284 REPOET— 1893. 



thermometei' in the Stevenson screen, wliicli was published in the last 

 ' Journal ' of the Scottish Meteorological Society. The results are interest- 

 ing and suggestive. He has prepared a paper on the height of the lower 

 edge of the cloud layer on Ben Nevis, based on observations taken at In- 

 verlochy during some months of the present summer ; and has also insti- 

 tuted a comparison of the temperature observations from August 1890 to 

 December 1891, made simultaneously by himself at the new observatory 

 and by Mr. Livingston at the old station with the instruments in use 

 there since 1883. 



At last year's Meeting of the Association a grant of 501. was made to 

 aid in the payment of assistants to perform the strictly routine work of 

 Dr. Buchan and Mr. Omond, so that their time would be set free for the 

 discussion of the observations of the two observatories beginning with 

 August ] 890. This arrangement has been carried out, and the following 

 is a detailed statement of the work which has been completed or is still 

 in progress. 



From the first eight years' observations of the rainfall at the top of 

 Ben Nevis the mean hourly variations for the twelve months of the year 

 have been calculated, and the hourly values reduced to percentages above or 

 below the monthly means. The results were then ' bloxamed ' in the usual 



way, that is, the value for 1 a.m. of January equals "^ — ; for 



o 



1 A.M. of February -— ^ — , &c., where the Roman numerals repre- 



o 



sent the values of the months December, January, February, &c., for 

 these years. In this way Table IV. has been constructed, which shows 

 the diurnal variation in the precipitation throughout the year. As was to 

 have been expected, the curves for the warmer months of the year are 

 best marked. These show a clearly defined double maximum and mini- 

 mum. The larger maximum occurs from 11 a.m. to 8 P.M., or during the 

 warmer hours of the day after the ascending current has set in. Then a 

 minimum occurs from 8 p.m. to 1 a.m., or during the hours when tem- 

 perature falls most rapidly, and the evening maximum of pressure prevails. 

 For the next six hours precipitation is above the average, the greatest 

 increase being from 5 to 6 a.m. ; and finally from 7 to 11 a.m. the next 

 minimum occurs, or during the hours atmospheric pressure and tempera- 

 ture increase, and terminates with the formation of the ascending current, 

 which is so pronounced a feature in the meteorology of Ben Nevis. During 

 the colder months the curves are less distinctly marked, except a decided 

 maximum during the coldest hours of the day, and a minimum during the 

 hours of the morning barometric maximum, when temperature is rising. 



The hourly variation of the rainfall is more clearly shown than at any 

 other observatory at which hourly observations have been made from 

 results extending over a comparatively short term of years. 



The discussion of the hourly barometric and thermometric means at 

 the two observatories for the three years is nearly complete. 



An inquiry into the diurnal variation of the barometer and thermo- 

 meter on Ben Nevis during days of clear weather on the one hand, and days 

 of fog or mist throughout on the other, is completed for the three years 

 ending August 1893. The inquiry had not proceeded far when it was 

 apparent that the curves for clear weather and those for clouded weather 

 while fog or mist was absent were in all essential respects the same ; but 

 the curves were of quite a different character when fog or mist prevailed. 



