358 Actinism of the Suns Rays and of Daylight. [Apr. 29, 



Effect of temperature. Tubes exposed to daylight during a dull day. 



B solution. C solution required. 



0-2 0-15 



0-4 0-90 Temperature =12°-8 C. 



0- 8 l'OO 



1- 3-20 



1-6 6-00 



These were in duplicate to begin with, but finding after an hour 

 and a half that almost no action had taken place, one-half were put 

 into the dark. At the end of the day the result was : — 



33 solution. C solution required. 



0-2 -0~ 



0- 4 0-0 



0'8 0-1 Temperature =11°1 C. 



1- o-i 



1-6 0-2 



It is seen that with an almost equal temperature the action is very- 

 decided in light on a dull day, but scarcely measurable in darkness. 

 To examine further the effect of heat the following were tried : — 



Temp. 12°-8 C. in light. Temp. 25° C. in darkness. 



E sol. C sol. required. 33. sol. C sol. required. 



0-4 0-4 0-4 



0- 8 1*3 0-8 



10 1-9 1*0 ...... 



1- 6 5-2 1-6 ? 



It was suspected that not only did the iodide solution change by 

 keeping, but the nitric acid also, weak as it was. Indeed I had once 

 a mode projected of measuring light by the decomposition of nitric 

 acid or nitrates, but I did not expect this to take place in such weak 

 solutions. 



To avoid this change, sulphuric acid was tried with the following 

 result. This trial serves also as a test for the effect of light separate 

 from heat. 



(1) 2| hours' exposure to not very bright clouds ; (2) dark : 



(1) Temp. 12° C. in light. (2) Temp. 20° C. in dark. 



Sulphuric acid used, .. . „, . , 



C sol. required. Sulphuric acid. C sol. required, 



same acidity. i r -i 



0'4 0-5 0-4 ...... .0 



0- 8 3-9 0-8 



1- 6 4 9 16 



3'2 6-1 3-2 



11. There seems, therefore, no reason to doubt that this is a true 



