50 



85° in the shade, and when it does, a thunderstorm is the usual result, 

 and this cools the atmosphere for a time. 



The amount of Solar radiation in the summer months is from 30° 

 to 50°. It is greater during June than July : the mean of the former 

 month being 43-9°, and of the latter 42-0'. In August the mean falls to 



By Solar radiation is meant the excess of temperature registered by 

 a thermometer, with a blackened bulb, fully exposed to the sun's rays on 

 the grass, above that recorded by an instrument in the shade. In like 

 manner, a thermometer exposed on the grass at night usually reads much 

 lower than a similar one in the shade, at four feet above the ground. 

 The difference between the readings being greatest when the air is clear, 

 and the sky free from clouds. Under such circumstances, there is 

 generally a difference of 10° or 12'', or even more. This is called 

 terrestrial radiation, and is shewn in Table III. 



Ozone. 



Except in the first month of 1862, a daily record of the amount of 

 ozone in the atmosphere has been kept during the fifteen year period. 



Some Meteorologists are so sceptical as to the value of the tests used 

 for the detection of this agent, that they take no account of it. The 

 test which I employ is Dr. Moffat's, or rather a modification of it; the 

 test papers being prepared and sold by Messrs. Negretti and Zambra. 

 I believe it is generally admitted that these papers may occasionally be 

 affected by other gases than ozone, e. g. by free nitric or nitrous acid 

 fumes, present in the atmosphere. However, I give my results for 

 what they are worth. 



The ozone scale is divided into ten parts, according to the degree 

 of coloration : (I show you here the scale employed, from o up to 10): 

 The strip of test paper is exposed to the air for twelve hours, and then 

 compared with the chromatic scale. The mean degree of coloration 

 imparted to it at Cockermouth was only 2-2. It was greatest in January, 

 and smallest in June. Since the tint was also, in general, deeper by 

 night than during the day, I am inclined to think that it was influenced 



A 



