Africa it snows in places where the mean temperature
is above 19 degrees.
The vicinity of the sea renders the climate of Laguna more mild in
winter than might be expected, arising from its elevation above the
level of the ocean. I was astonished to learn that M. Broussonnet
had planted in the midst of this town, in the garden of the Marquis
de Nava, the bread-fruit tree (Artocarpus incisa), and
cinnamon-tree (Laurus Cinnamomum). These valuable productions of
the South Sea and the East Indies are naturalized there as well as
at Orotava. Does not this fact prove that the bread-fruit might
flourish in Calabria, Sicily, and Granada? The culture of the
coffee-tree has not equally succeeded at Laguna, though its fruit
ripens at Teguesta, as well as between the port of Orotava and the
village of St. Juan de la Rambla. It is probable that some local
circumstances, perhaps the nature of the soil and the winds that
prevail in the flowering season, are the cause of this phenomenon.
In other regions, in the neighbourhood of Naples, for instance, the
coffee-tree thrives abundantly, though the mean temperature
scarcely rises above 18 centigrade degrees.
No person has ascertained in the island of Teneriffe, the lowest
height at which snow falls every year. This fact, though easy of
verification by barometrical measurements, has hitherto been
generally neglected under every zone. It is nevertheless highly
interesting both to agriculture in the colonies and meteorology,
and fully as important as the measure of the limit of the perpetual
snows. My observations furnished me with the data, set down in the
following table: -
Column 1: North latitude.
Column 2: Lowest height in toises at which snow falls.
Column 3: Lowest height in metres at which snow falls.
Column 4: Inferior limit in toises of the perpetual snows.
Column 5: Inferior limit in metres of the perpetual snows.
Column 6: Difference in toises of columns 4 and 5.
Column 7: Difference in metres of columns 4 and 5.
Column 8: Mean temperature degrees centigrade.
Column 9: Mean temperature degrees Reaum.
0 : 2040 : 3976 : 2460 : 4794 : 420 : 818 : 27 : 21.6.
20 : 1550 : 3020 : 2360 : 4598 : 810 : 1578 : 24.5 : 19.6.
40 : 0 : 0 : 1540 : 3001 : 1540 : 3001 : 17 : 13.6.
This table presents only the ordinary state of nature, that is to
say, the phenomena as they are annually observed. Exceptions
founded on particular local circumstances, exist. Thus it sometimes
snows, though seldom, at Naples, at Lisbon, and even at Malaga,
consequently as low as the 37th degree of latitude: and, as we have
just observed, snow has been seen to fall at Mexico, the elevation
of which is 1173 toises above the level of the ocean. This
phenomenon, which had not been seen for several centuries, took
place on the day that the Jesuits were expelled, and was attributed
by the people to that act of severity. A more striking exception
was found in the climate of Valladolid, the capital of the province
of Mechoacan. According to my measures, the height of this town,
situate in latitude 19 degrees 42 minutes, is only a thousand
toises: and yet, a few years before our arrival in New Spain, the
streets were covered with snow for some hours.
Snow had been seen to fall also at Teneriffe, in a place lying
above Esperanza de la Laguna, very near the town of that name, in
the gardens of which the artocarpus flourishes. This extraordinary
fact was confirmed to M. Broussonnet by very aged persons. The
Erica arborea, the Myrica Faya, and the Arbutus callicarpa,* (*
This fine arbutus, imported by M. Broussonnet, is very different
from the Arbutus laurifolia, with which it has been confounded, but
which belongs to North America.) did not suffer from the snow; but
it destroyed all the vines in the open air. This observation is
interesting to vegetable physiology. In hot countries, the plants
are so vigorous, that cold is less injurious to them, provided it
be of short duration. I have seen the banana cultivated in the
island of Cuba, in places where the thermometer descends to seven
centesimal degrees, and sometimes very near freezing point. In
Italy and Spain the orange and date-trees do not perish, though the
cold during the night may be two degrees below freezing point. In
general it is remarked by cultivators, that the trees which grow in
a fertile soil are less delicate, and consequently less affected by
great changes in the temperature, than those which grow in land
that affords but little nutriment.* (* The mulberries, cultivated
in the thin and sandy soils of countries bordering on the Baltic
Sea, are examples of this feebleness of organization. The late
frosts do more injury to them, than to the mulberries of Piedmont.
In Italy a cold of 5 degrees below freezing point does not destroy
robust orange trees. According to M. Galesio, these trees, less
tender than the lemon and bergamot orange trees, freeze only at ten
centesimal degrees below freezing point.)
In order to pass from the town of Laguna to the port of Orotava and
the western coast of Teneriffe, we cross at first a hilly region
covered with black and argillaceous earth, in which are found some
small crystals of pyroxene. The waters most probably detach these
crystals from the neighbouring rocks, as at Frascati, near Rome.
Unfortunately, strata of ferruginous earth conceal the soil from
the researches of the geologist. It is only in some ravines, that
we find columnar basalts, somewhat curved, and above them very
recent breccia, resembling volcanic tufa. The breccia contain
fragments of the same basalts which they cover; and it is asserted
that marine petrifactions are observed in them. The same phenomenon
occurs in the Vicentin, near Montechio Maggiore.
