judging of the respective qualities of the different woods found in the two continents. I shall make known those of America, which are the object of a considerable commerce between the central, southern, and northern states, and those which are exported to the West-Indies and to Europe, as well as the interior parts of the country, whence they are derived, and the sea-ports, from which the different exportations take place. I will also point out the best kinds of trees for fuel, and those the barks of which are used for tanning, and give their comparative prices.

"In travelling from the north to the south, I carefully observed, the place of growth and disappearance, of different species of trees, in consequence of a milder temperature, or of a marked change of soil. I gathered, in the different states of the Union, all the common names, to annex them to the scientific appellations. I observed the forests, either as they presented a primitive appearance, or as changed by the vicinity of civilized or domestic animals, the influence of which diversifies so rapidly the face of nature. Such are the principal objects, which attracted my attention, and of which I intend to give an account. also faithfully point out the species of trees, which I think useful to propagate for the amelioration of the European forests; and those that only deserve to be introduced into parks and gardens, on account of the beauty of their foliage.

I will

"Such is the outline of the researches to which I have devoted myself, and the result of which I have the honour to offer to the public. I thought that the manner in which I have viewed my subject, in directing my observations to a point of general utility, and which had not been done before, would secure my work in Europe and the United States a more favourable reception than if I had treated it in a scientific point of view.

"The work will be composed of twenty-five numbers. But if, contrary to my expectations, it does not meet with that encouragement, which I hope the importance of the subject entitles it to, and if at any time I am obliged to suspend my publication, I announce to my subscribers, that I have adopted a plan of keeping the genera separate, so that one, two, or three numbers will contain a complete history of one genus of trees, as pines, nutbearers, maples; so that they will possess so many complete and

separate treatises, which will also give the facility of procuring the particular genera which they may desire. One number will be published every month, and be composed of six coloured plates, with descriptions to each. The plates are engraved from drawings by Messrs. Redouté and Bessa, eminent painters in natural history. The best will be in royal octavo, and printed on very fine paper. The price of each number will be 13 francs and 50 centimes, [ 2 50.] An edition in English will be published in Philadelphia, accompanied by plates, precisely similar to the French edition, with this difference only, that the common names of trees will be given in place of the botanical ones."

The Editor is well acquainted with Mr. Michaux; has witnessed his assiduity in collecting information from workmen in Philadelphia, and has no doubt of his work proving eminently useful. The execution of the plates will be in the highest style of elegance. Every college, and public school ought to possess a coру of this work, and also of the superb work by the father of Mr. Michaux, on the American oaks, which may be bought for the low price of $10. But our seminaries of education unfortunately deem such knowledge degrading, and set a value only on those branches of learning, which are. inapplicable to the common purposes of life, or to the business of the world, and which, to nine-tenths of those who get a smattering of it, is totally useless, and forgotten after they leave college or school.

TUBULAR IRON BRIDGES.

A PROJECT has been some time in circulation for the construction of iron bridges, upon a new plan, by J. Joshua Dyster, from England, who, we are informed, is now constructing a bridge of 150 feet span, which is intended to be put up in some convenient place, in or near the city of Philadelphia, in order to exhibit the principles of the tubular bridge, and as a specimen of its advantages over other bridges.

This construction of an iron bridge, is said to be upon an entire new principle, and to possess the following advantages over any yet erected:

That it may be made at less expense, and in half the time which a wooden bridge will require; uniting great durability, with a superior elegance of appearance :

That it may be formed of one single arch, much wider than any present mode of constructing stone or wooden bridges will admit of, sufficient to stretch over most navigable streams, where bridges are required, without any intermediate piers, and will not not need an inconvenient height corresponding to its length; although its extension may be from six hundred to one thousand feet span: : And

That it will stand for ages without repairs; being of prodigious strength, the effect of its peculiar principle.

To lay a number of foundations in the beds of rivers, particularly where they are wide and deep, is attended with great expense and labour ; and to obtain firm bases for a stone bridge, the laying of the piers is frequently as expensive as all the rest of the superstructure; and if composed of wooden piles, as they must be very numerous, the expense cannot be inconsiderable : therefore, any good and substantial mode which will either require few piers, or supersede them altogether, except the buttresses on each shore, must be extremely valuable and important: the proposer of this system ascribes these properties to his plan.

Piers obstruct the flowing of the tide, and are likewise subject to be affected by the strong and impetuous action of the stream, and by the floating down of timber; and in the winter season, are liable to receive much injury by floating bodies of ice. They are exposed also to shocks from timber, rafts and craft. The truth of these observations is obvious to every one who duly considers the subject. Mr. Dyster says his system obviates these objections.

Public companies or private individuals, who may wish any bridge executed upon these patent tubular principles, are requested to send their letters, post paid, addressed to Joseph Joshua Dyster, Philadelphia. These iron tubular bridges may be made from 30 feet to 1000 feet span in one arch, and une durability with economy.

ON THE DECAY OF WOOD.

Inquiry into the causes of the Decay of Wood, and the Means of preventing it, by DR. PARRY.

(From the Eleventh Volume of the " Letters and Papers,” selected from the Correspondence of the Bath and West of England Society for the encou ragement of Arts, Agriculture, Manufactures, and Commerce, p. 226.)

1. THE power of wood in different forms to supply luxury, to promote science, and to guard and prolong human life, has made the means of preserving it from decay highly interesting to mankind. With this view various premiums have been offered by this and other economical societies. The object of the following discussion is to suggest the best means of prevention, chiefly by inquiring into the nature and sources of the evil against which it is intended to guard.

.

Wood, when killed by being separated from its root, is subject to gradual destruction from two causes---rotting, and the depredations of insects.

Of the rot there are two supposed kinds, as they affect wood, first, in the open air, or secondly, under cover.

The first is that which in the terms of our premium, Class VII. No. 3, is said to occur to "barn and other outside-doors, wea ther-boarding, gates, stiles, and implements of husbandry." To

which, if there were any need of this minute specification, might have been added, posts, rails, paling, water-shoots, and various other objects.

The second is well known under the name of the dry-rot, the cause and prevention of which are the subjects of a premium by the Society of Arts in London.

Animal and vegetable substances possess certain common properties and movements, which constitute what is called life. When that state ceases, and these properties and motions no longer exist, the bodies become subject to the chemical and mechanical laws of all other matter.

When perfectly dry, and in certain degrees of temperature, both seem to be scarcely capable of spontaneous decay. On this principle vast quantities of salmon are annually conveyed in a frozen state to London from the north of England and Scotland; and the inhabitants of the still more northern regions constantly preserve there food by freezing, unchanged through the longest winters. The gelatinous and other soluble parts of animal substances, when extracted by boiling and kept in a soft moist state, very readily putrefy. But if the same matter be dried by a gentle heat, and secluded from moisture and air by being kept in bottles or metallic cases, it will remain very long without decay. This is the theory of that well-known and useful substance, portable soup. In the burning climate of Africa, when it is intended to preserve a dead animal for food, all that is necessary is to cut the muscular parts into thin strips, from which, in a few hours, the heat of the sun exhales all moisture, reducing them to a substance like leather or horn, which proves to be unsusceptible of future decay from putrefaction. So also entire human bodies, buried in the arid sands of those countries, have often been found converted by exhalation and absorption of their natural moisture into a dry hard sort of mummy, incapable of any further change from the agency of those causes, to which, in such situations, they are exposed.

Similar causes produce the same effects on wood. Even under less rigid circumstances of this kind, as in the roofs and other timber of large buildings, it continues for an astonishing length of