■ 987 



also made use of for the suspension, the axis of tlie tube represent- 

 ing the axis of revolution of the sphere. The equatorial radius of 

 the sphere was 2.0049 ± 0.0025 ems. The sphere with its tube 

 was sealed (accurately centred)' to an oscillating system, consisting 

 of a glass tube and a copper tube with disc, as in Comm. N". 149^ 

 § 2, only thinner and lighter (weight 26.5 grms). This oscillating 

 system to which also, as in the previous experiments, a hollow 

 cylinder belonged which was put round the copper tube and rested 

 on the disc was suspended from a thin raanganin wire ( • 04 mm. 

 thick and 55 cms. long). For the rest the apparatus was the same 

 as in the preliminary experiments with liquid hydrogen. 



As in the experiments with liquid air two hollow cylinders were 

 used. The one (6\) made of brass weighed 33.125 grms (= in) and 

 had the dimensions Re (external radius) := J .1915 =b 0.0017, Ri (in- 

 ternal radius) = 0.3970 d= 0.0019, A (height) =: 1 cm. about. Its 

 moment of inertia was therefore 



K^ = i VI (Ra' + Ri') = 26.12 ± 0.07. 



The other one (C,) was made from retort-coaP) and covered with 

 a thin layer of varnish; it had very nearly the same dimensions 

 as the former, weighed 7.26 grms. and had a moment of inertia 

 /iT, = 5.77 ± 0.01^ This value was not as in the previous case 

 derived directly from the dimensions and the mass, but was deter- 

 mined by oscillation-experiments in which the oscillating system, 

 leaving out the sphere, was first loaded with the one 

 and then with the other cylinder. The times of oscillation were 

 measured with a stop-watch with an accuracy of at least 

 Viono^J- These same experiments gave for the moment of inertia of 

 the system without cylinder or sphere /iTy = 3.95 =b O.OJ. Similarly 

 by the oscillation-method the moment of inertia of the sphere at 

 room-temperature was found to be /u == 20.26 ± 0.05^ ") 



1) This material was selected on the ground of its having the desiied specific 

 gravity (see further on). 



2) The chronometer had been previously compared with the standard-clock and 

 was found to fully guarantee an accuracy of '/lo.o •" ^he time-readings. 



3) The times of oscillation at 15° C. and in vacuo were as follows; 



System without sphere and without cylinder (weight: 26.5 gr.) T =14.40 sec. 

 , with „ C\ { , 59.6 . ) 40.16 , 



n n 1, t, n n C^ i n 33.8 „ ) 22.75 „ 



with „ „ without , ( , 35.4 „ ) 35.89 , 



n with „ C'l ( „ 68.5 „ )• 52.05 , 



n C,i . 42.7 „ ) 39.97 , 



These observations give as previously (comp. Comm. 149/> IV § 5) a small 



