308 Part III. — FJcvcnth Annual Report 



im,ly, the Stranraer curve for 1891 was studied along with the tidal 

 curve, but without yielding any definite results. 



Special points call for detailed attention. For instance, the effect of 

 the flooded river at the end of August 1892 on the fishing in the estuary 

 of the Forth. The freshening of the water is not the only factor to 

 be considered in this case ; the influence of the muddier stream on the 

 transparency may be of great importance. Another point is the marked 

 arrest in the fall of temperature during November 1892. 



The great value of the ' Garland ' observations on the transparency of 

 the water was pointed out in the last Report and is corroborated in the 

 present one. It is desirable that the necessary apparatus for transparency 

 observations be supplied to the two lightships. From regular records 

 made at the North Carr and Abertay stations comparisons of trans- 

 parency with tidal conditions may be made ; and these results being- 

 studied along with fishery statistics, will propably yield valuable infor- 

 mation. At present it is possible to show that the water in the middle 

 of the Firth of Forth is clearest, and that that on the north side, while a 

 little less transparent than the central waters, is notably clearer than 

 that near the southern shores. The fishing returns might be so arranged 

 to be comparable with these physical results, which probably have con- 

 siderable influence in determining the visibility of the nets. 



In the Report for 1890, a full account was given of the apparatus used 

 at the various stations. 



The temperature continues to be read in Centigrade degrees, but there are 

 some exceptions which have to be dealt with and reduced from the 

 Fahrenheit to the Centigrade scale before the Report can be prepared. 



The instrumental errors are all very small, and no correction has been 

 applied for them. 



The Scientific Superintendent inspected some of the West Coast 

 stations in 1892, but no other inspection has been made since last Report 

 until March and April of the present spring, when Mr Herbertson was 

 instructed to visit the East Coast stations. The surface thermometers in 

 the case of the Bell Rock Lighthouse and the North Carr Light- Vessel 

 were found to be defective, and new ones have been supplied. The 

 hydrometers in all cases compared with the standard instruments within the 

 necessary limits. The density observations at the Bell Rock during June, 

 July, and part of August 1892, were made with a defective hydrometer, 

 and, unfortunately, cannot be properly corrected. The specific gravity 

 determinations at the Oxcar Lighthouse during some weeks of the spring 

 of 1893 were made with a repaired hydrometer which, when tested, 

 gave readings somewhat different from those of the standard instrument. 

 The differences have been noted, and corrections must be applied to all 

 the readings of that period in which that hydrometer was used before the 

 tables for the present year can be compiled. 



The specific gravity determinations are made with hydrometers graduated 

 to register accurately at 17° 5 C, the density of pure water at that tem- 

 perature being taken as = 100O0. The temperature of the water is noted 

 at the time the observation is made, and in order to reduce the observed 

 specific gravity to what it would be at the standard temperature of 

 17°*5 C, a special table must be used. This has been calculated from 

 that given by Professor Dittmar in his ' Challenger ' Report on the 

 Chemistry of Ocean Water. His table is calculated for a different 

 standard temperature — that at which the density of water is a maximum 

 = 4° C. 



In order to reduce the figures of Professor Dittmar's table to those 

 applicable to the Fishery Board's instruments, the following equation is 

 given by Dittmar : — 



4 S t +l -283 ± 0-0063 = l7 . 6 S t . 



