In the above tables Rosetti's determination of the amount of the terrestrial atmospheric absorption has been used. It may be well, however, to give the results obtained by using other estimates of this quantity. Taking Langley's transmission coefficient when the sun is in the zenith as 59 per cent., compared to Rosetti's 71 per cent., the temperature would be multiplied by ^(71/59) and thus become 5773 x 1 '054, which is 6085 absolute. And, as in the previous memoir, to make the case general, if any later investigation shows the zenith transmission coefficient to be per cent., the effective absolute tempera- ture becomes
5773 x y(71/s).
It may also be of interest to see what effect is produced if absorption in the atmosphere of the sun itself is taken into account. First, con- sidering the falling off in radiation from the central to the peripheral parts of the sun's disc, we may deduce that, if the absorption were everywhere equal to that at the centre, the radiation would be multiplied by 4/3 and the temperature would become
5773xy(4/3) = 5773x1-074 = 6201.
Secondly, assuming Wilson and Rambaut's* result for the total loss due to absorption in the solar atmosphere as equal to one-third, our estimate of the temperature would have to be multiplied by v / (3/2), and we get finally
6201 x i/(3/2) = 6201 x 1-107 = 6863 absolute = 6590* C.
I wish to express my thanks to Dr. Rambaut for some valuable suggestions during the progress of the work.
In February, 1901,t we read a short paper on the results of chilling copper-tin alloys, and at the Glasgow meeting of the British Associa- tion, 1901, we gave an account of some of the conclusions that we had arrived at concerning the nature of the alloys rich in copper.J The present paper extends our conclusions to all alloys of copper and tin, and the accompanying diagram presents the result in a concise but very complete form.
- " The Absorption of; Heat in the Solar Atmosphere," ' Proceedings Royal
Irish Academy,' 1892, TO!. 2, No. 2. t ' Roy. Soc. Proc.,' yol. 68, p. 171. If ' Report on Alloys,' Sec. B.
