BAEOMETEIC GEADIENTS. 119 



" III. To extract each strong wind which was recorded at any station, 

 and compare therewith the barometrical differences recorded along the 

 lines in the vicinity of that station. 



" By these three enquiries it was sought to ascertain : — 



"1. What is the connexion between general barometrical disturbances 

 and weather succeeding it. 



" 2. What accordance do the strong winds actually observed show with 

 the directions over each district of the area as given by the Law. 



" 3. What amount of indication was given of each strong wind by 

 barometrical differences in its vicinity." 



(40.) We cannot here follow out the discussion into the details, but 

 Mr. Scott drew this conclusion from them : — 



" It appears, then, as a final result, that if we notice on any morning a 

 difference of 0'60 inch between any two stations, the chance is 7 to 3 that 

 there will be a storm within the succeeding twenty-four hours. On the 

 other hand, the chance is 9 to 1 that any storm which sets in will be pre- 

 ceded by unmistakeable signs of its approach, although the barometrical 

 difference of readings may not amount to 0'60 inch at 8 a.m. 



" Before leaving this branch of the enquiry, there is one result which 

 seems of sufficient importance to deserve a special notice. 



" I find that although there is a preponderance of instances in which the 

 difference of six-tenths is followed by a gale, yet on several occasions the 

 barometrical inequahty exists after the violent motion of the air has come 

 to an end. In ten instances during the whole nine months, I find that at 

 8 a.m. on the day after a serious gale there was a difference of, or exceed- 

 ing, 0*6 inch, while there was not a gale during the remainder of the day. 

 This seems to me to be a very remarkable result, and one well deserving 

 of future investigation. 



" It appears, also, that as regards direction the Law receives strong 

 confirmation : — 



" Southerly gales are preceded by a relatively low pressure in the West. 



" Westerly gales are preceded by a relatively low pressure in the North. 



" Northerly gales are preceded by a relatively low pressure in the East. 



" Easterly gales are preceded by a relatively low pressure in the South. 



" In devising a system for testing the Law as applied to the different 

 districts of the British Islands, and the North and West Coasts of France, 

 we are met by various difficulties. The simplest statement of the Law is 

 that according to it the wind at any point wiU blow in the direction of a 

 tangent, at that point, to the isobaric curve which represents the atmo- 

 spherical conditions existing a short time previously. 



" Firstly, the whole system of isobaric curves, or the whole distribution 

 of atmospherical pressure, is known to be subject to a motion of transla- 

 tion over the earth's surface ; but of this motion the direction and the 

 rate vary, from day to day, to a considerable extent, and in a manner 

 independent of each other. Neither of these points have been as yet 

 satisfactorily investigated. Secondly, the wind, especially in storms, seldom 

 blows for many hours consecutively from the same point, but either veers 

 or backs, the former motion being much more usual than the latter. 



" These considerations show us that we must not interpret the Law too 



