Connected ivith the Earth's Field of Force. 139 



much as possible of its weight may be concentrated there ; 

 for simplicity of explanation we shall suppose an ideal 

 case in which the entire weight is divided equally between 

 the two ends and concentrated there. This simple affair, 

 rod and fiber, is the schematic form of the Eotvos torsion 

 balance of the first type (see fig. 4).i« Now suppose 



Fig. 4. 



POP' 



Fig. 4. — Schematic form of the Eotvos balance, first type. 



the earth's field of force to be normal and the suspended 

 rod to hang in a vertical plane coinciding neither with the 

 meridian nor with the prime vertical. Let us disregard 



^* For the description and use of the Eotvos balance and the numerical 

 results obtained with it the foUomng articles may be consulted. Each arti- 

 cle in the list is given a letter by which — to save space — it is hereinafter 

 referred to as needed. 



A. Eotvos, TJntersuchungen iiber Gravitation und Erdmagnetismus ; Wiede- 

 mann's Annalen der Physik und Chemie,Vol. 295, new Ser. 59 (1896), p. 

 354. 



Also the following articles by Eotvos in the Proceedings of the Con- 

 ferences of the International Geodetic Association: 



B. Budapest meeting (1906), Vol. I, p. 337. 



C. Cambridge meeting (1909), Vol. I, p. 319. 



D. Hamburg meeting (1912), Vol. I, p. 427. 



E. Brillouin, Sur I'ellipticite du geoide dans le tunnel de Simplon; mem- 

 oires presentes par divers savants a 1 'Academic des Sciences de I'lnsti- 

 tut National, Vol. 33, No. 3. 



F. Soler, Primi Esperimenti con la bilancia di Eotvos; Memorie del Eeale 

 Istituto Veneto di Scienze, Lettere ed Arti, Vol. 28, No. 8 (Venice, 

 1913). 



G. Soler, Prima Campagna con la bilancia di Eotvos nei dintorni di Padova; 

 Eeale Commissione Geodetica Italiana (Venice, 1914). 



H. Soler, Seconda Campagna con la bilancia di Eotvos, Eeale Commissione 



Geodetica Italiana (Padua, 1916). 

 I. For a good brief account see Bouasse; Geographie Mathematique, 



Paris, 1919, p. 351. 



