Emission and Transmission of Heat 69 



Density. C. 



Fir, do do parallel do do .48 1.37 



Walnut, do perpendicular do do .48 .86 



Walnut, do parallel do do 1.40 



Oak, do perpendicular do do 1.70 



Cork . . . , . . . . .22 1.15 



India rubber . ...... .22 1.37 



Gutta-percha . . . . . . .22 1.39 



Starch paste ...... 1.02 3.43 



Glass ....... 2.44 6.05 



Glass ........ 2.55 7.10 



MATERIALS IN A STATE OF POWDER 



Density. C- 



Quartz sand ....... 1.47 2.18 



Brick dust large grains ..... i.oo 1.12 



Brick dust passed through a sieve of silk . . 1.76 1.33 



Brick dust fine powder obtained by decantation 1.55 1.13 



Chalk, in powder, slightly damp ... .92 .897 



Chalk, in powder, washed and dried . . . .85 .694 



Chalk, in powder, washed, dried and compressed 1.02 .855 



Flour of potatoes . . . . . . .71 .790 



Wood ashes . . .45 .484 



Mahogany sawdust . . . . . . .31 .524 



Charcoal, powdered . . . . . . .49 .637 



Charcoal, powdered and passed through silk . .41 .653 

 Coke, in powder ...... .77 1.290 



TEXTILE MATERIALS 



Density. C. 



Canvas of Hemp, new ..... .54 .420 



Canvas, do do, old ..... .58 .347 



White writing paper 85 .347 



Gray blotting paper ...... .48 .274 



Calico, new, of any density .... .403 



Cotton wool, do do . . . . . .323 



Sheep's wool, do do . . . . . .323 



Eider down, do do . . . . . .315 



860. It is important to notice that as the conductivity of 

 textile materials is independent of their density, it follows that 



