31 



regard to the main fact, that the emission of moisture by the leaves of the forest is very 

 great, we are at one. " 



The Marquis's views thus largely corroborated are : — 



" It is an accepted fact, and not without reason, that the neighbourhood of forests is 

 cold and damp. This is far from astonishing when one thinks of the enormous volume of 

 water transformed by forests into vapour, and the quantity of heat absorbed in this trans- 

 formation. This heat must have been obtained somewhere, perhaps from the soil of the 

 forest and that of the neighbourhood. 



" In the same way there should be great damp in the neighbourhood of forests, 

 especially when the temperature is high, and it cannot be otherwise, on account of the 

 enormous amount of water in the form of vapour which is discharged by forests into the 

 adjacent atmosphere. 



" This vapour is emitted ^in much greater abundance during the day than during 

 the night. Towards night, a little after sunset, when the general temperature begins to 

 fall, the transpiration not yet having time to slacken, and ascending into a colder air 

 changes into visible fog, like our own breath in like circumstances, and this fog in its turn 

 becomes a cloud on the following morning, when the sun warms its particles ; but whether 

 clouds or fogs, they will be carried away by the first breeze to descend in showers. 



" If these details as to the formation of forest fogs be correct, such fogs should be more 

 frequent in calm weather, when the air is naturally more moist and especially when the 

 contract is greater between the cool of the evening and the heat of the day. The test of 

 conditions for the formation of thick fogs is especially complete,- at least in our climate, 

 towards the end of summer and the first half of autumn ; and it is during this period that 

 the phenomenon is most frequent and noticeable. 



" If the transpiration carried on by the leaves were coloured and perceptible, it 

 would be a grand sight to see great columns of vapour ascending majestically into the air, 

 diminishing by their heights the distance between the tops of the trees and the stormy 

 clouds ; and as this vapour facilitates the passage of electricity, by increasing the moisture 

 of the air with which it mingles, the facility with which isolated trees are struck with 

 lightning can be accounted for." 



If my readers have followed me, and we have succeeded in arriving at a clear explana^ 

 tion, we will now have had : — 



1. A short account of the manner of growth of a tree. 



2. The system of the winds and their method of conveying moisture. 



3. The causes of the moisture being precipitated and falling to the earth a's rain. 

 We will now proceed to notice : — 



The CoNNEOTioisr op Forests with the Production op Rain. 

 We have observed that the winds returning, charged with heat and moisture, from 

 the equator in their course to the north pole, bear with them an immense quantity of 

 water. As has been said, the torrid seas send their surface, sixteen feet deep, to the skies 

 in the form of vapour in a year. Of this it has been computed that six feet are dis- 

 charged in rain in the tropics, the remainder sent towards the poles, towards the north 

 pole about six feet— a tremendous mass of water. In addition, we must remember, vast 

 though lesser amounts of water, are taken up from the rest of the surface of the world, 

 'both land and sea, and though the south-west winds, evident or concealed by changing 

 currents, must be our chief supply, yet water-charged clouds from other sources pass 

 over in all directions as well. 



