HUMBOLDT'S TRAVELS THROUGH SPANISH AMERICA.

The following letter from this enterprising philosopher to Fourcroy has lately been published in one of the French journals:

"Guyara, January 25, 1800.

"As the yellow fever, which desolates this part of South America, obliges us to make our stay here as short as possible, I snatch this opportunity of sending you a few lines, and repeating, from the middle of the torrid zone, how much my thoughts are occupied with you and your illustrious colleagues, among whom I met with such a flattering reception during my last stay at Paris.

Since our departure from Saint Croix in Teneriffe, where I descended into the crater of the volcano, the atmospheric air being there at 0·8 of R. and at 0·19 of oxygen, I have written to you twice.

I have sent to Delambre and Lalande an extract of my astronomical labours; the longitude of some important places; an observation of the eclipse on the 28th of October last; immersions of the satellites, and researches respecting the intensity of light of the austral stars, measured by means of diaphragms.

I have addressed to the Institute a chemical memoir on the phosphorescence of the sea; observations on a particular gas furnished by the fruit of the coffea arabica when exposed to the sun; on a snow white feld-spar, which, when moistened, absorbs all the moisture of the atmosphere; experiments on the milk of the cecropia peltata and the euphorbia curassavica, which will form a supplement to your excellent memoir on the cahout-chouc, and to that of our friend Chaptal; and on the air which circulates in vegetables.

"The cruisers which cover the seas here make me apprehend that a part of my letters may not have reached you; though I sent them sometimes by way of Guadaloupe, and sometimes by that of Spain.

These few lines I have sent by an American vessel, which will fail in a few days for Boston; and, though they cannot reach you but through Hamburgh, they will, perhaps, be less liable to miscarry.

People here are accustomed to make four or five duplicates of their letters.

But how can I find time, when I have so many things to observe, arrange, and calculate?

"I shall confine myself, therefore, to letting you once more know that I still enjoy the best health possible, and that I am treated with the utmost kindness by the inhabitants of these countries: that the passports and letters of recommendation from the Spanish government procure me every facility for making researches useful to the sciences: that none of my instruments, even the most delicate, such as barometers, thermometers, hygrometers, Bordas' dipping needle, &c. are deranged: and that, at the extremity of the missionary establishments among the Chayma Indians, in the mountains of Toumiriquiri, I have my laboratory mounted as if I were in the Hotel Boston, in the Rue du Colombier.

My fellow-traveller, Bonpland, educated in the Jardin des Plantes, becomes every day more valuable to me.

To an extensive knowledge of botany and comparative anatomy he unites indefatigable zeal.

I hope one day to restore him to his country, worthy of attracting public attention.

Never did any foreigner enjoy such permission as that granted to me by the king of Spain.

This idea alone is capable of exciting us to redouble our activity.

During the seven months we have been in this beautiful continent, we have dried (with duplicates) nearly 4000 plants, written more than 800 descriptions of new species or species little known, particularly new genera of palms, cryptogamia, bifaria, melastoma; collected insects and shells, and made many drawings respecting the anatomy of marine worms; with observations on magnetism, electricity, humidity, the temperature of the atmosphere, and the quantity of oxygen it contains.

We have measured that immense and high chain of mountains extending to the coast of Paria, and examined their volcanoes, which vomit forth kindled inflammable air, sulphur, and hydro-sulphurous water.

We have also collected many seeds, which we shall send off in three or four weeks for Europe, addressed to the Jardin des Plantes.

We have spent five months in the interior of New Andalusia and on the coasts of Paria, where we experienced very violent earthquakes in the end of last year.

One part of these countries is still inhabited by the savage Indians, and others have began to be cultivated only within sive or six years.

In what words shall I describe to you the majesty of the vegetation here; the forests of Ceiba, Hura, Hymenea, which the rays of the sun never penetrate; the variety of the animals; the superb plumage of the birds; the apes, the tigers; the hideous aspect of the crocodiles (caimans) which swarm in the rivers, and of which some are thirty feet in length?

From Cumana we proceeded to Caraccas, where we remained during the month of November and part of December:

A charming capital situated in a valley which has 426 toises of elevation; and, though in latitude 10° 31', enjoys the coolness, and I might say the cold, of Paris!

From this place we ascended to the summit of the famous Silla de Caraccas, or Sierra de Avila, where, at the height of 1316 toises, we discovered beautiful crystals of titanium. I found also dendrites similar to those of manganese, which are oxyd of titanium.

We shall proceed hence for Varina and the snow-covered mountains of Merida, the cataracts of Rio Nigro, and the unknown world of Oronoco, in order to return by Guyana to Cumana, from which we shall set out for the Havannah and Mexico.

"We shall take care to transmit the seeds we have collected for the Jardin des Plantes at Paris, the Museum, and Sir Joseph Banks, as we agreed with Jussieu - - - -.

"How much I lament the fate of Dolomieu, detained a prisoner in Sicily!

If he should return, communicate to him the following fact: -- It is more than three years since I announced to Lametherie, that, in the primitive mountains of Italy, France, Swisserland, Poland, and I can now add Spain, there exists a parallelism of direction between the strata of foliaceous granites, slate, micaceous schists, corneous schists:

that these strata incline (sink down) towards the north-west, and that their direction makes with the axis of the globe an angle of 45° 57': that this inclination and direction in no manner depend on the form and direction of the mountains: that it is not any way affected by the valleys, but that it announces a cause much greater, and more general: that it depends on a phenomenon of attraction which has acted at the time of the consolidation of the globe.

Having travelled over the greater part of Europe on foot, and with sextants and compasses, I have a very extensive collection of observations on that subject.

My manuscript on the identity of strata in the construction of the globe, is in the hands of my brother.

I was employed on it since 1791, but it will not appear till I have seen more of the globe.

To my great astonishment, I have observed in the Cordillera of Paria, New Andalusia, New Barcelona, and Venzuela, that in the new world, near the equator, the strata follow the same laws and the same parallelism.

"You remember the last ingenious observations of Coulomb on the air which issues with explosion from the trunks of trees when they are pierced.

I have made experiments on the clusea rosea, in which (in the interior of the pneumatochimiser, vessels of Hedwig, the vasa cochleata of Malpighi,) there circulates an immense quantity of air.

This air contains as far as [Formel] of oxygen.

The leaves of the same tree, when exposed to the sun under water, do not give a cubic mellimetre of air.

This air, which circulates, certainly serves, as in the animal body, to coagulate the fihrous part by absorption of oxygen.

The clusea is a milky plant, and elastic gluten is formed in it.

"Though the purity of the atmospheric air amounts here, particularly in the night, to 0·305 of oxygen, I have found that the air contained in the pods and capsules of equinoctial plants, for instance the paullinia, is more azotous than our atmospherie air.

It does not exceed 0·24 or 0·25 of oxygen.

The air in the culmi geniculati here, has only 0·15 of oxygen.

All this proves that the air which circulates is purer, and that the air which is in a state of rest, deposited in the capsules or utriculi, is less pure than atmospheric air.

The former is recently produced by the organs which decompose the water: it proceeds to those parts where it ought to serve, by its abundance of oxygen, to precipitate the fibrous principle to form the fibrous tissue.

The other is the residuum of a gas which has already discharged these functions.

ALEX.

HUMBOLDT."