ON METEOROLOGICAL OBSERVATIONS ON BEN NEVIS. 283 



pared the raiDfall at tie Fort William Observatory with the monthly 

 amounts collected with the old gauge at Mr. Liyingston's during the year 

 and a half tnding with December 1892, with the result that the rainfall at 

 the observatory is 4'6 per cent, less than at Mr. Livingston's. The largest 

 rainfall of any month at the top was 22'32 inches in January, and at Fort 

 William 14"42 inches in September, the smallest amounts being respectively 

 5'42 inches and 1'84 inch, both occurring in March. The heaviest fall on 

 any single day at the top was 5'76 inches on January 25, and at Fort 

 William 2-83 inches on November 28. 



The number of days on which the rainfall was nil, or less than one- 

 hundredth of an inch, was 116 at the top, and 152 at Fort William. At 

 the top the largest number of days was 16 in July, and the smallest, 5, 

 in January ; and at Fort William the numbers were 23 in March and 

 5 in January. At Fort William a fall of an inch of rain a day or more 

 occurred on 13 days during 1892, but at the top of Ben Nevis on 50 days, 

 or nearly four times as often. From one to nine such wet days were 

 recorded at the top each naonth, whereas at Fort William no such wet 

 days occurred in March, April, June, July, and September, and on four of 

 the other months only one day each. 



At Fort William the mean atmospheric pressure at 32° and sea-level 

 was 29"852 inches, and at the top 25'284 inches, thus giving a diflerence 

 of 4"568 inches. The lowest pressure at the top for the year was 24'147 

 inches at 2 p.m. of February 2, and the highest 25*960 inches at 7 p.m. of 

 March 22, the difference being ] "813 inch. 



Mr. A. J. Herbertson is carrying on at the two observatories the 

 research on the hygrometry of the atmosphere referred to in our report of 

 last year. During last autumn and early winter he spent upwards of 

 four mouths at the Ben Nevis Observatory, and there measured the- 

 aqueous vapour by direct weighing, obtaining a new and valuable series 

 of experiments at very low temperatures and humidities. Since July last 

 a similar set of experiments are being conducted by him and two skilled 

 assistants, involving measurements of the aqueous vapour simultaneously 

 at both high- and low-level observatories. Observations are made at the 

 same times with the dry and wet bulb, both in a Stevenson screen and 

 in an Assmann aspirator psychrometer ; with Reguault's hygrometer; 

 and of the numbers of dust particles present, the general weather con- 

 ditions as to barometric pressure, sunshine, wind, &c. Mr. Herbertson 

 has communicated a preliminary report on the results of last year's- 

 observations and experiments to the Boyal Society of Edinburgh, in 

 which among other points of interest the very unsatisfactory character of 

 the hygrometric tables now in use is clearly shown for low temperatures 

 and great dryness. The experiments at present in progress give the cor- 

 responding data for summer temperatures and humidities ; and, seeing they 

 are conducted simultaneously both on the top of the Ben and at Fort 

 William, the eflfect of large differences of pressure will be seen on the rela- 

 tions of the dry and wet bulb readings to the amounts of aqueous vapour 

 actually present in the air at the time. The Dirpctors regard these 

 experiments as of great importance, not only as furnishing data towards a 

 better knowledge of the hygrometry of the atmosphere, but also as leading 

 to much needed improvements in the methods of reducing the readings of 

 the dry and wet bulb theimometers. 



Mr. Omond has written a paper on hourly readings of a black bulb 

 thermometer in vactio as compared with the readings of the dry bulb 



