322 



BEN NEVIS OBSERVATORY. — LOG-BOOK. 



[1891. 



str.-fog on hill tops to N. and E. at night. Sun set at 

 15 h 50 m just hehind eastmost hill of Mull. Earth 

 shadow anil Ben shadow distinct just before and after 

 sunset. After-glow with streamers at 16 u 15 m . Ther- 

 mometer box shifted at 10 u 15 m . Height above snow 

 not altered. The snow at first gorge to-day was found 

 to be projecting 214 inches. 



Dec. 17. — Fog lay on hill tops to E. in early morning, 

 and gathered again on them after sunrise. Haze in 

 valleys all forenoon. Cum.-fog on hills to S.W. after 

 noon, which after 15 h spread over Ben Nevis also. 



Dec. 19. — Owing to a leak in one of the raingauges, 

 some of the rainfall entries between 20 b on the 18th, 

 and 4 h on the 19th, are doubtful. 



Dec. 20. — Very thick fog all afternoon, but at 20 h 

 the stars began to be visible, and for the rest of the 

 night the sky was cloudless, but fog lay over the hills 

 round, thickest to S.E., and blew over Ben Nevis also 

 occasionally. Lunar corona seen on this fog frequently. 

 Thermometer box shifted at 22 h 24 m . Height above 

 snow not altered. 



Dec. 21. — Sky cloudless all day, but fog on hills at 

 about 4000 feet till 6 h . At 2 h it was blowing over the 

 top, and the temperature fell 6°. Sun rose at 8 h 47 m . 

 Upper glow before sunrise and after sunset, also Earth 

 shadow and Ben shadow. Some haze in the valleys in 

 the middle of the day, but air clear above it over the 

 hill tops. Green flash seen as the sun sank behind the 



eastmost hill of Mull. Aurora, single arch, seen from 

 21 h till l h on 22nd. At 16 h the wet bulb was dry, and 

 the entry on daily sheet is interpolated, after that it 

 was wetted between hours. 



Dec. 22.— Aurora seen at l h , and at 20 h , 21 h , and 22 h . 

 Sky cloudless all day. From 8 L onwards haze in the 

 valleys, which rose just after ll h , and covered the top 

 as fog. Sun set at 15 h 47 m . Green flash seen faintly. 



Dec. 25.— Fog most of the day, but at 10 h and ll h 

 it sank below the hill top, leaving sky cloudless. The 

 air became dry ; humidity about 60 per cent, at these 

 hours. 



Dec. 26. — St Elmo's Fire at 23 h , very blue in colour, 

 seen on snow covering anemometers and on kitchen stove 

 pipe ; not felt by observer. Ordinary rather small grained 

 snow falling at the time, not the usual conical soft hail. 



Dec. 28.— Thermometer box shifted at 3 h 20 m . 

 Height above snow not altered. At 21 h and 22 h the 

 strong squalls and drift made it almost impossible to 

 carry a lantern outside. The tower thermometer readings 

 were therefore used at these hours, and a correction 

 applied. Heavy rain, hail, and icy drift at 22 h , 23 h and 

 midnight. 



Dec. 28. — Strong earth current in telegraph cable at 

 3 h 54 m . Hard conical snow falling at 8 h . 



Dec. 29 — Strong earth current in telegraph cable at 

 3 h 54 m , and a weaker one at 7 h 20 m . Hard conical snow 

 was falling at 8 h . 



INSTRUMENTS ETC., 1891. 



Barometers.— No. 1385 was in use during the whole 

 year, No. 1252 being kept in reserve; the latter is 

 supposed to have a trace of air in its vacuum. 



The following Dry and Wet Bulb Thermometers were 

 used : Nos. 535541, 535542, 192671, 192672, 192677, and 

 up to March 4th, 192660. On March 4th the last men- 

 tioned was accidently broken. 



Max. 117293, min. 116918 were in use in large 

 screen from June 15th to Nov. 12th. Up to July 17th 

 the large screen was the old one formerly in use ; after 

 that date a new screen fixed up close alongside of the old 

 screen was used. Up to June 14th and after Nov. 12th 

 mins. 138533 and 138545 were used in small screens on 

 Ladder Stand No. 2. 



On Dec. 7th the Tower Box was modified to suit a 

 new thermometer. The tube extends inside, so that the 

 temperature is read inside the top story of tower. It 

 hits been in occasional use. 



The usual 5-inch raingauges, rain or snow pattern 

 according to circumstances, have been used. 



The Campbell-Stokes Sunshine Recorder has been 

 in use throughout the year. The Sunshine is now 



entered to Mean Local Time, instead of as formerly (up 

 to 31st Dec. 1890) to Mean Greenwich Time. 



Black Bulb in vacuo max. No. 186 was in use when 

 possible, but was sent to Adie and Wedderburn for 

 repairs on Nov. 14th, the outer jacket being cracked, 

 and has been returned to the Low Level Observatory, 

 where it is being tested. Black Bulb No. 484108 common 

 thermometer in vacuo was also in use for hourly readings 

 in summer. 



The Direction and Force of the Wind has been 

 estimated, as usual, on the roof at the hourly observations, 

 and the Robinson H.C. Anemometer has been in use 

 when practicable. The Chrystal Direction Anemometer 

 has not been used. The clock of the latter is used as 

 standard G.M.T. clock in office. 



The llainband observations have been continued with 

 a direct vision spectroscope. From Nov. 27th to Dec. 

 22nd the instrument was away being repaired. 



Several photographs have been taken. 



The Stephanome has been employed as usual for 

 measuring glories, corona?, etc. 



The depth of snow was taken at post A as before. 



