of the Fishery Board for Scotland. 



303 



With respect to the other observations the influence of the hot weather 

 is shown by the greater value of the mean density for 1893 at most 

 stations than in the two previous years ; and the absence of great floods 

 makes the extremes less marked than in some seasons. 



Now these years, since the physical observations were first begun, 

 differ very much, each having its own characteristics, and the comparison 

 of the physical results with the biological and economic data should not 

 be delayed much longer. At the close of 1895 many of the stations will 

 have the records of almost six years observations, sufficient to calculate 

 approximate mean values with which the results of the various years may 

 be separately compared. When the other statistics collected by the 

 Board have been similarly treated and compared with the physical 

 results, it is reasonable to hope that some conclusions of practical utility 

 may be drawn, and it is highly desirable that their value should be 

 tested by a thorough investigation of the relationship between them and 

 the biological data at the Board's disposal. In this Report, as in past 

 reports, a number of special peculiarities in the conditions of the sea 

 water have been pointed out, and the investigation of their influence on 

 fishes urged as possibly of considerable importance. Such special investi- 

 gations should not be lost sight of in the general research as to the 

 relationship between the various sections of the Board's scientific work. 



In 1893 the stations were all inspected. As a considerable period had 

 elapsed since the previous inspection, it was found that several of the 

 instruments were out of order, more particularly some hydrometers whose 

 stems were so badly made that the instrumental errors varied at all parts 

 of the scale. The result is that the work of preparing the tables for the 

 present Report has been excessively troublesome, almost every observation 

 at some stations having to be specially corrected. Further, it must be 

 noted that some of these imperfect instruments were in use before 1893, 

 and the figures in the Eleventh Annual Report in many cases must be 

 slightly modified when the means for a number of years come to be 

 calculated. This will entail considerable labour ; but it should be under- 

 taken, as the practical worth of the present observations can be realised 

 only when this is done and a comparison made between physical and 

 biological observations during the same periods. 



The degree of accuracy of the observations varies at different stations, 

 and it is to be regretted that every observer cannot have some special 

 training before he is entrusted with taking observations. Several months' 

 observations have been lost through an observer not understanding how 

 to read the thermometer below zero : in another case a small but constant 

 correction had to be made because another observer held the instrument 

 wrongly when reading it. The rolling of the lightships is another 

 difficulty to be met, but it must be remarked that, while the North Can- 

 observations are not altogether trustworthy, those made at Abertay and 

 on the 1 Garland ' are quite satisfactory. 



The tables in the present Report have been prepared from the observa- 

 tions as recorded in the books of the various stations, corrected for 

 instrumental and observational errors. In the Eleventh Annual Report 

 a full account was given of the way in which the hydrometer observations 

 were treated, in order that they might be comparable, and that the 

 proportion of salts might be calculated. The same method has been 

 adopted in the present instance. 



The result of recent hydrometric work (see Twelfth Annual 

 Report, p. 345) is to show that the hydrometer is a very reliable instru- 

 ment for the estimation of specific gravities and indirectly of salinity, 

 provided a proper vessel be used to hold the water tested. The glass 

 cylinders supplied by the Fishery Board are rather under the diameter 



