No. 15. — The Harvard Deep-Sea Thermograph. 

 By Harry Clark. 



The study of ocean temperatures interests the oceanographer 

 because it furnishes a means of tracing out both the horizontal and 

 vertical movements of the water below the surface. It is also of use 

 to the biologist because the distribution of marine organisms is de- 

 termined largely by temperature. The temperature of surface water 

 varies within wide limits. In high latitudes it may go below 0° 

 Centigrade in winter and rise to 5°, more or less, in summer. In the 

 tropics it averages 27°, with a variation of perhaps 4° either way. 

 Below the surface the temperature falls very rapidly at first, and the 

 seasonal differences and other irregularities become less marked. At 

 500 fathoms, in middle latitudes, the temperature commonly varies 

 from 4° to 8°, and at great depths approximates 0° throughout the 

 year. A modern discussion of ocean temperatures is contained in 

 The depths of the ocean by Murray and Hjort (London, 1912). 



A surface temperature may be taken by drawing a bucket of water 

 and putting an ordinary thermometer in it. Several methods have 

 been used for work at small depths. Well-insulated water bottles 

 can be filled at considerable depth, and then drawn up rapidly and 

 tested before the contents have appreciably changed in temperature. 

 The Pettersson-Nansen bottle has been used with success at several 

 hundred fathoms. The thermophone, first devised by Warren and 

 Whipple and described in the Technology quarterly, July, 1895, has 

 been suggested for this work. This device measures temperature by 

 determining the electrical resistance of a wire having a large known 

 temperature-coefficient. It has been used with success at 100 fathoms, 

 but for deep work the insulation of the wires presents a problem. It is 

 difficult to handle a long insulated wire because its weight is great 

 compared to its tensile strength. 



The most widely used instrument is a special mercury thermometer, 

 such as that made by Negretti and Zambra of London. A constric- 

 tion of the capillary near the bulb allows the mercury column to 

 separate at a definite point when the instrument is inverted, and the 

 peculiar form of the capillary near the constriction makes it impossible 

 for any subsequent change of temperature to change the quantity of 

 mercury which has fallen to the other end of the tube. The thermo- 



