THE EXTERNAL ENVIRONMENT 235 



Let T be the ordinary temperature of the surface, t that of the 

 external environment. Then : 



q 1 = K[ [(T+273) 4 (t + 273) 4 ]. 



The factor of proportionality K; = 1-355 X 10~ 12 , according 

 to A. Shakespeare, 1-27 x 10~ 12 , according to Bauer, for per- 

 fectly black surfaces. In the case of the human skin, the co- 

 efficient K; = 1-02 x 10- 12 approximately^ 1 ) 



172. Co-efficient of Utility of Clothing. To estimate the 

 protective effect of a garment, without taking into account its 

 matter or its thickness, Coulier ( 2 ) covered a cylindrical brass 

 vessel, filled with hot water, with the material to be studied. 

 Bergonie ( 3 ) used a copper bust in which the water was at a tem- 

 perature of 37 C. He noted the time t in which the temperature 

 of the bust, when covered with a given garment, fell 1C. 



The external temperature was 12C. 



The time taken in a fall of temperature of 1C, when the bust 



was bare was 0. The ratio - = c f gave the co-efficiency of utility 



or the protection afforded by the garment. 



Bergonie obtained the following practical co-efficients : 



GARMENTS. C f 



Cyclists' costume, (close fitting) 1 TO 



Woollen shirt 1-50 



Swanskin waistcoat 1 -55 



Hunting waistcoat 1-60 



Leather jacket, black, lined 1-60 



Flannel shirt 1 '75 



Coarse cloth jacket 1-90 



Rainproof cloak (Inverness) 2TO 



Pyrenese wool waistcoat 2-50 



Winter overcoat silk lined 2-50 



furlined 4-50 



Rubner's tables can be used to calculate the protective power of 

 a garment according to the nature of its tissue and its thickness. 



At the same time the practical, hygienic value of a material also 

 depends on the way it behaves as regards perspiration. This 

 is an important though not absolutely essential factor in the 

 utility of the garment. One must not neglect to be well covered, 

 though the workman and the peasant, although badly clothed 



( 1 ) G. A. Shakespeare (Proced. Roy. Soc., llth Jan., 1912. Bauer and 

 Moulin (Jouvn. de Physique, 1910, p. 468). Rubner (Arch. f. Hygiene, 

 vol. xvi., p. 357, 1893). 



( 2 ) Coulier (Journ. de Physiol., 1858, vol. i.). 



( 3 ) Bergonie (Comptes Rendus Biologie, 1904, pp. 265, 314). 



