Chap. 7] 



GRAVITATIONAL METHODS 



109 



Pendulum apparatuses have gone through a process of slow development. 

 Although they have been largely replaced by the gravimeter in geophysical 

 exploration, they still retain a fairly important place for deep water marine 

 exploration where it is impracticable to lower remote indicating gravimeters 

 to ocean bottom. The pendulum apparatus for regional geodetic work on 

 land generally consists of an evacuated receiver with one to four pen- 

 dulums, a lens and prism arrangement for visual observation and recording, 

 a flash box, and a chronometer or reference pendulum. The earlier 

 representatives are the U.S. Coast and Geodetic Survey apparatus, the 



e 



f 



K h'-'. 



H^^H 



.^ 



^. 



cMa 



q: 



4- 



n,o 



k^ 





^i> 



\m. 



4.51 Z 3 



m 



1 1 ♦ f 



4.5 / 23 



Fig. 7-17. Optical paths in Vening Meinesz pendulum apparatus. No. 1 records 

 Oi — 02 . No. 2 records 62 — 63 . No. 3 records 02 (the prisms a and b are fastened 

 to the ^rs< auxiliary pendulum, moving in a plane parallel to the plane of oscillation 

 of the principal pendulums). No. 4 records air temperature (prism c is fastened 

 to a temperature recording device). No. 5 records the position of the second 

 auxiliary pendulum moving in a plane perpendicular to the plane of oscillation of 

 the principal pendulums (prism d is fastened to this pendulum). The horizontal 

 projections of the rays numbered 4 and 5 coincide; the other prisms have a height 

 of 30 mm, but c, d, n, and have a height of only 12 mm and are above one another. 

 The prisms e, /, g, h, i, k, I, n, 0, and p and the lenses are attached to the top plate 

 of the apparatus. 



Fechner-Potsdam pendulum, the Askania-Sterneck apparatus, the Meisser 

 4-pendulum instrument, the Numerov pendulum apparatus. Reference 

 is made to the literature^^ for descriptions and illustrations of these types. 

 Only the- Vening Meinesz marine apparatus, the Askania 3-pendulum 

 instrument, and the Brown gravity pendulum of the U.S. Coast and 

 Geodetic Survey will be briefly described here. 



In the Vening Meinesz pendulum apparatus, three pendulums are sus- 



^ H. Swick, loc. cit. A. Berroth, Handb. d. Phys., 11(9), 447 (1926). 

 Handb. Exper. Phys., 25(2), 216-238 (1931). 



H. Schmehl, 



