OBSERVATIONS IN PHYSICAL OCEANOGRAPHY 41 



obtain a continuous record at or near the sea surface. On board ship 

 the thermometer bulb, usuall}^ containing mercury, is mounted on the 

 ship's hull or in one of the intake pipes and connected to the recording 

 mechanism by a fine capillary. The recording mechanism traces the 

 temperature on a paper-covered, revolving drum. Records of tempera- 

 tures obtained by a thermograph should be checked at frequent intervals 

 against temperatures obtained in some other way. 



Various types of electrical resistance thermometers have been designed 

 to be lowered into the water and to give a continuous reading, but these 

 devices have not proved satisfactory. Recently Spilhaus has developed 

 an instrument called a bathythermograph, which can be used to obtain a 

 record of temperature as a function of depth in the upper 150 m, where 

 the most pronounced vertical changes are usually found. Essentially, 

 the instrument is similar to a Jaumotte barograph. The temperature- 

 sensitive part activates a bourdon-type element which moves a pen 

 resting against a small smoked-glass slide which, in turn, is moved by a 

 pressure-responsive element. As the instrument is lowered into the 

 water and again raised, the pen traces temperature against pressure 

 (hence, depth). This device has the great advantage that it can be 

 operated at frequent intervals for obtaining a very detailed picture of the 

 temperature distribution in the upper 150 m while the vessel is under way. 

 Mosby has devised an instrument called a thermo-sounder for measuring 

 temperature against depth which can be used for observations to great 

 depths. The thermal element, mounted on an invar steel frame, is a 

 75-cm length of specially treated brass wire attached to a pen which 

 makes a trace upon a circular slide that is slowly turned by means of a 

 propeller as the instrument is lowered through the water. 



Water-Sampling Devices 



Water-sampling devices are of two general types ; in one the closing is 

 accomplished by means of plug valves, and in the other the closing is 

 accomplished by plates seated in rubber. The Nansen bottle is an example 

 of the first type and is the one most widely used in oceanographic research. 

 The Ekman bottle is of the second type. 



The Nansen bottle (fig. 5) is a reversing bottle fitted with two valves 

 and holds about 1200 ml. The two plug valves, one on each end of the 

 brass cylinder, are operated synchronously by means of a connecting rod 

 that is fastened to the clamp securing the bottle to the wire rope. When 

 the bottle is lowered, this clamp is at the lower end and the valves are 

 in the open position so that the water can pass through the bottle. The 

 bottle is held in this position by the release mechanism, which passes 

 around the wire rope, but, when a messenger weight is sent down the rope 

 and strikes the release, the bottle falls over and turns through 180 degrees, 

 shutting the valves, which are then held closed by a locking device, and 



