PEIRCE. THERMAL CONDUCTIVITIES OF CERTAIN ROCKS. 659 



TABLE IL 



fereut substanoe.s arc of course rather indefinite. INIy own experience 

 shows that even thick sheets of fine phite gla.ss bought at different times 

 of the same maker may have conductivities wliich dilTcr from each other 

 by as much as eight per cent; while the conductivities of slabs of dry 



