Tin- Effective Temperature of the Sun. 



313 



For the details of the apparatus and the complete method of reduc- 

 tion of the observations, the original memoir in the ' Phil. Trans.' may 

 be referred to. 



QF 



G. T 



H 

 R 



In order to protect the incandescent strip from draughts of air it 

 was covered with a water-jacket of gilded brass. This was provided 

 with a circular hole in one of its longer sides, through which its 

 radiation could reach the aperture of the radio-micrometer. The 

 internal walls of this water-jacket being highly polished,it has occurred 

 to me, since the publication of the memoir referred to, that possibly 

 some of the radiation from distant parts of the platinum strip may 

 have been reflected backwards and forwards from the^polished walls 

 and the strip itself, ultimately escaping through the aperture and 

 reaching the radio-micrometer, thus increasing the amount of radiation 

 which should have reached it directly from the strip alone. 



In order to test this surmise I first took a number of readings at 

 known temperatures with the walls of the water-jacket polished as 



