22 
UNCERTAINTY OF METEOROLOGY. 
We are very imperfectly acquainted with the present mean 
and extreme temperature, or the precipitation and the evap¬ 
oration of any extensive region, even in countries most densely 
peopled and best supplied with instruments and observers. 
The progress of science is constantly detecting errors of method 
in older observations, and many laboriously constructed tables 
of meteorological phenomena are now thrown aside as falla¬ 
cious, and therefore worse than useless, because some condition 
necessary to secure accuracy of result was neglected, in obtain¬ 
ing the data on which they were founded. 
To take a familiar instance: it is but recently that atten¬ 
tion has been drawn to the great influence of slight changes of 
favorable to the growth of the fruits of the garden and the orchard, but 
usually becomes much less so in a very few years. Plums, of many varie¬ 
ties, were formerly grown, in great perfection and abundance, in many 
parts of New England where at present they can scarcely be reared at all; 
and the peach, which, a generation or two ago, succeeded admirably in the 
southern portion of the same States, has almost ceased to be cultivated 
there. The disappearance of these fruits is partly due to the ravages of 
insects, which have in later years attacked them ; but this is evidently by 
no means the sole, or even the principal cause of their decay. In these 
cases, it is not to the exhaustion of the particular acres on which the fruit 
trees have grown that we are to ascribe their degeneracy, but to a general 
change in the condition of the soil or the air ; for it is equally impossible 
to rear them successfully on absolutely new land in the neighborhood of 
grounds where, not long since, they bore the finest fruit. 
I remember being told, many years ago, by one of the earliest settlers 
of the State of Ohio, a very intelligent and observing person, that the 
apple trees raised there from seed sown soon after the land was cleared, 
bore fruit in less than half the time required to bring to bearing those 
reared from seed sown when the ground had been twenty years under cul¬ 
tivation. 
In the peat mosses of Denmark, Scotch firs and other trees not now 
growing in the same localities, are found in abundance. Every generation 
of trees leaves the soil in a different state from that in which it found it; 
every tree that springs up in a group of trees of another species than its 
own, grows under different influences of light and shade and atmosphere 
from its predecessors. Hence the succession of crops, which occurs in all 
natural forests, seems to be due rather to changes of condition than of cli¬ 
mate. See chapter iii, post. 
