METEOROLOGY. 505 



1830, when I quitted the country, Marmato had the most flourishing 

 appearance • it was covered with workshops, it had a foundry of 

 gold, machinery for grinding and amalgamating the ores, &c., and a 

 free population of nearly three thousand inhabitants. It may be 

 readily imagined, that in the course of these four years an immense 

 quantity of timber had been cut down, not only for the construction 

 of machinery and of houses, but as fuel, and for the manufacture of 

 charcoal. For facility of transport, the felling had principally gone 

 on upon the table-land of San Jorge. But the clearing had scarcely 

 been effected two years before it was perceived that the quantity of 

 water for the supply of the machinery had notably diminished. The 

 volume of water had been measured by the work done by the ma- 

 chinery, and actual gauging at diiferent times showed the progressive 

 diminution of the water. The question assumed a serious aspect, 

 because at Marmato any diminution in the quantity of the water, 

 which is the moving power, would be of course attended with a pro- 

 portional diminution in the quantity of gold produced. Now, in the 

 Island of Ascension, and at Marmato, it is highly improbable that 

 any merely local and limited clearing away of the forest should have 

 had such an influence upon the constitution of the atmosphere as to 

 cause a variation in the mean annual quantity of rain which falls in 

 the country. More than this, as soon as the diminution of the 

 stream at Marmato was ascertained, a pluviometer, or rain-gauge, 

 was set up, and in the course of the second year of observation a 

 larger quantity of rain was gauged than in the first year, although 

 the clearing had been continued ; still there was no appreciable in- 

 crease in the size of the running stream. 



A couple of years of observation are unquestionably insufficient to 

 show any definitive variation in the annual quantity of rain that falls. 

 But the observations made at Marmato still establish the fact thai 

 .he mass of running water had diminished in spite of the larger quanti- 

 'y of rain which fell. It is therefore probable that local clearings of 

 •brest land, even of very moderate extent, cause springs and rivu- 

 fets to shrink, and even to disappear, without the effect being ascri- 

 bable to any diminution in the amount of rain that falls. 



We have still to inquire, whether extensive clearings of the 

 forest — clearings which embrace a whole country — cause any dimi- 

 nution in the quantity of rain that falls. Unfortunately, the observa- 

 ions which we have upon the quantity of rain which falls in par- 

 ticular districts, are only of sufficient antiquity and accuracy in 

 Europe to be worthy of any confidence, and there the soil was cleared 

 before observation, in the generality of instances, began. 



The United States of America, where the forests are disappearing 

 with such rapidity, will probably one day afford elements for the 

 complete and satisfactory solution of the question, whether or not 

 the cutting down of forests causes any diminution in the quantity of 

 rain which falls in the course of the year. 



In studying the phenomena accompanying the fall of rain in the 

 tropics, I have come to a conclusion which I have already made 

 known to many observers. My own opinion is, that the felling of 



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