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vapour, the last two to that of carbonic acid. It should be emphasized that Langley has applied the greatest diligence in the measurement of the intensity of the moon's radiation at angles between 36° and 38°, where this radiation possesses its maximum intensity. It may, therefore, be assumed that the calculated absorption-coefficients for this part of the spectrum are the most exact. This is of great importance for the following calculations, for the radiation from the earth^[1] has by far the greatest intensity (about two thirds, cf. p. 250) in this portion of the spectrum.

II. The Total Absorption by Atmospheres of Varying Composition.

As we have now determined, in the manner described, the values of the absorption-coefficients for all kinds of rays, it will with the help of Langley's figures^[2] be possible to calculate the fraction of the heat from a body at 15° C. (the earth) which is absorbed by an atmosphere that contains specified quantities of carbonic acid and water-vapour. To begin with, we will execute this calculation with the values ${\text{K}}=1$ and ${\text{W}}=0.3$. We take that kind of ray for which the best determinations have been made by Langley, and this lies in the midst of the most important part of the radiation (37°). For this pencil of rays we find the intensity of radiation at ${\text{K}}=1$ and ${\text{W}}=0.3$ equal to 62.9; and with the help of the absorption-coefficients we calculate the intensity for ${\text{K}}=0$ and ${\text{W}}=0$, and find it equal to 105, Then we use Langley's experiments on the spectral distribution of the radiation from a body of 15° C., and calculate the intensity for all other angles of deviation. These intensities are given under the heading M. After this we have to calculate the values for ${\text{K}}=1$ and ${\text{W}}=0.3$. For the angle 37° we know it to be 62.9. For any other angle we could take the values A from Table II. if the moon were a body of 15° C. But a calculation of the figures of Very^[3] shows that the full moon has a higher temperature, about 100° C. Now the spectral distribution is nearly, but not quite, the same for the heat from a body of 15° C. and for that from one of 100° C. With the help of Langley's figures it is, however, easy to reduce the intensities for the hot body at 100° (the moon) to be valid for a body at 15°

1. After having been sifted through an atmosphere of ${\text{K}}=1.1$ and ${\text{W}}=0.3$.
2. 'Temperature of the Moon,' plate 5.
3. "The Distribution of the Moon's Heat," Utrecht Society of Arts and Sc. The Hague, 1891.