24 PRESIDENTIAI, ADDRESS SECTION A. 



west, and west. Any wind direction differing from these will 

 be more or less abnormal according to the degree of divergence. 



The winds may be abnormal also in strength or velocity. T 

 have mentioned before that there exists an evident relation 

 between the force of the wind anrl the closeness of the isobars. 

 To get an idea of this relation, we must have some means of 

 measuring the force of the wind on the one hand and the degree 

 of closeness of the isobars on the other. The force of the wind 

 on the weather charts is generally estimated on a scale (the 

 IJtaufort scale) ranging from o to lo. o standing for calm and 

 lO for hurricane winds. The degree of closeness of the isobars 

 is measured by the barometric gradient. If the distance between 

 isobars drawn through points which differ by one millimeter in 

 pressure is 60 geographical miles, the gradient is i, if the isobars 

 are twice closer the gradient is 2, and so on. From the analysis 

 of a vast number of observations meteorologists have found that 

 on the West Coast of Europe the normal wind for a given 

 gradient is denoted on the Beaufort scale by a number which is 

 twice the gradient; a gradient 2, for instance, gives normally rise 

 to a wind force of 4, a gradient 3 to a wind force of 6, etc. Wind 

 forces differing from this proportion are. according to Air. 

 Guilbert's way of speaking, abnormal, either by excess or by 

 deficiency, as the case may be. 



Mr. Guilbert's rules, twenty-five in number, may all be 

 derived from the following, which may be said to be absolutely 

 new. If in a depression we have winds abnormal in excess with 

 regard to the gradient, the winds will produce a rise in the pres- 

 sure, the propagation of the rise being from the right to the 

 left. (In the southern hemisphere, of course, the propagation 

 would be from left to right.) In other words, put your back 

 to the wind that is proportionally too strong, and you will find 

 the high pressures gradually encroaching on the low pressures 

 from right to left. If this principle be correct, and Mr. Brunhes's 

 investigations lead us to consider it so, we have a most important 

 principle for solving problems of pressure transformation. Take, 

 for instance the case where, on going all round a depression, we 

 find evervwhere winds too strong in proportion to the gradient. 

 In this case the pressure will rise everywhere from right to left — 

 that is, towards the centre, the depression will be filled up in a 

 short time, and be replaced by a high-pressure system, explaining 

 thus the puzzling phenomena of the sudden vani.shing of a storm 

 area and the substitution of a fine weather system. 



A cyclone has, generally, a more complex system of wind 

 circulation. If at one point we have winds abnormally strong, 

 we have usually also at others winds abnormally weak. In this 

 case the cyclone will deepen and move on towards the regions 

 of least resistance. Regions of least resistance are precisely 

 :those where the winds are abnormal by deficiency, and more 

 especially those where the winds are abnormal in direction. 



