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It is well known to seamen and philosophers, of the atmosphere, the effects of different effluvia that after the numerous improvements produced upon metals, the power of heat and cold upon by the extensive commerce of the later ages, the all matter, the changes of gravitation and the great defect in the art of sailing is ignorance of hazard of concussion, I cannot but fear that they longitude, or of the distance to which the ship will supply the world with another instance of has passed eastward or westward from any fruitless ingenuity, though I hope they will not given meridian.

leave upon this country the reproach of unreThat navigation might at length be set free warded diligence. from this uncertainty, the legislative power of I saw therefore nothing on which I could fix this kingdom incited the industry of searchers with probability of success, but the magnetical into nature, by a large reward proposed to him needle, an instrument easily portable, and little who should show a practicable method of find subject to accidental injuries, with which the ing the longitude at sea; and proportionable sailor has had a long acquaintance, which he recompenses to those, who, though they should will willingly study, and can easily consult. not fully attain this great end, might yet make The magnetic needle from the year 1300, such advances and discoveries as should facili- when it is generally supposed to have been first tate the work to those that might succeed them. applied by John Goia, of Amalphi, to the sea

By the splendour of this golden encourage- man's use, seems to have been long thought to ment many eyes were dazzled, which nature point exactly to the north and south by the nanever intended to pry into her secrets. By the vigators of those times; who sailing commonly hope of sudden riches many understandings were on the calm Mediterranean, or making only set on work very little proportioned to their short voyages, had no need of very accurate obstrength, among whom whether mine shall be servations; and who, if they ever transiently numbered, must be left to the candour of pos- observed any deviations from the meridian, terity: for I, among others, laid aside the busi- either ascribed them to some extrinsic and acciness of my profession, to apply myself to the dental cause, or willingly neglected what it was study of the longitude, not indeed in expectation not necessary to understand. of the reward due to a complete discovery; yet But when the discovery of the new world not without hopes, that I might be considered turned the attention of mankind upon the naval as an assistant to some greater genius, and re- sciences, and long courses required greater ceive from the justice of my country the wages niceties of practice, the variation of the needle offered to an honest and not unsuccessful labourer soon became observable, and was recorded in in science.

1500 by Sebastian Cabot, a Portuguesc, who, at Considering the various means by which this the expense of the king of England, discovered important inquiry has been pursued, I found the northern coasts of America. that the observation of the eclipses, either of the As the next century was a time of naval adprimary or secondary planets, being possible but ventures, it might be expected that the variation at certain times, could be of no use to the sailor; once observed, should have been well studied : that the motions of the moon had been long yet it seems to have been little heeded; for it attended, however accurately, without any con- was supposed to be constant and always the sequence; that other astronomical observations same in the same place, till in 1625 Gellibrand were difficult and uncertain with every advan- noted its changes, and published his observatage of situation, instruments, and knowledge: tions. and were therefore utterly impracticable to the From this time the philosophical world had a sailor, tost upon the water, ill provided with new subject of speculation, and the students of instruments, and not very skilful in their ap- magnetism employed their researches upon the plication.

gradual changes of the needle's direction, or the The hope of an accurate clock or time-keeper variations of the variation, which have hitherto is more specious. But when I began these stu- appeared so desultory and capricious, as to dies, no movements had yet been made that elude all the schemes which the most fanciful of were not evidently inaccurate and uncertain : the philosophical dreamers could devise for its and even of the mechanical labours which I now explication. Any system that could have united hear so loudly celebrated, when I consider the these tormenting diversities, they seem inchined obstruction of movements by friction, the waste to have received, and would have contentedly of their parts by attrition, the various pressure numbered the revolutions of a central magnet,

with very little concern about its existence, * An Account of an attempt to ascertain the Longitude could they have assigned it any motion, or vicisAt Sea, by an exact Theory of the Variation of the Mag: situde of motions, which could have correspondremarkable cities in Europe, from the year 1660 to 1960. ed with the changes of the needle. By Zachariah Williams.

Yet upon this secret property of magnetism I

yentured to build my hopes of ascertaining the Yet even this may be borne far better than the longitude at sea. I found it undeniably certain petulance of boys whom I have seen shoot up that the needle varies its direction in a course into philosophers by experiments which I have eastward or westward between any assignable long since made and neglected, and by improveparallels of latitude: and supposing nature to ments which I have so long transferred into be in this as in all other operations uniform and my ordinary practice, that I cannot remember consistent, I doubted not but the variation pro- when I was without them. ceeded in some established method, though per When Sir Isaac Newton had declined the office haps too abstruse and complicated for human assigned him, it was given to Mr. Molineux, one comprehension.

of the commissioners of the Admiraliy, who enThis difficulty however was to be encoun- gaged in it with no great inclination to favour tered; and by close and steady perseverance of me; but however thought that one of the instruattention I at last subdued, or thought myseltments, which, to confirm my own opinion, and to have subdued, it; having formed a regular to confute Mr. Whiston's, I had exhibited to the system in which all the phenomena seemed to Admiralty, so curious or useful, that he surrepti

. be reconciled; and being able from the varia- tiously copied it on paper, and clandestinely tion in places where it is known to trace it to endeavoured to have it imitated by a workman for those where it is unknown; or from the past to his own use. predict the future: and consequently knowing This treatment naturally produced remon. the latitude and variation, to assign the true strances and altercations, which indeed did not longitude of any place.

continue long, for Mr. Molineux died soon afierWith this system I came to London, where wards; and my proposals were for a time for having laid my proposals before a number of gotten. ingenious gentlemen, it was agreed that during I will not however accuse him of designing to the time required to the completion of my condemn me, without a trial; for he demanded experiments, I should be supported by a joint a portion of my tables to be tried in a voyage subscription to be repaid out of the reward, to to America, which I then thought I had reason which they concluded me entitled. Among the lo refuse him, not yet knowing how difficult it subscribers was Mr. Rowley, the memorable was to obtain, on any terms, an actual examiconstructor of the orrery; and among my fa- nation. vourers was the Lord Piesley, a title not unknown About this time the theory of Dr. Halley was among magnetical philosophers. I frequently the chief subject of mathematical conversation; showed upon a globe of brass, experiments by and though I could not but consider him as too which my system was confirmed, at the house much a rival to be appealed to as a judge, yet of Mr. Rowley, where the learned and curious his reputation determined me to solicit his acof that time generally assembled.

quaintance and hazard his opinion. I was At this time great expectations were raised by introduced to him by Mr. Lowthorp and Dr. Mr. Whiston, of ascertaining the longitude by Desaguliers, and put my tables into his hands; the inclination of the needle, which he supposed which, after having had them about twenty days to increase or diminish regularly. With this under consideration, he returned in the presence learned man I had many conferences, in which of the learned Mr. Machin, and many other I endeavored to evince what he has at last con- skilful men, with an entreaty that I would publish fessed in the narrative of his life, the uncertainty them speedily; for I should do infinite service to and inefficacy of his method.

mankind. About the year 1729, my subscribers explained It is one of the melancholy pleasures of an my pretensions to the Lords of the Adiniralty, old man, to recollect the kindness of friends, and the Lord Torrington declared my claim just whose kindness he shall experience no more. to the reward assigned in the last clause of the I have now none left to favour my studies; and act to those who should make discoveries con- therefore naturally turn my thoughts on those ducive to the perfection of the art of sailing. by whom I was favoured in better days; and I This he pressed with so much warmth, that the hope the vanity of age may be forgiven, when commissioners agreed to lay my tables before I declare that I can boast among my friends, Sir Isaac Newton, who excused himself, by almost every name of my time that is now rereason of his age, from a regular examination : membered: and that in that great period of but when he was informed that I held the varia- mathematical competition scarce any man failed tion at London to be sull increasing, which he to appear as my defender, who did not appear as and the other philosophers, his pupils, thought my antagonist. to be then stationary, and on the point of re By these friends I was encouraged to exhibit gression, he declared that he believed my system to the Royal Society, an ocular proof of the visionary. I did not much murmur to be for a reasonableness of my theory, by a sphere of time overborne by that mighty name, even when iron, on which a small compass moved in variI believed that the name only was against me: ous directions, exhibited no imperfect sysiem of and I have lived till I am able to produce, in my magnetical attraction. The experiment was favour, the testimony of time, the inflexible shown by Mr. Hawkesbee, and the explanation enemy of false hypotheses; the only testimony with which it was accompanied, was read by which it becomes human understanding to op- Dr. Mortimer. I received the thanks of the pose to the authority of Newton.

society; and was solicited to reposit my theory My notions have indeed been since treated properly sealed and attested among their arwith equal superciliousness by those who have chives, for the information of posterity. I am not the same title to confidence of decision; men informed, that this whole transaction is recorded who, though perhaps very learned in their own in their minutes. studies, have had little acquaintance with mine. After this I withdrew from public notice,

and applied myself wholly to the continuation titude 50 40"; but that this is its true situation, of my experiments, the confirmation of my I cannot be certain. The latitude of many places system, and the completion of my tables, with is unknown, and the longitude is known of very no other companion than Mr. Gray, who shared few; and even those who are unacquainted with all my studies and amusements, and used to re- science, will be convinced that it is not easily to pay my communications of magnetism, with his be found, when they are told how many degrees discoveries in electricity. Thus I proceeded Dr. Halley, and the French mathematicians

, with incessant diligence; and perhaps the place the Cape of Good Hope distant from each zeal of inquiry did not sufficiently reflect on other. the silent encroachments of time, or remember, Those who would pursue this inquiry with that no man is in more danger of doing little, philosophical nicety, must likewise procure betthan he who flatters himself with abilities to do ier necdles than those commonly in use. The all. When I was forced out of my retirement, needle, which after long experience I recomI came loaded with the infirmities of age, to mend to mariners, must be of pure steel, the struggle with the difficulties of a narrow fortune, spines and the cap of one piece, the whole length cut off by the blindness of my daughter from three inches, each spine containing four grains the only assistance which I ever had; deprived and a half of steel, and the cap thirteen grains by time of my patron and friends, a kind of and a half. stranger in a new world, where curiosity is now The common needles are so ill formed, or so diverted to other objects, and where, having no unskilfully suspended, that they are affected by means of ingratiating my labours, I stand the many causes besides magnetism: and among single votary of an obsolete science, the scoff of other inconveniences have given occasion to the puny pupils of puny philosophers.

idle dream of a horary variation. In this state of dereliction and depression, I I doubt not but particular places may produce have bequeathed to posterity the following table; exceptions to my system. There may be, in which, if time shall verify my conjectures, will many parts of the earth, bodies which obstruct show that the variation was once known; and or intercept the general influence of magnetism; that mankind had once within their reach an easy but those interruptions do not infringe the the method of discovering the longitude.

ory. It is allowed, that water will run down I will not however engage to maintain, that a declivity, though sometimes a strong wind all my numbers are theoretically and minutely may force it upwards. It is granted, that the exact; I have not endeavoured at such degrees sun gives light at noon, though in certain conof accuracy as only distract inquiry without junctions it may suffer an eclipse. benefiting practice. The quantity of the varia These causes, whatever they are, that intertion has been settled partly by instruments, and rupt the course of the magnetical powers, are partly by computation ; instruments must al- least likely to be found in the great ocean, when ways partake of the imperfection of the eyes and the earth, with all its minerals, is secluded from hands of those that make, and of those that use the compass by the vast body of uniform water. them; and computation, till it has been recti- So that this method of finding the longitude

, fied by experiment is always in danger of some with a happy contrariety to all others, is most omission in the premises, or some error in the easy and practicable at sea. deduction.

This method, therefore, I recommend to the It must be observed, in the use of this table, study and prosecution of the sailor and philothat though I name particular cities for the sake sopher; and the appendant specimen I exhibit of exciting attention, yet the tables are adjusted to the candid examination of the maritime naonly to longitude and latitude. Thus when I tions, as a specimen of a general table, showing predict that at Prague, the variation will in the the variation at all times and places for the whole year 1800 be 24 W. I intend to say, that it will revolution of the magnetic poles, which I have be such if Prague be, as I have placed it, after long ago begun, and, with just encouragement, the best geographers, in longitude 14 30 E. la-should have long ago completed.







may be demonstrated to excel in strength the Sir,

Dec. 1st, 1759.

elliptical arch, which approaching nearer to a

straight line, must be constructed with stones The Plans which have been offered by differ- whose diminution downwards is very little, and ent architects, of different reputation and abili- of which the pressure is almost perpendicular. ties, for the construction of the Bridge intended It has yet been sometimes asserted by hardy to be built at Blackfriars, are, by the rejection ignorance, that the elliptical arch is stronger than of the greater part, now reduced to a small num- the semicircular; or in other terms, that any ber; in which small number, three are supposed mass is more strongly supported the less it rests to be much superior to the rest ; so that only upon the supporters. If the elliptical arch be three architects are now properly competitors for equally strong with the semicircular, that is, if an the honour of this great employment; by two of arch, by approaching to a straight line, loses whom are proposed semicircular, and by the other none of its stability, it will follow, that all arcuelliptical arches.

ation is useless, and that the bridge may at last The question is, therefore, whether an ellipti- without any inconvenience, consist of stone laid cal or semicircular arch is to be preferred ? in straight lines from pillar to pillar. But if a

The first excellence of a bridge built for com- straight line will bear no weight, which is evimerce over a large river, is strength; for a bridge dent at the first view, it is plain likewise, that an which cannot stand, however beautiful, will boast ellipsis will bear very little ; and that as the arch its beauty but a little while ; the stronger arch is is more curved, its strength is increased. therefore to be preferred, and much more to be Having thus evinced the superior strength of preferred, if with greater strength it has greater the semicircular arch, we have sufficiently proved, beauty.

that it ought to be preferred; but to leave no obThose who are acquainted with the mathe-jection unprevented, we think it proper likewise matical principles of architecture, are not many; to observe, that the elliptical arch must always and yet fewer are they who will, upon any single appear to want elevation and dignity; and that occasion, endure any laborious stretch of thought, if beauty be to be determined by suffrages, the or harass their minds with unaccustomed inves- elliptical arch will have little to boast, since the tigations. We shall therefore attempt to show only bridge of that kind has now stood two hunthe weakness of the elliptical arch, by arguments dred years without imitation. which appear simply to common reason, and If in opposition to these arguments, and in dewhich will yet stand the test of geometrical ex- fiance at once of right reason and general auamination.

thority, the elliptical arch should at last be chosen, All arches have a certain degree of weakness. what will the world believe, than that some other No hollow building can be equally strong with a motive than reason influenced the determination ? solid mass, of which every upper part presses And some degree of partiality cannot but be susperpendicularly upon the lower. Any weight pected by him, who has been told that one of the laid upon the top of an arch, has a tendency to judges appointed to decide this question, is Mr. force that top into the vacuity below; and the M-1-r, who having by ignorance, or thoughtarch thus loaded on the top, stands nly because lessness, already preferred the elliptical arch, will the stones that form it, being wider in the upper probably think himself obliged to maintain his than in the lower parts, that part that fills a own judgment, though his opinion will avail but wider space cannot fall through a space less little with the public, when it is known that Mr. wide; but the force which laid upon a flat would s-ps-n declares it to be false. press directly downwards, is dispersed each way He that in the list of the committee chosen for in a lateral direction, as the parts of a beam are the superintendency of the bridge, reads many pushed out to the right and left by a wedge driven of the most illustrious names of this great city, between them. In proportion as the stones are will hope that the greater number will have more wider at the top than at the bottom, they can reverence for the opinion of posterity, than to less easily be forced downwards, and as their disgrace themselves, and the metropolis of the lateral surfaces tend more from the centre to each kingdom, in compliance with any man, who, inside, to so much more is the pressure directed stead of voting, aspires to dictate, perhaps with. laterally towards the piers, and so much less per- out any claim to such superiority, either by greatpendicularly towards the vacuity.

ness of birth, dignity of employment, extent of Upon this plain principle the semicircular arch | knowledge, or largeness of fortune.



continue to obtain whatever he deserves; but let

it not be presumed that a prize granted at Rome, SIR,

Dec. 8th, 1759.

implies an irresistible degree of skill. The comIn questions of general concern, there is no petition is only between boys, and the prize given law of government or rule of decency, that for to excite laudable industry, not to reward conbids open examination and public discussion. I summate excellence. Nor will the suffrage of shall therefore not betray, by a mean apology, the Romans much advance any name ainong that right which no man has power, and, I sup- those who know, what no man of science will pose, no wise man has desired to refuse me; but deny, that architecture has for some time degeshall consider the Letter published by you last nerated at Rome to the lowest state, and that the Friday, in defence of Mr. M—'s* design for a Pantheon is now deformed by petty decorations. new bridge.

I am, Sir, yours, &c, Mr. M.— proposes elliptical arches. It has been objected that elliptical arches are weak: and therefore improper for a bridge of commerce, in a country where greater weights are ordinarily carried by land than perhaps in any other part of the world. That there is an elliptical


Dec. 15th, 1759. bridge at Florence is allowed, but the objectors

It is the common fate of erroneous positions, maintain, that its stability is so much doubted, that they are betrayed by defence, and obscured that carls are not permitted to pass over it. by explanation; that their authors deviate from

To this no answer is made, but that it was the main question into incidental disquisitions, built for coaches; and if it had been built for and raise a mist where they should let in light. earts, it would have been made stronger : thus Of all these concomitants of errors, the Letter all the controvertists agree, that the bridge is too of Dec. 10th, in favour of elliptical arches, has weak for carts; and it is of little importance, afforded examples. A great part of it is spent whether carts are prohibited because the bridge upon digressions. The writer allows, that the is wcak, or whether the architect, knowing that first excellence of a bridge is undoubtedly strength: carts were prohibited, voluntarily constructed a but this concession affords him an opportunity of weak bridge. The instability of the elliptical telling us, that strength, or provision against dearch has been sufficiently proved by argument, cay, has its limits; and of mentioning the Monuand Ammanuti's attempi has proved it by ex ment and Cupola, without any advance towards ample.

evidence or argument. The iron rail, whether gilt or varnished, ap The first excellence of a bridge is now allowed pears to me unworthy of debate. I suppose to be strength; and it has been asserted, that a every judicious eye will discern it to be minute semi-ellipsis has less strength than a semicircle. and trifling, equally unfit to make a part of a To this he first answers, that granting this posigreat design, whatever be its colour. I shall only tion for a moment, the semi-ellipsis may yet have observe how little the writer understands his own strength sufficient for the purpose of commerce. positions, when he recommends it to be cast in This grant, which was made but for a moment, whole pieces from pier to pier. That iron forged needed not to have been made at all; for before is stronger than iron cast, every smith can in. he concludes his Letter, he undertakes to prove form him; and if it be cast in large pieces, the that the elliptical arch must in all respects be supefracture of a single bar must be repaired by a rior in strength to the semicircle. For this daring new piece.

assertion he made way by the intermediate paraThe abrupt rise which is feared from firm cir- graphs ; in which he observes, that the convexity cular arches, may be easily prevented, by a little of a semi-ellipsis may be increased at will to any deextension of the abutment at each end, which gree that strength may require: which is, that an will take away the objection, and add almost elliptical arch may be made less elliptical, to be nothing to the expense.

made less weak ; or that an arch, which by its The whole of the argument in favour of Mr. elliptical form is superior in strength to the semiM-, is only that there is an elliptical bridge circle, may become almost as strong as a semiat Florence, and an iron balustrade at Rome; circle, by being made almost semicircular. the bridge is owned to be weak, and the iron That the longer diameter of an ellipsis may be balustrade we consider as mean; and are loth shortened, till it shall differ little from a circle, is that our own country should unite two follies in indisputably true; but why should the writer a public work.

forget the semicircle differs as little from such an The architrave of Perault, which has been ellipsis? It seems that the difference, whether pompously produced, bears nothing but its en small or great, is to the advantage of the semitablature; and is so far from owing its support circle; for he does not promise that the elliptical to the artful section of the stone, that it is held arch, with all the convexity that his imagination together by cramps of iron; to which I am afraid can confer, will stand without cramps of iron, and Mr. M - must have recourse, if he persists in melted lead, and large stones, and a very thick arch; his ellipsis, or, to use the words of his vindicator, assistances which the semicircle does not require, forms his arch of four segments of circles drawn and which can be yet less required by a semifrom four different centres.

ellipsis, which is in all respects superior in That Mr. M obtained the prize of the

strength. architecture at Rome, a few months ago, is will Of a man who loves opposition so well, as to ingly confessed; nor do his opponents doubt be thus at variance with himself, little doubt can that he obtained it by deserving it. May he be made of his contrariety to others ; nor do I

think myself entitled to complain of disregard * Mr. Myine.

from one, with whom the performances of anti

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