Intelligence and Miscellaneous Articles. 



469 



ON SOLAR RADIATION. BY M. SORET. 



In prosecuting my researches on the solar heat by the aid of the 

 actinometer which I have briefly described*, I have lately made 

 some observations on the nature of the rays absorbed by the atmo- 

 sphere. 



The intensity was measured either by allowing the rays to fall di- 

 rectly on the thermometer of the actinometer, or by first causing them 

 to pass through a layer of distilled water of about 5 centims. thick- 

 ness. This water was contained in a brass tube closed by two glass 

 plates. 



If T be the increase in temperature in the first case, and t the in- 

 crease in the second case, the ratio — will be greater the greater is 



the proportion of rays not absorbed by the tube with water f. Now 

 water, like glass, allows luminous heat to pass freely, but absorbs in 

 great part obscure heat, and especially the least-refrangible rays. 

 Hence, making these observations for different heights of the sun 

 above the horizon (that is, for different thicknesses of the atmospheric 

 layer traversed by the rays), indications will be obtained as to the 

 nature of the heat arrested by the atmosphere. 



The absolute values of T and t for the same solar height vary with 

 atmospheric conditions, such as the transparency and the moisture 

 of the air. Hence, to appreciate the influence of an increase in the 



atmospheric thickness, the values of — should be compared which are 



obtained at different times of the same day. It will be seen that this 

 ratio is greater in the middle of the day than when the sun is at a 

 small height above the horizon. 



The following are some observations made at Geneva : — 



Date. 



Time. 



T. 



t 



t 

 T" 





h m 









Feb. 27. 



1 45 



1419 



8-25 



0-581 



„ 27. 



4 25 



907 



5-31 



0545 



March 9. 



12 30 



14-58 



8-66 



0594 



„ 9. 



5 10 



7-81 



3-66 



0-409 





, 13. 



11 30 



1470 



8-35 



0-56S 





, 13. 



4 46 



10-78 



577 



0-535 





, 13. 



5 20 



7 06 



3-41 



0-484 





, 14. 



7 10 



7-04 



304 



0-432 





, 14. 



12 24 



14-85 



8-51 



572 





, 14. 



5 30 



6-74 



3-37 



0-500 



April 3. 



12 3G 



1389 



8-27 



0-596 



„ 3. 



5 36 



7 51 



337 



0-449 



* Phil. Mag. S. 4. vol. xxxiv. p. 404. 



t In order that t may exactly give the amount of heat not absorbed by 

 the tube full of water, a correction should be introduced for the heat re- 

 flected at the limits of the media; but as this correction is proportional to 

 the quantity of heat transmitted, it would not modify the conclusions to be 

 drawn from the results cited below. 



Phil. Mag. S.4. Vol. 35. No. 239. June 1868. 2 1 



