KINETIC MEASUREMENT OF THE ELASTICITY OF ROCKS. 9 



Another term of correction clue to the effect of the wire 

 being connected at the free end may be easily ascertained as we 

 see that the effect of the small load d3I is the same as a 

 lengthening of the sj^ecimen, whose weight is M, in the ratio 



M: M+cUL 

 Now, calculating the number of vibrations for the tuning- 

 fork from the data above given, we have 



91 = 191 '9 from the first experiment, 

 7i=191'6 ,, ,, second ,, 



The difference between each of these and the registered value 

 192 is within the error of observation. 



As to the verification for the fulfilment of the condition of 

 a clamped end, the case of a tuning-fork with two prongs is 

 wholly out of place, so that it may not be superfluous to cite 

 here the following observations with a prism of soft iron. Any 

 continuation of the specimen beyond the clamped section would 

 be without effect, as it acquires no motion ; but as the first clamp 

 is relaxed, the pitch rapidly falls, in consequence of the increase 

 of the length. Hence, in tapping the specimen care must be 

 taken to give no impact to the clamped section, i.e. the specimen 

 should be tapped at a position corresponding to the centre of 

 percussion with respect to the clamped section. 



The result of the first observation is as follows : — (c.g.s. units). 



f> =7-779 

 b =0-763 

 Z = 13-4 

 Tr=30-718 

 «;=.5-19xl()-' 

 ^' = 1-221x10^' 

 // =8-667 



