PHYSICAL INVESTIGATIONS. 163 



from Anvil Point back to Bolt Head (see Plate XI) . Column 1 gives 

 the laboratory number of each sample of water; columns 2 and 3^ 

 the date and hour ; columns 4 and 5^, the position and depth of the 

 sounding ; column 6^ state of the tide ; 7 and 8, direction and force of 

 the wind ; 9^ weather at the time of observation ; 10, temperature of 

 the air as ascertained by a sling thermometer; 11, depth of obser- 

 vation ; 12, the temperature (corrected) at that depth ; 13 and 14, 

 the densities, referred to 4° C, at ]5'56° C, and in situ. Column 15 

 shows the density at 0° C. referred to distilled water at 0° C, as 

 determined by the Sprengel tubes ; and column 16 the alkalinity. 



The values given in column 13 are the means of at least three 

 double determinations, and may be taken as accurate to + 3 in the 

 fifth place of decimals. The reductions, as before stated, have all 

 been effected by means of Dittmar's tables ; and as the deviations 

 from standard water are in most cases very small, it is improbable 

 that additional error has been introduced. 



The numbers in column 15 are the means of at least two deter- 

 minations in each case, and may be taken as correct within + 2 in 

 the fifth place. 



The alkalinities have in great part been estimated twice, and are 

 subject to an actual eri'or not exceeding unity, the relative error 

 being probably considerably less. 



Table II gives extra observations of surface temperature, taken 

 at intervals of about half an hour. The positions are given with 

 reference to the sounding stations I, II, III, &c., as in Table I. 



The route followed in the trips under consideration was chosen 

 simply with the view of finding the most promising fields of inves- 

 tigation. I hope under more favourable conditions to repeat the 

 observations in various parts of the Channel at intervals of two or 

 three months. If this could be done regularly for several seasons 

 we cannot doubt that a good deal of light would be thrown on 

 variations of climate on different parts of our coasts, as well as on 

 the distribution of fish at different periods. 



Any general discussion of the observations made in June last is 

 of course useless until material for comparison has been obtained^ 

 but a few noticeable features may be pointed out. It appears in 

 the first place that the water in the area surveyed is extremely 

 uniform. The densities at 15'56° C. show but little variation, the 

 highest values, 1"02618 and 1-02612 at surface, and 1*02625 and 

 1*02612 at bottom, occurring at stations Ila and VIII ; and the 

 lowest, 1'02588 at surface and 1*02582 at bottom, at station X, off 

 St. Catherine's. The mean density is pi'actically that of normal 

 sea water, both at surface and bottom, except off St. Catherine's. 



The alkalinities also show great uniformity, vai-ying only between 



