A General History and Collection of Voyages and Travels - Volume 18 / Historical Sketch of the Progress of Discovery, Navigation, and / Commerce, from the Earliest Records to the Beginning of the Nineteenth / Century, By William Stevenson

by Robert Kerr; William Stevenson

The grand objects of a navigator are the accurate knowledge of where he exactly is, in any part of his course, and how he ought to steer, in order to reach his destination in the shortest time. The means of ascertaining his latitude and longitude, of calculating how far he has sailed, and at what rate he is sailing, and the direction of his course with reference to the port to which he is desirous to proceed, are what he principally requires. We do not intend, by any means, to enter at any length, or systematically, on these subjects; but a brief and popular notice of them seems proper and necessary in such a work as this.

Astronomy here comes essentially to the aid of navigation: we have already seen how, even in the rudest state of the latter, it derived its chief assistance from this sublime science, confined as it then was to a knowledge of the position of a few stars. Astronomy enables the navigator to ascertain his latitude and longitude, and to find the variation of the compass. The principal difficulty in ascertaining the latitude at sea, arose from the unsteady motion of the ship: to remedy this, several instruments were invented. We have already alluded to the astrolobe; but this, as well as the others, were imperfect and objectionable, till such time as Hadley's quadrant was invented, the principle and uses of which were first suggested by Newton.

To ascertain the longitude was a much more difficult task: there are evidently two methods of doing this,--by time-keepers or chronometers, and by making the motions of the celestial bodies serve instead of time-keepers. About the middle of the seventeenth century, Huygens proposed the pendulum clock for finding the longitude at sea; but it was unfit for the purpose, for many and obvious reasons. Watches, even made with the utmost care, were found to be too irregular in their rate of going, to be depended upon for this purpose. In the reign of Queen Anne the celebrated act was passed, appropriating certain sums for encouraging attempts to ascertain the longitude. Stimulated by this, Mr. Harrison invented his time-keeper, which on trial was found to answer the purpose with such tolerable accuracy, that he was deemed worthy to receive the sum awarded by parliament: it went within the limit of an error of thirty miles of longitude, or two minutes of time, in a voyage to the West Indies. Since this period, chronometers have been much improved, and excellent ones are very generally used: perhaps the most trying circumstances in which any were ever placed, existed during the voyage for the discovery of a northwest passage by Captain Parry; and then most of those he had with him were found to be extremely accurate.

It is evident, however, that chronometers are liable to a variety of accidents, and that in very long voyages the means of verifying their rate of going seldom occur. Hence the lunar method, or the method of ascertaining the longitude by means of the motions of the moon, is more useful and valuable. Here again, the profoundest researches of Clairaut, Euler, D'Alembert, and La Place, were brought practically to bear on navigation. Guided and aided by these, Tobias Mayer, of Gottingen, compiled a set of solar and lunar tables, which were sent to the lords of the admiralty, in the year 1755; they gave the longitude of the moon within thirty seconds. They were afterwards improved by Dr. Maskelyne and Mr. Mason, and still more lately by Burg and Burckhardt; the error of these last tables will seldom exceed fifteen seconds, or seven miles and a half. The computations, however, necessary in making use of these tables, were found to be very laborious and inconvenient; to obviate this difficulty, the nautical almanack, suggested by Dr. Maskelyne, was published, which is now annually continued. The longitude is thus ascertained to such a nicety, as to secure the navigator from any danger arising from the former imperfect modes of finding it; "he is now enabled to make for his port without sailing into the parallel of latitude, and then, in the seaman's phrase, running down the port, on the parallel, as was done before this method was practised. Fifty years ago, navigators did not attempt to find their longitude at sea, unless by their reckoning, which was hardly ever to be depended on."

Not long after the mariner's compass was employed, its variation was noticed; as it is obvious that, unless the degree and direction of this variation are accurately known, the compass would be of little service in navigation, the attention of navigators and philosophers was carefully directed to this point; and it was ascertained that the quantity of this variation is subject to regular periodical changes. By means, therefore, of a table indicating those changes, under different latitudes and longitudes, and of what are called variation charts, the uncertainty arising from them is in a great measure done away. Another source of error however existed, which does not seem to have been noticed till the period of Captain Cook's voyages: it was then found, "that the variation of the needle differed very sensibly on the same spot, with the different directions of the ship's head." Captain Flinders attributed this to the iron in the ship, and made a number of observations on the subject; these have been subsequently added to and corrected, so that at present the quantity of variation from this cause can be ascertained, and of course a proper allowance made for it. It does not appear that any material improvement has been made in the construction and use of the log,--that useful and necessary appendage to the compass,--since it was invented about the end of the sixteenth century.

These are the most important improvements in nautical knowledge and science, which renders navigation at present so much more safe and expeditious than it formerly was; there are, however, other circumstances which tend to the same object; the more full, accurate, and minute knowledge of the prevalent winds at different times of the year, and in various parts of the ocean; the means of foretelling changes of weather; and, principally, a knowledge of the direction and force of the currents must be regarded as of essential advantage to the seaman. When to these we add, the coppering of ships, which was first practised about the year 1761, and other improvements in their built and rigging, we have enumerated the chief causes which enable a vessel to reach the East Indies in two-thirds of the time which was occupied in such a voyage half a century ago.

Nor must we forget that the health of the seamen has, during the same period, been rendered infinitely more secure; so that mortality and sickness, in the longest voyages, and under great and frequent changes of climate, and other circumstances usually affecting health, will not exceed what would have occurred on land during the same time.

The great advantages which the very improved state of all branches of physical science, and of natural history, bestow on travellers in modern times, are enjoyed, though not in an equal degree, by navigators and by those who journey on land. To the latter they are indeed most important, and will principally account for the superiority of modern travels over those which were published a century ago, or even fifty years since. It is plain that our knowledge of foreign countries relates either to animate or inanimate nature: to the soil and geology, the face of the surface, and what lies below it; the rivers, lakes, mountains, climate, and the plants; or to the natural history, strictly so called:--and to the manners, institutions, government, religion, and statistics of the inhabitants. Consequently, as the appropriate branches of knowledge relating to these objects are extended, travellers must be better able, as well as more disposed, to investigate them; and the public at large require that some or all of them should at least be noticed in books of travels. The same science, and many of the same instruments, which enable the seaman to ascertain his latitude and longitude, and to lay down full and accurate charts of the shores which he visits, are also useful to the land-traveller; they both draw assistance from the knowledge of meteorology which they may possess, to make observations on the climate, and from their acquaintance with botany and natural history, to give an account of the plants and animals. But it is evident that so far as the latter are concerned, as well as so far as relates to the inhabitants, the land traveller has more opportunities than he who goes on a voyage.

But there are other advantages enjoyed by modern travellers besides those derived from superior science: foreign languages are at present better and more generally understood; and it is unnecessary to point out how important such an acquisition is, or rather how indispensible it is to accurate information. The knowledge of the languages of the East which many of the gentlemen in the service of the East India Company, and the missionaries, possess, has been of infinite service in making us much better acquainted with the antiquities, history, and present state of those countries, than we could possibly have otherwise been. There is at present greater intercourse among even remote nations; and prejudices, which formerly operated as an almost insurmountable barrier, are now either entirely destroyed, or greatly weakened: in proof of this, we need only refer to the numerous travellers who have lately visited Egypt,--a country which it would have been extremely dangerous to visit half a century ago. At the same distance of time, natives of Asia or Africa, especially in their appropriate costume, were seldom or never seen in the streets of London, or, if seen, would have been insulted, or greatly incommoded by the troublesome curiosity of its inhabitants; now there are many such, who walk the streets unmolested, and scarcely noticed.

Commerce, which has derived such advantages from the progress of geographical knowledge, has in some measure repaid the obligation, by creating a much greater, more intimate, and more frequent mutual intercourse among nations; and by doing away with those prejudices and antipathies which formerly closed many countries effectually against Christian and European travellers: and to the zeal and perseverance of modern travellers, assisted as they are by commercial intercourse, we may reasonably hope that we shall, before long, be indebted for a knowledge of the interior of Africa. Those countries still imperfectly known in the south-east of Asia will, probably, from their vicinity to our possessions in Hindostan, be explored from that quarter. The encreasing population of the United States, and the independence of South America, will necessarily bring us acquainted with such parts of the new world as are still unknown. But it is difficult to conjecture from what sources, and under what circumstances, the empires of China and Japan will be rendered more accessible to European travellers: these countries, and some parts of the interior of Asia, are cut off from our communication by causes which probably will not speedily cease to operate. The barriers which still enclose all other countries are gradually yielding to the causes we have mentioned; and as, along with greater facilities for penetrating into and travelling within such countries, travellers now possess greater capabilities of making use of the opportunities thus enjoyed, we may hope that nearly the whole world will soon be visited and known, and known, too, in every thing that relates to inanimate and animate nature.