on the terrestrial Rays that occasion Heat. 485 



146^ Experiment. 



Fire. White persian. 



5 8ii 68| .. . 15I : 2f = ,171 



This substance stops 829 scattered rays of fire-heat. 



147JJ& Experiment. 



Fire. Black muslin. 



o' 66 66 



5 82|- 7°t--- 16$: 4^. cor. + i° = ,294 



This substance stops 706 scattered 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,* will also do for the invisible part 

 of the heat spectrum : it is only required to add two or three 

 more parallel lines, one- tenth of an inch from each other, be- 

 low 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. 



148^ Experiment. 



Invisible rays. Bluish-white glass. 



o' 48 47 



5 49l 48|. i :if:jf = ,929 



This glass stops only 71 invisible rays of heat. 



" * See Plate XXII. Fig. 3. 

 MDCCC. 3 R 



