544 



perfection, after many years of continuous, ver}' refined, studies on 

 the local variations of gravity, and which he applied also to the problem 

 now under consideration. ') The force acting on a body at the 

 surface of the earth is the resultant of two forces: the attraction 

 of the earth and the centrifugal force. The direction of the resultant 

 is dependent upon direction and magnitude of these components. 

 At a given place of the earth the centrifugal force is directed per- 

 pendicularly to the earth's axis and dependent upon the mass. If 

 for various substances of equal masses the attractions were different, 

 then the resulting force for these substances would have different 

 direction, and a couple would act on a torsion balance, the rod of 

 which is placed perpendicularly to the meridian and carries at 

 its ends different substances. 



VoN EöTvös used a torsion balance with a rod, 25— 50 cm. long; 

 the torsion wire was of platinum, 0,04 mm. thick, and charged 

 with various substances all of 30 gms. weight. The rod is placed 

 perpendicularly to the meridian and its position relati\e to the case 

 of the intrument determined accurately by means of mirror and 

 scale. The whole intrument, rod with case, is then rotated through 

 180 degrees, the substance that first hung at the east side, now hanging 

 at the west side. The position of the rod relatively to the instrument 

 is now read again. The kind of effect considered must produce a 

 torsion of the suspension wire. With a brass ball at one end, with 

 glass, cork or stibnite crystals at the other end of the rod no effect 

 was to be observed. A difference of weight of various substances 

 of equal mass, must be for brass, stibnite and cork less than one 

 tweutymillionth, for air and brass less than one hundred thousandth. 



4. The astonishing fact of the equivalence of mass and weight, 

 the expression of the narrow tie between the phenomena of inertia 

 and gravitation is of fundamental importance for Einstein's theory 

 of gravitation. This theory, only possible, if there exists a field of 

 force giving the same acceleration to all bodies, even enables us to 

 "create" a gravitation field by a transformation of coordinates. ^) 



The fact mentioned therefore merits to be tested in all possible 

 directions. It has been my aim to extend the work of von Eötvös 

 in two directions, viz.: by the investigation of t>ri(??z/(7<f^t/ crystals and 

 of radioactive substances. I also hoped, that I might be able to 



1) V. EöTvös. Ann. d. Phys. 59. 354 1897, especially p. 372—373, and 

 Mathem. u. Naturw. Berichten aus Ungarn. 8. 64. 1891. 

 -) Einstein. Ann. d. Phys. 49. 769. 1916. 



