ason than a southern aspect,
because the sun's declension is southerly during the dry and cloudless
season of the year, and thus, on the northern slopes, the rays of the sun
do not penetrate and parch the soil. A northern aspect has also the
advantage of preserving a much more uniform temperature than a southern
aspect, because the excessive radiation and evaporation in the southern
slopes greatly reduces the temperature at night, while in the day they are
heated to excess by the action of the sun's rays striking the surface
nearly at right angles. The practical effects of aspect on the plants are
so great that they cannot be overlooked with impunity, and, in order to
impress this on the minds of all those who may have the selection of
localities for cinchona cultivation, I may mention that the difference of
temperature is almost incredible; for example, at this elevation (probably
about 7,000 feet) a thermometer laid on the surface of the southern face
of a hill exposed to the sun at 3 p.m., will frequently indicate from 130 deg.
to 160 deg. Fahr.; the same thermometer, if left in its position, and examined
at 6 a.m., will generally be observed to indicate from 30 deg. to 40 deg., while
on a similar slope, if selected with a northern aspect, the thermometer,
under the same circumstances, at 3 p.m., will generally indicate from 70 deg.
to 80 deg., and at 6 a.m. from 40 deg. to 50 deg.."

There is, then, about twice as much heat upon a southern as on a northern
aspect, and, of course, a corresponding difference as regards the effect
of sun and drought on plant and soil, and it is therefore obvious that our
shade policy should be governed accordingly.

As regards the comparative heat on western and eastern exposures, Mr.
MacIvor does not seem to have made any experiments with the thermometer,
but where the slope is at all sharp the rays of the fierce western sun
beat strongly into the soil, while it is quite off an easterly slope, of
similar gradient, for the whole of the afternoon, and there is an enormous
difference perceptible in the temperature. The effect, however, is in some
degree counterbalanced by the fact that the soil and the plants on the
easterly slope are swept by the withering and desiccating winds which
sweep over the arid plains of the interior.

We have seen, then, that the heat is very largely affected by the aspect,
but the relative amount of heat and coolness is of course controlled, to a
very consid