National Geographic : 1903 Feb
THE NATIONAL GEOGRAPHIC MAGAZINE 72 which is below that of fog, in which percentages for a force of 8 and over of the Beaufort's scale-from 40 to ioo miles an hour-are given in 50 squares. No vessel other than a regular high powered liner, unless absolute necessity demands, takes a route in which such gales are frequent, on account of the danger to life and property, the wear on the vessel, and the consequent delay. This sub-chart tells them the only things they want to know-how to avoid the stormy area and what route to choose. The best routes for low - powered steamers, from the English Channel to the Gulf and from Gibraltar to New York, are also shown. The latter, for instance, is longer in distance than a direct route. Experience has shown, however, that by reason of encounter ing more favorable winds, seas, and cur rents, it is shorter in time, with much less wear and tear on the vessel and crew. Down in the lower left-hand corner are some red symbols to designate ice bergs and field ice. No bergs or field ice were reported during January, so none are indicated on the accompanying chart. On the pilot charts of the sum mer months, however, the region above and about the Grand Banks is dotted with these little red symbols. If we were issuing a pilot chart of the south Atlantic Ocean for this month, these ice symbols would be very numerous in its southern portion. You may remember that it was not many years ago that we had frequent reports of vessels colliding with ice bergs; but such is now very much less the case, principally due, I feel that I can say with absolute truthfulness, to the efforts of the Hydrographic Office, as a result of which the transatlantic lines were, some years ago, induced to adopt regular lanes of transit to and from England and the United States lanes which take them over a safer route, in that it is practically clear of ice. Over on the right-hand side of the pilot chart is a sub-chart of isobars and isotherms for the month of February, showing the average heights of barom eter and temperature to be expected, and indicating, by reference to the areas of low and high barometer, what move ment of the atmosphere may generally be looked for. The intelligent mariner knows that any marked deviation from these normal values denotes a change in weather. Above this sub-chart will be found a forecast-not a prediction-of the weather, the average of thousands of observations taken during the past fif teen years. The main or sea part of the chart is divided up into 50 squares, in the center of each one of which will be found a small circle from which radiate arrows, each one pointing towards the center. These arrows indicate the di rection in which winds may be expected to blow, the number of feathers indicat ing the force by Beaufort's scale. Take the example noted in blue under the heading of "Prevailing Winds and Calms," at the bottom of the chart on the left side. The arrows fly with the wind, and the number of hours in each one hundred during which the wind may be expected to blow from that direction is found by transferring the length of the arrow to the scale below, the number of feathers indicating the force. Thus, in this example, we will in each one hundred hours expect to find a northeast wind with a force of 3 for 18 hours; an east wind, force of 3 for io hours; a southeast wind, force of 4 for 24 hours; a south-south east wind, force of 3 for 25 hours, and a southwest wind, force of 3 for io hours. The figure 13 within the cen tral circle indicates 13 hours of calms, light airs, and variable winds. The small black arrows point out the average set of currents, whether regular or drift.