4722 HYDROGRAPHIC MANUAL PaGE 40(3 



The Tanner-Sigsbee reversing frame has been improved in recent years; the propeller is now built 

 with three blades and with an increased pitch. The improved models are faster-acting and have been 

 pbserved to capsize the thermometer when raised through only 1 foot of water. The propeller shaft 

 must be thoroughly oiled and maintained in good condition in order to retain this rapid action. 



Certain diflaculties may be experienced in operation. When the thermometer holder fails to 

 capsize it is probably due to improper adjustment of the propeller blades. One of the blades of 

 the propeller is slightly wider than the other two and is adjusted to strike a stop pin when the instru- 

 ment is lowered, to prevent the propeller screw from jamming against the threads. The stop pin 

 must have a fiat top and project just enough so that the propeller blade will not touch it at all on the 

 revolution just preceding that when it strikes the pin and stops. If readjustment is necessary in the 

 field the pin should be filed to a flat end of the required length. 



Another possible difficulty is that the long spring clamp may lose its tension which will permit 

 the frame to slip on the sounding line. The spring is made of bronze to resist corrosion, but it does 

 not have much tension. The tension may be increased by pulling the long part of the spring away 

 from the frame. Serving the sounding line with sail twine to provide a larger diameter for the two 

 clamps will prevent the frame from slipping; or better still, the frame itself may be lashed to the 

 sounding line with sail twine. 



4722. Other Reversing Thermometer Frames 



Another reversing frame of modified design operates on the same principle as the 

 Tanner-Sigsbee reversing frame. This instrument also utilizes a propeller but it con- 

 tains two thermometer holders — one for a protected and the other for an unprotected 

 thermometer. The holders are pivoted near the center between two vertical members 

 of the frame, and when released by the action of the propeller, they are mverted by a 

 weight attached to the upper end. This frame is provided with clamps by which it 

 may be attached to the small-diameter sounding wire. 



The Knudsen type of reversing frame is constructed exactly like the one described 

 in the preceding paragraph, except that the mechanism is actuated by a messenger 

 (see 4742) that releases a spring trigger which permits the thermometers to capsize. 

 The messenger type of release is more positive acting than the propeller type. With it 

 the reversal occurs with certainty at the desired depth, while the propeller type may 

 be reversed prematurely in a rough sea by the rolling or pitching of the vessel raising 

 the instrument through the water sufficiently to revolve the propeller. 



These two types of reversing frames are not used by the Coast and Geodetic Survey. 



473. Bathythermograph 



The bathythermograph is a device for obtaining a continuous graphic temperature- 

 depth record of sea water. With it temperatures can be measured rapidly, and better 

 information can be obtained on the vertical distribution of temperatures. The instru- 

 ment is new and should be considered in the development stage, but it certainly em- 

 bodies desirable features that simplify the problem of determining the changeable tem- 

 peratures of the upper layers of water adequately for use in hydrographic surveying, 

 particularly where these data are needed for the computation of the velocity of sound. 



There are two types of bathythermographs, the bimetallic-reed and the Bourdon, 

 differing only in the device employed to measure the temperature and in the construc- 

 tion necessary to accommodate this device. Both measure temperatures between 0° 

 and 30° C. 



