PRESSURE AND TEMPERATURE AT THE BEN NEVIS OBSERVATORIES. 497 









Number of Comparisons made. 



Difference 



Difference of 

 Pressure. 











of Temperature. 





Upper Barometer was — 







Inch. 





Total. 



Higher. 



Lower. 



+ 6° to + 4° 



+ 0-047 



5 







5 



+ 4 „ + 2 



+ 0-044 



13 







13 



+ 2 „ + 



+ 0-041 



19 







19 



- „ - 2 



+ 0-031 



18 







18 



- 2 „ - 4 



+ 0-020 



13 



3 



16 



- 4 „ - 6 



+ 0-009 



38 



15 



53 



- 6 „ - 8 



+ o-oii 



76 



21 



97 



- 8 „ -10 



+ 0-009 



160 



50 



210 



-10 „ -12 



+ 0-006 



280 



122 



402 



-12 „ -14 



- o-ooi 



378 



312 



690 



-14 „ -16 



- 0-005 



323 



677 



1000 



-16 „ -18 



- o-oio 



241 



802 



1043 



-18 „ -20 



- 0-017 



66 



722 



788 



-20 „ -22 



- 0-023 



15 



414 



429 



-22 „ -24 



- 0-026 







204 



204 



-24 „ -26 



- 0-029 







50 



50 





Total, 



1645 



3392 



5037 



at Fort- William, and on every one of these occasions the reduced barometer of the top 

 was the lower of the two. 



The greatest relative excess of the higher barometer occurs at those times when the 

 absolute temperature at the top of the mountain most exceeds that at Fort- William. 

 On the five occasions when the temperature at the top was from 4° to 6° higher than 

 at Fort-William, the excess of the top barometer was 0*038, 0*042, 0*044, 0*055, and 

 0*057 inch. It may be added that in these cases this excess is always large, and occurs 

 in anti-cyclonic weather, when the air is not only singularly warm, but also singularly 

 dry. The cases of the larger excesses of the upper barometer occur at all hours of the 

 day, but most frequently from about 10 p.m. to 8 a.m. 



On the contrary, the greatest diminutions of the top barometer, as compared with 

 that at Fort- William, occur during cyclonic weather, when the air is loaded with more 

 than the normal amount of moisture ; or when the influence of the sun's heat is great, 

 and very much greater at Fort- William than on the top of the Ben. Of the 254 cases 

 which have occurred when the temperature at Fort- William was from 22° to 26° higher 

 than at the top of the mountain, all the barometric observations at the top, when 

 reduced to sea-level, were, as stated, lower than those at the foot of the mountain. 



During the anti-cyclones, when the temperature at the top of the mountain, with 

 reference to that at Fort- William, is highest, the pressure at the top, reduced to sea-level, 



ROY. S0C. TKANS. EDIN. — VOL. XLII. 3 S 



