392 Royal Society: — Mr. J. P. Harrison on the Relation 

 Monthly Means of Radiation and Vapour at Greenwich (1860-64). 



Month. 



Solar 

 radiation. 



Tension of 

 vapour. 



Weight of 

 vapour. 



May 



97*8 F. 



103-2 



108-2 



107-5 



97-5 



0-314 in. 



0-364 



0-393 



0-397 



0-361 



3-5 grs. 



4-1 



4-4 



4-4 



4-0 



June 



July 



August 



September .. 



The dependence of the maximum temperature in the day on the 

 quantity of moisture in the air, in winter, at Toronto, was referred 

 to to show the effects of slight variations of vapour in that country. 



Postmeridian maxima of solar radiation. — Though it is well 

 known at observatories that the hour of mean maximum solar heat 

 occurs in England after midday, there is no numerical proof of the 

 fact available, excepting the results of six days' observations by Pro- 

 fessor Daniell. From experiments made by him in June (1822) 

 between 9 h 30 m a.m. and 7 h 30 m p.m., the mean highest readings 

 of a black-bulb thermometer were obtained at l h 30 m . The following 

 are the means before and after noon : — 



h m 





10 30 .. 



. . 46 



12 30 .. 



.. 63 



1 30 .. 



.. 65 



2 30 .. 



.. 63 



Daily maxima of vapour. — The means of vapour-tension have been 

 deduced at 10 h a.m., noon, and 2 h p.m. from the bi-horary observations 

 at Greenwich in 1842-47; the following Table, which contains the 

 monthly results for these hours, shows that the means at 2 h are 

 higher than those at 10 h -A.M., or at noon, in each month from March 

 to September : — 



Monthly Means of Vapour-Tension at Greenwich at 22 h , 0\ and 2 h 

 (1842-47). 



Hour. 



March. 



April. 



May. 



June. 



July. 



August. 



Sept. 



h 



22 

 

 2 



•236 



•246 



+ •249 



0-284 



0-294 



+0-297 



0-357 



0-365 



+0-368 



0-437 



0-446 



+0-449 



0-462 



0-469 



+0-475 



0-473 



0-483 



+0-486 



0-427 



0-441 



+0-444 



The mean increase of vapour from 10 h a.m. to noon is *010; and 

 the mean increase from noon to 2 h is '0034. 



Actinometer-observations. — The observations of the actinometer 

 made by Mr. Nash at the Royal Observatory in 1864 supply further 

 evidence of the fact that the maxima of radiation occur in the autumn, 

 and after midday. 



On extracting the mean results of the several groups of observa- 



