METEOROLOGY OF BEN NEVIS. xli 



11 



the greatest intensity since being last set. With this thermometer it is remark- 

 able that the maximum occurred almost exactly at noon, and the mean hourly 

 diurnal varied from the minimum 38° '1 at 4 a.m. to the maximum 67°"0 at noon, 

 showing thus a variation of 28°'9 in the temperature thus observed. 



Quite different was the temperature shown by the thermometers in the 

 Stevenson screens, in both cases the minimum occurring at 5 a.m. and the maxi- 

 mum 4 p.m. At 48 inches above ground the minimum was 38°'4, and the maxi- 

 mum 42°*0 ; and at 112 inches the figures were 38°'5 and 41° # 8, being thus nearly 

 the same. The diurnal variation was 3° "6 and 3° '3 respectively, the smaller 

 variation, as was to have been expected, at the greater height. During the time 

 there was an entire absence of calm days with bright sunshine, when the stones 

 which strew the summit get so heated as to be disagreeable to handle, and conse- 

 quently the diurnal variation was less than would otherwise have been the case. 

 Two days only could be characterised as fine days, and on these days a relatively 

 greater range was observed at the lesser elevation.* 



Rainband Observations. — After some preliminary and fragmentary observations, 

 rainband observations began to be a regular part of the work of the Observatory in 

 June 1885. The instrument employed is one of Hilger's small pocket spectroscopes 

 fitted with a glass cap as a slit-protector. It is 2 inches long, and shows the 

 prominent lines in the solar spectrum very distinctly, and the rainband as a 

 separate line. The part of the sky observed is always about 40° above the south- 

 western horizon. The observations were discussed by Mr Rankin in 1887, and 

 were compared with the rainfall and temperature. The mean results show that a 

 heavier rainband indicates a heavier rainfall. The rainfall is greater for the three 

 hours than for the twelve hours after the observation for the higher values of the 

 scale ; and it is less for the lower values. Hence the observed higher values are 

 accompanied or soon followed by a heavy rainfall, which tends to become less 

 heavy in the next twelve hours. The lower values, on the other hand, though they 

 may be neither accompanied nor followed in the next three hours by any rain, are 

 followed by a considerable rainfall before the twelve hours are run. 



A great many of the anomalies the observations show are explained when the 

 effects of temperature are taken into consideration. Thus for any rainband value 

 the precipitation is less with a higher, and greater with a lower temperature. 

 Again, when the temperature falls after the observation, the subsequent rainfall is 

 greater ; but when it rises, the rainfall is less than it would have been if the tem- 

 perature had remained constant. The very highest values, which were almost all 

 accompanied or followed by heavy rain, appear to be characteristic of, or part and 

 parcel of the cyclones which sweep in from the Atlantic laden with warmth and 

 moisture. 



* " Temperatures at Different Heights above Ground," by E. T. Omond, Proc. Boy. Soc, vol. xiv. 

 p. 24. 



