642 



MR R. C. MOSSMAN ON 



A point of interest in connection with these temperature changes is that there 

 is, as a rule, no corresponding change at Fort-William, but that, before a rise of 

 temperature at Achariach, the temperature there was several degrees colder than at Fort- 

 William, and after the change several degrees warmer, showing that Fohn conditions had 

 set in in the Glen. The following, taking the values for the two places at the hours 

 for which data from Fort- William are available, shows this very clearly : — 



Date. 



Hour. 



21 

 20 

 10 



4 



2 



Temperature. 



Hour. 



Temperature. 



Glen. 



F.W. 



Difference. 



Glen. 



F.W. 



Difference. 



November 23 

 December 12 



19 . 

 February 2 



14 . . 



29 ? 8 

 23-1 

 23-5 

 27-0 

 136 



31 f 4 

 31-5 



27-8 

 37-5 

 170 



- 1-6 



- 8-4 



- 4 3 

 -105 



- 3-4 



22 



21 



11 



5 



3 



39 f l 

 36-0 

 36-1 

 42-6 

 32-4 



31 f 6 

 31-0 

 28-5 

 37-0 

 273 



+ 7 ? 5 

 + 5-0 

 + 7-6 

 + 5-6 

 + 5-1 



At Achariach the average relative humidity at the hour before these temperature 

 changes was 87, and at the next hour 66, showing a fall of 21 per cent, accompanying 

 the temperature rise ; but at Fort- William no such change in humidity took place, 

 the corresponding values being 77 and 75 respectively. 



Wind Direction, Force, and Velocity. 



There was no anemometer giving a continuous record of wind direction and force, 

 so we are restricted to a discussion of the observed directions as noted at the four 

 principal hours of observation, viz. 9 and 10 a.m., 2 p.m. and 9 p.m. 



An analysis of the observations taken at these hours, for the 122 days in which the 

 record is complete at all hours, gave the following results, the force being as estimated 

 on the scale of to 12, in which 1 represents a mean velocity of 7 miles per hour : — 



Hour. 



9 

 10 

 14 

 21 



N". 



N.E. 



E. 



S.E. 



S. 



S.W. 



W. 



N.W. 



Calm. 



Var. 



Mean 

 Force. 



4 

 6 



7 

 



6 

 4 

 3 



1 



13 

 12 



8 

 7 



12 

 16 

 15 

 20 



8 



5 



4 



11 



15 

 9 



7 

 7 



24 

 18 

 20 

 17 



7 

 15 

 16 

 22 



33 

 36 



41 

 37 



147 





 1 

 1 

 



0-82 

 0-79 

 078 

 084 



17 



14 



40 



63 



28 



38 



79 



60 



2 



0-81 



Hence the prevailing winds in the Glen were west and south-east, while the least 

 frequent were north-east and north. Calms were very frequent, accounting for nearly 

 one- third of the whole. As regards the diurnal variation of wind direction and force, 

 the hours of observation are not sufficiently numerous or well distributed to give results 



