1867.] 



Insolation to Atmospheric Humidity. 



359 



alluded to are respectively 21°'7 and -098, as deduced from the hourly ob- 

 servations which were taken in 1842-48 at the Ordnance Office. 



The mean readings of the standard thermometer at 2 p.m. (the warmest 

 hour in the winter at Toronto) and the contemporaneous mean tensions 

 of vapour, in January and February, are exhibited in Table IV. 



Table IV. 



Monthly Mean Results at Toronto at 2^ p.m. (1842-48)*. 



Month. 



Maximum 

 temperature 



Wet-bulb 

 thermometer. 



Tension of 

 vapour. 



January ... 

 February... 



28-6 

 28-3 



o 



26-7 

 25-9 



0-129 

 0-117 



At 2^" on the 7th to the 1 7th days of February the temperature was 26°'4, 

 and the mean tension of vapour '111. 



Postmeridian maxima of solar radiation. — Though, it is well known at 

 observatories, the hour of mean maximum solar heat occurs in this country 

 after midday, there is no numerical proof of the fact available, excepting the 

 results of six days' observations by Professor Daniell. From experiments 

 made by him in June (1822) at every hour between Q*" 30™ a.m. and 

 7^ 30™ p.m., the mean highest readings of a black-bulb thermometer were 

 obtained between 1^ 30^^' and 2^. The following are the means for five 

 days : — 



h m o 

 At 10 30 .... 46 

 12 30 .... 63 



1 30 65 



2 30 .. .. 63t 



It may be assumed, then, that on days when the sun is shining both in the 

 morning and afternoon, solar radiation is of highest apparent force after 0^+. 



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

 duced at 10^ a.m., noon, and 2'' from the bi-horary observations at Greenwich 

 in 1842-47 ; the following Table, which contains the monthly results for 

 each of these hours, shows that the means at 2'* are higher than those at 

 10^ A.M., or at noon, in every month from March to September : — 



From Tables LY., LYIII.; and LX., Toronto Observations, vol. ii. The maxima 

 of heat and vapour occur at Toronto in Jidy and August, Tapoiu--tension at '2^ in July 

 being -069 higher, and in August -108 higher than in June, 

 t Daniell's 'Meteorology,' toI. ii. p. 113. 



+ Ibid. pp. 114-118. On another favourable day in June, Professor Daniell obtained 

 tlie following residts with a solar thermometer covered with black wool : — at lO'^ a.m. 1 11°; 

 at noon 129°; at 2^ r.M. 143^ ; at 2iiS0'« p.m. 138°. Since this paper was in type, I 

 find these results are confirmed by observations made in March 1858 by Mr. H. S. Eaton. 



