KINETIC MEASUREMENT OF THE ELASTICITY OF KOCKS. 19 



for forty-two hours to moisten it throughout. It was then found 

 that the corresponding half wave length had increased to about 

 double, i.e. 



1=20-25 cm. 

 which indicated that the modulus of elasticity had decreased to 

 about one-fourth of its original value ! Not without some doubt 

 as to the result the author waited for one complete day till the 

 specimen had apparently become dry, when it was found that 

 it had nearly returned to its original state of elasticity ; i.e. 



1=10-65 cm. 

 On heating the specimen by hot air to drive out all the moisture, 

 and then rapidly cooling it to the ordinary temperature, its 

 elasticity increased slightly ; i.e. 



/=9'89 cm. 

 After three hours, it having returned to its ordinary state 

 mth regard to temperature and moisture, the elasticity became 

 weakened to 



l=10-ß2 cm. 

 The result of such cyclical observations shows clearly that 

 the enormous diminution of the modulus of elasticity is actually 

 caused by the effect of moisture. The difference between the 

 initial /=10'o9 and the final l=10'62 may be due to some varia- 

 tions of surrounding conditions, — probably a little relaxation of 

 the clamp. As the first clamp is relaxed it results in an increase 

 of the effective length of the specimen. The last difference 

 corresponds to an increase of one mm. (or a little more) of the 

 effective length. 



The following result of the experiment may serve to give a 

 rough notion as to the effect of moisture. 



