543 



carrying out such experiments, but only now, in connection with 

 connected material I intend to give an account of the results. Weighings 

 were made with different crystals, but the greatest accuracy was 

 obtained in a comparison of the weights of two quartz spheres, 

 42 m.m. in diameter and weighing about 127 gms. Each sphere 

 was mounted in a ring of argentan, and could be turned about a 

 horizontal axis, the ends of which were supported by the suspending 

 wires of the pans of the balance. The spheres were of nearly equal 

 weight, so that it was only necessary to nearly cancel the difference 

 of the weight of the spheres. The optical axes of the spheres hanging 

 from the left and right arms of the balance were placed alternatively in 

 vertical and horizontal positions by means of a simple mechanism, 

 allowing the ?iece.s.'iari/ operations witltout 0})ening of the halance case. 



From 15 different series of weighings it resulted that the double 

 effect sought for is less than 0.01 mg. in 127 gms. or less than 1 in 

 13000000. 



1 have much pleasure in thanking Miss C. M. Peereboom, phil. 

 nat. cand., who has taken part in the investigation, and made many 

 weighings. 



^ Experiments with the torsion balance. 



3. By means of the common balance we are able to ascertain the 

 equality of two weights. In how far equal weights correspond to 

 equal masses, in the meaning introduced in the science of mechanics, 

 can be found out only by experiments. A rough experiment to prove 

 the proportionality of weight and mass consists in observing the 

 equality of the time of fall of various bodies. Much more accurate 

 results were obtained by Newton's pendulum experiments (descent 

 along a circular arc). Pendulums of equal form and hanging by 

 equal threads, but of various composition, have the same time of 

 oscillation. In his fundamental experiments Newton ^) was able to 

 ascertain the equality of the times with an accuracy of one part in 

 1000 and this therefore is also, at the same place, the accuracy of 

 the proportionality of weight and mass. Bessel '^) i-efined Newton's 

 method, and came to the conclusion that a difference of attraction, 

 experienced by various bodies of equal mass, must be less 'than 

 1/60.000 of the total attraction. 



A much more accurate result was obtained by von Eötvös with 

 Cavendish's torsion balance, which he brought to a high degree of 



1) Newton. Principia. 



3) Bessel. Abh. Berliner Akademie. 1830. 



40* 



