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Proceedings of the Royal Society 
feet higher than Hacquita, and the mean temperature lias here 
fallen nearly two degrees. Go up another five hundred feet to 
Tambo de la Orquita, and again we find no fall in the mean tem- 
perature. Go up some five hundred further to Chami, and there is 
a fall in the mean temperature of nearly six degrees. Such num- 
bers are evidently quite untrustworthy; and hence we may judge 
how much confidence can be placed in any generalisation from these 
South American mean temperatures. 
The question is probably considered too simply — too much to the 
neglect of concurrent influences. Until we know, for example, 
somewhat more of the comparative radiant powers of different soils, 
we cannot expect any very definite result. A change of temperature 
would certainly be effected by the plantation of such a marshy dis- 
trict as the Sologne, because, if nothing else were done, the roots 
might pierce the impenetrable subsoil, allow the surface-water to 
drain itself off, and thus dry the country. But might not the change 
be quite different if the soil planted were a shifting sand, which, 
fixed by the roots of the trees, would become gradually covered with 
a vegetable earth, and thus be changed from dry to wet ? Again, 
the complication and conflict of effects arises, not only from the 
soil, vegetation, and geographical position of the place of the 
experiment itself, but from the distribution of similar or different 
conditions in its immediate neighbourhood, and probably to great 
distances on every side. A forest, for example, as we know from 
Herr Bivoli’s comparison, would exercise a perfectly different 
influence in a cold country subject to warm winds, and in a warm 
country subject to cold winds; so that our question might meet 
with different solutions even on the east and west coasts of Great 
Britain. 
The consideration of such a complexity points more and more to 
the plantation of Malta as an occasion of special importance ; its 
insular position and the unity of its geological structure both tend 
to simplify the question. There are certain points about the 
existing climate, moreover, which seem specially calculated to throw 
the influence of woods into a strong relief. Thus, during four 
summer months, there is practically no rainfall. Thus, again, the 
northerly winds when stormy, and especially in winter, tend to 
depress the temperature very suddenly ; and thus, too, the southerly 
