April 19, 1907] 



SCIENCE 



623 



granitic magmas in the final stages of their 

 consolidation, such viscosity ensuing after the 

 crystallization of the feldspars and due to the 

 behavior of the residual free silica of the 

 magma which crystallized as quartz. It was 

 well known that while rhyolitic magmas were 

 more viscous than basaltic lavas, they were 

 nevertheless fluid enough to flow as expansive 

 sheets ; and many granitic batholiths approx- 

 imated such rhyolites in their composition 

 sufficiently to indicate that they were not, 

 except in the final stages of solidification, so 

 highly viscous as to be regarded as solids 

 rather than fluids. The speaker was glad to 

 hear Dr. Day minimize the influence of pres- 

 sure. He recalled the case of vertical basic 

 dykes which in horizontal section graded from 

 very dense compact porphyritic rocks on their 

 margins to coarse gabbroic rocko in their 

 middle part, 50 feet or less distant. This 

 gradation in structure and texture necessarily 

 occurred under the same pressure, and proved 

 that pressure exercised but little control upon 

 the development of these features. 



Mr. G. 0. Smith cited observations on in- 

 trusion phenomena in Washington, Utah and 

 Massachusetts. In the Tintic Mountains the 

 intrusive monzonite includes angular frag- 

 ments of quartzite and limestone which have 

 been carried upward after detachment from 

 the wall rock, showing absence of assimilation 

 by the magma and of sinking of the frag- 

 ments in the same. 



Mr. F. E. Wright described briefly ex- 

 amples of batholithic intrusion of granites in 

 southeast Alaska, and of local recrystalliza- 

 tion and assimilation of invaded rocks, and 

 emphasized the important role of magmatic 

 solutions in producing such alterations, rather 

 than direct melting and absorption by the 

 magma and recrystallization of the whole on 

 cooling. 



Mr. Waldemar Lindgren cited a number of 

 examples of intrusions of granitic and dioritic 

 rocks in the Sierra Nevada from which it was 

 clearly apparent that a very considerable 

 pressure was exerted by the intruding magma 

 on the surrounding, steeply dipping slates. In 

 many cases the intrusive rocks cut across the 

 slates in jagged and irregular lines, but in 



nearly all cases the lateral pressure, resulting 

 in the bending of the slates, is extremely weU 

 marked. Practically no evidence of assimila-. 

 tion on a large scale in this region was 

 obtained. Fred. E. Wright, 



THE PHILOSOPHICAL SOCIETY OP WASHINGTON 



The 631st meeting was held on March 16, 

 1907. Dr. L. A. Bauer read a paper on " The 

 Eelation between ' Potential Temperature ' 

 and 'Entropy.'" 



The purpose of this paper was to show the 

 precise relationship between von Hebnholtz's 

 term ' waermegehalt ' used incidentally by him 

 in connection with his investigations ' On 

 Atmospheric Motions ' or of the alternative 

 term 'potential temperature' suggested and 

 used by von Bezold in his papers ' On Thermo- 

 dynamics of the Atmosphere,' and entropy. 

 It was found that a simple relation existed so 

 that for certain thermodynamic problems the 

 second law of thermodynamics, or the prin- 

 ciple of the increase of entropy, could be 

 easily and directly expressed in terms of po- 

 tential temperature. For these cases when- 

 ever the entropy increased during the carrying 

 out of a thermodynamic process, the potential 

 temperature was likewise accompanied by an 

 increase. This was shown by application to 

 certain well-known tjrpical cases of natural, 

 or irreversible processes, e. g., free expansion 

 of gases and heat conduction. 



The second paper of the evening was pre- 

 sented by Mr. W. W. Coblentz, upon ' Selective 

 Keflection of Minerals and Lunar Constitu- 

 tion.' 



Throughout the spectrum from the ultra- 

 violet into the remote infra-red, various sub- 

 stances show bands of selective absorption and 

 selective reflection. Experiments made to de- 

 termine whether these bands are due to chem- 

 ical composition, to molecular weight or to the 

 arrangement of the atoms in the molecule, 

 have always given more or less contra- 

 dictory evidence; and especially as to the 

 effect of molecular weight. Only recently had 

 the speaker been able to account for most of 

 the contradictions. 



