376 EXPLORATION GEOPHYSICS 



When an observation is made, the meter is removed from the field truck 

 and set on three stakes driven into the ground. Usually 40 to 50 stations 

 a mile apart can be made in an 8-hour day by an observer and one helper. 

 An exterior view of the instrument is shown in Figure 221. 



Fig. 221. — Gulf gravimeter, showing yoke (near cen- 

 ter of gravity for support during transportation), carry- 

 ing handles, leveling screws, and dust cover, which is 

 removed. An operator is shown making final adjust- 

 ments. The weight of the instrument proper is 25 lbs. 

 The complete equipment weighs 95 lbs., while the bat- 

 tery and control equipment weigh from 45 to 85 lbs. 



Thyssen Gravimeter. t — The principle of this meter will be evident 

 from a consideration of Figure 222. Mass M, which is made of platinum and 

 weighs approximately 20 grams, is fastened to one end of the quartz beam 

 B. This beam is supported by a knife-edge K. At the other end of the beam 

 is a spring 6" (of relatively small weight compared to M) fastened at its 

 lower end to a micrometer screw /. The spring is enclosed within a closely 

 fitted metal tube which in turn is enclosed in an insulating medium. Verti- 

 cally above the knife edge there is supported an adjustable astatizing 

 weight A. By suitable adjustment of this weight the astatizing force can be 

 made to approach the spring force. Ordinarily, the astatizing mass is 

 adjusted to give a period of from 6 to 10 seconds. The end of the mass 

 carries a small scale which is read by means of a microscope and prism P 



t A. Schleusener, "Messungen mit Transportablen Statischen Schweremessern," Zeitschrift fur 

 Ceophysik, Vol. 9, 1934, p. 369. 



St. V. Thyssen, "Ueber die Wirkungsweise von einigen Federgravimetern," Zeitschrift filr 

 Ceophysik, Vol. 15, 1939, p. 121. 



