402 



Part IIL— Eleventh Annual Rr/>orf 



great detail in the report for 1890; and the figures for 1891 bear out 

 the points emphasised therein, both as regards the variations of conditions 

 with the tides and their practical bearing on fishery. 



'The mean annual temperature of the surface layer was 8°*3 at 9 a.m. and 

 8°*7 at 3 p.m., respectively 0°*6 and 0°*3 lower than 1890. The mean 

 annual temperature of the bottom water was 8° "5 at 9 a.m. and 8°*8 at 

 3 p.m., being 0°*4 and 0°T lower than 1890. 



The surface water was hottest in afternoons of August (13°*4), and cold- 

 est in January and March mornings (4° '4), giving an annual range of 9 

 degrees, nearly a degree and a half more than at the Bell Rock. (PL 

 XVIII. fig. 1.) The mean monthly temperature of the bottom water varied 

 from 13°*0 in August to 4° 3 in March. 



The hottest surface water was 15 0, 6 at 9 a.m. on June 21, and the 

 coldest was measured on March 11 at 9 a.m. and found to be 3°*2, an 

 extreme range of 12°'4 The maximum temperature of the bottom water 

 was 14°*2 at 3 p.m. on July 16, and the minimum was 3°T on March 11 

 at 9 a.m., an extreme range of 11°T. 



The curve of the air temperature shows two minima — one in January 

 and one in March — and the surface temperature curve has the same 

 number of turning points. This is a feature of the temperature curves of 

 1891 both for air and for water at all the stations both on the east and on 

 the west coasts, and affects the bottom water (24 fathoms in the case of the 

 North Carr Rock) as well as the surface layers. 



The salinity fluctuates greatly and is a function of tidal influence as 

 was shown in the Report for 1890. The mean surface density for 1891 

 was 1023-4 (2-90 per cent, of salts) in the morning, and 1024*3 (2*87 per 

 cent, of salts) in the afternoon ; while the specific gravity of the deepest 

 water was 1024*4 (3*06 per cen*. of salts) at 9 a.m. and 1025T (3*20 per 

 cent, of salts) at 3 p.m.; the diligence evidently being due to the fresher 

 river water flowing on the top. 



The water is saltest on the surface in July afternoons (average 1025*2 

 for the month), and freshest in October or December mornings (mean 

 1021*5). The mean density of the deep water is constant from July to 

 September at 1025'5, and has a minimum density of 1023 3 in October 

 and December mornings. (PI. XVIII. tig. 3.) 



But this by no means gives an accurate idea of the great variations in 

 salinity of the water at Abertay. The freshest surface water was found in 

 1891 on October 17 at 9 a.m., and had a density of 1012*8, and the 

 saltest 1026-1 was measured three times (July 5 and 31, August 9). 

 The least dense bottom water was 1015*6 on October 17 at 9 A.M., and 

 the densest 1026*3 on August 31 at 3 p.m. 



The variations are greatest at the surface, but the curve of density of 

 the bottom water has the same form as that of the surface water ; and 

 bo ih are analogous to the curve of temperature. 



North Carr Light- Vessel. 



The station is situated opposite Fife Ness, and, although influenced 

 by the proximity of land, it is less affected by the river waters (of the 

 Tay coming through St Andrews Bay and of the Forth sweeping to the 

 N.E.) than Abertay or Oxcar. 



The observations give a useful mean between those of the Bell Rock 

 and Abertay. 



The mean surface temperature for 1891 was 8°*5 C. at 9 a.m. and 8°*7 

 at 3 p.m., while the bottom (24 fathoms) water was not affected by daily 

 range of temperature, and averaged 8°*7 both morning and afternoon. 

 Here, again, the mean surface temperature was lower than that of last 



