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of Edin b urgh , Session 187 2-7 3 
part of the earth’s surface, probably with more or less difference 
in amount and progression, which we still lack the information 
necessary to estimate. 
All this done, I am afraid that there can be little doubt that the 
more general climatic investigations will be long and vexatious. 
Even in South America, with extremely favourable conditions, the 
result is far from being definite. Glancing over the table pub- 
lished by M. Becquerel in his book on climates, from the observa- 
tions of Humboldt, Hall, Boussingault, and others, it becomes 
evident, I think, that nothing can be founded upon the compari- 
sons therein instituted ; that all reasoning, in the present state of 
our information, is premature and unreliable. Strong statements 
have certainly been made ; and particular cases lend themselves to 
the formation of hasty judgments. “ From the Bay of Cupica to 
the Gulf of Guayaquil,” says M. Boussingault, 11 the country is 
covered with immense forests and traversed by numerous rivers ; 
it rains there almost ceaselessly; and the mean temperature of this 
moist district scarcely reaches 78° 8 F At Payta 
commence the sandy deserts of Priura and Sechura ; to the con- 
stant humidity of Choco succeeds almost at once an extreme of 
dryness ; and the mean temperature of the coast increases at the 
same time by 1°*8 F.” * Even in this selected favourable in- 
stance it might be argued that the part performed in the change 
by the presence or absence of forest was comparatively small; 
there seems to have been, at the same time, an entire change 
of soil; and, in our present ignorance, ‘it would be difficult to say 
by how much this of itself is able to affect the climate. Moreover, 
it is possible that the humidity of the one district is due to other 
causes besides the presence of wood, or even that the presence of 
wood is itself only an effect of some more general difference or 
combination of differences. Be that as it may, however, we have 
only to look a little longer at the table before referred to, to see 
how little weight can be laid on such special instances. Let us 
take five stations, all in this very district of Choco. Hacquita is 
eight hundred and twenty feet above Novita, and their mean tem- 
peratures are the same. Alto de Mombu, again, is five hundred 
■# Becquerel, “ Climats,” p. 141. 
