Page:Scientific Memoirs, Vol. 1 (1837).djvu/69

Rh 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 transmitted in a greater proportion by a second plate of the same substance and the same thickness; the rays issuing from the second will be transmitted 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 certain 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 transmission is made.

The same phænomena may be traced in a continuous mass of diathermanous matter; that is to say, that if we imagine a piece of glass divided into 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.