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AN ACCOUNT OF AN ATTEMPT TO ASCERTAIN THE LONGITUDE[1].

FIRST PRINTED IN THE YEAR 1755.

It is well known to seamen and philosophers, that, after the numerous improvements produced by the extensive commerce of the later ages, the great defect in the art of sailing is ignorance of longitude, or of the distance to which the ship has passed eastward or westward, from any given meridian.

That navigation might be at length set free from this uncertainty, the legislative power of this kingdom incited the industry of searchers into nature, by a large reward proposed to him who should show a practicable method of finding the longitude at sea; and proportionable recompenses to those, who, though they should not fully attain this great end, might yet make such advances and discoveries as should facilitate the work to those that might succeed them.

By the splendour of this golden encouragement many eyes were dazzled, which nature never intended to pry into her secrets. By the hope of sudden riches many understandings were set on work very little proportioned to their strength, among whom whether mine shall be numbered, must be left to the candour of posterity: for I, among others, laid aside the business of my profession, to apply myself to the study of the longitude, not, indeed, in expectation of the reward due to a complete discovery; yet, not without hopes that I might be considered as an assistant to some greater genius, and receive from the justice of my country the wages offered to an honest and not unsuccessful labourer in science.

Considering the various means by which this important inquiry has been pursued, I found that the observation of the eclipses, either of the primary or secondary planets, being possible but at certain times, could be of no use to the sailor; that the motions of the moon had been long attended, however accurately, without any consequence; that other astronomical observations were difficult and uncertain, with every advantage of situation, instruments, and knowledge; and were, therefore, utterly impracticable to the sailor, tost upon the water, ill provided with instruments, and not very skilful in their application. The hope of an accurate clock or time-keeper is more specious. But when I began these studies, no movements had yet been made that were not evidently unaccurate and uncertain: and even of the mechanical labours which I now hear so loudly celebrated, when I consider the obstruction of movements by friction, the waste of their parts by attrition, the various pressure of the atmosphere, the effects of different effluvia upon metals, the power of heat and cold upon all matter, the changes of gravitation and the hazard of concussion, I cannot but fear that they will supply the world with another instance of fruitless ingenuity, though, I hope, they will not leave upon this country the reproach of unrewarded diligence. I saw, therefore, nothing on which I could fix with probability of success, but the magnetical needle, an instrument easily portable, and little subject to accidental injuries, with which the sailor has had a long acquaintance, which he will willingly study, and can easily consult. The magnetick needle, from the year 1300, when it is generally supposed to have been first applied by Flavio Gioia, of Amalfi, to the seaman’s use, seems to have been long thought to point exactly to the north and south by the navigators of those times; who sailing commonly on the calm Mediterranean, or making only short voyages, 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.