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Mean Daily Temperatures at the Ben Nevis and Fort- William Observatories. 



By R. T. Omond. 



Tables have been prepared of the average temperature at the Ben Nevis and Fort- 

 William Observatories on each day of the year, using the records of the twenty years 

 1884 to 1903 inclusive. Table I. gives the average daily temperature at Ben Nevis, 

 Table II. that at Fort- William, and Table III. the differences between them. These 

 tables have been prepared as follows : — 



Ben Nevis Observatory. — In summer the dry- and wet-bulb thermometers were 

 exposed in an ordinary Stevenson screen 4 feet above ground, and in winter in a 

 smaller-sized double-louvred screen, placed on a ladder-like stand, and moved up or 

 down so as to be always about 4 feet above the surface of the snow. These 

 thermometers were read hourly, and the average of the dry-bulb readings for the 

 24 hours of each day is taken as the temperature of that day. Table I. is the 

 arithmetical mean of the values so computed on each day of the year. 



Fort- William Observatory. — The observations at Fort- William, from 1st January 

 1884 to 31st July 1890, were made by Mr Colin Livingston at the Public School. 

 The thermometers were placed in a Stevenson screen 4 feet above ground, and the 

 daily temperature was assumed to be the mean of the readings of the maximum and 

 minimum thermometers on each day. From 1st August 1890 to 31st December 1903 

 the temperature was obtained from the hourly records of the self-recording photographic 

 thermograph at the Fort- William Observatory, which was placed against a north wall 

 of the Observatory, the bulbs of the thermometers being 5 feet above ground. The 

 average of the 24-hourly values of the dry bulb on each day is taken as the temperature 

 of that day. A table was prepared giving the mean temperature of each day of the 

 year from these data by simple averaging, but a comparison of the monthly mean 

 temperatures of seventeen months (August 1890 to December 1891 inclusive), during 

 which Mr Livingston continued the observations at the Public School after the 

 Observatory records began, showed a small difference between the monthly mean 

 temperatures, as computed from the Max. and Min. in the Public School screen and 

 from the hourly values of the Observatory dry bulb. The differences between the 

 observations at the Public School and at the Observatory in Fort- William have been 

 discussed with some fulness,* but the following table, showing the mean monthly 

 temperatures at the Observatory, at the Public School, and the difference between them, 

 for these seventeen months, gives all that is necessary for the comparison of daily mean 



* Joum. of Scot. Met. Soc, vol. x. p. 49. 

 TRANS. ROY. SOC. EDIN. — VOL. XLIV. 4 T 



