Page:Encyclopædia Britannica, Ninth Edition, v. 17.djvu/265

Rh NAVIGATION 253 There is a table of difference of latitude and departure in proportion to the tangent of the course. The third part of Martin Cortes s work is upon charts ; he laments that wise men do not produce some that are correct, and that pilots and mariners will use plane charts which are not true. In the Mediterranean and Channel of Flanders the want of good charts is (he says) less inconvenient, as there they do not navigate by the altitude of the pole. As some subsequent writers have attributed to Cortes the credit of first thinking of the enlargement of the degrees of latitude on Mercator s principle, his precise words may be cited. In making a chart, it is recom mended to choose a well-known place near the centre of the intended chart, such as Cape St Vincent, which call 37, &quot; and from thence towards tho Arctic pole the degrees increase ; and from thence to the equinoctial line they go on decreasing, and from the line to the Antarctic pole increasing.&quot; l It would appear at first sight that the degrees increased in size as well as being called by a higher number, but a specimen chart in the book does not justify that conclusion. It is from 34 to 40, and the divisions are unequal, but evidently by accident, as the highest and lowest are the largest. He states that the Spanish scale was formed by counting the Great Berling as 3 from Cape St Vincent (it is under 2^). Twenty English leagues are equal to 17^ Spanish or 25 French, and to 1 of latitude. Cortes was evidently at a loss to know the size of a degree, and consequently the circumference of the globe. The degrees of longitude are not laid down, but for a first meridian we are told to draw a vertical line &quot; through the Azores, or nearer Spain, where the chart is less occupied.&quot; It is impossible under such circumstances to understand or check the longitudes assigned to places at that period. Martin Cortes s work was held in high estimation in England for many years, and appeared in several transla tions. One by Richard Eden in 1609 gives an improved table of the sun s declination from 1609 to 1625 the greatest declination being 23 30. The declinations of the principal stars and the times of their passing the meridian, and other improved tables, are given, with a very poor traverse table for eight points. The cross-staff, he said, was in most common use; but he recommends Wright s sea quadrant. William Cuningham published in 1559 a book called his Astronomical Glass, in which he teaches the making of charts by a central meridional line of latitude in equal parts, with other meridians on each side, distant at top and bottom in proportion to the departure at the highest and lowest latitude, for which purpose a table of departures is given very correctly to the third place of sexagesimals. The chart would be excellent were it not that the parallels are drawn straight instead of being curved. In another example, which is one-fourth of the sphere, the meridians and parallels are all curved ; it would be good were it not that the former are too long. The hemisphere is also shown upon a projection approaching the stereographic ; but the eighteen meridians cut the equator at equal distances, instead of being smaller towards the primitive. He gives the drawing of an instrument like an astrolabe placed horizontally, divided into 32 points and 360 degrees, and carrying a small magnetic needle to be used as a prismatic compass, or even as a theodolite (fig. 4). A sketch is given of Ptolemy observing the sun with a primitive instrument, likely from its great size to give good results after being correctly fixed, except for the amount of error caused by the shrinkage or expansion of the parts. Gerhard Mercator s great improvements in charts have 1 &quot; Y d alli hazia el polo artico los grades se axigmentan: y d alli a la linea equinoctial van diminuyendo : y de la linea al polo antartico augmentando.&quot; vanes and pinules at the side ; CD is a scale of chords which is lifted up to touch the pointer and indicate the angle from 90 near C to zero near D. By the size of the observer in the drawing the standard ST was 10 or 12 feet in length. been noticed in the article MAP, where a sketch is given of his map of the world, of 1569 (vol. xv. p. 521). From facsimiles of his early charts in Jomard, Le.s Monuments de la Geographic, the following measurements have been made. A general chart of 1569, of North America, 25 to 79, is 2 feet long north and south, and 20 inches wide. Another of the same date, from the equator to 60 south s ,/ is 15 8 inches. The charts agree with each other, a slight allowance being made for remeasuring. As com pared with Dr Inman s table of meridional parts, the spaces between the parallels are all too small. Between and 10 the error is 8 ; at 20 it is 5 ; at 30, 16 ; at 40, 39 ; at 50, 61 ; at 60, 104 ; at 70, 158 ; and at 79, 182, that is, over three degrees upon the whole chart. As the measures are always less than the truth it FlQ 4 __ STis the standard gR is possible that Mercator was the radius bar and pointer, with afraid to give the whole. In a chart of Sicily by Romoldus Mercator in 1589, on which two equal degrees of latitude, 36 to 38, subtend 9^ inches, the degree of longitude is quite correct at one-fourth from the top ; the lower part is a mile too large. One of the north of Scotland, published in 1595, by Romoldus, measures 10| inches from 58 20 to 61 ; the divisions are quite equal and the lines parallel ; it is correct at the centre only. A map of Norway, 1595, lat. 60 to 70 = 9^ inches, has the parallels curved and equidistant, the meridians straight converging lines; the spaces be tween the meridians at 60 and 70 are quite correct. Norman s discovery of the dip (1576) has been spoken of at vol. xv. p. 221. He mentions and condemns the practice of each country having compass cards set to their variation, and sailors using them indiscriminately in any part of the world. In 1581 Michael Coignet of Antwerp published sea charts, and also a small treatise in French, wherein he exposes the errors of Medina. He was probably the first who said that rhumb lines form spirals round the pole. He published also tables of declination, and observed the gradual decrease in the obliquity of the ecliptic. He described a cross-staff with three transverse pieces, which was then in common use at sea. Coignet died in 1623. The Dutch published charts made up as atlases as early as 1584, with a treatise on navigation as an introduction. In 1585 Roderico Zamorano, who was then the lecturer at the naval college at Seville, published a concise and clearly-written compendium of navigation; he follows Cortes in the desire to obtain better charts. Andres Garcia de Cespedes, the successor of Zamorano at Seville, published a treatise on navigation at Madrid in 1606. In 1592 Petrus Plancius published his universal map, con taining the discoveries in the East and West Indies and towards the north pole. It possessed no particular merit ; the degrees of latitude are equal, but the distances between the meridians are noted. He made London appear in 51 32 N. (which is near enough) and long. 22, by which his first meridian should have been more than 3 east of St Michael. In 1594 Blundcville published a description of Mer-