1849.] exercised by Trees on Climate. 4St7 



great workshops, a foundry for gold, and powerful machines for the 

 division and amalgamation of this precious metal. There was now 

 a free population of nearly 3,000 inhabitants settled on the mountain 

 side. All this implies that the wood had been extensively cut down 

 for the manufacture of the machines, the construction of the build- 

 ings and the preparing of charcoal. That it might be the more easily 

 carried on all this was done upon the plateau of San Jorge itself. 

 The clearing had been going on for scarcely two years, when it was 

 noticed that the quantity of water which was required for the ma- 

 chines had conspicuously diminished. Tlie volume of water is in fact 

 measured by the work which the machines perform ; and trials by 

 gaging, at different times, have likewise proved the diminution of the 

 water. But this is at Marmato an all important subject, for a dimi- 

 nution of the fluid moving power is always followed by a diminution 

 in the production of gold. 



In these two cases of Marmato and Ascension it is not at all pro- 

 bable that an extent of clearing so local and limited could have such 

 an effect upon the meteorological condition of the atmosphere, as in 

 any degree to vary the annual amount of the rain which falls through- 

 out the country. But the question need not be left in this uncertain- 

 tv. At Marmato as soon as the diminution of the supply of water 

 was ascertained a rain-guage was established, and it was found, b;y 

 the observation of the second year that a greater quantity of rain 

 had fallen than during the first, although the clearing had been con- 

 tinued and there was no appreciable increase of the quantity of water 

 at the wheels. Two years of hydrometrical observations are sufnci- 

 ent even in the tropics to exhibit the variation in the annual quanti- 

 ty of rain, and the observations at Marmato establish that the mass 

 of running water has diminished at the very time that the quantity 

 of rain had increased. 



It is then probable that local clearings of no great extent may 

 diminish the copiousness of springs and rivers, and even cause them 

 to disappear, and under circumstances where these effects can in no 

 degree be attributed to a diminution of the fall of rain. 



Finally, we have still to examine if the extensive clearing of forests, 

 extending over considerable districts has any effect in making the rain 

 less copious ? In reply we remark that it is only hydrometrical obser- 

 vations that can lead to the solution of this question. And unfor- 



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