I 'J 



I 



V 



Figure 22. Becausi 01 im gri weh simplicity ol 

 its use, the invariable pendulum superseded the 

 convertible pendulum towards the end of the 19th 

 century, except at various national base stations 

 (Kew, Paris, Potsdam, Washington, D.C., etc.). 

 Shown here .in-, right to left, a pendulum of the 

 type used by Peirce at the Eioosac runnel in 

 1873-74. the Mendcnhall '-second pendulum of 

 1890. and the pendulum designed by Peirce in 



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Figure 23 1 in overali sizi of portable pendulum 

 apparatus was greatly reduced with the introduction of 

 this ' .-second apparatus in 1887. by the Austrian military 

 officer, Robert von Sterneck. Used with a vacuum 

 chamber not shown here, the apparatus is only about 3 

 feet high. Coincidences are observed by the reflection of 

 a periodic electric spark in two mirrors, one on the support 

 and the other on the pendulum itself. 



Von Sterneck and Mendcnhall 

 Pendulums 



While scientists who had used the Repsold-Bessel 

 pendulum apparatus discussed its defects and limi- 

 tations lot gravit) surveys, Maj. Robed von Sterneck 

 of Austria-Hungary began to develop an excellent 

 apparatus for the rapid determination of relative 

 values of gravity/-' Maj. von Sterneck's apparatus 

 contained a nonreversible pendulum J^-meter in 



"Papers b) Mm von Sterneck in Mitleilungen dts 1. 

 MUitar-geographischen Institute, H'ien, 1882-87; see, in particular, 

 vol. 7 (1887). 



PAPER 44: DEVELOPMENT OF GRAVITY PEND1 LUMS IN Till I'll! CENTURY 



331 



