98 Adams and Coker — Elastic Constants of Rooks. 



quently unsatisfactory owing to the low ultimate shearing 

 value of many rocks. 



While a glance at the list of rocks whose elastic constants 

 have been measured by Nagaoka will at once show that most 

 of them are rocks whose elasticity must be of a very imperfect 

 kind, e. g., weathered clay slate, schalstein, tuff, etc. ; the 

 method which he has employed for the determination of 

 Young's modulus gives very low results, even in the case of 

 rocks such as marble and granite, where the elasticity might 

 be supposed to be of a high order and comparable to that 

 which these rocks are shown to possess in the case of the types 

 selected for investigation in the present paper. This is seen 

 in the following figures representing the values obtained by 

 him for each of the marbles and granites contained in his list : 



Paleozoic Marble : E (Young's modulus). 



No. 11A 10,120,000 



11B._. 7,950,000 



12A 5,440,000 



1 2B 4,770,000 



Granite 



No. 69 (Shodoshima) ._. 6,140,000 



68 (Hitachi) 2,853,000 



71 ( " ) 2,175,000 



56 ( " ) 1,588,000 



52 ( " ) 3,265,000 



Of these, marble No. 11, if a mean of the two readings be 

 taken, has about the same modulus as the average of those on 

 our list, while No. 12 is very much lower. The highest value 

 given for any granite in Nagaoka's list, viz : No. 69, is some- 

 what higher than that of the lowest of the granites in our 

 series, that from Stanstead. The other granites examined by 

 Nagaoka have values for ^assigned to them which are so low 

 that they are comparable only to that of the sandstone in our 

 series. Of the three sandstones included in Nagaoka's list the 

 Izurni sandstone of the Mesozoic has modulus of 1,322,000, 

 while the other two, which belong to the Diluvium, have values 

 for E of 587,500 and 583,000 respectively. 



And so when an attempt is made to calculate the cubic com- 

 pression (D) from the values given in Nagaoka's list and 

 obtained by his method, it is found that a negative value is 

 actually obtained in about one-third of the rocks which he has 

 examined. His figures, however, were intended chiefly for the 

 purpose of calculating the velocity of the propagation of earth- 

 quake shocks. 



In consequence of a number of somewhat unsatisfactory 

 results obtained by the writers in some preliminary experiments 



