380 



EXPLORATION GEOPHYSICS 



11:3: 



Fig. 227. — Schematic view of the 

 hydraulic gravimeter. (Evjen, U. S. 

 2,117,471.) 



astatic 

 Patent 



V' vary in such manner that the total net gas pressure on the ends of the fluid column 

 is equal to the weight of the fluid. By making the ratio of the area of the containers 

 Z and Z' to the area of the capillary tubes containing the toluol very large, the displace- 

 ment of the liquid in the capillary tubes can be made many times the displacement of 

 the mercury in the containers so that a high sensitivity can be obtained by readings of 

 the toluol menisci. Furthermore, if the proper choice of volumes is made the tempera- 

 ture eff^ect can be somewhat decreased, but at best, the meter is quite sensitive to 

 temperature and is usually used in an ice bath. The instrument is highly damped and 

 has been used with considerable success for coarse work on ship board. 



Astatic Hydraulic Gravimeter. i — This instrument is an astatic type which utilizes 

 the flow of liquid as an astatizing means. The meter comprises a specially shaped con- 

 tainer connected to a vertical spring and a fluid system whereby, upon lengthening of 

 the spring, fluid flows into the mass, thus 

 increasing its weight and further length- 

 ening the spring. A schematic view of 

 one form of the meter is shown in Figure 

 227. The tube system is completely filled 

 with the fluid and the containers 4 and 13 

 are partially filled. Stops 8 and 9 on the 

 scale 10 define the limits within which the 

 balance can move. 



The operation of the instrument may 

 be summarized as follows. The gravimeter 

 is leveled by means of the leveling screws 

 so that the liquid in the container or pan 

 4 is at the same level as in the container 

 13. Any increase in the value of the force 

 of gravity acting on the mass of the pan 4 will cause the pan to move downward, thereby 

 stretching the spring 1. The liquid in the pan 4, however, will tend to remain at the 

 same level as in the container 13, so that a certain amount of liquid will flow into the 

 pan 4 from 13 through the tube system 12. The resulting increase in the quantity of 

 liquid in pan 4 will cause a further stretching of the spring 1 and accentuate the down- 

 ward movement of 4. A decrease in the value of gravity will cause a reverse process 

 to take place. It is claimed that the instrument is capable of high precision provided 

 it is leveled with very great accuracy. 



Mott-Smith Gravimeter. t — This instrument is an astatic meter em- 

 ploying an auxiliary quartz fiber as a labilizing spring to effect a further 

 movement of the "weight" after it is 

 initially moved by gravity. 



The component parts of the meter 

 are shown schematically in Figure 228. 

 A T-shaped frame 3 having arms 4 is 

 rigidly attached to a casing by means 

 of a clamp 2. A torsion fiber 5, which 

 is about \y^ inches long and about 

 0.002 inches in diameter, carries a 

 weight arm 7, which, in turn, is con- 

 nected to the labilizing fiber 8. The lat- Fig. 228.— Perspective view of the Mott- 

 ter is connected to the T-frame 3 Smkh^^ravimeter. (Mott-Smith. U. S. Patent 



t H. M. Evjen, "Gravimeter," U. S. Patent 2,117,471, issued May 17, 1938. (Assignor to 

 Shell Development Company.) 



t L. Mott-Smith, "Torsion Gravimeter," U. S. Patent 2,130,648, issued Sept. 20, 1938. 



