69G MR R. T. OMOND ON THE MEAN DAILY TEMPERATURES AT THE 



at Fort-William, 5th August 1897, temperature 70 o, 4, and 11th February 1900, 

 temperature 16° - 9 ; and at Ben Nevis, 24th June 1887, temperature 60°"7, and 7th 

 February 1895, temperature 3°'2. The absolute maxima on the warmest days and the 

 minima on the coldest days were of course a little above and below these values, but 

 on Ben Nevis the shade temperature never attained 70° and never fell below zero. 



In 1867 the late Dr Bdchan drew attention to certain "Interruptions in the 

 Regular Rise and Fall of Temperature in the course of the Year " in Scotland,* and 

 showed that there were six periods when the mean temperature was lower than might 

 be expected for the time of year, and three warm periods when it was correspondingly 

 unduly high. These periods are : — 





Cold. 





Cold. 



Warm. 



1. 



7-10 Feb. 



4. 



29 June, 4 July. 



1. 12-15 July 



2. 



11-14 April. 



5. 



6-11 Aug. 



2. 12-15 Aug. 



3. 



9-14 May. 



6. 



6-12 Nov. 



3. 3-9 Dec. 



Dr Buchan examined the temperature records of ten years at five stations in 

 Scotland, namely, Sandwick in Orkney, Braemar, Milne-Graden in Berwickshire, 

 Glasgow, and Callton-Mor (Poltalloch) in Argyllshire, and he found evidence of the 

 regular return of these warm and cold periods at each. He also showed that their 

 occurrence is "determined and regulated by the wind," t which, again, is determined by 

 the distribution of barometric pressure. At the time Dr Buchan wrote there were no 

 records available from the more northerly of the western parts of Scotland, and it is of 

 interest to see how far these warm and cold periods prevail at the two Observatories, 

 situated as they are on the western side of the mountain mass of the Scottish High- 

 lands, and protected by it from the dampness of cold easterly winds. 



Looking at Tables I. and II., there is no sign of the first cold period, 7th to 10th 

 February, but the subsequent week, 10th to 16th February, has low temperature at both 

 places. The second spell, 11th to 14th April, is apparent at both as a delay in the rise 

 of temperature, as is the third, 9th to 14th May, which indeed may be regarded as 

 continuing to about the 20th. There is no trace of the fourth cold spell, 29th June to 

 4th July, nor of the fifth, 6th to 11th August, while the sixth, 6th to 12th November, 

 appears almost as a mild spell, being followed by a few distinctly colder days at both 

 stations. The first of the warm periods, 12th to 15th July, is not evident at either 

 station, and the second, 12th to 15th August, is doubtful, while the third, 3rd to 9th 

 December, is a time of falling temperature at both places. The twenty years' averages 

 at Ben Nevis and Fort- William thus show distinctly the cold periods in April and May, 

 but not the other cold and warm spells found in other parts of Scotland. It is not 

 surprising that cold spells due to an excess of north or east winds should not be felt at 

 these Observatories, where such winds are dry, and often with warmth in them of a 



* Joum. of Scot. Met. Soc, vol. ii. pp. 4, 41, and 107 ; Handy Book of Meteorology, by Alex. Buclian, second 

 edition, p. 141. 



t Handy Book of Meteorology, gecond edition, p. 142. 



