Page:Physical Geography of the Sea and its Meteorology.djvu/97

 Rh Delaware in winter to be blown off and to go the West Indies, and there wait for the return of spring before they would attempt another approach to this part of the coast.

186. Thermal navigation.—Accordingly, Dr. Franklin's discovery with regard to the Gulf Stream temperature was looked upon as one of great importance, not only on account of its affording to the frosted mariner in winter a convenient refuge from the snow-storm, but because of its serving the navigator with an excellent land-mark or beacon for our coast in all weathers. And so viewing it, the doctor, through political considerations, concealed his discovery for a while. The prize of 20,000l., which had been offered, and partly paid, by the British government, to Harrison, the chronometer maker, for improving the means of finding longitude at sea, was fresh in the minds of navigators. And here it was thought a solution of the grand problem—for longitude at sea was a grand problem—had been stumbled upon by chance; for, on approaching the coast, the current of warm water in the Gulf Stream, and of cold water on this side of it, if tried with the thermometer, would enable the mariner to judge with great certainty, and in the worst of weather, as to his position. Jonathan Williams afterwards, in speaking of the importance which the thermal use of these warm and cold currents would prove to navigation, pertinently asked the question, "If these stripes of water had been distinguished by the colours of red, white, and blue, could they be more distinctly discovered than they are by the constant use of the thermometer?" And he might have added, could they have marked the position of the ship more clearly?

187. Commodore Truxton.—When his work on Thermometrical Navigation appeared, Commodore Truxton wrote to him: "Your publication will be of use to navigation by rendering sea-voyages secure far beyond what even you yourself will immediately calculate, for I have proved the utility of the thermometer very often since we sailed together. It will be found a most valuable instrument in the hands of mariners, and particularly as to those who are unacquainted with astronomical observations; * * * * these particularly stand in need of a simple method of ascertaining their approach to or distance from the coast, especially in the winter season; for it is then that passages are often prolonged, and ships blown off the coast by hard westerly winds, and vessels get into the Gulf Stream without its being known; on which account they are often hove to by the captains supposing