Physical Geography Of The Sea 1855/18
CHAPTER XVIII. — A LAST WORD.
Brussels Conference, § 584. — How Navigators may obtain a Set of Lieutenant M. F. Maury’s “Wind and Current Charts”, 585. — The Abstract Log, 586.
I HAVE, I am aware, not done more in this little book than given only a table or two of contents from the interesting volume which the Physical Geography of the Sea is destined some day to open up to us. The subject is a comprehensive one: there is room for more laborers, and help is wanted. Nations, no less than individuals; “stay-at-home travelers,” as well as those who “go down to the sea in ships,” are concerned in the successful prosecution of the labors we have in hand. We are now about to turn over a new leaf in navigation, on which we may confidently expect to see recorded much information that will tend to lessen the dangers of the sea, and to shorten the passages of vessels trading upon it. We are about to open in the volume of Nature a new chapter, under the head of MARINE METEOROLOGY. In it are written the laws that govern those agents which “the winds and the sea obey.” In the true interpretation of these laws, and the correct reading of this chapter, the planter as well as the merchant, the husbandman as well as the mariner, and states as well as individuals, are concerned. All have a deep interest in these laws; for with the hygrometrical conditions of the atmosphere, the wellbeing of plants and animals is involved. The health of the invalid is often dependent upon a dry or a damp atmosphere, a cold blast or a warm wind. The atmosphere pumps up our rivers from the sea, and transports them through the clouds to their sources among the hills; and upon the regularity with which this machine, whose motions, parts, and offices we now wish to study, lets down that moisture, and the seasonable supply of rain which it furnishes to each region of country, to every planter, and upon all cultivated fields, depend the fruitfulness of this country, the sterility of that. The principal maritime nations, therefore, have done well by agreeing to unite upon one plan of observation, and to co-operate with their ships upon the high seas with the view of finding out all that patient research, systematic, laborious investigation, may reveal to us concerning the winds and the waves; and philosophical travelers, and every sailor that has a ship under his foot, may do even better by joining in this system.
584. By the recommendations of the BRUSSELS CONFERENCE [1853], every one who uses the sea is commanded or invited to make certain observations; or, in other words, to propound certain queries to Nature, and to give us a faithful statement of the replies she may make. Now, unless we have accurate instruments, instruments that will themselves tell the truth, it is evident that we can not get at the real meaning of the answers that Nature may give us. An incorrect observation is not only useless of itself, but, when it passes undetected among others that are correct, it becomes worse than useless; nay, it is mischievous there, for it vitiates results that are accurate, places before us wrong premises, and thus renders the good of no value.
585. Those ship-masters who, entering this field as fellow-laborers, will co-operate in the mode and manner recommended by the Brussels Conference, and keep, voyage after voyage, and as long as required, a journal of observations and results according to a prescribed form — and which form is annexed, under the title of Abstract Log — are entitled, by sending the same, at the end of the voyage, to the Superintendent of the National Observatory, for a copy of my "Sailing Directions", and such sheets of the Charts as relate to the cruising-ground of the co-operator.
586. There are two forms of abstract logs: one, the more elaborate, for men-of-war; the other for merchantmen. The observations called for by the latter are a minimum, the least which will entitle the co-operator to claim the proffered bounty. It must give, at least, the latitude and longitude of the ship daily; the height of the barometer, and the readings of both the air and the water thermometer, at least once a day; the direction and force of the wind three times a day — first, middle, and latter part — at the hours eight P.M., four A.M., and noon; the variation of the compass occasionally; and the set of the current whenever encountered. These observations, to be worth having, must be accurately made; and as every thermometer and every barometer has its sources of error, consequently, every ship-master who undertakes hereafter to co-operate with us, and keep an abstract log, should have his barometer and thermometer accurately compared with standard instruments, the errors of which have been accurately determined. These errors the master should enter in the log; the instruments should be numbered, and he should so keep the log as to show what instrument is in use. For instance, a master goes to sea with thermometers Nos. 4719, 1, 12, &c., their errors having been ascertained and entered on the blank page for the purpose in the abstract log. He first uses No. 12. Let it be so stated in the column of Remarks, when the first observation is recorded, thus: Thermometer No. 12. During the voyage, No. 12 gets broken, or for some reason is laid aside, and another, say 4719, is brought into use. So state when the first observation with it is recorded, and quote in the column of Remarks the errors both of Nos. 12 and 4719. Now, with such a statement of errors given in the log for each of the instruments, according to the number, the observations may be properly corrected when they come up here for discussion. It is rare to find a barometer or a thermometer that has no error, as it is to find a chronometer without error. A good thermometer, the error of which the maker should guarantee not to exceed in any part of the scale one degree, will cost, in the United States, not less than $2, perhaps $2.50. The errors of thermometers sometimes are owing to inequalities in the bore of the tube, sometimes to errors of division on the scale, &c. Therefore, in comparing thermometers with a standard, they should be compared, at least, for every degree between melting ice and blood heat.