230 DEPTHS OF THE OCEAN 



degree, then the heat given off would be sufficient to raise the 

 temperature of a stratum of air covering the whole of Europe 

 to a height of 4000 metres on an average ten degrees. This 

 Gulf Stream, explains how the Gulf Stream renders the climate of northern 

 Europe so much milder in winter than would be expected from 

 its northerly latitude. We shall see later on that the oceano- 

 graphical researches of the last few years give reason to hope 

 that it will even be possible to predict the winter temperature 

 of northern Europe from the temperature of the sea some time 

 in advance. 



The salts of 

 the sea. 



Salinity 

 determined 

 from water - 

 samples. 



Obtaining 

 samples from 

 surface and 

 shallow water. 



Obtaining 

 samples from 

 deep water. 



Buchanan's 



stopcock 



water-bottle. 



There are many different salts in the sea. Salinity means 

 the total amount of salts in a given quantity of sea-water, and 

 is usually stated in parts per thousand (per mille), indicating how 

 many grams of salt are contained in one kilogram of sea-water. 

 The salinity of the sea varies considerably both horizontally 

 and vertically, and its distribution is determined by examining 

 samples of water from different parts and different depths ; these 

 samples are secured by means of various water-bottles. From 

 the surface a sample may be drawn with an ordinary bucket. 

 For shallow waters down to 30 or 40 metres a common glass 

 bottle is often employed ; the Hne is bound to the neck of the 

 bottle and a weight is suspended underneath. The stopper is 

 fastened to the line a little way above the bottle, and is inserted 

 when the bottle is lowered. When this simple water-bottle has 

 arrived at the depth from which the sample is to be taken, the 

 line is given a sharp pull, so that the stopper is drawn out and 

 the bottle fills. In hauling up, a little water from the upper 

 layers may, of course, enter the bottle, but this simple method 

 does well enough for shallow water 

 variations are so great as to render 

 necessary. 



Many varieties of water-bottles for investigations in deep 

 water have been constructed. A few of those most in use, and 

 most effective in working, may be described, and the different 

 principles involved explained. 



We will begin with an apparatus designed by J. Y. Buchanan 

 for the "Challenger" Expedition, a so-called stopcock water-bottle 

 (Fig. 161). It consists of a brass tube (A), which can be closed 

 at both ends by means of metal stopcocks (B,B) ; the latter are, 

 through two levers (D,D), connected with a rigid rod (0,0). 

 When the side-rod is in the upper position, as seen in the left- 

 hand and central figures, the cocks are open. A tilting plate 



near land, where the 

 extreme accuracy un- 



