OF RADIANT HEAT THROUGH DIFFERENT BODIES. 57 



prisms of flint or crown glass, water, alcohol, or some other diaphanous 

 body. It was exactly the same as if they pretended to be able to analyse 

 solar light with a prism formed of coloured glass. 



Of the properties of the calorific rays immediately transmitted by different 



bodies. 



The radiant heat which has passed through a plate of glass is trans- 

 mitted in a greater proportion by a second plate of the same substance 

 and the same thickness ; the rays issuing from the second will be trans- 

 mitted in a still greater proportion by a third, and so through any number 

 of successive screens. The losses sustained by the calorific rays in their 

 passage through a succession of screens, as compared with the quantity 

 incident on each plate, will therefore form a decreasing series. But the 

 difference between every two terms of this series becomes less and less 

 as the number of terms increases, so that there must be somewhere a 

 limit beyond which the difference has a tendency to vanish. We may 

 conclude therefore that the rays after they have passed through a cer- 

 tain number of screens, will in their further transmission be subject to 

 a loss reducible to a constant quantity as compared with the quantity of 

 heat incident to each of the screens through which this further transmis- 

 sion is made. 



The same phsenomena may be traced in a continuous mass of diatlier- 

 manous matter ; that is to say, that if we imagine a piece of glass di- 

 vided i;ito several equal layers and measure the loss sustained by the 

 radiant heat in its passage through each layer, the greater the distance 

 of the layer from the surface at which the heat enters, the less will be 

 the diminution suffered by the rays passing through that layer, and the 

 losses have a tendency to become constant within a limit depending 

 on the thickness of the layers. Some of these results Me have already 

 verified in the preceding memoir, and it is easy to establish their truth, 

 in reference to the sources of heat employed in our present inquiry, by 

 means of the numbers which represent the transmissions of the plates 

 contained in the first table*. 



* Let us imagine the screen of 8""" divided into seven layers having for tlieir 

 degrees of thickness the differences between two consecutive plates. (See the first 

 table in this Memoir.) The quantities of heat incident on the layers when the 

 radiation is from a Locatelli lamp are 



100, 77, 54, 46, 41, 37, 35, 33-5, 

 and the quantities lost in the successive transmissions are 

 23, 23, 8, 5, 4, 2, 1-5. 

 Now the mean losses for the hundredth part of a millimetre of each screen will be 

 23 23 _8 _5_ _4_ 2^ 1-5 



y 43' 50' ioo' 100' 100' Too' 



or 3-280, 0-535, 0160, 0-050, 0-020, OOiO, 0007.* 

 Ilcnce the looses sushiined by the rays of the lamp in the first hundredth part 



