its specific gravity; each specimen, on an average, having swelled 0.05 cubic inch in every solid inch of original dimensions, and gained 84 grains on every 100 grains of original weight; that is, an increase of one-twentieth in size, and twenty-one twentyfifths in weight.

I have little doubt, but the degree of impregnation always increases with the increase of pressure; but the air contained in the pores of the wood, which is never wholly disengaged, exerting an expansive force when the load of pressure is removed, forces part of the water out again. This was clearly discernible in some of the specimens used in the foregoing experiments, at the moment they were hauled up, their surfaces being covered with a thin pellicle of froth. Hence pieces of fir sometimes become buoyant, after being a few hours relieved from pressure, though kept constantly under water; but all other kinds of wood yet tried, though they lose a little of their moisture, yet remain specifically heavier than water, as long as they are kept immersed. Blocks of wood, indeed, are now in my possession, that were soaked with sea-water in the year 1817, and yet remain, at the bottom of a vessel of water, nearly as heavy as when first drawn up out of the sea.

The degree of pressure at the depth to which I sounded in my last experiment, is not a little astonishing, being, under a column of water, 6348 feet in length, at least 2823 lb. or 25 cwt. 23 lb. on one square inch of surface. Hence on the larger cubes of ash used in the experiment, though measuring only 1.59 inches in diameter, the whole pressure must have exceeded nineteen tons!

XXIV. Sketch of a Journey through Brazil in 1817 and 1818. By Mr SWAINSON of Liverpool. In a Letter to Professor Jameson.

I

DETERMINED on going to South America in the autumn of 1816. The enlightened policy which influenced several of the Continental Sovereigns in sending scientific men to explore those treasures which the country of Brazil offered to philosophical investigation, the moment universal peace was restored, induced me to hope that our own Government would gladly have

paid attention to any proposals made to them, of a similar nature. For this purpose I wrote to Sir Joseph Banks, who highly approved of my resolutions, and, I believe, recommended it in the warmest manner. The motives of my travels had been, in the first instance, only individual gratification and improvement; but considering that with very little assistance, and liberal patronage, my plans might have been enlarged, and the sphere of observation more extended, I made the proposal of remitting home as extensive collections as possible, in all the branches of natural history, for our national museums and gardens, provided adequate assistance in a pecuniary way, or even a nominal patronage as naturalist to the British Government, was given me: Both, however, were declined; and thus, from being entirely left to myself and my own resources, the results of my investigations and travels have been comparatively confined within certain limits.

Instead of following the example of all my fellow-labourers, by going in the first instance to Rio de Janeiro, I landed, about the end of December, 1816 at Recife, in the province of Pernambuco, 8 degrees south of the line. This province had never been visited by any modern naturalist, and I found that it possessed features, both in its geography and natural history, widely different from the southern provinces. After gaining general ideas of the climate, manners, &c. I made preparations for a journey into the interior, but these were suddenly rendered useless, by the memorable revolt of the 6th March 1817, of which I was an eye witness. This event confined my researches to a limited extent of country round the city; yet so many new and striking objects presented themselves, that I was amply employed during all the time that the country remained in this disturbed state. I had besides made the acquaintance of most of the principal men, who were all more or less involved in this effort to liberate their country, and I thus possessed ample means both of narrating the events, and enquiring into the causes which led to this political convulsion. On the restoration of tranquillity, after remitting all my collections, drawings, &c. home to England, I quitted Pernambuco in June 1817, and, with a small train, directed my course (by a circuitous route towards the interior) for the great river St Francisco.

The face and productions of the inland parts differ most essentially from those of the coast. Water in these dreary tracts is at all times scarce, and the excessive drought that had prevailed frequently exposed us to great privations, and even danger; sometimes our only resource was the water found in crevices and hollows of rocks, rendered putrid by decomposed vegetables. At length we reached the village of Penedu, in the beginning of August. The botanical subjects collected on this journey were numerous and interesting, particularly among the parasitic plants and cryptogamia, which, with the birds, insects, &c. were mostly new. The drought in the interior rendered it impossible to proceed by that route to St Salvador, and I accordingly embarked for that place in a canoe, and arrived in eight days. Here I found the two Prussian naturalists, Messrs Sellow and Freyeries, who had come overland from Rio de Janeiro with the Prince of Neuwied, and had remained in the city from ill health, and also to arrange their collections. I left them, however, soon, and made nearly a complete tour of the bay, and again set out for the Sertem or inland country, where I continued, varying my residence, until the month of March following, having in this space made immense collections in every branch of natural history, particularly in the ornithology of the interior, which differs both in species and novelty from those procured by the Prussian travellers on the coast.

I have considered it much more essential, in the observations I have made in this country, to survey Nature as a whole, than simply in its minute parts; by studying her operations in the natural habits and affinities of each particular class or tribe of animals and vegetables. The formation of systems and of genera, and the minute discrimination of species, belong to the naturalist when seated in his closet; but the habits and modes of life which characterise each in a state of nature, are highly interesting, and the accurate observation of them must be conducive to the exaltation and expansion of the human mind.

In the month of April I embarked for Rio de Janeiro, more for the sake of comparing the southern with the equinoctial regions of Brazil, than of increasing my collections in a part already well explored. I found the summer nearly terminated, but the heat far above that of Pernambuco, though

Rio de Janeiro is in lat. 22° 54', and Pernambuco in lat. 8. Travellers and men of science from the Austrian, French, Russian and Tuscan Courts, were here. Few of them, however, had been out of the province, and, by some unfortunate mismanagement, five of the Austrian party returned home shortly after my arrival. Among these travellers was Professor Raddi, director of the museum at Florence, who was indefatigable in forming a fine collection of the fruit and seeds of the country: With him I made an excursion to the immense range of mountains, called the Organ Mountains, which for leagues are covered with almost impenetrable forests, abounding in ferns, melastomas, and insects quite peculiar to them. From Dr Langsdorff, the Russian Consul-General in Brazil, I received every assistance and the most liberal attention; and having with his aid embarked my collection, with many desiderata, I returned to England in August 1818.

The number of species, in all the classes of natural history, which I have brought home, cannot be ascertained; but the following statement may give a general idea of the whole.

Of Birds, there are 760 specimens, among which are many entirely new species, and others exceedingly rare, particularly in the genus Trochilus, of which family I am now engaged in making a general arrangement; two or three new toucans, a singular goat-sucker, with a tail doubly forked, &c.

The specimens of insects amount to more than 20,000. Of course there is a large proportion of duplicates, but it may safely be said to exceed greatly any collection of South American insects ever seen in this country. The family of Hesperia (Latreille) alone exceeds 280 species, and, by a peculiar mode of preservation, this part of the collection is in an uncommonly fine state. Drawings and ample descriptions were also made of nearly 120 species of fish, mostly unknown, and such as were of a convenient size were sent home in spirits.

Seeds of many new and little known plants have been sent to Kew and other botanic gardens, where they are now flourishing. An interesting collection of parasitic plants, together with another of cryptogamia, I presented to my friend W. J. Hooker, Esq. These last have begun to appear in his elaborate work, Musci Exotici. My herbarium, containing about 1200 species, is particularly well preserved, the plants having