MEASUREMENTS 



323 



The following table gives the emissive powers of various sub- 

 stances as obtained by Peclet. The accuracy of the values has, 

 however, been disputed (Wiedelburg, 1898) ; 



Polished silver 



Copper 



Glass 



Fine sand 



Oil paints 



Paper 



Wood 



Woollen fabrics 



Calico 



Silk fabrics 



Water 



Oil 



0-0000036 

 0-0000044 

 0000808 

 0001000 

 0001030 

 0001040 

 0001000 

 0001020 

 0001010 

 0001020 

 0001470 

 0002010 



c. 



The above figures give the radiation in still air. In moving 

 air, the calorific loss is greater, being proportional to the speed of 

 the horizontal air current, as Oberbeck ( 2 ) found with inanimate 

 bodies and Jules Lefevre ( 3 ) with man ( 175). 



Lefevre's physiological calorimeter comprises a large zinc 

 casing 3 metres long (fig. 230) supported internally by a wooden 

 framework and composed of three parts, namely : a cylindrical 

 central chamber for the subject and inlet -and outlet compart- 

 ments for the air. 



FIG. .230. 

 Lefevre's Physiological calorimeter. 



(!) As the radiation of clothing, Rubner takes Ki = O'OOOllS c. (Die 

 Gesetze. Ch. xiii). 



( 2 ) Oberbeck (Wied. Ann., vol. Ivi., p. 397, 1895). 



( 3 ) Jules Lefevre (loc. cit., p. 103). 



