On the Surface- Temperatures of the Planets. 749 

 Summary of Results. 



(1) Over the time of observation (P05 days) radium is 

 produced in actinium preparations at a constant rate. 



(2) By suitable chemical treatment actinium preparations 

 can be obtained which grow radium extremely slowly. 



(3) The active deposit of actinium does not change directly 

 into radium. 



(4) The results indicate that in the ordinary actinium pre- 

 parations there exists a new substance which is slowly trans- 

 formed into radium. This direct parent of radium can be 

 chemically separated both from actinium and radium. 



(5) Observations have not extended over sufficient time to 

 settle whether this direct parent of radium has any direct 

 genetic connexion with actinium or not. 



Experiments are in progress to devise more definite methods 

 for separation and isolation of this new substance in order 

 to examine its physical and chemical properties, and to deter- 

 mine its position in the long series of transformations of 

 uranium. 



Manchester, Sept. 20, 1907. 



LXXIV. On Prof. LoicelVs Method for Evaluating the Surf ace- 

 Temperatures of the Planets; with an Attempt to Represent 

 the Ejffecl of J)ay and JVight on the Temperature of the 

 Earth. By J. H. Poynting, F.R.S.* 



PROF. LOWELL'S paper in the July number of the 

 Philosophieal Magazine marks an important advance 

 in the evaluation of planetary temperatures, inasmuch as he' 

 takes into account the effect of planetary atmospheres in a 

 much more detailed way than any previous writer f. But 

 he pays hardly any attention to the " blanketing effect," or, 

 as 1 prefer to call it, the "greenhouse effect'" of the atmo- 

 sphere. He assumes in fact that the fourth power of the 

 temperature is proportional to tie fraction of solar radia- 

 tion reaching the surface, and he neglects both the surface 



* Communicated by the Author. 



t In Phil. Trans. A. vol. ccii. p. 525 I attempted an evaluation, in 

 which the atmosphere was taken into account as keeping the tempera- 

 ture at a given point practically the same day and night. I did not 

 then know that Christiansen {Beibliitter zn den Ami. tier Pkysik and 

 Chemie, x. 1886, p. 532) had nearly twenty years earlier app.ied the 

 iourth power law to calculate planetary temperatures. His work deserves 

 recognition as the first in which this law was applied. 



