where it is picked up by the hydrophone. The impulse received will 

 be amplified electrically and recorded by a stylus moving over a roll 

 of recording paper, the ruled graduations of the paper translating the 

 time-interval into the depth of water under the vessel, or the impulse 

 may be registered by a rotating disk the time-interval required recording 

 as the depth on the rotating disk. Thus by the flick of an electric switch 

 the fathometer is caused to function and the depth of water under the 

 moving vessel recorded in a few seconds. Hundreds of thousands of 

 soundings have been obtained, abysmal chasms and troughs have been 

 charted, and many seamounts have been discovered. Several papers 

 to be presented later will undoubtedly treat the fathometer in more 

 detail and the corrections necessary to be applied to the observed readings 

 for proper geological interpretation. The intensity of the impulse 

 received by the hydrophone will also indicate to a trained observer 

 much about the nature of the ocean bottom. The fathometer has often 

 been used by fishermen for locating schools of fish as the sound is 

 reflected from the backs and sides of the fish, thus indicating the exact 

 depth at which the fish are and the distance from the sea bottom. 



The bathythermograph is an instrument devised by Dr. A. F. Spilhaus 

 and developed by him and his associates at the Woods Hole Oceano- 

 graphic Institution. Originally it was intended to serve as an instrument 

 for detecting the depth of mixing of the surface waters of the sea by the 

 wind. However, the instrument as now used presents an excellent 

 portrayal of the temperature gradient down to depths of about 150 

 metres and clearly indicates the depth of a thermocline when one exists. 

 The instrument is being further developed so that records of the 

 temperature gradients to even greater depths may be obtained. 



The bathythermograph consists of a cylinder with a heavy brass nose- 

 piece. Within the cylinder are sylphon bellows attached to a slide 

 carrier into which a smoked-glass slide is inserted. A stylus, which 

 moves over the slide, is connected to a bourdon tube, which in turn is 

 attached to a coil of copper capillary tubing. The copper tubing contains 

 xylol, and the expansion or contraction of this liquid gives a means 

 for noting thermal changes. The sylphon bellows is a spring that will 

 be compressed 1 in. with a tension of 320 lb. The adapter, carrying the 

 smoked-glass slide, is firmly secured to the sylphon bellows and moves 

 with the pressure, the indication of depth, on the long axis of the 

 instrument. The stylus, fitted to the Bourdon tube, moves with the 

 temperature change on the transverse axis. A change of 0T° f. can be 

 detected. 



Each instrument must be carefully calibrated in a pressure tank at 

 known temperatures and pressures. At present there are two institutions 

 in the United States equipped for calibration of the bathythermograph — 

 namely, the Woods Hole Oceanographic Institution and the Scripps 

 Institution of Oceanography — and in Great Britain at the Teddington 

 Laboratories. The bathythermograph has the decided advantage of 

 being used while a vessel is underway. The observations may be made 

 just as rapidly as the sHdes can be adjusted, the instrument put in place, 

 then dropped to a given depth and hauled in again. In practice the 

 instrument functions to a depth of about 150 metres, giving a continuous 

 curve showing the changes of temperature with the depth. Within a few 

 hours much detailed information on the nature of a water area can be 



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