394 



MK. W. T. DAVID ON TIIK KADIATION IN 



dotted Curves A P ' and A B ' (fig. 13) which are the differentials of the radiation Curves 

 A P and A B . The fourth column gives the ratio of the figures in the second column to 

 those in the third column. 



1200 



800 



400 



05 



/$ v? 



Time offer 



-ZS 



35 



2 



45 



Fig. 13. 



From this tahle it will be seen that the gaseous mixture when enclosed in the 

 vessel with reflecting walls radiates from 70 per cent, to 90 per cent, more strongly 

 than the same mixture does when enclosed in the black- walled vessel. 



With the object of analysing this effect measurements were made of the radiation 

 emitted by a small sectioned cylinder (or more correctly a cone of small solid angle) of 

 the gaseous mixture of different (effective) lengths, first, when the walls were made 

 reflecting, and, secondly, when the walls were black. 



These experiments were carried out with the silver-plated explosion, vessel. The 

 same bolometer holder was used, but the bolometer was placed some distance behind 

 the plate of diathermanous substance, and the interior of the tube, into which the 

 bolometer is pushed, blackened over so as to prevent radiation from any point in the 

 gas outside the cone reaching the bolometer by reflection from its surface. 



The emission was measured from two lengths of the gas, viz., 30 cm. and an 

 effective length of 59 cm., these lengths being chosen because they could be 

 conveniently obtained in the vessel. The vessel was 30 cm. in length, and when the 

 walls were black the first length was directly obtained. The second length, which is 



