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Part 111. — Thirteenth Annual Report 



lines as that of other west coast stations, a marked maximum occurring 

 at the middle of June and early in July ; but while there is a slight rise 

 in the curve in August, the prominent maximum is not until the first 

 period of September. The curve is almost a mean between that of 

 Ardrishaig and West Loch Tarbert. 



SALINITY OBSERVATIONS, 1893. 



The difficulty of preparing some of the specific gravity and salinity tables 

 has been very great, and those for the North Carr cannot be regarded as 

 perfectly satisfactory, though they certainly exhibit the general change of 

 salinity day by day. Some of the observations made at the North Carr in 

 summer are suspiciously constant. At the Oxcar station the hydrometer in 

 ordinary use was broken at the beginning of the year, but mended by one 

 of the observers. Although this was skilfully done, it was found on test- 

 ing that the instrument was not reliable, and accordingly the readings taking 

 from it have not been used. At Abertay there are some very curious 

 afternoon readings in spring, and in December, when the salinity of the 

 surface water were abnormally low compared with that of the lower strata. 

 These might be caused by heavy floods in the river, but may also be due to 

 an observational error, especially those of the 11th, 24th and 25th of 

 February. 



The salinity curves for 1893 show a great steadiness in the case of 

 the Bell Rock, and considerable variation in that of Abertay ; North Carr 

 and Oxcar being intermediate, both as regards average density and range. 

 The density for 1893 is higher than 1892 at all stations (the apparent 

 exception of the North Carr being explained by the corrections made in 

 1893 and not on 1892 observations as has been explained), and only the 

 Bell Rock observations show a higher density in 1891 than 1893. Both 

 maxima and minima are higher, though the range is smaller than in 

 1892 or 1891, except for Abertay in 1892, and for North Carr in 1891. 

 The mean annual density of the water at 9 a.m. at the Bell Rock for 1893 

 was 1025*9 (3*33 per cent, of salts), of the surface water at Abertay 

 1024*1 (301 per cent, of salts), and of the bottom water at Abertay 

 1024*8 (3*15 per cent, of salts). Eleven months at North Carr show a 

 mean density of surface water of 1025*2 (3*21 per cent, of salts), and of 

 bottom water 1025*3 (3*22 per cent, of salts). There are only ten months' 

 observations at Oxcar, which give a mean value of 1025*2 (3*21 per cent, 

 of salts), which is certainly considerably above the mean for the year, 

 since the observations which are lacking are those of the months when 

 the water is freshest. 



The curves drawn from monthly means show a minimum of salinity in 

 February at all stations, and a marked maximum in July at Abertay in 

 the morning, in June and August in the morning. The maximum is not 

 so sharply distinguished in the case of the other stations, though it is 

 evident in the afternoon observations at the North Carr lightship. 



There is no very striking rise in the salinity curves corresponding to 

 the periods of excessive heat which affected the temperature of the sur- 

 face water, especially on the west coast. The influence of these hot days 

 is not immediately shown by the salinity curves, but rather by the 

 general raising of the mean salinity for the year at all stations. The 

 curve for the monthly mean density at the Bell Rock station, that furthest 

 removed from fresh water influences, shows this clearly, for while it 

 never was over 1026*0 in 1892, and in 1891 it was so only from June 

 till October; in 1893 it did not sink below this figure after June until 

 the end of the year, except in December afternoons when it was either 

 1025*9 or 1025*8. 



