14 



PROCEKl'INCS .if THE AMERICAN ACADEMY. 



TABLE I. 



Sp. Gr. 



1. Carrara .... 

 Mexican Onyx 



3. Vermont Statuary 



4. American White . 

 Egyptian . . . 



6. Sienna .... 



7. Bardiglio . . . 



8. Vermont Cloudy White 



9. Vermont Dove Colored 



10. Lisbon 



1 1. American Black . . . 



\'l Belgian 



13. African Rose Ivory 



11. Tennessee Fossiliferous 



15. Knoxville Pink . . . 



10. St. Baume 



2.71 

 •J 71 

 2.72 

 2.74 

 2.68 

 2.69 

 2.75 

 2.74 

 2.75 



2.75 

 2.75 

 2.71 

 2 73 

 2.70 



Conductiv- 

 ity. 



0.00505 



0.0055G 



0.00578 



0.00596 



0.00623 



0.0067G 



O.Of 



0.0c 



0.001 



0.00685 



0.00 



0.00755 



0.00756 



0.00750 



0.00757 



0.00761 



Diffnaiv. 



itv. 



0.0087 



0.0094 

 0.0102 

 0.0102 

 0.0107 

 0.0117 

 0.0116 

 0.0118 

 0.0120 

 0.0118 

 0.0119 

 0.0133 

 0.0130 

 0.0130 

 0.0131 

 0.0134 



After the absolute conductivity of a particular specimen has been care- 

 fulh determined, between various pairs of temperature limits, the conduc- 

 tivity of any other specimens can be easily obtained bj determining the 

 temperature-gradient, in the final state, on the axis of a prism built up of 

 the Blab already tested, and the slab to be examined, with their attendant 

 thermopiles and such other thin slabs a-- may be conveniently used. I;. 

 varying the order of the Blabs on different occasions, the temperatures at 

 the il the slab to be examined can be altered, it being always 



undi that the thermal elements must be placed between slabs 



approximately the same conductivities. The relative conductivities 

 lifferenl materials il these conductivities are not widely different, can 

 i with great accuracy by thi~ method ; and it is possible to 



