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with the coast, at an elevation of from 7,000 to 8,000 feet, we travel about six miles over a region bare of forest, where we nearly at all times find a very strong breeze from the south, rushing up the declivity and over the ridge, hurries off to the north towards the ocean. The ocean can be plainly seen from this elevation. That this great current of air does not sink down along the northern slope, but, on the contrary, is somewhat projected upwards by the shape of the mountain, can be seen by the course of the condensed vapors which, in the form of fog and mist, are driven along. May not this current of air sink gradually lower and lower until it reaches abont latitude 18°, where it strikes the sea ? I have found this south wind at sea always much colder than any of the other winds in these latitudes.
I wish I was in possession of some good work on the winds and the currents of the ocean.
Vegetation at the colony is uninterrupted throughout the whole year, except in a small class of plants which cannot thrive without a great deal of moisture. Even in the dry season, when the lower regions are parched up with heat, if there is any moisture at all in the atmosphere capable of being condensed, the mountainous districts, especially those covered with forests, are sure to get some of it. Trees here are evergreens; they keep their branches and twigs clothed with leaves until death. Day after day, and month after month, the surrounding forest presents the same unchanged view in its deep green garment. Single leaves fall here and there one by one; and new leaves appear as slowly and gradually as the old ones die away-unnoticed and unobserved. The pleasing and hope-inspiring spectacle of returning spring, in the sudden appearance of the new and tender foliage, as seen in the temperate regions, is here unknown.
COLONIA TOVAR, January 8, 1857. DEAR SIR: Under date of August 5 I sent you a letter and some registers of meteorological observations up to the 31st of July, which, I hope, you will have received long before this.
Inclosed in a separate envelope I send you now four meteorological registers for the months of August, September, October and November. I would have sent one for December also, but I have no more blanks.
Besides these registers, I have inclosed diagrams* on four separate sheets, one table of half-hourly barometrical observations, and one about the course of the clouds.
The barometrical observations in the registers have their full value only up to October 30, at 2 p. m ; for when I looked at the height of the mercury one hour afterwards I found it more than one inch below its usual level. This was so extraordinary that I expected something wrong with the instrument. As soon as I touched it the whole column of mercury sank rapidly down. In unscrewing the brass cup which contains the little leather bag I found the former half filled with mercury. On the surface of the bag, a little below
The diagrams and curves could not be given in this report.
where it is tied and where it was in contact with the surrounding brass tube, I found a spot of one-eighth of an inch diameter, as if corroded by some kind of acid In the centre of this spot was a hole onesixteenth inch diameter. The corroded rim around the hole was very smooth and viscid, similar to partly dissolved india rubber. After sewing up the whole and giving it a coat of glue, to prevent the mercury from leaking out, I filled the glass tube again as cautiously as possible, to prevent the formation of air bubbles. In this I succeeded pretty well, and, with the exception of one minute portion of air, which escaped into the vacuum, the latter seemed to be complete. The mercury then showed but a small difference (ốo to to parts of an inch lower) compared with its former state. Hoping to succeed still better the second time, I tried my hand once more at it, but did not succeed so well this time, as some moisture had settled in the glass tube. The mercury is now at least one-tenth of an inch lower than it ought to be.
The barometrical observations made with this instrument since the 1st November, 1856, can, of course, not be considered as normal, and can be used only with a view to institute comparisons among themselves.
I feel this defect the more acutely as I hoped to measure a number of mountains and other localities, and to complete a twelve months' register, to find out the mean height of the barometrical column for the different months of the year. Up to the 1st November I found the mean height greatest in July. Hitherto I have measured only the pass over the mountains on the road from the colony to Victoria. On this spot the barometer was 23.334 at 7h. 30m. a. m., September 9, with the thermometer at 61o.
In the diagrams on sheet No. 1, I have laid down, in a graphical manner, the hourly and half-hourly rise and fall of the barometer from 6 a. m. till 9 p. m. for 12 days. We can see here, at once, the greater amplitude of the daily periodical variations in October compared with that of June; also that the hours of maximum of the different days in October are not far apart from each other and near to 101 a. m., and the hours of minimum not far from 4 p. m.; while, on the contrary, in June, the hours of maximum, as well as those of minimum, are much more scattered, and therefore not so regular.
On sheet No. 2 are the half-hourly observations laid down for 24 hours, from 4 a. m., October 7, till 4 a. m. next day. Here we observe that, in the morning, the maximum, as well as the minimum, is somewhat higher than the maximum and the minimum in the evening. This seems to be a general rule with all the daily periodical variations.
On sheet No. 3 the daily mean barometer heights from June 10 to October 30 are put down and connected by straight lines to denote the course of the barometer from day to day throughout the several months. A kind of periodical rising and sinking is observable here, alternately taking place in periods of 4 or 5 days, at least for June, July, August and September.
On sheet No. 4 is to be found a comparison of the mean monthly barometer heights of Colonia Tovar with those of St. Louis, Mo.,
made by Dr. G. Englemann in 1851, which shows the remarkably small monthly variation in the colony against the extreme range of atmospheric pressure at St. Louis.
In all these illustrations the barometer height has not been reduced to the freezing point for want of the necessary tables ; but, as the difference of temperature connected with these observations does not range much over 8 degrees F., the results may be considered not far from their true value
Table No. 5 shows that the most prevailing currents of air at an elevation of about 7,000 or 8,000 feet above the level of the sea, in the months of June, July, August, September and October, are here from E., E.SE., SE., S.SE., and S., but especially from SE.
Table No. 6 contains half-hourly barometrical observations for 17 days, taken down at three different periods of the year. From this and from sheet No 1 we see that the amplitude of the daily periodical variations is not a constant quantity in one and the same place, but changes with the different periods of the year; as also does the hour of maximums and minimums. To find out, by continued observation, the mean amount of amplitude and the precise time of the maximums and minimums for each month of the year seemed to me desiderata of much interest to meteorology.
With a view to investigate this matter I have made observations accordingly. The first set I made from 18th to 24th June; the second, from 1st to 7th October; the third, from 10th to 12th November, and the fourth, from 22d to 28th December. These observations give the mean amplitude for the latter part of June 0.058; for the first part of October, 0.079; for November, 0.060, and for the end of December, 0.043.
By a peculiar view of the cause of periodical variations, and by the aid of an artificial globe, I had calculated as early as last September that the amplitude at Colonia Tovar ought to be greatest about the 16th May and 26th September, and least on the 21st January. The above-inentioned numbers of amplitude for October, November, and December coincide with my calculations so far, and it remains to be seen how they will do for the remaining portion of the
year. With regard to temperature I will only say that the mean of the three months of June, July, and August, (that is, of the meteorological summer,) is 58 9; the mean of September, October, and November (the meteorological autumn) is 58.9, or exactly the same. The mean temperature of December is 56.6. During 204 days (from June 10 to December 31) the sky was only once free of clouds at 2 p. m., 18 times free at 7 a. m., and 41 times at 9 p. m. Of these 204 days 143 were rainy days.
On the 5th of January I made a botanical excursion to one of the highest mountains of this region, about twelve miles to the east of the colony. The mountain, according to my estimation, may be about 7,800 feet above the level of the sea, and is a kind of central point or knot, from which several rivers, flowing in different directions, take their origin. This mountain is covered by a dense forest, with the exception of a level spot of about half a mile in length and a quarter
of a mile in width, which forms a kind of shallow basin, only sparingly covered by a thin coat of short grass and other small plants. These plants I found the next morning at six o'clock white and stiffened with heavy hoar frost, which augmented and lasted till the rays of the sun fell upon it. The stiffened leaves of the herbs broke under the least pressure, like thin layers of ice. The thermometer was 37° at 6h, 30m. From all the information I could gather, hoar frost seems to be common in this spot throughout the months of January and February. The wind blew during the night from northeast, and was very piercing.
Notwithstanding this low temperature, the forests of the neighboring heights surrounding this basin are clothed in perpetual green, and the stately wax palm, with its straight and polished trunk of 70 or 80 feet, (by actual measurement,) rears, uninjured, its slender form and its leaf adorned head high above all other trees.
In this excursion I had also an opportunity to form some idea of the vast extent of destruction which was carried into the mountain forest last February by a lucifer match and a thoughtless boy. Over whole tracts of this primeval forest the trees lie dead one over the other, as if uprooted by a whirlwind, scarcely showing any marks of fire on their trunks. I was struck more than ever with the easy manner in which fire can destroy these dense and humid forests, which, by their shade, preserve a cool and moist atmosphere, and thereby cause the vapors of the adjacent strata of air to condense into clouds, that rest upon them, with little intermission, during nine months in the year. In these high regions the temperature is so low and equable that the vegetable matter which is gathered on the ground between the trees is decomposed very incompletely and very slowly. It forms a stratum of loose half-decomposed matter, in some places two to three feet thick, which, in the rainy season, like an immense layer of sponge filled with water, feeds and supplies the rivulets and rivers gradually. In the midst of the dry season this layer becomes sometimes dry enough to burn, when kindled, with but little flame, and more like tinder, spreading in all directions.
In this way the fire extends until met by a river or a road, or sone other obstacle. The sub-soil which underlies the spongy stratum on these mountains is also very shallow and resting on hard rocks. roots of the trees. therefore, do not go down very deep, but extend more in a horizontal direction. When the spongy layer, with the smaller roots, are burnt, the trees lose their hold eotirely and fall, one over the other, in all directions. They die less from being burnt than from being uprooted. Many different kinds of tall reeds soon take the place of the trees. In a few years these reeds exclude everything else. The fertile mould that may perhaps have escaped destruction by fire is by and by carried down the declivities by the frequent rains. The region, no longer shaded by high trees, becomes dry. Subsequent conflagrations of adjacent savannahs, which are intentionally set on fire to procure a new growth of young grass, take hold of the reeds of the ruined forest, until, by the repeated attacks of these fires, the roots of the reeds can stand it no longer, and the smaller grasses, interspersed with a few other plants, take their places.
On the road from the colony to Caracas we pass through a region in which this process is going on; the reeds giving gradually way to the smaller grasses. Here the great number of half burnt yet standing trunks of the wax palm tell plainly enough that there existed not long ago a dense and humid forest, in which they luxuriated in all their beauty, for these palms are never found, in their natural state, growing in any other but humid forests. Here they stand isolated in the midst of reeds. Most of them have died already, but many linger yet in a dying condition, until their last green leaf has turned brown, and then they stand like tall and slender pillars, the mournful remnants of a once stately forest.
This is the same extensive region of which I spoke in my first letter, where a strong southern breeze, sometimes amounting to a gale, sweeps constantly over the mountain ridge towards the sea. I have traversed this region since at four different times, in the months of August and September, and found every time the same southern wind blowing there, only somewhat more violent.
Before closing this letter I wish to add to the statement made in my first letter* about the gale of December 24, 1853, that my informant here, in saying that the gale was felt at Laguayra, forgot to mention that it was felt only in the unprecedented agitation of the ocean, but not in the atmosphere. This agitation of the sea is observed every time a violent gale from the north has been blowing in the higher latitudes, not the least breeze from the north being felt at the same time at Laguayra, although it is an open roadstead, not in the least sheltered against the north winds. This agitation of the sea, when the air was perfectly calin, I have seen myself several times at Laguayra; but at the time above mentioned the sea was so unusually high that long, enormous, foam-crested waves rolled up to the very parapet of the custom-house, a phenomenon scarcely ever seen before.
During my stay in Victoria, a town twenty miles south of the colony, situate in a valley about 1,700 feet above the level of the sea, I made the following observations as to the temperature of that place:
The dry season has already set in, and my time is so much taken up by botanical labors, on which my sustenance depends, that I am unable to give at present a more full and extended account of the climate and other atmospherical phenomena of this region.
• See page 183.