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distances of four inches, and the water is immediately let in The 

 second irrigation takes place in 12 days, and the third in 24 days; 

 .after this, the soil is watered every eight days ; the ground is then 

 left 10 days without watering, and the onions ripen and are unearthed; 

 they are known to be mature when the tops become dry. The culti- 

 vator plants the sprouts in the furrows, head downwards, burying 

 them to the depth of four fingers' breadth. — [Journal of the Society of 

 .Arts]. 



FORESTRY. 



In Bulletin No 45 will be found some notes on Timber Trees. I 

 then advocated the extensive planting of West Indian Cedar, Ma- 

 hogany, Mahoe, Juniper Cedar, Yacca, &c, for the sake of the 

 valuable timber which they would eventually produce. Whilst still 

 of opinion that this is a subject of great importance in a commercial 

 sense, especially in a country where good timber is scarce, and the im- 

 ported article expensive, the matter may be viewed in another light, 

 of no less importance to agriculturists, and that is the effect forests 

 have on the temperature and rainfall. Dr. Schlich, Professor of 

 Forestry at the Royal Indian Engineering College, Cooper's Hill, 

 and late Inspector-General of Forests to the Gfovernment of India, in 

 his " Manual of Forestry" gives much useful and interesting informa- 

 tion bearing on this subject. Speaking of the effect of forests on the 

 moisture of the air he says : Air can hold only a certain maximum 

 quantity of vapour, which increases and decreases with the tempera- 

 ture. When the maximum has been reached, and more vapour is in- 

 troduced, a part becomes fluid. The absolute vapour in the air is 

 measured by its tension upon a column of mercury, as represented in 

 a barometer. The proportion of the absolute tension to the maximum 

 tension of vapour, which is possible at a certain temperature and pres- 

 sure, is called the relative humidity of the air. Although the humidity 

 of the air depends in the first place upon the general distribution of 

 heat and air pressure over the large sheets of water on the earth, 

 which govern the direction and force of the moist air currents, the 

 vegetation of the earth must also affect the degree of humidity, 

 chiefly because it reduces the temperature locally. That effect may be 

 felt n the degree of humidity of the air, the amount of precipitation, 

 the degree of evaporation, and in the feeding of springs and rivers " 

 " That forests can affect precipitations follows from the facts, that 

 forest air is relatively moister than air in the open, and that the trees 

 mechanically affect the movement of the air." " On the whole it may be 

 said, that various physical factors act towards rendering forests excellent 

 condensators of vapour, because they have a lower temperature, a moister 

 air, and break the force of air currents." Speaking of the feeding of 

 springs and rivers he says : " Most of the rain-water falling on a bare 

 slope rushes down into the nearest watercourse in a comparatively short 

 time, thus causing a rapid rise in the level of the stream. Only a com- 

 paratively small portion sinks into the ground, so as to become available 

 for the feeding of springs. Of the rain falling over a forest, close on 

 one-fourth is intercepted by the crowns of the trees, and the other 

 three-fourths fall upon a layer of humus, which possesses a great 



