The errors arising from the use ofthe plane chart, ac cording to the principles on which it had hitherto been constructed, (which in fact were none other than the ex ploded opinion that the surface of the carth was an ex tended plane) were too obvious long to escape the no tice of intelligent navigators; and we accordingly find, that about the beginning of the 16th century, some un skilful attempts were made to correct the ship's place on the chart, by means of a kind of equation table, which showed, upon an alteration of one degree of latitude, what distance had been run on each rhumb, together with the corresponding departure from the meridian. In the year 1537, the illustrious Nunez, or Nonius, a Portuguese mathematician, to whom the world is indebt ed for a very ingenious method of obtaining the subdivi sions of an arch. without actually dividing it, published a dissertation, De dfrte et ratione .A'avigandi, in which Ile pointed out, very distinctly and accurately, the cause of these errots, and explained, among a variety of other useful problems, a method of finding the latitude by two altitudes of the sun, and the azimuthal angle contained by the coll.( sponding zenith distances He also remark ed, that the oblique rhumbs, cutting the meridians at the same angle, are in reality spiral lines, which by each revolution round the glohe. approach nearer and nearer to the pole ; and that the eoul se to be observed, in sail ing from one place to another, so as to reach it by the shortest distance, ought to be the arch of a great circle of the terrestrial sphere. These views were afterwards taken up by Dr. Halley, who di duced from them a sim ple and ingemous method of calculating the enlarged portions of the meridian, adapt, d each latitiole. and Itnenan at present by the appell..tion of meridional parts.
Of the Log, that useful ancl necessary appendage to the mariner's compass, we find no mention in any of the treatises on navigation published before 1577, when it was described, probably for the first time, by Air. Wil liam Bourne, in a work entitled, a Regiment for the Sec. The inventor of this simple contrivance for determining, the rate of a ship's sailing is unknown ; but the device itself is noticed by every subsequent writer on naviga tion. Other methods have been suggested for the same purpose, but they have generally proved either imprac ticable at sea, or too complicated to be brought into fa miliar use.
The period was now at hand, when the plane chart, the errors of which, on account ot the sphericity of the earth, had become too manifest to admit or its being used any longer for nautical purposes, was about to re ceive a most important improvement, by which the me ridians were still to be allowed to retain their parallelism, while the course and distance were to be laid down with equal simplicity as formerly, and the difference of longi tude was to be indicated with a precision not hitherto ob tained in any latitude. The means by which this desira ble object was to be attained, were sought for by some augmentation of the distance of the parallels of latitude, from the equator to the poles, so as to compensate for the convergency of the meridians on the globe; but Gerard Alereator, a geographer of the 'Low Countries, by whom the method was first recommended, seems to have been unable to point out the precise law according to svhich it may be carried into effect. This was reserved
for our countryman Edward Wright, who is generally allowed to have been the first person by whom the pro jection, which now bears the name of Alereator, WaS reduced to precise and accurate principles. Ile de monstrated that, if the meridian be supposed to be divided into small portions, the portions must suffer a gradual enlargement from the equator towards the poles, in a ratio corresponding, at each point, to the secant of the latitude. Wright explained the reason of this division, and its use in navigation, in a work which lie published in 1599. In a second edition of his book, which came out in 1610, he added several improvements of consider able value, and recommended the measurement of a por tion of the terrestrial meridian, as the best means of procuring an accurate basis for linear mensurations.—a standard of reference which has since been adopted in France, as the ground work of the national weights and measures. This edition of Wright's treatise contains a table of meridional parts, computed on the principles he had proposed for enlarging the meridian, and adapted to each minute of the quacIrant,—a table of great value at that time, hut which the ignorance and prejudices or the age prevented from being at first duly. appreciated In the same ivork, the learned atehor describes an inStEll ment which he called the Sea.Rings, by which do. alti tude of the sun, the hour of toe dai, and the Tneridian or the compass, might all he detei mined by inspection, in situations where the latitude NVaS known. He also gave, what was then much wanted, a table of the declination of the sun for four consecutive years, and ai,othcr ()I' the places of a considerable number of the fixed stars, from observations of his own, made with a six-foot quadrant. His reputation as a mathematician having procured his appointment to the office of preceptor in geometry to Prince Henn of England, a y outh of the most promising hopes, but who was prematurely cut off before he reached his eighteenth year, lie contrived, for the instruction of his royal pupil, a large inechanical sphere, with which he exhibited all the celestial movements, and more espe cially those of the sun and moon, in so much that the eclipics of these luminaties could be predicted by means of i; for a period of 17,100 years. A few years before his death, which took place in 1618 or 1620, his attention WaS directed to the calculation of logarithms, a species of numerical quantities first made known to the world by Lord Napier in 1614, and of the most oxtensive use in navigation and astronomy, as well as in some of the higher branches of the mathematics. See LOGARITHMS.