AND THE ACTINIC CONSTITUTION OF THE ATMOSIMIEIU-:. 



27 



Date. 



Sejilember 



Combustion. 



KeiiiarUs 



3 

 4 



5 

 6 



7 

 lo 

 1 1 



12 



13 

 14 

 15 

 16 



17 

 18 



19 



20 

 21 

 22 

 26 



27 

 28 



'5 ^ 



10 j^ 



24 ;ii 



255^ 

 '5 i 



29 f^ 



30?* 

 10 '^ 



iT/o 

 49^ 



Same weather as day l)eforc. 

 Middling day. 



Quite a line day. Many cirri. 

 Middling day. 



Quite a fine day. Some cumuli early. 



Middling day. 



Quite a fine dav with a few clouds. 



it a' ii u 



Fine day, hot sun, a few cumuli. 



Fine in the morning, middling later. 



Fine day, very warm. 



Very fine day, as yesterday. 



Middling day. Warm and heavy. 



Day divided between sun and clouds. 



Dark day. 



Superb day. 



Sky fine early ; covered in the evening. 



Day rather finer than day before. 



Quite fine in the morning. Cloudy at night. 



Cumulus concealing about \ of sky. 



Rather better than the day before. 



Rather a dull day, but no clouds. 



Between the 20th and 30th August there followed a long period of rain and overcast sky. 



What stfikes us in reading these figures is theii' snialluess even ou fine days. 

 They are the smallest I have ever had to record in August and September, on an 

 average, and this although the latter month was I'ather fine at Mont Dore during 

 1888 ; there is also to be noticed a gi'eat lack of agreement between the apparent 

 character of the day and its actiuoraetric character. Thus the very fine day of Sep- 

 tember 15th gave only a combustion of 9 per cent, when the slightly veiled day of 

 September 28th gave a combustion of 49 per cent. This is a new confirmation of 

 what has been stated before. 



I partly atti'ibute the very great want of agreement noticed at Mont Dore to 

 the fact that this station is surrounded on all sides by pine woods which diffuse 

 through the air a large quantity of terebinthine exhalations, so that the odor be- 

 comes sti'iking. This explanation also agrees with the notions which I have 

 suggested before. Nevertheless I admit that it would require very special com- 

 parative experiments to establish it firmly, and to draw from it the proper signifi- 

 cation. We must be content, for the present, to I'emark that if our explanation is 

 correct, it will also account, as a whole, for the want of agreement already 

 mentioned. If the exhalations of essential oils are really able to arrest actinic 

 radiations, the effect of what we call a fine day will be very variable according as 

 it will succeed a period of rains which may have washed the atmosphere, as in the 



