Page:Encyclopædia Britannica, Ninth Edition, v. 17.djvu/266

Rh 254 NAVIGATION cator s charts and globes ; he confesses to not having known upon what rule the meridians were enlarged by Mercator, unless upon such a table as Wright had sent him (see below). Wright s table of meridional parts is here pub lished, also an excellent table of sines, tangents, and secants, the former to seven places of figures, the latter to eight. These are the tables made originally by Regio- montanus, and improved by the Jesuit Clavius. In 1594 the celebrated navigator John Davis published a pamphlet of eighty pages, in black letter, entitled The Seaman s Secrets, in which he proposes to give all that is necessary for seamen^not for scholars on shore. He defines three kinds of sailing : horizontal, paradoxical, and great circle. His horizontal sailing consists of short voyages which may be delineated upon a plain sheet of paper. The paradoxical or cosmographical embraces longi tude, latitude, and distance, the getting together many horizontal courses into one &quot; infallible and true,&quot; i.e., what is now called traverse and Mercator s sailings. His &quot; para doxical course&quot; he describes correctly as a rhumb line which is straight on the chart and a curve on the globe. He points out the errors of the common or plane chart, and promises if spared to publish a &quot;paradoxall chart.&quot; It is not known whether such a chart appeared or not, but he assisted Wright in producing his chart a few years later. Great circle sailing is clearly described by Davis on a globe ; and to render it more practicable he divides a long distance into several short rhumb lines quite cor rectly. His list of instruments necessary to a skilful sea man comprises the sea compass, cross-staff, chart, quadrant, astrolabe, an &quot; instrument magnetical &quot; for finding the variation of the compass, a horizontal plane sphere, a globe, and a paradoxical compass. The first three are sufficient for use at sea, the astrolabe and quadrant being uncertain for sea observations. The importance of knowing the time of the tides when approaching tidal or barred harbours is clearly pointed out, also the mode of ascer taining it by the moon s age. A table of the sun s decli nation is given for noon each day during four years, 1593-97, from the ephemerides of Stadias. The greatest is 23 28. Several courses and distances, with the resulting difference of latitude and departure, are correctly worked out. A specimen log-book provides one line only for each day, but the columns are arranged similarly to those of a modern log. Under the head of remarks after leaving Brazil, we read, &quot; the compass varied 9, the south point westward.&quot; He states that the first meridian passed through St Michael, because there was no variation at that place ; the meridian passed through the magnetic pole as well as the pole of the earth. He makes no mention of Mercator s chart, nor of Cortes or other writers on navigation. Rules are given for finding the latitude by two altitudes of the sun and intermediate azimuth, also by two fixed stars, by the globe. There is a drawing of a quadrant, with a plumb line, for measuring the zenith distance, and one of a curious modification of a cross-staff with which the observer stands with his back to the sun, looking at the horizon through a sight on the end of the staff, while the shadow of the sun, from the top of a movable projection, falls on the sight box. This remained in common use till superseded by Hadley s quadrant. The eighth edition of Davis s work was printed in 1657. Edward Wright, of Caius College, Cambridge, published in 1599 a valuable work entitled Certain Errors in Navi gation Detected and Corrected. One part is a translation from Roderico Zamorano ; there is a chapter from Cortes, and one from Nunez. A year after appeared his chart of the world, upon which both capes and the recent discoveries in the East Indies and America are laid down truthfully and scientifically, as well as his knowledge of their latitude and longitude would admit. Just the northern extremity of Australia is shown. Wright said of himself that he had striven beyond his ability to mend the errors in chart, compass, cross-staff, and declination of sun and stars. He considered that the instruments which had then recently come in use &quot;could hardly be amended,&quot; as they were growing to &quot; perfection,&quot; especially the sea chart and the compass, though he expresses a hope that the latter may be &quot;freed from that rude and gross manner of handling in the making.&quot; He gives a table of magnetic declina tions, and explains its geometrical construction. He states that Medina utterly denied the existence of variation, and attributed it to bad making and bad observations. Wright expresses a hope that a right understanding of the dip of the needle would lead to a knowledge of the latitude, &quot; as the variation did of the longitude.&quot; He gives a table of declinations for every minute of the ecliptic, and another for the use of English mariners during four years the greatest being 23 31 30&quot;. The latitude of London he made 51 32. For these determinations a quadrant over 6 feet in radius was used. He also treats of the &quot; dip &quot; of the sea horizon, refraction, parallax, and the sun s motions. With all this knowledge the earth is still considered as stationary, although Wright alludes to Copernicus, and says that he omitted to allow for parallax. Wright ascertained the declination of thirty-two stars, and made many improvements or additions to the art of navi gation, considering that all the problems could be per formed arithmetically by the doctrine of triangles, without globe or chart. He devised sea rings for taking observa tions, and a sea quadrant to be used by two persons, which is in some respects similar to that by Davis. While deploring the neglected state which navigation had been in, he rejoices that the worshipful society at the Trinity House, under the favour of the king (James I.), had removed &quot;many gross and dangerous enormities.&quot; He joins the brethren of the Trinity House in the desire that a lectureship should be established on navigation, as at Seville and Cadiz ; also that a grand pilot should be appointed, as Sebastian Cabot had been in Spain, who examined pilots (i.e., mates) and navigators. Wright s desire was partially fulfilled in 1845, when an Act of Parliament paved the way for the compulsory qualification of masters and mates of merchant ships ; but such was the opposition by shipowners that it was left voluntary for a few years. England was in this respect more than a century behind Holland. It has been said that Wright accompanied the earl of Cumberland to the Azores in 1589, and that he was allowed 50 a year by the East India Company as lecturer on navigation at Gresham College, Tower Street. The great mark which Wright made in the world was the discovery of a correct and uniform method for dividing the meridional line and making charts which are still called after the name of Mercator. He considered his charts as true as the globe itself ; and so they were for all practical purposes. He commenced by constructing a meridional line, upon the proportion of the secants of the latitude, for every ten minutes of the arc, and in the edition of his work published in 1610 his calculations are for every minute. His calculations were based upon the discovery that the radius bears the same proportion to the secant of the latitude as the difference of longitude does to the meridional difference of latitude a rule strictly correct for small arcs only. One minute is taken as the unit upon the arc and 10,000 as the corresponding secant, 2 becomes 20,000, 3 = 30,000, &c., increasing uniformly till 49 , which is equal to 490,001 ; 1 is 600,012. The secant of 20 is 12,251,192, and for 20 1 it will be 12,251,192 + 10,642, practically the same as that used