METEOROLOGY OF BEN NEVIS. 



xxix 



the tower of the Observatory, which admits of easy egress to the thermometers 

 outside when the top of the mountain is deeply covered with snow, was not 

 erected till the summer of 1884, occasional interruptions in the thermometric 

 readings occurred during the first five months, on to April 1884, when blinding 

 snowdrifts rendered it unsafe for the observers, even though roped together, to 

 go outside. As the season advanced the interruptions became less frequent, and 

 from May 7, 1884, the observations of temperature have been made without the 

 break of an hour, except for 14 consecutive hours from 6 p.m. of February 21, 

 1885, to 8 a.m. of the 22nd, this period being signalised by a storm of such 

 unprecedented severity as absolutely precluded the possibility of any egress to 

 the Stevenson screen. In the following tables of temperature observations, 

 the omitted hours of observations have been interpolated, — the maximum and 

 minimum temperatures and the barometric, wind, and other observations that 

 happened to be made in the interval being used as guides in interpolating. 

 In all cases the interpolated observations are printed within brackets. 



Table I. gives the mean hourly temperatures of the months for the four 

 years, and the hourly variations from the monthly means. The following table 

 shows for the seasons the means and the mean coldest and warmest hour of 

 the day, and their differences from the daily means : — 





Minimum. 



Maximum. 





Hour. 





Hour. 



Winter, 



Spring, 



Summer, 



Autumn, 



Year, .... 



-0°3 

 -1-2 



-1-6 

 -06 

 -09 



5 A.M. 

 5 „ 



5 „ 



6 „ 

 5 „ 



+°0-5 

 + 1-3 



+ T8 

 + 10 



+ 1-2 



1 P.M. 



2 „ 



3 „ 



1 „ 



2 „ 



Thus for the whole year, the difference between the mean coldest hour, 

 5 a.m., and the warmest hour, 2 p.m., is 2° 1. In winter the difference is only 

 o, 8, but in summer it is 3°*4. The month of least range 0°*6, is January. 

 For the five months from October to February, the mean daily range of 

 temperature varies only from 0°6 to 1°5. 



This is the time of the year when storms are most frequent, and this small 

 range in the diurnal march of the temperature is an important feature in the 

 climatology of Ben Nevis, inasmuch as it presents in nearly their simple form 

 the great changes of temperature accompanying storms and other weather 

 changes, which it is so essential to know in forecasting weather. On the other 

 hand, the cyclonic changes of temperature are markedly large, and may be 



