52 PROCEEDINGS OF THE AMERICAN ACADEMY. 



Takiug a certain piece of " Pyrenees Marble " as a standard, Dr. Less 

 found the conductivities of specimens of " Carrara Marble " and " Italian 

 Marble " to be 0.769 and 0.763 respectively. 



In determining the thermal conductivities of the specimens of marble 

 mentioned below, the prism clamped between the hot and the cold box 

 of our apparatus was made up of six slabs in series, a plate of standard 

 glass 0.935 cm. thick between two thin plates of glass, and the shib to be 

 tested between two thin slabs of marble. A ribbon thermal element 

 and tinfoil wings were placed on each side of the standard glass, and on 

 each side of the marble to be experimented on, so that there were four of 

 these thermal elements in all. When the prism had sensibly reached its 

 final state, the temperatures of the thermal junctions were determined and 

 the ratio of the conductivities of the glass and the marble was assumed 

 to be etjual to the reciprocal of the ratio of the gradients in the two 

 slabs. By introducing an extra plate or a sheet or two of blotting paper 

 into the prism, the two gradients could be altered at pleasure but not 

 their ratio. So far as we could see, it was immaterial in the case of 

 these substances whether the marble base of the prism or the glass base 

 was placed uppermost, but we generally placed the marble on top, so that 

 the mean temperature of each specimen might be about 30° C. In stating 

 the results of some of these determinations, we shall give the tem])era- 

 tures of the four thermal junctions in order, then the ratio of the con- 

 ductivities of the marble to be tested and the standard glass, and finally 

 the absolute conductivity of the marble on the assumption that that of the 

 glass is 0.00277. We shall give the absolute conductivity of the marble 

 to three significant figures, but it is evident that the last of these is not 

 determined. All the specimens were artificially dried for some time in 

 the hot air space over the boilers which furnish steam for heating the 

 Jefi'erson Laboratory, and were then allowed to stand for some weeks 

 at ordinary room temperatures so that their conditions might be normal. 

 The artificial heating drove off the excess of moisture acc^uired by the 

 marble while being cut under water at the mill. 



Most of our stone was obtained from Messrs. Bowker and Torrey of 

 Boston, who kindly collected for us representative specimens of such 

 materials as are commonly used for decorative and monumental purposes. 

 We have given to the slabs the names used by stone workers and have 

 called them all "marbles," though one or two might more properly be 

 called " limestones." The " Mexican Onyx " is really travertine. Our 

 thanks are due to Prof. J. E. Wolff for help in identifying our specimens. 



