1887.] 



BEN NEVIS OBSERVATORY.— LOG-BOOK. 



355 



colours were — J, green, yellow, red. Sky was cloudless at 

 midnight. 



Dec. 22. — Aurora seen at l h , with bright horizontal 

 streaks. Top of aurora was about 10° altitude, and was not 

 well defined, but thinned off into the general tint of the 

 sky; at the same time the horizon to northward and north- 

 westwards was very dark. The top continued clear and the 

 sky cloudless till 3 h . At 2 h the south-western lights were 

 visible, and at same hour stratus streaks were seen low 

 to N.W., lying N.E. and S.W. Fog came on at 4 h , 

 changed to mist at 15 h , and cleared away at 22 h . Glazed 

 frost was forming in afternoon. A lunar corona was seen 

 at 23 h . At midnight fog covered the hills around to 

 4000 feet, leaving Ben alone clear ; at same hour sky was 

 cloudless. All afternoon the thermometer box was rather 

 badly choked with ice. 



Dec. 23. — The thermometer box was shifted at h 25 m . 

 The summit was clear till ll h . The air was very dry in 

 early morning, the humidity at 4 h being only 10 per cent 

 Glazed frost formed heavily and rapidly from a very wet 

 mist which prevailed all afternoon. The thermometer 

 box got so heavily encrusted that at 17 h there was diffi- 

 culty in opening it, and the readings of the dry and wet 

 were 7 m late in consequence. 



Dec. 24.— The top cleared at 15 h , and from then till 23 h 

 the sky (except for a little cir. at 22 h ) was cloudless. At 

 19 h , 20 h , and 21 h there was neither fog below nor cloud 

 above, but at 22 h there was fog all round, except to 

 southward, on hills to about the level of summit, occa- 

 sionally passing summit, and causing coronas, of which the 

 following measurements per stephanome were obtained: — 



Red 1 . 



Red 2 . 



Red 3 . 



1° 20' 30" 



C° 47' 0" 



4° 25' 0" 



1° 27' 0" 



2° 37' 0" 



4° 0' 30" 



1st set, 

 2nd set, 



Triple coronas were also seen at 23 h , but were too fleeting 

 to measure. At 16 u the earth shadow was seen, sharply 

 defined, topped by a belt of rosy colour rising to eastward 

 to about 20° alt. At same hour the sunset colours to 

 westward were red, at horizon sickly green to about 20° 

 alt., and pink afterglow above this to 45° alt. The ther- 

 mometer box was shifted at 15 h . Fog-bows were seen at 

 22 h and midnight. 



Dec. 25. — The top was clear from 18 h to 21 h , but fog lay 

 in detached masses on hills around. The sky was cloudless 

 at 18 h and 19 h , but cloudy afterwards, and coronas were 

 seen at 20 h and 21 h . Needle-shaped snow crystals were 

 falling at 22 h and 23 h . 



Dec. 26. — The fog cleared away after 6 h , and till 15 h the 

 sky was cloudless, but there was a good deal of stratus-fog 

 on the other hills all round. The top was covered in fog 

 again from 16 h till 22 h , and at 23 h and midnight fog was 

 passing at times. After ll h the thermometer box was 

 shifted. At 23 h and midnight coronas were observed 

 (double) ; at former hour following measurements were 

 obtained : — Inner red, 5° 3'; and outer red, 9° 28'. 



Dec. 27. — A double corona was first seen at l h and the 

 following measurements per stephanome were obtained, 

 viz. : — 



Inner Red. Outer Red. 



1st set, . 4° 34' 8° 4' 



2nd set, . 4° 46' 8° 22' 



The summit was clear till 19 h , but fog on after that. 



The thermometer box was shifted after 10 h . At 22 h a 



TRANS. ROY. SOC. EDIN. VOL. XXXIV. 



corona was observed, with white and red as only colours ; 

 measurements of outside of red gave 2° 6' as radius. 



Dec. 28.' — Double and triple coronas were seen at 3 h , 4 h , 

 and 5 h , and fog-bows at 4 h and 5 h . At 3 h the extreme 

 outer edge of the first red (i.e., red nearest moon) was 

 measured, with following result: — Radius on 1st red, 3 31'; 

 2° 6'; 2° 6'; 3° 42'. At times the 2° 6' red was the inner 

 red in a double corona, in which the 3° 42' red was the 

 outer. Fog was on summit, or passing till 18 h , after 

 which it sank, and gradually diminished in quantity till at 

 23 h and midnight there were only detached str.-fog pieces 

 low to north and north-eastward. 



Dec. 29. — At l h there was a little str.-fog to northward 

 and eastward, but by 5 h there was fog all round, with very 

 few breaks. After 7 h it began to rise as a whole, at 8 h it 

 was passing eastern end of summit, and at 9 h it was pass- 

 ing generally, and the air (till then dry) was saturated. 

 At 10 h the fog began to break up, the south-western hills 

 clearing first ; but after 14 u it began to close all round again, 

 and from 18 h till midnight it was either on or passing the 

 summit. At 7 h and 8 h cir. and cir.-str. clouds were seen at 

 north-eastern horizon. From 13 h to 16 h the sky was 

 almost covered with cirrus; but at 18 h and till midnight 

 the upper sky was cloudless. The following measurements 

 of the radii of red rings in lunar coronas were obtained at 

 night : — 



20 hours. 



1st Red. 



2nd Red. 



3rd Red 



1° 42' 



3° 28' 



5° 52' 



1° 55' 



4° 20' 





1°54' 



3° 25' 





1° 44' 



3° 15' 



5°0' 



2° 24' 



4° 13' 





2° 24' 



3° 46' 





1°54' 



2° 59' 



5° 0' 



No. of Red 





Rings seen. 





3 





2 



1st. set. 



3 



2nd „ 



3 



3rd „ 



2 



1st ,, 



2 



2nd „ 



3 



3rd „ 



23 hours, 



Midnight 



(measurements made in each case to extreme outside of red). 

 When the corona was triple all the colours of spectrum 

 were seen between red 1 and red 2 , the blue usually brightest. 

 The broken cup-arm of the Robinson anomometer was 

 spliced after 14 h to-day. 



Dec. 30. — Thin fog on summit till 4 h , after which it 

 sank, remaining on hills for the rest of the day with its 

 upper surface from 3000 to 4000 feet above sea-level. In 

 the early morning the following measurements of radii of 

 red rings in lunar coronas were obtained per stephanome ; 

 the measurements were made to outside of red in each case, 

 viz. : — 



No. of Red 

 Rings seen. 

 4 

 3 

 3 

 3 

 3 

 3 

 3 

 3 

 4 

 3 

 3 

 3 

 3 

 3 

 4 

 4 

 3 

 4 

 2 

 4 

 3 



4 B 







1st Red. 



2nd Red. 



3rd Red. 4th Red. 



fist set, 



1°43' 



3° 13V 



4° 43' 6° 48' 



1 2nd,, 



1°41' 



3° 9' 





1 4th „ 



1°43' 



2° 56' 



5°' 0' .'." 



1°44' 



2° 52' 





I 5th ,, 



1°43' 



3° 10V 



4°56' 



1 6th ,, 



1° 43' 



3° 4' 



4° 43' 





'1st set, 



1° 33' 



2" 47' 







2nd,, 



1°22' 



2° 30' 





2b- 



3rd „ 



1° 49V 



2° 33' 



3° 56' 



4th ,, 



1° 21' 



2° 33' 



3° 46' 





5th ,, 



1° 27V 



2° 39' 



3° 58' 





.6th ,, 



1° 21V 



2° 27' 



3° 38' 





' 1st set, 



1° 5' 



2° 6' 







2nd „ 



1° 4' 



2° 4' 





3h- 



3rd ,, 



1° 10' 



2° 5' 



3° 13V 



4th ,, 



1°14' 



2° 17V 



3° 12' 4° 37' 





.5th ,, 



1° 6' 



2° 11' 



3° 4' 



f 1st set, 



1° 36' 



2° 43' 



4°5V 



4 hJ2nd„ 

 | 3rd ,. 



0° 55V 



1° 51' 





0° 56V 



1° 35' 



2° 41' '.'.'. 





14th ,, 



0° 56' 



1° 42' 



2° 51' 



