644 



MR K. C. MOSSMAN ON 



Mean Amount of Cloud. 



The mean amount of cloud at the hours of 9, 10, 14, and 21 has been computed for 

 the 120 days during which the observations are complete at each of the four hours. 

 The results are as follows, on the scale 0-10 : — 



9 



10 



14 



21 



Mean. 



8-5 



8-4 



8-5 



75 



8-2 



It will be seen that the cloud amount continues high in the morning and afternoon 

 hours, but in the evening there is a distinct clearing of the sky, this coinciding with 

 the setting in of what may be termed the diurnal Form period. 



During the same days at Fort- William the mean amount of cloud was as follows : — 



9 



10 



14 



21 



Mean. 



81 



8-1 



8-0 



6-9 



7-8 



Hence the values at Fort- William show that the sky there was somewhat clearer 

 than in the Glen, but one cannot dogmatise in this connection, as there may be a slight 

 personal equation affecting the direct comparability of the results at the two places. 



Mist on Hills. 



The presence of mist or fog was noted on the Cairn Dearg of Ben Nevis (3348 feet), 

 Sgor-a-Mhaim (3601 feet), the Corrie Derrack or Mullach nan Coirean (3077 feet), and 

 the Meall-Cumhann (2306 feet). The following table shows the percentage frequency 

 of cases in which mist was observed on these hills at the hours of 9 a.m., 10 a.m., 

 2 p.m., and 9 p.m. on 90 days, between 25th October 1901 and 28th February 1902, 

 when observations were available at each of the hours specified. The values for Ben 

 Nevis Observatory for the same 90 days have also been given for comparison. 







Percentage Frequency of Mist. 





Station. 



Height. 









Mean. 





I 









9" 



10h 



14 1 ' 



21 1> 

 % 









% 



% 



% 



% 



Ben Nevis 



4406 



73 



70 



66 



64 



67 



Cairn Dearg 



3348 



52 



54 



50 



38 



49 



Sgor-a-Mhaim . 



3601 



54 



55 



51 



42 



51 



Mullach nan Coirean 



3077 



46 



48 



46 



36 



43 



Meall Cumhann 



Mean 



2306 



26 



27 



16 



11 



20 



46 , 



3346 



50 



51 



46 



38 



