and will for ever remain, barbarous and nomadic, because the ground, being destitute of vegetable humus, presents to the flocks, instead of nourishing and aromatic herbs, the withered blades of unpalatable grass.

The bad effects of scarcity of wood upon all the domestic, public, and social concerns of the people, are visible in many woodless countries, several of which are so deficient in trees, that the natives are obliged to eat their food half cooked, as also to employ the excrements of cattle (and even they are often hard to get) as a substitute for fuel. Thus the inhabitants of the Hebrides are compelled to undertake long journeys, in order to procure materials for the construction of ploughing implements, thankful if, at home, they chance to pick up what serves for the handle of a spade. Thus Greenland was deserted by Danish colonies, because the sea ceased to cast ashore the only timber to which they could have access in such a cold country; and in the western parts of France, as also in England, the scarcity of wood imposes the sacrifice of many comforts. On the other hand, Sweden has derived, for the last 1000 years, its principal revenue from the mere sale of timber; whilst England is obliged to spend immense sums for the building and preservation of its fleets; and Spain, which, owing to its extent of sea-coast, and its abundance of harbours, was formerly in the undisputed possession of the main (a claim to which nature seems to have entitled it), is now entirely blotted out from the list of naval powers. This, and a similar misfortune which presses equally heavily upon Greece and Italy, justify the assertion, that scarcity of wood is an evil, affecting every kind of national transactions, and by no means easily overcome; we are, therefore, still of opinion, that forests have from the beginning exerted, and will never cease to exert, a powerful influence upon the manners and customs of nations, as also upon their mode of living, their commerce, industry, and domestic concerns. Taking it, then, for granted, that the preceding discussions have demonstrated the intimate connection between. the great historical events of the human race and the existence of forests; that mountain forests are politico-economical elements worthy of particular attention and care; and

that they are as indispensable as the erection of dykes along rivers, channels, and public roads, as well as other measures intended to improve the physical condition of a country, and to adapt it to the necessities of the population; that the countries possessing a sufficient expanse of forests combine well-attested advantages, are highly favourable to the health of the people, and fully equal to the gratification of all their wants; that they are noted for their charming climate, abundance of water, fertility of the soil, as also for the number and variety of vegetable productions, —taking all this for granted, geographers ought to consider forests as an element exceedingly important, as regards the investigation of the physical condition of countries and the geographical relations of the population; moreover, as regards inferring from the excess of forests the original state of some countries, and from their scarcity, the final state of others; and, lastly, as regards the comparison of the results of these inquiries with the character of the population.

The geographer who has neglected to pay due attention to this subject, is unable to give a faithful and accurate description of the physical condition of countries, to compare the geographical relations of the people, both with the last and with one another, and thus to arrive at a system of solid geographical knowledge. Forests may be considered in many points of view, which geographers have hitherto slightly treated. They form a basis for a general outline of the geographical relations of continents, as well as of individual countries. On this basis, the geographer may build his system, derive from it his leading maxims, and be guided by it when treating of the development of the general relations of nations and countries. It is our most anxious desire that the above observations may draw the attention of geographers to this matter, which deserves, indeed, a more minute investigation, as it tends to reduce geographical data to general principles, and to render the study of geography more and more interesting and instructive.

Suggestions for the better Ventilation of Sailing and SteamVessels. By ROBERT RITCHIE, Esq., F.R.S.S.A., &c., CivilEngineer, Edinburgh. (Communicated by the Royal Scottish Society of Arts).

(Concluded from page 182.)

I could easily suggest other plans to attain the object, viz., a current determined to one point; for instance, the use of hot-water-tube apparatus, in which case the foul-air-extracting-trunk could pass through a coil of pipes heated by the galley-fire, and of which there might be several so heated, or the hot-water pipes could be placed within the trunk itself to raise the temperature of the air. See Richardson's work, London, 1839. A very old plan used in buildings was to have the hot smoke-pipe encircled by a tube of larger diameter, the air passing upward between.

The failure, however, of so many ingenious, schemes, extending over so many years, for improving successfully the ventilation of ships, has tended very strongly to impress me with the idea, that any method to be extensively useful, especially as regards sailing-vessels, must enter into the original construction of ships. And with this view I would suggest the introduction into timber and iron-built ships, of a thorough and efficient system of spontaneous or self-acting ventilation, affording at all times an ample supply of fresh air in every part of a ship, by means of a judicious arrangement of airflues in the former, and pipes in the latter. In a large class of vessels now afloat, by application of the openings or interstices between the timbers (presently in use for airing the frame-work) where the plan of close timbers has not yet been adopted, a free circulation of air might be effected at all times in lower decks and cabins. As regards the airing of the framework itself, its importance has long been a point of much interest for the preservation of the parts below the surface, though much difference of opinion among practical men is entertained on this point, one class advocating a free circulation of

air about the timbers, and another the exclusion of air.* In a communication to the Royal Society of London in 1820, by Sir Robert Seppings, F.R.S., when giving suggestions for a new principle of construction of ships for the mercantile navy, he alludes to the ventilators of Dr Hales, and the utility of general ventilation, but attaches importance to the exclusion of atmospheric air for the preservation of the frame-work, though he was not inattentive to the value of admitting air to the interior of ships. Another view is taken of this subject in the able treatise on ship-building in the Encyclopædia Britannica, where the suggestion is made that the preservation of the timbers might be assisted by adopting the openings between the timbers themselves for the purpose of circulating air about them; and it is stated that, in the year 1827, the author had proposed this plan to the Admiralty. This opinion strengthens the view I entertain of the practicability of combining in a very simple way the general ventilation of the ship, with due attention to the ventilation of the frame-work.

The defect at present in airing the frame, where the interstices of timbers are made use of, arises from the difficulty of obtaining a current or circulation, from the inlet for the air being placed between decks, and no outlet being provided. But were it so contrived as to allow at all times a free current of external air by points of ingress and egress, the effect would be very different. It seems often overlooked, but there is no point more important to be attended to in spontaneous ventilation than that where openings are provided for the escape of impure air, others must also be provided for the supply of fresh air, and vice versa. It must not be forgotten that air, like other fluids, can only fill a given space, or, as one of the earliest writers remarks, "that unless openings are properly adapted to suffer air to pass freely through, the external air proves a stopper to the internal, and only mixes with the next in contact." The same law which regulates the effect of currents in

*Captain Symmonds, Surveyor-General of Dock Yards, has, in a man of war now ready for launching at Woolwich, carried the timbers solid about as high as the lower gun ports. Mr Lang, who is naval architect for the Prince Albert, 120 guns, now building, I am informed, does not intend carrying up the solid frame nearly so high.

natural caverns, and which has been successfully applied to the ventilation of mines, will apply with equal force here. We know that the air in a well remains stagnant and pent up; but, as has been remarked,* if two wells or shafts are sunk at a given distance from each other, and a horizontal passage cut from the bottom of one well to the other, so soon as the communication is made, there will be a tendency in the air to descend one shaft and ascend the other, whenever the temperature of the external air varied from that below. Applying the principle to the general ventilation of ships, there is nothing to prevent the converting of the open spaces between the timbers or ribs, into fresh or foul air flues or conduits. One series of these being arranged to convey down pure airnot to be taken from below, but from above the upper deck-to points of discharge at the floors of the gun and orlop decks, cabin-floors, or wherever requisite, and another series of openings, entirely separated from the first, to commence at the beams or ceilings of these respective places, and pass upward above decks as high as convenient, for the escape of the foul or vitiated air. The points of ingress or egress for the air between decks may be in the form of a horizontal slit covered with perforated sheet copper or zinc, to break the force of the current. The points of inlet and outlet for the air above deck might have their effect increased, by having the orifices so arranged, that, while protected from the weather, the former would open to, the latter from, the wind. A portion of the interstices of the timbers similarly arranged, communicating directly with the open air, could be made to circulate fresh air for the timbers of the ship; but the apertures for the ventilation requisite for crews and passengers, must have no communication with the former, so as to prevent the corrupt gases from the bilge entering the latter. Inconveniences may be experienced practically, in having the air openings as described, from the difficulty of constructing those on the upper deck so as to keep out the water; but were the principle adopted and carried into practice, the skill and ingenuity of ship-builders would soon overcome any such slight obstacles. Ventilation

*Letter of John Buddle, Northumberland, 1815.