THE EXTERNAL ENVIRONMENT 233 



The co-efficient, c., for various materials depends, therefore, 

 much less on their nature than on the air, which they can imprison. 

 Skins, furs and various porous tissues are bad conductors of heat, 

 because of the air in their interstices. The less dense the tissue 

 the better the material as a heat insulator. See the tables ( 251) 

 in Technics. 



Here are a few average co-efficients of conductivity obtained 

 byRubnerf 1 ), 



CO-EFFICIENT 

 SUBSTANCES. OF 



CONDUCTIVITY 



Air 0-0000532 c. 



(of peasants) { jjJOOgg 



Feathers (eider down) 0-0000574 



Skins and horse hair 0-0000570 



Smooth cotton fabric 0-0000810 



wool 0-0000686 



silk 0-0000684 



Cashmere 0-0000686 



Linen cambric (Batiste) 0-0000810 



Flannel 0-0000723 



Knitted wool 0-0000650 



Flannelette 0-0000757 



Knitted cotton 0-0001002 



Tricot linen 0-0001158 



silk 0-0000916 



Blue winter stuffs 0-0000756 



Winter cloth "0-0000733 



Summer cloth 0-0000714 



Winter overcoat 0-0000676 



POKKU oi \ f fur outside 0-0000689 



Rabbit skin | fur inside 0-0000682 



Water ( 2 ) (at about 37 C) 0-001350 



10% Solution of sea salt ( 3 ) 0-001080 



Human skin ( 4 ) ! 0-000600 



Lard (solid fat) ( 5 ) 0-000480 



Ox hide ( 6 ) 0-000420 



(See a supplementary table in Technique). 



(!) Rubner (loc. cit., p. 350 to 380. 



( 2 ) Lees (Proceed. Roy. Soc., vol. Ixii., p. 286, 1898 ; Phil. Trans., vol. 

 cxci, p. 399, 1898). 



( 3 ) Winckelmann (Wied. Ann., vol. x., p. 668, 1880). 

 (*) Jules Lefevre, Bioenergttique, p. 398. 



() Lees (loc. cit.): 



( 9 ) Lees and Chorlton (Phil. Mag., vol. xli., p. 495, 1896). 



