4 INTRODUCTION. 



day, the highest and lowest in each month being put in bold-faced type. Self- 

 registering Maximum and Minimum thermometers are not used, as their frequent 

 incrustation with ice in winter would vitiate their readings. The record for each 

 month occupies a page, the upper part containing the readings from 1 to 12 hours, 

 with the Max. and Min. for the day at the right hand side, and the lower part the 

 afternoon hours with the daily means : the mean values for the month of each hour 

 are given at the foot of each part. 



During very stormy weather, when it would be dangerous to go out to the 

 ordinary screen owing to violent wind and blinding snow drift, the temperature is taken 

 in a screen attached to the wall of the Observatory Tower, the thermometers in 

 which can be read without going outside. Comparisons of this screen with the 

 Stevenson Screen show that when the wind rises to force 9 or more, there is practi- 

 cally no difference between their thermometers at night. But this Tower screen 

 has only been used once or twice each year, and then only for a few hours at a 

 time, since it was erected in August 1890. 



The Rainfall at Ben Nevis Observatory is recorded hourly ; the gauge is circular, 

 of five inches diameter, and with its rim as nearly as may be one foot above the 

 surface. Two gauges are kept in use ; the observer at each hour takes one out 

 with him, places it on a prepared base on the stones in summer, or in a slight 

 concavity of the snow in winter, levels it with a spirit level, and brings in the 

 other gauge, w T hich has been out for an hour, to be thawed if necessary and measured 

 at leisure. These gauges are made with an enlarged rounded base for stability and 

 convenience in levelling. The hourly values are given in the tables to thousandths 

 of an inch. The column at the right hand side of each table gives the total amount 

 for each day ; the sum of the twenty-four hourly readings, and the heaviest daily 

 fall in each month, are printed in bold-faced type. At the foot of each table is given 

 the sum total of each hour for the month. All snow, hail, etc., is melted and 

 measured as rain. 



Sunshine is recorded at Ben Nevis Observatory by a Campbell- Stokes Recorder 

 of the usual pattern ; it is placed on a stone pillar rising from the south side of 

 the roof of the Observatory, and is clear of all obstructions from sunrise to sunset 

 at all seasons of the year. This is the only automatically recording instrument used 

 outside the Ben Nevis Observatory, and its use is only rendered possible by constant 

 attention. It is only put out when the hill top is clear of mist, and has to be ex- 

 amined frequently to see that snow does not lodge on the glass ball or card. After 

 sunset the whole instrument is taken into the Observatory, and usually has to be 

 thawed and dried for some time before the card can be withdrawn from the frame. 

 The cards are set in the frame so as to register the sunshine in hours of mean local 



