﻿G. Barus and V. Strouhal — Strain-effect, etc. 181 



pie, during the Carboniferous, Permian and whole Mesozoic 

 times was a region of subsidence to the extent of 15,000 feet* 

 (for such is the thickness of these strata there). Since that 

 time it has been a region of elevation and has risen probably 

 at least 20,000 feet. But the extreme general erosion (i. e. 

 leaving out the canon-catting) has been only about 12,000 feet, 

 leaving the region still 8000 feet high in its highest parts. Now 

 first, why did the rise commence at all ? and 2d, how can a 

 lightening by removal of 12,000 feet cause an elevation of 

 20,000 feet? In fact at every step the erosion has lagged be- 

 hind the elevation, as it ought, if it be effect. The fundamen- 

 tal cause of subsidence and elevation over great areas must 

 therefore be sought elsewhere, although doubtless weighting 

 and lightening, by adding to the force or lessening resistance, 

 will cause these movements to go farther than they otherwise 

 would. This is but an example of reaction of effect on cause, 

 of which we find so many in all cases of complexly related 

 phenomena. As to the real and fundamental cause of the 

 oscillatory crust-movements we are not }^et prepared to speak 

 with any certainly. We must wait for more light. 



Aet. XIX. — The Strain-effect of Sudden Cooling as Exhibited by 

 Glass and by Steel; Second Paper ;f by C. Barus and Y. 

 Strouhal. 



In our last papery we compared the strains experienced by 

 glass and by steel on sudden cooling, by aid of the density 

 variations observed when the bodies carrying strain were an- 

 nealed, as a whole. In this paper we desire to substantiate and 

 to give sharper expression to our earlier inferences relative to 

 the temper-strain in glass. To do this we repeat Professor 

 Kood's experiments on the polariscopic effect of continuous 

 annealing of cooled glass, at low temperatures. Our second 

 purpose in this paper is to investigate the density relations of 

 consecutive similar shells of the Prince Kupert drop, and the 

 optical character of the successive cores. Availing ourselves 

 of all the evidence adduced in our investigation at its present 

 stage, we endeavor in general to show that the optical effect of 

 the temper-strain in glass may be regarded as the analogon of 

 the electrical effect of the temper-strain in steel. 



* Powell, 2d Report of U. S. Geol. Survey, Introduction, p. xv. 



f Communicated with the permission of the Director of the Geological Survey. 



JThis Journal, III, xxxi, p. 439, 1886. 



