706 



Thermal Conductivity of Solid Insulators. 



original memoirs. The elasticity of pure graphite was deter- 

 mined specially by the author, and the velocity of sound 

 where not known has been calculated from E and p. The 

 conductivities of: crystals though functions of elasticity are 

 too complex to satisfy the above relations. 



Density, Elasticity. 



Material. p# E 1Q _n c 



Quartz 266, KL. G8, K L. 



Flint Glass 29, K.L. 4'8, L.B. 



Crown „ 2-5, K.L. 73, L.B. 



Soda „ 2-8, K.L. 7 9, L.B. 



Graphite 23, T. 525 T. 



Marble 27, K.L. 26, K.L. 



Mahogany, Hond. -62, K. "88, K.L. 



Deal -5, K.L. 9, K.L. 



Ice -91, K.L. -28, K.L. 



Paraffin Wax ... -91, L.B. 151, 7J L.B. 



V. Indiarubber... 102, K.L. "05, K.L. 



Cork 0-24, K.L. -0055, cal. 



Velocity of 



Sound. V. 



3rn.sec.10 - ' 



5-0, cal. 



4-1, K.L. 

 54, K.L. 



ij'o, cal. 

 4'65, cal. 

 3-10, cal. 

 3*7, cal. 

 4-2, L.B. 

 1-74, cal. 

 130, L.B. 



07, K.L. 

 7. cal. 

 ■48, L.B. 



Epx 



io-". 



18-1 



14-1 

 18-3 

 22-2 

 121 



7-0 



054 



0-45 



0-25 



0-137 



005 

 0-0013 



io- 11 . 



ft 



i 



141 

 183 

 220 

 11-5 



7-0 

 052 

 044 

 25 



014 



Thermal 



Conductivity, Jc, 

 in calories. 

 Observed. 



f 23 . 10 3 , fused, 

 i 16 ±, K.L. 

 14-3, L.B. 

 18*3, L.B. 

 22 2, L.B. 

 120, K.L. 



71, K.L. 



5, K.L. 



4, K.L. 



22. E. 



0141, L.B. 



0-45, K.L. 



0-0005 



0-05 



00013 013, K.L. 



It was not to be expected that a qnasi-solid such as 

 indiarubber should conform to the rule. Its velocity of 

 sound calculated from E and p is 0*7 . 10° centimetres a 

 second ; the observed value (K.L.) is 0*07 . IO 5 . In either 

 case the values of Ep or Y 2 p 2 are of a lower order than the 

 conductivity observed by Lees, though the numeral is the 

 same. 



The elasticity of cork calculated from the velocity of 

 sound is 00055 . 10 11 . Its value for steady stress is about 

 one half of this; E/? = "00132 . IO 11 , or exactly one hundredth 

 of Lees' value 0*13. The cellular structure of cork makes it 

 difficult to say how far the vibrations are transmitted by the 

 walls or contained air. Baking the cork to a dark brown 

 softens it and improves its value as a heat insulator. The 

 cell- walls are then seen under the microscope to be slack and 

 collapsed, so that they undoubtedly have some part in the 

 transmission. On the other hand, pumice-stone has a con- 

 ductivity much the same as cork and has a more rigid 

 structure. 



The agreement between the values of Jc, Ep, and Y 2 p 2 , for 

 substances of such different composition as quartz and wax, 

 indicates that there is some fundamental process, a conse- 

 quence possibly of the electrical structure of matter, certainly 

 independent of molecular structure, beneath these phenomena. 

 On the electron theorv of matter mechanical forces are 



