National Geographic : 1902 Apr
THE NATIONAL GEOGRAPHIC MAGAZINE 142 actual position of the vessel at noon the second day is at B. In this case B'B will be set down in the log as the current experienced during the inter vening 24 hours. In case no astronom ical observations can be obtained, as happens in fog or cloudy weather, the position by dead reckoning has to be adopted as the best obtainable, with the result that if such weather con tinues for several days in succession, as sometimes happens at certain seasons of the year, the true position of the vessel may differ considerably from the assumed position, which is frequently accompa nied with disaster upon approaching shore. To lessen this danger these cur rent charts have been constructed, giv ing the results of current observations in the past, and the master of a vessel, by reference to them, is able to profit by the experience of those who have sailed over the same waters in previous years, and to some extent correct his own dead reckoning. The current charts of the various oceans published by the British Admi ralty-the charts which are universally employed by navigators-are the result of many, many thousands of observa tions-in fact, of all the reliable current observations taken since 1830. A glance at these charts will make plain the dif ficulty which confronts the navigator when approaching a dangerous coast, such as that of Newfoundland or of France, and compelled to rely upon his dead reckoning. For a knowledge of the motions of the water throughout longer periods of time we are forced to depend upon the drift of floating objects, derelicts, wreck age, floating bottles bearing messages, and the like. Two attempts recently made to study the currents of the sea by this method deserve mention. The first is an effort to obtain a knowledge of the currents in the Arctic Ocean. Stout oaken casks, each one numbered and bearing a message, have been dis tributed by the Philadelphia Geograph ical Society among the whalers bound for the Arctic by way of Bering Sea, where they winter in the vicinity of the mouth of the Mackenzie River. These casks are to be placed upon the ice as far eastward as circumstances permit, and the expectation is that they will enter the Atlantic either by Davis Strait or Barents Sea, be noticed by passing vessels, and picked up. A letter from Dr. Bryant, the president of the society, states that 35 out of the 50 casks have been already set out, and that in his opinion they may be looked for on the other side of the circumpolar area about a year from the spring of 1902. The second project is the proposed investigation of the current in the neighborhood of Ushant and Finisterre by means of floating bottles. This has been undertaken by Lloyds, the great ship underwriting firm, and has prob ably been brought about by the number of vessels lately lost in that vicinity, owing to the fact that they were out in their reckoning. The bottles, which are of gutta-percha, are to be sealed and thrown into the sea by passing vessels, each one containing a label showing the date and the position at which it was cast adrift. They are then supposed to drift ashore and to be recovered. The ex pense involved is considerable. On the bottle it is stated that a reward of five francs will be paid for the return to any of His Majesty's consuls-an instance of liberality of expenditure in the acqui sition of knowledge which is almost unprecedented.