12 THE EXPLORATION OF THE SEA [PART I 



The water bottle which I have just described is a triumph of 

 mechanical skill and it is greatly to the credit of the Inter- 

 national Fishery Organisation that it has placed at the service of 

 oceanography an apparatus of such efficiency. 



It is then possible to obtain (1) a sounding at any depth of 

 the sea, (2) a sample of the deposits at the bottom, (3) a sample 

 of the water at the bottom, or at any desired depth, and (4) a 

 determination of the temperature of the water at the bottom or 

 at any depth. Knowledge of the density, chemical composition, 

 and salinity of the water samples studied is also required for the 

 statement of the physical characters of the sea in the region 

 investigated. 



Formerly the important values, salinity, specific gravity, and 

 density were obtained by means of the salinometer. The salino- 

 meter is really a hydrometer adapted to the study of sea water. 

 The Kiel '' araometers," Fig. 3, are hydrometers constructed to 

 give the specific gravity of sea water. Since they are used in 

 water of very different degrees of salinity a set of six is required 

 to cover the range of variation. The instrument is a double glass 

 bulb. The upper bulb is long and capacious and contains air 

 only ; the lower bulb is weighted with lead shot. At the upper 

 end of the upper bulb is a long stem in which is a graduated scale. 

 Each instrument is constructed to float in water of a certain mean 

 density in which it is immersed up to the middle of the scale, the 

 whole thing at the same time floating freely in the liquid. If the 

 density is slightly greater the araometer rises, if it is lighter it 

 sinks. The readings given by the araometer are values representing 

 the specific gravity of the water at the temperature at which the 

 observation is made. 



The specific gravity of a sample of sea water is the number 

 representing its weight as compared with that of an equal volume 

 of pure water at the same temperature. The latter is usually 

 called 1"000 so that the specific gravity of a sample of sea water 

 may be some such number as 1"025. The density is the weight in 

 grams of one c.c. of water at the temperature in situ (f) compared 

 with that of one c.c. of pure water at 4° C. It is usually expressed 

 as f 



