£t AKT. 9. S. KUSAKABE. 



author, on the modulus of rigidity of rocks.* Some of the speci- 

 mens were identical with those used in the last investigation, 

 and the others were prepared in a similar manner. The principal 

 object of the present investigation is not to determine any accurate 

 value of the modulus of elasticity, but to determine whether the 

 modulus is constant within tolerably wide limits or not, and if 

 it is not constant, how it varies with the amount of stress or 

 with time and other factors which affect the change. The modulus 

 is measured by the method of flexure ; but the apparatus is more 

 complex than the one which is generally employed. It may 

 therefore not be superfluous to give the following detailed descrip- 

 tion of it. 



ARRANGEMENTS AND FLEXURE-APPARATUS. 



In the measurement of flexure, the use of the cathetometre 

 or of the micrometrescrew are generally dispensed with. The 

 method with mirror and scale, as modified by A. KöNiG,t is 

 generally adopted, though that by optical interference is more 

 accurate. The apparatus as designed in the present experiment 

 combines the advantages of König's arrangement with other 

 necessary appliances. The principal improvements are : — (1) the 

 bending of the specimen cyclically from one side to the other, 

 with increasing and decreasing force passing through zero conti- 

 nuously ; (2) the elimination of external disturbances such as any 

 minute rotation of the specimen or slight displacements of the 

 scale and telescope. 



* Ibid. Vol. I., No. 14, Oct. 1902. Pub. of the E. I. C. in F. L. No. 14, Tokyo, 1903. 

 The Journal of the College of Science, Imperial University of Tokyo. Vol. XIX., Art. 6. 

 1903. 



+ A. König. Ueber eine neue Methode zur Bestimmung des Elasticitätsmoduls. Wied. 

 Ann. 28, 1886. 



