228 THE SCOTTISH MARINE STATION AND ITS WORK. 



was tried a few weeks ago in the Firth of Clyde and found 

 to work admirably. 



The salinity is a measure of the extent to which the fresh 

 water brought down by the rivers has undergone admixture 

 with the sea-water. It is determined by means of a delicate 

 hydrometer, in the manner adopted by Mr. J. Y. Buchanan 

 on the " Challenger " expedition.* When it is desired 

 merely to study the surface water the collection of samples 

 is, of course, extremely simple, but when it is necessary to 

 observe the salinity of the water at various depths recourse 

 is had to a special water-bottle which has been devised by 

 Dr. Mill for the work. 



This instrument is shown open in section in the accom- 

 panying figure. The sounding line is threaded through the 

 central axis, A A, a strong tube which supports the whole 

 apparatus, its lower end resting on a knob or a short cross- 

 bar. The sides of the vessel are constituted by the cylinder, 

 11, p p, the bottom by the base-plate, b ; this carries a ring 

 of very soft rubber, c, forming a water-tight joint with 

 the lower edge of the cylinder, f p. Above, complete closure 

 is ensured by the flange, 1 1, pressing down upon the india- 

 rubber saucer, h h. The weight of the cylinder, of course, 

 drives it well home upon these pads, and so soon as this is the 

 case it is held down by the spring catches, o o. Whilst the 

 bottle is being lowered the cylinder is held up in the posi- 

 tion shown by the hooks, l l, which spi'ing outwards. A 

 short tube, m, fits over these, and when this is driven down- 

 wards by a messenger detached from the lowest thermometer 

 it compresses these springs and withdraws them from the 

 flanged gallery, k, so that the cylinder is free to fall upon the 

 base-plate and enclose the water-sample. The water is drawn 

 off by the cock, d, air being admitted by e. 



In the Firth of Forth twelve stations were fixed upon at 

 approximately equal intervals between Alloa and the Isle 

 of May, and serial temperatures were taken at these positions 

 at frequent intervals. The general result of these observa- 

 tions is that in the landward part of the Firth the range of 

 temperature is greater and the period of the annual maximum 

 * 'Narr. Chall. Exp.,' vol. i, p. 108, 1885. 



