464 Dr. Herschel's Experiments on the solar, and 



whether they act equally ; and the candle, during the time they 

 cool down to the temperature, must be put out by an extin- 

 guisher, large enough to rest on the bottom of the box, without 

 touching any part of the wax. Many other precautions I need 

 not mention, as they will soon be discovered by any one who 

 may repeat such experiments. 



6%d Experiment. 



Candle. Bluish-white glass. 



5 6 *i 6of . . . 3 : i| = ,375 



From this experiment we find, that while the rays of the 

 candle gave 3 degrees of heat to the thermometer openly ex- 

 posed to their action, the other thermometer, which received 

 the same rays through the medium of the interposed glass, rose 

 only l-i degrees. Hence we calculate, that this glass stops 625 

 rays of flame-heat, out of every thousand that fall on it. It 

 stops only 86 rays of candle-light ; but this, having been re- 

 ferred to before, will not in future be repeated. 



r 6^tb Experiment. 



Candle. Flint glass. 



°' 59ir 59i 



5 62f 6of . . . sf : ii = ,409 



It stops 591 rays of flame-heat, and light as before. 



65th Experiment. 



Candle. Crown glass. 



o' 59i 59i 



5 6af 6o% . . . &f : 1 = ,364 



It stops 636 rays of flame-heat. 



