766 



PHILOSOPHICAL TRANSACTIONS. 



[ANNO 1800, 



This glass stops 849 scattered 

 151. rays of fire-heat. 



This substance stops 912 scattered 

 rays of fire-heat; it was turned a 

 little yellow by the exposure. 



This substance stops 9 10 scat- 

 .0897. tered rays of fire-heat. 



This substance stops 829 scat- 

 tered rays of fire-heat. 



This substance stops 706 scat- 

 .294. tered rays of fire-heat. 



Transmission of the Invisible Rays of Solar Heat. — The same apparatus which 

 I have used for the transmission of coloured prismatic rays, fig. 17, pi. 13, will also 

 do for the invisible part of the heat spectrum: it is only required to add 2 or 3 

 more parallel lines, -±$ of an inch from each other, below the two which inclose 

 the transmitting holes, in order to use them for directing the invisible rays of heat, 

 by the position of the visible rays of light, to fall on the place required for coming 

 to the thermometers. 



This glass stops only 71 invi- 

 sible rays of heat. 



This glass stops no invisible 

 rays of heat 



It stops 1S2 invisible rays of heat. 



It stops 143 invisible rays of heat. 



This substance stops 250 invisible 

 rays of heat. 



This glass stops no invisible rays 

 of heat. This accounts for the strong 

 sensation of heat felt by the eye, in 

 are used. 



It stops 273 invisible rays of heat. 



It stops 200 invisible rays of heat. 



It stops 375 invisible rays of heat. 



It stops 500 invisible rays of heat. 



It stops 800 invisible rays of heat. 



