Webb. — On Local Variations of Atmospheric Pressure. 



107 



There being no attendance at tlie appointed hour, nor for long after it, the 

 indefatigable honorary secretary of the club, not caring for a lonely walk, 

 abandoned the excursion. Mr. Blair and the writer arriving late, and each 

 supposing the usual party to be ahead, undertook the ascent, and they 

 presently joined one another. Mr. Blair, who has a keen eye for possible 

 railway tracks wherever he goes, was, when I overtook him, engaged in noting 

 the height of the barometer, with the view of estimating the elevation of the 

 point he had reached. Similar observations were continued throughout our 

 walk, which extended to a mile or so beyond the summit, and were repeated 

 during the descent at most of the points adopted during the upward 

 journey. 



Coming down we noticed an increasing discrepancy between the two sets 

 of observations, the new ones showing decreased atmospheric pressure. We 

 were, of course, prepared to find that the barometer at the sea level had fallen 

 during the afternoon, and expected that the reduction of our observations 

 would give us much trouble in consequence, and probably be far from reliable 

 as measurements of height. As we began to emerge from the narrower part 

 of the gorge through which the Water of Leith flows, we found the difference 

 between the first and second observations began to decrease, and finally, when 

 we reached the sawmills, the two coincided, which was again the case at the 

 intersection of Castle-street and Albany-street, where Mr. Blair made his first 

 observation of the barometer. This curious phenomenon caused us some 

 perplexity. After consideration I am inclined to attribute it to the effect of a 

 fairly strong wind which was blowing from the S.W. when we started, but 

 which subsided during the afternoon. In a valley so completely shut in as 

 that of the Leith during its upper course, and descending so rapidly from the 

 saddle, which lies at about 1,100 feet above the level of the sea, it is certain 

 that a strong breeze blowing almost directly into it at the lower end must 

 cause increased pressure in the lower strata of air. 



The following is a list of our observations : — 

 Table of Observations or Atmospheric Pressure, 2nd December, 1871. 



Poiuts of Observation. 



— 



During Ascent. 



During Descent. 



Difference. 



Castle Street 



29-69 



29-69 





Leith. Bridge 







29-60 



29-60 





Ross' Creek 







29-58 



29-53 



•05 



N.W. comer, Section 7 .. 







29-42 



29-36 



•06 



Nichol's Stream... 







29-30 



29-23 



•07 



Cedar Creek 







29-20 



29-12 



•08 



Ford of Leith ... 







29-19 



29-11 



•08 



Cuthbertson's ... 







28-8.3 



28-78 



•05 



Section peg ^ ••■ 







28-78 



28-74 



•04 



Saddle 







28-43 



... 





