mr> 
NAVIGATION. 
the art; for Medina, in his dedication to Philip prince of 
Spain, laments that multitudes oflhips daily perifhed at fea, 
becaufe there were neither teachers of the art nor hooks 
by which it might be learned ; and Cortes, in his dedica¬ 
tion, boafts to the emperor, that he was the firlt who had 
reduced navigation into a compendium, valuing himfelf 
much on what he had performed. Medina defended the 
plane chart; but he was oppofed by Cortes, who Ihowed 
its errors; and endeavoured to account for the variation 
of the compafs, by fuppofmg the needle to be influenced 
by a magnetic pole (which he called the point aUradive) 
different from that of the world; which notion has been 
farther profecuted by others. Medina’s book was foon 
tranflated into Italian, French, and Flemifh; and ferved 
for a long time as a guide to foreign navigators. How¬ 
ever, Cortes was the favourite author of the Englifli na¬ 
tion, and was tranflated in 1561 ; while Medina’s work 
was entirely neglected, though tranflated alfo within a 
fhort time of the other. At that time the fyftem of navi¬ 
gation confided of the fo'lowing particulars, and others 
ffmilar: An account of the Ptolemaic hypothefis, and 
the circles of the (phere ; of the roundnefs of the earth, 
the longitudes, latitudes, climates, &c. and eclipfes of 
the luminaries ; a kalendar ; the method of finding the 
prime, epaft, moon’s age, and tides ; a defcription of the 
compafs, an account of its variation, for the difcovering 
of which Cortes laid an inftrument might ealily be con¬ 
trived ; tables of the fun’s declination for four years, in 
order to find the latitude from his meridian altitude ; 
direftions to find the lame by certain ftars ; of the courfe 
of the fun and moon; the length of the days; of time 
and its divifions; the method of finding the hour of the 
day and night; and iaftly, a defcription of the lea-chart, 
on which to difcover where the (hip is, they made ufe of a 
finall table, that Ihowed, upon an alteration of one degree 
of the latitude, how many leagues were run in each 
rhumb, together with the departure from the meridian. 
JBefides, fome inftruments were defcribed, efpecially by 
Cortes ; Inch as one to find the place and declination of 
the fun, with the days, and place of the moon; certain 
dials, the aftrolabe, and crofs-ffaff; witli a complex ma¬ 
chine to difcover the hour and latitude at once. 
About the fame time were made propofals for finding 
the longitude by obfervations of the moon. In 1530, 
Gemma Frifius advifed the keeping of the time by means 
of fmall clocks or watches, then, as he fays, newly in¬ 
vented. He alfo contrived a new fort of crols-ftaff, and 
and an inftrument called the nautical quadrant; which 
3 aft was much praifed by William Cunningham, in his 
“ Aftronomical Glafs,” printed in the year 1559. 
In 1537 Pedro Nunez, or Nonius, publifhed a book in 
the Portuguefe language, to explain a difficulty in navi¬ 
gation propoled to him by the commander Don Martin 
Alphonfo de Sufa. In this he expofes the errors of the 
plane chart, and likewife gives the folution of feveral 
curious aftronomical problems; amongft which is that of 
determining the latitude from two obfervations of the 
fun’s altitude, and the intermediate azimuth. He ob- 
ferved, that, though the rhumbs are fpiral lines, yet the 
direft courfe of a fliip will always be in the arch of a great 
circle, whereby the angle with the meridians will conti¬ 
nually change : all that the fteerfrnan can here do for the 
preferving of the original rhumb is to correfit thefe devi¬ 
ations as foon as they appear fenfible. But thus the fhip 
will in reality defcribe a courfe without the rhumb-line 
intended ; and therefore his calculations for ailigning the 
latitude, where any rhumb-line erodes the feveral meri¬ 
dians, will be in fome meafure erroneous. He invented a 
method of dividing a quadrant by means of concentric 
circles, which, after being much improved by Dr. Halley, 
is ufed at prefent, and is called a nonius. 
In 1577, Mr. William Bourne publifhed a treatife, in 
which, by confidering the irregularities in the moon’s 
motion, he fhows the errors of the failors in finding her 
age by the epaff, and alfo in determining the hour from 
obferving on what point of the compafs the fun and moon 
appeared. He advifes, in failing towards the high lati¬ 
tudes, to keep the reckoning by the globe, as there the 
plane chart is molt erroneous. He defpairs of our ever 
being able to find the longitude, unlefs the variation of 
the compafs fhould be occafioned by fome l'uch attraftive 
point as Cortes had imagined ; of which, however, he 
doubts: but, as he had fliown how to find the variation 
at all times, he advifes to keep an account of the obferva¬ 
tions, as ufeful for finding the place of the fliip ; which 
advice was profecuted at large by Simon Stevin, in a 
treatife publifhed at Leyden in 1599; the fubftance of 
which was the fame year printed at London in Englifli by 
Mr. Edward Wright, entitled The Haven-finding Art. 
In this ancient traft alfo is defcribed the way by which 
our failors eftimafe the rate of a fhip in her courfe, by an 
inftrument called the /os;. This was fo named from the 
piece of wood, or log, that floats in the water while the time 
is reckoned during which the line that is faftened to it is 
veering out. See Log, vol. xii. 
In 1581, Michael Coignet, a native of Antwerp, pub¬ 
lifhed a treatife, in which he animadverted on Medina. 
In this he (flowed, that, as the rhumbs are fpirals, making 
endlefs revolutions aboutthe poles, numerous errors mult 
arife from their being reprefented by ftraight lines on the 
fea charts; but, though he hoped to find, a remedy for 
thefe errors, he was of opinion that the propofals of No¬ 
nius were fcarcely practicable, and therefore in a great 
meafure ufelefs. In treating of the fun’s declination, he 
took notice of the gradual decreafe in the obliquity of 
the ecliptic; he alfo defcribed the crofs-ftaff with three 
tranfverfe pieces, as it is at prefent made, and which he 
owned to have been then in common ufe among the failors. 
He iikewife gave fome inftruments of his own invention ; 
but all of them are now laid afide, excepting perhaps his 
noCturnal. He conftruCted a fea-table to be ufed by fuch 
as failed beyond the fixtieth degree of latitude; and at 
the end of the book is delivered a method of failing on a 
parallel of latitude by means of a ring-dial and a twenty- 
four-hour glafs. The fame year the dif'eovery of the 
dipping-needle was made by Mr. Robert Norman. In his 
publication on that art he maintains, in oppofition to 
Cortes, that the variation of the compafs was caufed by 
fome point on the furface of the earth, and not in the 
heavens : he alfo made confiderable improvements in the 
conftruftion of compaffes themfeives ; fhowing efpecially 
the danger of not fixing, on account of the variation, the 
wire direCtly under the fleur-de-luce; as compafles made in 
different countries have it placed differently. To this 
performance of Norman’s is always prefixed a difeourfe 
on the variation of the magnetical needle, by Mr. Wil¬ 
liam Burrough, in which he fhows how to determine the 
variation in many different ways. He alfo points out 
many errors in the practice of navigation at that time, 
and fpeaks in very fevere terms concerning thofe who had 
publifhed upon ir. 
All this time the Spaniards continued to publifh trea¬ 
ties on the art. In 158^5, an excellent compendium was 
publifhed by Roderico Zamorano; which contributed 
greatly towards the improvement of the art, particularly 
in the fea-charts. Globes of an improved kind, and of a 
much larger fize than thofe formerly ufed, were now con- 
ltruCled, and many improvements were made in other 
inftruments ; however, the plane-chart continued ftill to 
be followed, though its errors were frequently complained 
of. Methods of removing thefe errors had indeed been 
fought after; and Gerard Mercator feems to have been 
the firft who found the true method of doing this, fo as 
to anfwer the purpofes of leamen. His method was to 
reprefent the paralleis both of latitude and longitude by 
parallel ftraight lines, but gradually to augment the 
former as they approached the pole. Thus the rhumbs, 
which otherwife ought to have been curves, were now 
alfo extended into ftraight lines ; and thus a ftraight line 
drawn between any two places marked upon the chart 
£ would 
