320 Messrs. C. T. Heycock and F. H. Neville. 



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. 



" On the Constitution of Copper-Tin Alloys." By C. T. HEYCOCK, 

 F.R.S., and F. H. NEVILLE, F.R.S. Received December 9, 

 Read December 12, 1901. 



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. 



