Investigations on the Oscillations of Balances. 459 



and we put in the place of the middle agate plane (the knife-edges 

 being of flint) planes of the same size but of different material, we 

 find a change in the time of the oscillation ; from thirty-two oscil- 

 lations in each case we have obtained the following mean results 

 (P = 2178 grams) : 



Material of the Time of one 



middle plane. oscillation, 15 . D 15 . Jc. 



Hard steel 33'3 sees. 1'034 O043 



Agate 327 1*031 0'044 



Copper 25-4 1-065 0-071 



Horn 18-2 1-115 0'093 



That is to say, the time of one oscillation in the last case is one-half 

 of that when an agate plane is used, although the load and the 

 position of the centre of gravity were the same in both cases. 



Therefore the experiment shows a great dependence of the time of 

 one oscillation decrement and of the sensibility from the friction of 

 the knife-edges, although usually it is assumed that t and k do not 

 directly depend upon the friction. Further experiments are going 

 on, especially as regards the changes found in the value of the 

 decrement.* 



Y. Variation of t and D depending upon the Dimensions of the 

 Horizontal Section of the Load. 



If we put on the pans of the Ruprecht's balance two platinum- 

 iridium pounds (Russian) (cylinders of which the height and diameter 

 are equal and the weight 409*5 grams), we find k = 0'033 milligram, 

 t about 44'4 sees., and D about T0175 ; replacing these weights by 

 two plates of 914 square cm. section (of the same weight 409'5 grams), 

 we find t about 397 sees., and D about T0240. 



VI. Variation of t and D with the Variation of the Volume of the 



Load. 

 VII. Influence of the Variation of the Density of the Air e, and 



VII I. The Inner Friction of the Gas in which the Oscillations are 



going on. 



The experiments will be continued and extended, and I hope to 

 obtain results which will throw more light on the little explored 

 regions of the oscillation of a balance considered as a physical 

 pendulum of peculiar properties. 



Some results will probably be applicable to the ordinary physical 

 pendulum. 



But, for the moment, I would not like to make any theoretical 

 generalisations. 



* Vide Bessel and F. Baily, 1832, " Pendulum. Experiments." 

 VOL. LXllF. 2 M 



