510 



DR BUCHAN ON THE 



As regards the Hygrometer, the depression of the wet bulb at Fort-William was 

 comparatively small, being from 2 a.m. to 9 a.m., and again from 9 p.m. to midnight, 

 only about 1 0, 3. From 9 a.m. the difference increased from hour to hour to a maximum 

 of 5° '3 at 3 p.m., from which time it fell gradually to half a degree at midnight. In 

 striking contrast with this was the great and continuous aridity of the air at the top 

 during the whole twenty-four hours, the depression of the wet bulb being at no time 

 less than 8°*2, attaining a maximum of 11°'5 at noon. Throughout, the sky was 

 absolutely cloudless at both Observatories, and the sunshine strong and continuous. 



In the strong sunshine, temperature rose quickly at both Observatories from 8 a.m. 

 to mid-afternoon, much more quickly, however, at Fort- William than at the top. At 

 Fort-William at this time it rose from 16°'0 to 35 o, 0, but at the top only from 31°"5 to 

 38°*5, being respectively an increase of 19°"0 at Fort-William, but only 7°'0 at the top. 

 It will be noted during the hours when the humidity at Fort- William was great or near 

 saturation and the humidity at the top small, as shown by the great depression of the 

 wet bulb, that the sea-level pressure for the top was greatly in excess of the sea-level 

 pressure at Fort- William ; but that as the temperature at Fort- William rapidly rose 

 and the depression of the wet bulb greatly increased, so that the excess of the sea- 

 level pressure for the top steadily diminished till, from noon to 5 p.m., it fell to a 

 little lower than the sea-level pressure at Fort- William. Further, as the humidity at 

 Fort- William increased from 5 p.m. to midnight, so the excess of sea-level pressure at 

 the top increased with it. 



Another similar case may be here added. On 31st January 1902 the sea-level 

 pressure at Fort- William rose to 31 •111 inches at 11 p.m. The following are the observa- 

 tions at the two Observatories from 7 p.m. to midnight, the barometric differences 

 being in thousandths of an inch : — 





Barometer at 32° and 

 Sea Level. 



Temperature. 



Hygrometer Depression 

 of Wet Bulb. 



Port- 

 William. 



Ben 



Nevis. 



Difference. 



Fort- 

 William. 



Ben 



Nevis. 



Mean. ■ 



Difference. 



Fort- 

 William. 



Ben 



Nevis. 



• 7 P.M. 



8 ,, 



9 ,, 

 10 „ 



*? ." 



Midnight 



Mean 



Ii 



31 



31 



is. 



089 



103 



108 



108 



111 



103 



104 



Ins. 

 31-135 

 •140 

 •172 

 •149 

 •157 

 •142 



31-149 



Ins. 

 + 46 

 + 37 

 + 64 

 + 41 

 + 46 

 + 39 



+ 46 



21-8 



22-3 

 20-5 

 20-0 

 20-0 

 21-3 



21-0 



22°-l 

 21-3 

 21-2 

 22-1 

 22-1 

 21-5 



21-7 



22°0 

 21-8 

 20-9 

 211 

 21-1 

 21-4 



21-4 



+ 6-3 



— 1-0 

 + -7 

 + 21 

 + 21 

 + 07 



+ 07 



. °8 



11 



•5 



•6 



1-2 



1-4 



0-9 



5-8 



5-2 

 51 

 5 1 

 4-5 

 3-6 



4-9 



No rain fell at either Observatory during the day. The sky was clear all day at 

 the top, but at Fort- William there were no clouds in the afternoon ; in the forenoon, 

 however, the sky was clouded, and no sunshine was recorded. 



The highest recorded pressure at Fort- William was 31 '111 inches at 11 p.m. of the 



