention of mankind upon the naval sciences, and long courses required greater niceties of practice, the variation of the needle soon became observable, and was recorded, in 1500, by Sebastian Cabot, a Portuguese, who, at the expense of the king of England, discovered the northern coasts of America.

As the next century was a time of naval adventures, it might be expected that the variation once observed, should have been well studied: yet it seems to have been little heeded; for it was supposed to be constant, and always the same in the same place, till, in 1625, Gellibrand noted its changes, and published his observations.

From this time the philosophical world had a new subject of speculation, and the students of magnetism employed their researches upon the gradual changes of the needle's direction, or the variations of the variation, which have hitherto appeared so desultory and capricious, as to elude all the schemes which the most fanciful of the philosophical dreamers could devise for its explication. Any system that could have united these tormenting diversities, they seem inclined to have received, and would have contentedly numbered the revolutions of a central magnet, with very little concern about its existence, could they have assigned it any motion, or vicissitude of motions, which would have corresponded with the changes of the needle.

Yet upon this secret property of magnetism I ventured to build my hopes of ascertaining the longitude at sea. I found it undeniably certain that the needle varies its direction in a course eastward or westward between any assignable parallels of latitude: and, supposing nature to be in this, as in all other operations, uniform and consistent, I doubted not but the variation proceeded in some esta

blished method, though, perhaps, too abstruse and complicated for human comprehension.

This difficulty, however, was to be encountered; and by close and steady perseverance of attention I at last subdued, or thought myself to have subdued it: having formed a regular system in which all the phænomena seemed to be reconciled; and, being able, from the variation in places where it is known, to trace it to those where it is unknown; or from the past to predict the future; and, consequently, knowing the latitude and variation, to assign the true longitude of any place,

With this system I came to London, where, having laid my proposals before a number of ingenious gentlemen, it was agreed that during the time required to the completion of my experiments, I should be supported by a joint subscription to be repaid out of the reward, to which they concluded me entitled. Among the subscribers, was Mr. Rowley, the memorable constructor of the orrery; and among my favourers was the lord Piesley, a title not unknown among magnetical philosophers. I frequently showed, upon a globe of brass, experiments by which my system was confirmed, at the house of Mr. Rowley, where the learned and curious of that time generally assembled.

At this time great expectations were raised by Mr. Whiston, of ascertaining the longitude by the inclination of the needle, which he supposed to increase or diminish regularly. With this learned man I had many conferences, in which I endeavoured to evince what he has at last confessed in the narrative of his life, the uncertainty and inefficacy of his method.

About the year 1729, my subscribers explained my pretensions to the lords of the Admiralty, and the lord Torrington declared my claim just to the reward assigned, in the last clause of the act, to those who should make discoveries conducive to the perfection of the art of sailing. This he pressed with so much warmth, that the commissioners agreed to lay my tables before Sir Isaac Newton, who excused himself, by reason of his age, from a regular

examination: but when he was informed that I held the variation at London to be still increasing; which he and the other philosophers, his pupils, thought to be then stationary, and on the point of regression, he declared that he believed my system visionary. I did not much murmur to be for a time overborne by that mighty name, even when I believed that the name only was against me: and I have lived till I am able to produce, in my favour, the testimony of time, the inflexible enemy of false hypotheses; the only testimony which it becomes human understanding to oppose to the authority of Newton.

My notions have, indeed, been since treated with equal superciliousness by those who have not the same title to confidence of decision; men who, though, perhaps, very learned in their own studies, have had little acquaintance with mine. Yet even this may be borne far better than the petulance of boys, whom I have seen shoot up into philosophers by experiments which I have long since made and neglected, and by improvements which I have so long transferred into my ordinary practice, that I cannot remember when I was without them.

When Sir Isaac Newton had declined the office assigned him, it was given to Mr. Molineux, one of the commissioners of the Admiralty, who engaged in it with no great inclination to favour me; but, however, thought one of the instruments, which, to confirm my own opinion, and to confute Mr. Whiston's, I had exhibited to the Admiralty, so curious or useful, that he surreptitiously copied it on paper, and clandestinely endeavoured to have it imitated by a workman for his own use.

This treatment naturally produced remonstrances and altercations, which, indeed, did not continue long, for Mr. Molineux died soon afterwards; and my proposals were for a time forgotten.

I will not, however, accuse him of designing to condemn me, without a trial; for he demanded a portion of my tables to be tried in a voyage to America, which I then thought I had reasou to refuse him, not yet knowing how

difficult it was to obtain, on any terms, an actual examination.

About this time the theory of Dr. Halley was the chief subject of mathematical conversation; and though I could not but consider him as too much a rival to be appealed to as a judge, yet his reputation determined me to solicit his acquaintance and hazard his opinion. I was introduced to him by Mr. Lowthorp and Dr. Desaguliers, and put my tables into his hands; which, after having had them about twenty days under consideration, he returned in the presence of the learned Mr. Machin, and many other skilful men, with an entreaty that I would publish them speedily; for I should do infinite service to mankind.

It is one of the melancholy pleasures of an old man, to recollect the kindness of friends, whose kindness he shall experience no more. I have now none left to favour my studies; and, therefore, naturally turn my thoughts on those by whom I was favoured in better days: and I hope the vanity of age may be forgiven, when I declare that I can boast among my friends, almost every name of my time that is now remembered: and that, in that great period of mathematical competition, scarce any man failed to appear as my defender, who did not appear as my antagonist.

By these friends I was encouraged to exhibit to the Royal Society, an ocular proof of the reasonableness of my theory by a sphere of iron, on which a small compass moved in various directions, exhibiting no imperfect system of magnetical attraction. The experiment was shown by Mr. Hawkesbee, and the explanation, with which it was accompanied, was read by Dr. Mortimer. I received the thanks of the society; and was solicited to reposit my theory, properly sealed and attested, among their archives, for the information of posterity. I am informed, that this whole transaction is recorded in their minutes.

After this I withdrew from publick notice, and applied myself wholly to the continuation of my experiments, the confirmation of my system, and the completion of my tables, with no other companion than Mr. Gray, who shared

all my studies and: amusements, and used to repay my communications of magnetism, with his discoveries in electricity. Thus I proceeded with incessant diligence; and, perhaps, in the zeal of inquiry, did not sufficiently reflect on the silent encroachments of time, or remember, that no man is in more danger of doing little, than he who flatters himself with abilities to do all. When I was forced out of my retirement, I came loaded with the infirmities of age, to struggle with the difficulties of a narrow fortune; cut off by the blindness of my daughter from the only assistance which I ever had; deprived by time of my patron and friends; a kind of stranger in a new world, where curiosity is now diverted to other objects, and where, having no means of ingratiating my labours, I stand the single votary of an obsolete science, the scoff of puny pupils of puny philosophers.

In this state of dereliction and depression, I have bequeathed to posterity the following table; which, if time shall verify my conjectures, will show that the variation was once known; and that mankind had once within their reach an easy method of discovering the longitude.

I will not, however, engage to maintain, that all my numbers are theoretically and minutely exact: I have not endeavoured at such degrees of accuracy as only distract inquiry without benefiting practice. The quantity of the variation has been settled partly by instruments, and partly by computation: instruments must always partake of the imperfection of the eyes and hands of those that make, and of those that use them: and computation, till it has been rectified by experiment, is always in danger of some omission in the premises, or some errour in the deduction.

It must be observed, in the use of this table, that though I name particular cities, for the sake of exciting attention, yet the tables are adjusted only to longitude and latitude. Thus when I predict that, at Prague, the variation will in the year 1800 be 241 W. I intend to say, that it will be such, if Prague be, as I have placed it, after the best geographers in longitude, 14 30'. E. latitude 50 40′. but that

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