The investigation by measurements has since been largely adopted. In 1787, joint commissions were issued by England and France to connect the Greenwich and Parisian observations. Arcs of the meridian have since been measured across the whole breadth of France and Spain, and also near the Arctic circle, and in the Indian peninsula.
In navigation, the grand point for the sailor is to ascertain his latitude and longitude; in other words, to know where he is. The discovery of the latitude is easily effected by the quadrant, but the longitude is the difficulty. Any means which ascertained the hour at Greenwich, at the instant of making a celestial observation in any other part, would answer the difficulty; for the difference in quarters of an hour would give the difference of the degrees. But clocks could not be used on shipboard, and the best watches failed to keep the time. In the reign of Anne, Parliament offered a reward of L. 5000, perhaps not far from the value of twice the sum in the present day, for a watch within a certain degree of accuracy. Harrison, a watchmaker, sent in a watch which came within the limits, losing but two minutes in a voyage to the West Indies; yet even this was an error of thirty miles.
But, though chronometers have since been considerably improved, there are difficulties in their preservation in good order which have made it expedient to apply to other means; and the lunar tables of Mayer of Gottingen, formed in 1755, and subsequently improved by Dr Maskelyne and others, have brought the error within seven miles and a half.
Improvements of a very important order have also taken place in the mariner's compass; the variation of the needle has been reduced to rules, and some anomalies arising from the metallic attraction of the ship itself, have been corrected by Professor Barlow's experiments. The use of the marine barometer and thermometer have also largely assisted to give notice of tempests; and some ingenious theories have been lately formed, which, promising to give a knowledge of the origin and nature of tempests, are obviously not unlikely to assist the navigator in stemming their violence, or escaping them altogether.
The construction of ships for both the merchant and the public service has undergone striking improvements within this century. Round sterns, for the defence of a vessel engaged with several opponents at once; compartments in the hold, for security against leaks; iron tanks for water, containing twice the quantity, and keeping it free from the impurities of casks; a better general stowage; provisions prepared so as to remain almost fresh during an East Indian voyage; every means of preserving health, suggested by science, and succeeding to the most remarkable degree; a more intelligent system of shipbuilding, and a constant series of experiments on the shape, stowage, and sailing of ships, are among the beneficial changes of later times. But the one great change--steam--will probably swallow up all the rest, and form a new era in shipbuilding, in navigation, in the power and nature of a navy, and in the comfort, safety, and protection of the crews in actual engagement. The use of steam is still so palpably in its infancy, yet that infancy is so gigantic, that it is equally difficult to say what it may yet become, and to limit its progress. It will have the one obvious advantage to mankind in general, of making the question of war turn more than ever on the financial and mechanical resources of a people; and thus increasing the necessity for commercial opulence and intellectual exertion. It may expose nations more to each other's attacks; but it will render hostility more dreaded, because more dangerous. On the whole, like the use of gunpowder, which made a Tartar war impossible, and which rapidly tended to civilize Europe, steam appears to be intended as a further step in the same high process, in which force is to be put down by intelligence, and success, even in war, is to depend on the industry of peace; thus, in fact, providing a perpetual restriction on the belligerent propensities of nations, and urging the uncivilized, by necessity, to own the superiority, and follow the example of the civilized, by knowledge, habit, and principle.