C. Barns — Energy Potentialized, etc. 193 



fore, with the salient statigraphical and faunal features as pre- 

 sented, the evidence in considering the dual character of the 

 Lower Carboniferous in the continental interior indicates that 

 bj far the two most widely separated of the five generally re- 

 cognized divisions are the Keokuk and St. Louis. 



Recapitulating, it appears that in the Lower Carboniferous 

 of the Mississippi basin : (1) the most characteristic faunal 

 group was preeminently dual in its general aspect, the Cri- 

 noidea greatly predominating during the first part, and the 

 Blastoidea during the latter portion, of the period ; (2) that a 

 large proportion of the genera of echinoderms became extinct 

 toward the close of the Keokuk ; (3) that, of the crinoidal 

 genera represented in the St. Louis and Chester, nearly one 

 half of the number did not occur in the earlier epochs ; (4) 

 that among the Crinoidea in general the abrupt and extensive 

 differentiation in certain anatomical features toward the end 

 of the Keokuk are suggestive of decided changes in the 

 biological and physical conditions of environment ; (5) that the 

 faunas of the Burlington and Keokuk are very closely related 

 genetically, the two being practically continuous ; (6) that if 

 the members of the Lower Carboniferous of the Mississippi 

 basin are to be synchronized with the two divisions of the 

 Appalachian Lower Carboniferous, the line of demarkation is 

 far more apparent at the close, than at the beginning, of the 

 Keokuk epoch. 



Art. XX V. — The Energy Potentialized in Permanent Changes 

 of Molecular Configurations • by Carl Barus.* 



1 . In the following work a soft annealed wire is stretched by a 

 known weight falling from an initial position (strain minimum), 

 to the lowest position compatible with the given adjustment 

 (strain maximum). If the wire remains sufficiently soft through- 

 out the experiment the recoil is nearly zero. Hence the energy 

 expended in stretching is to this extent easily measurable ; and 

 if also the heat evolved during stretching, be measured, the 

 difference between the work done on each centimeter of wire 

 and the heat produced per centimeter of wire is the energy 

 potentialized ; i. e. the energy which permanently manifests 

 itself as tensile strain. Using the nomenclature of Maxwell's 

 theory of viscosity, the numerical datum, thus obtained, is an 

 expression for the amount of change in the history of the 

 typical molecular configuration, the dates being taken imme- 

 diately before and immediately after the tensile stress is applied. 



* la my paper, this Journal, xxxvii, page 346, Table II, exchange traction and 

 torsion. In the fourth line below read conductivity for resistance. 



