.516 



DR BUCHAN ON THE 



amount is only 0"16 inch for the top, and 0*09 inch for Fort- William, and it is to be 

 noted that the larger amounts in both cases occur in the three summer months of July, 

 August, and September, being 0"32 inch at the top, and only 0*15 inch or less than half 

 at Fort- William. Again, when the mean daily difference of temperature is 18°'0 or 

 greater, then the mean daily rainfall for the year is 0'38 inch at the top, but 

 at Fort-William only 012, and at both places the greatest amount is collected during 

 the last four months of the year, giving a mean daily value for these months of 0'52 

 inch for the top and 0"18 inch for Fort- William. 



Class V. — Mean Daily Depression of the Wet Bulb Thermometer. 







Jan. 



Feb. 



Mar. 



Apr. 

 07 



May. 



June. 



July. 



Aug. 



Sept. 



Oct. 



Nov. 



Dec. 



Year. 



Group I. — 



Temperature Differences, 

 all observed 



Ben Nevis. 



0-2 



6 



6 



1-3 



1-4 



1-0 



0-8 



11 



0-5 



07 



0-6 



0-8 



Do. do. do. 



Fort-William. 



17 



2-2 



2-6 



3-3 



4 



3-9 



3-4 



3-0 



2-8 



2-1 



2-0 



2-0 



2-8 



Group III. — 



Temperature Differences, 

 12°'0 or less 



Ben Nevis. 



1-0 



1 7 



2-9 



3-2 



3-8 



3-4 



2-6 



2-6 



4-0 



2-4 



2-4 



17 



2-6 



Do. do. do. 



Fort- William. 



0-9 



1-6 



2-5 



3-5 



4-4 



3-5 



3-1 



27 



2-4 



17 



1-3 



1-0 



2-4 



Group IV.— 



Temperature Differences, 































18° '0 or greater . 



Ben Nevis. 



o-i 



o-o 



0-2 



0-3 



0-3 



0-3 



o-i 



o-i 



o-i 



o-i 



o-o 



o-o 



o-i 



Do. do. do. 



Fort-William. 



2-6 



27 



3-1 



4-1 



4"2 



4-4 



4-5 



4-0 



3-5 



3-2 



3-0 



3-1 



3-5 



Lastly, as to the depression of the wet bulb, the observations (Group I.) for all differences 

 of temperature give us a daily mean for the year of o, 8 for the top and 2° '8 for Fort- 

 William. Otherwise, when the differences of mean daily temperature are 12 o, or less 

 (Group III.), there is a daily mean for the year of 2° "6 for the top, and 2° "4 for Fort- 

 William. In strong contrast, however, to the above, when the temperature differences 

 are 18°'0 or greater (Group IV.), the daily mean for the top is only o, l, and for Fort- 

 William 3°'5 ; on the top the daily mean in no month exceeds 0° - 3. 



Table II. — This Table shows the arithmetical ' Constants ' for each month and the. 

 year of the mean hourly differences between the sea-level pressures at the summit and at 

 Fort-William. For the reasons stated above they are classed into four groups, viz. : — 



Group I., including all the days entered in this discussion, irrespective of differences 

 of temperature at the two Observatories, 3716 days. 



Group II. — All days when the temperature differences ranged from 13°'0 to 17° "0, 

 2170 days. 



Group III. — All days when the temperature differences were 12 o, or less, including 

 also the days when the temperature of the top was higher than at Fort- William, 730 

 days. 



Group IV. — All days when the temperature differences were 18°'0 or greater, 

 816 days. 



The mean hourly differences of the sea-level pressures at the two Observatories for 

 each of the four groups are detailed in Table II. As already explained, the mean 



