Part III. — Eleventh Annual Report 



gravity of 1026*3 ; the water was least dense on the mornings of 9th and 

 10th August, and its specific gravity was 1024 - 6. 



The lightkeepers report that a very vivid display of St Elmo's fire 

 took place during a severe snowstorm last winter. The attention of the 

 keeper on duty was drawn to it when he was firing the explosive cartridges 

 used as alarm signals. 



Abertay Light-Vessel. 



Except from June 27 until July 14, when the ship was in dock, the 

 observations have been made very regularly. 



The mean morning temperature of the air was 7°*7, that of the surface 

 water 7°*5, that of 3-fathom water 7°'9, and that of the bottom water (6 to 

 10 fathoms) 8 o- 0. The corresponding means for the afternoon were — air 

 9°'9, surface 7°"6, 3 fathoms 8°T, and bottom 8°'l. The mean surface 

 temperature at 9 a.m. was lower by 0°'8, and at 3 p.m. by l°'l than in 

 1891. The mean temperature of bottom water was 0 o, 5 and 0 o, 7 lower 

 than in 1891 in the forenoon and afternoon respectively. 



The following table shows the maxima and minima of mean monthly 

 temperatures for 1891 and 1892, also the ranges : — 



Mean Monthly Temperatures, Abertay, Maxima and Minima. 





1892. 



1891. 





9 a.m. 



3 P.M. 



9 A.M. 



3 p.m. 



Minimum — 



3°6 (Mar.) 



3°9 (Mar.) 



4° 4 (Jan., Mar.) 





Surface . . 



47 (Jan.) 



Bottom 



4-0 (Mar.) 



4*2 (Mar.) 



4-3 (Mar.) 



4-8 (Jan., Mar.) 



Maximum — 











Surface . . 



12-0 (Aug.) 



12'1 (Aug,) 



13-3 (Aug.) 



13-4 (Aug.) 



Bottom 



12-1 (Aug.) 



12-1 (Aug.) 



13-0 (Aug.) 



13-0 (Aug.) 



Range — 











Surface . . 



8-4 



8*2 



8'9 



87 



Bottom 



8-1 



7-9 



87 



8-2 



The minimum monthly mean is fully half a degree lower than in 1891, 

 the maximum over a degree lower, and the range averages half a degree 

 less. 



The highest recorded temperature of the surface water was 14 0, 2 at 

 9 a.m. on August 22, and that of the bottom water was 13°*6 at same 

 time. The lowest reading for surface water was 2° "4 at 9 a.m. on January 

 13 and 14, and for bottom water 3° 4 on March 14. The extreme range 

 was therefore 11 0, 8 on surface and 10° *2 at bottom, compared with 12°'4 

 and ll°'l in 1891. 



In spring the mean air temperature was reached towards the end of 

 April, the mean surface temperature early in May, and that of the bottom 

 water about the middle of that month. In autumn the air temperature was 

 the same as the mean of the year early in October, the upper layers of 

 water at the beginning of November, and the bottom water at the end 

 of November and early in December. 



Looking at the curves (rig. 5) drawn from figures published in Table I., 

 1892, those for the surface and the bottom temperatures almost coincide 

 until August, but the curve for the deeper water is somewhat higher in the 

 early months of the year. From September onwards the temperature curve 



