of the Fishery Board for Scotland. 



407 



4. OBSERVATIONS ON THE EAST COAST, 1892. 

 Bell Rock Ligldhouse. 



The observations of the temperature and of the specific gravity of the 

 surface water are taken at 9 a.m. and at 3 p.m. The former are made in 

 the sea itself, the latter in the library of the lighthouse after the water 

 has been allowed to come to a steady temperature. 



Owing to the roughness of the sea at this station it often is impossible 

 to make direct observations at all states of the tide. There are many 

 blanks in the register, especially during the winter months. It has been 

 arranged that in future approximate readings be made on such occasions 

 by drawing a tub of water into the lighthouse and immediately deter- 

 mining its temperature, the records so obtained being specially marked. 

 Both for temperatures and for specific gravities, however, there is a 

 sufficient number of readings to give ten-day means very near what the real 

 figure must be. Special marks have been inserted in Table V., 1892, to 

 show what number of observations was used in determining the mean. 



One serious gap in the specific gravity and salinity tables is caused by 

 the hydrometer used during that period being damaged. The observer 

 writes — ' The specific gravity for die months of June and July and up 

 ' to the 9th August is not correct as our glass was damaged. The new 

 ' one arrived on the 9th August and then we found there was about 1 of 

 1 difference between the damaged one and the new one.' It is, however, 

 impossible to apply a satisfactory correction to the actual observations, for 

 the observer remarks — ' The difference would not be so great in the month 

 ' of June, but latterly water was getting into the glass, which caused so 

 ' great a difference.' (Table XIV., 1892.) 



The mean temperature of the air at the Bell Rock for 1892 was 7°*9 at 

 9 a.m., and 8° *8 at 3 p.m., the corresponding means of the temperature of 

 the surface water being 7°*7 and 7°'8. The surface water was 0 o, 9 colder 

 than in 1891, and nearly a degree and a half colder than in 1890. 



The curve of temperature for the surface water has the same form as 

 in previous years, except for a very sudden rise in May corresponding to a 

 period of very high air temperatures. The minimum month iy mean was 

 that of March, when the water was 4°T in the forenoon, and 4°*2 in the 

 afternoon, and the mean maximum at 9 a.m. was 1 1°*4 in August and 

 September, and at 3 p.m. was 11°'7 in August — a mean range of 7°3 in the 

 forenoon, and 7° "5 in the afternoon. (PL XVIII. fig. 4.) 



The extremes show a maximum of 12° -4 on the afternoons of August 

 17 and 24, and a minimum of 3° '8 at 9 a.m. on the 8th, 10th, and 

 15th of March— range 8°*6. 



The mean morning air temperature was reached about the middle of 

 May, and again in the second week of October. In the afternoon the 

 mean was the same as that of April 1-10 and 21-31, and of the 

 beginning of November. The surface temperature was the same as the 

 annual mean at the end of May, and again at the end of November. 



The mean annual density of the water was 1025*6 (pure water being 

 reckoned 1000), which is equivalent to a 3 2 7 percentage of total salts. 



The mean monthly specific gravity of the water was highest (10 J5*9) on 

 September mornings and May afternoons, and lowest in August (1025*2 

 at 9 a.m. and 1025 '3 at 3 p.m.), but the variations are very slight, and it 

 must be remembered that the early August readings gave too low specific 

 gravities, owing to the hydrometer being damaged. (See PL XVIII. 

 fig. 6, for curve.) 



The deusest water was found on May 19, at 3 p.m., and had a specific 



