Dynamic meteorology and hydrography; plates

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1911 Excerpt: ...represent the given angles we may come both to positive numbers which are greater than 64, and to negative numbers. In such cases we shall always by subtraction or addition of 64 (or a multiple of 64) reduce to a positive number smaller than 64. This will always be allowed by the general reason that there is no difference between the direction represented by a and that represented by a ± four right angles. This remark is of special importance in connection with the difference of angle /3--a, which represents the direction of the vector B relatively to that of A. When we agree always to represent this difference of angle by a positive number, it implies that we agree to count it as produced by a rotation in positive direction from the vector A, of which the anglea a ppears as subtractor to the vector B, of which the angle appears as minuend (see fig. 75). These agreements must be remembered for the understanding of our charts, where the isogons, whether they represent absolute angles a, /3...or differences of angle /3--a, are always numbered with positive numbers contained between o and 64. Two vectors which cut each other under constant angle will have the same system of isogons, only with different numbers appearing on the isogons. The difference will be zero, if the two vectors have the same direction, 32 if they have the opposite direction, and 16 or 48 if they cut each other under right angle. Evidently two opposite directions will have equal right to be called normal to a given direction. We shall therefore agree to distinguish between these two directions by a rule of signs, namely this: From a given direction we pass to that of its positive normal by a rotation of one right angle and to that of its negative normal by a rotation of three right an...