ePub 版

capable of absorbing the phosphoric acid from the human bones, on applying it to the skin, as expect it would neutralise the gallic

acid in the heart of oak.

Farther, alkaline solutions, owing to their great affinity for water, would hasten that decay in timber which they are intended to prevent; moreover, men could not live in a ship so saturated.

All the benefit, therefore, to be derived from lime-water, solutions of glue, common salt, oil, &c. is to be obtained from common paint alone; so far as they are capable of closing the pores, and rendering the wood less pervious to heat and humidity, are they useful, and no farther.'

Of the Growth and Properties of Moss in preserving Timber.

Moss is produced by an accumulation of dead vegetables, preserved in a partially decayed state, by a steady range of low temperature. Upwards of three hundred different species of Moss have been enumerated by naturalists; but as flow-moss only is capable of preserving timber from decay, I shall confine myself chiefly to that species.

Flow-mosses are to be found, in the greatest perfection, in flat situations, at considerable altitudes from the sea, and where water cannot easily make its escape. In Great Britain they thrive best when exposed to, and fed by, the moist winds of the western ocean. Hence it is that more extensive mosses are to be found on the west than on the eastern coast of Scotland; for, when these occidental winds, loaded with humidity, come in contact with the cold mountainous districts of the west, but more particularly with the flow-mosses there, condensation of moisture instantly takes place; and, owing to the prevalence of such winds, the most abundant supply of food is thus furnished to the different species of plants indigenous to moss. After the death of one race of flow-moss plants, the medium, (moss) in which they had vegetated, maintains so low a range of temperature, that their elementary parts are not suffered to be dissipated in the air, by

■ Moisture has another destructive influence on timber, viz. that of causing it to throw off its coat of paint. If a piece of timber is painted, after having been previously saturated with water, on the arrival of the first frost, the paint will be observed to scale off. This is owing to water obeying different laws from most other substances, or occupying a greater space in the frozen, than it did in the aqueous, state.

repulsive caloric, after the usual manner, but are arrested on the site of their germination: and thus, in process of time, mosses have accumulated from five to fifty feet in thickness.'

"Captain Duff, R. N. in a paper lately read before the Royal Society of London, after stating the well-known effects of peat moss in preserving wood for ages unaltered, suggests, that a series of experiments should be made to ascertain the effects of impregnating timber, both sound and already partially decayed by the dry rot, with the water from peat mosses, with a view to determine whether it possesses any power in preventing or suspending the insidious operation of that destructive agent."

The experiments here recommended to be tried by Captain Duff have been most extensively tried by Nature, in all the different varieties of moss, and have uniformly failed, except in deep flow mosses. For, neither in hill-moss, bent-moss, nor even in the edges of flow-mosses, (where it is of little depth) is timber ever found in a preserved state. But in deep flows, I have frequently seen the remains of stately trunks of fir trees in so high a state of preservation that part of them is often split by the country people, and made into a kind of rope.

The antiseptic qualities of flow-moss, therefore, is solely to be attributed to its maintaining an uniformly low temperature, and to the exclusion of atmospheric air by the interposition of several feet of wet moss, to the bottom of which solar heat never pene

1 A flow-moss, situated in the middle of a country, of perhaps thirty feet thick, ten miles long, and three or four miles in breadth, (there are several larger than this in Scotland and Ireland) is like an immense ice-berg floating in the ocean; it maintains a low temperature itself, and diminishes that of all surrounding bodies. During the continuation of westerly and southerly winds, such a huge mass of cold matter generally acts as a condenser; hence, we observe mist precipitating on the "mountain's brow," and fogs descending into the bosom of flows in such weather.

Under ordinary circumstances, condensation and evaporation are nearly equal on a given surface; but moss is of a more greedy nature; it takes more than it gives, and, in a great measure, preserves that which it had taken.

The action of moss on Boreal wind, on the other hand, is of a more negative kind, from such wind containing less moisture, and being nearer the heat of the flow, it seldom yields up much of its humidity.

On other occasions, when the atmosphere has a great capacity for moisture, the most exuberant and pernicious exhalations are carried off from these immense arsenals of humidity, chilling and deteriorating the ambient air to a great extent around. Indeed, when we consider the great quantity of water carried off from the equatorial regions, (where evaporation is excessive) to be eternally fixed near the Poles by congelation, as well as the immense reservoirs of water, arrested in all our accumulating mosses, we are enabled, in some measure, by those increasing receptacles, to account for the receding of the ocean.

trates, and where a thermometer, when buried, oscillates only from 35° of Fahr. in winter, to a few degrees above 40° in summer. In such mosses the bodies of certain human beings shot by the military in the reign of Charles II. in the struggle to establish episcopacy in Scotland, have lately been found in a state of high preservation.

Some individuals have attributed the preservation of fir-trees to a large quantity of resin and turpentine found in their composition; but these cannot be the antiseptic agents, otherwise, timber would be found equally fresh in all the different varieties of moss, which is never the case.

I have observed, in some wretched hovels in the Highlands of Scotland, where the smoke was suffered to find its way out of the house by different apertures, that the wood which supported the heath or thatch covering, had resisted the efforts of all-destroying Time, accompanied by heat and humidity, to an amazing degree. The timbers, in such houses, are covered with a black oleaginous substance, arising from the diffusion of the smoke of the wet peat fuel. Now, as an impure pyroligneous acid, and empyreumatic oil, may be obtained by destructive distillation from peat fuel, as well as from the beech and birch, there is no doubt it is through the agency of these substances the wood is preserved.

Smoking timber, therefore, deserves a trial, and bids fairer than any of the topical applications to preserve it to a good old age.

In these times of peace, when the growth of timber must be considerably more than its expenditure, it would be interesting to deposit a certain number of trees, annually, in some of our deep flow-mosses, for the double purpose of preserving them, and of ascertaining if wood, so saturated, possessed more durability than other timber afterwards.

On the principles laid down in this Essay, the driest and coldest haven ought to be selected for laying ships up in ordinary, in preference to a warm and moist one. Plymouth harbour, on account of the heat and humidity of the atmosphere, is undoubtedly the worst suited for this purpose of any in England.

To recapitulate-I feel convinced that I have made good the

' In chemical language, the cohesive attraction of all organised substances must first be overcome by caloric or insensible repulsion, before their constituent parts are suffered to enter into chemical affinities, or form new combinations. Now, owing to the great cold at the bottom of flow-mosses, the cohesive attraction of an animal or vegetable substance is never overcome there by heat; consequently, no putrefaction nor decomposition can rapidly follow.

burden of my charges against the abuse of water in so frequently washing decks. Its deleterious effects on the lower deck, in exciting inflammatory disease, in robbing the body of its heat, and saturating the decks, men's clothes and bedding, with moisture, no one can attempt to deny.

The cold and moisture to which seamen are exposed on the main and quarter decks, (early in the morning, even in the winter months) immediately after sleeping on a warm and crowded lower deck, must be equally evident to every unprejudiced mind; and the injury done to them, and His Majesty's ships, by the aggregate of moisture and impure air, arising from a great accumulation of filth and bilge water in a ship's hold, and the coiling down of wet hempen cables in the tier, cannot be calculated, because windsails and stoves afford little or no relief from such nuisances. Besides, it has been well authenticated, that if two ships shall happen to be cruizing together on salt provisions, the one making the most abundant use of water in washing decks will invariably have the greatest number of scorbutic patients on the sick-list.

The remedy pointed out against humidity on the lower deck is complete, and a more salutary time for washing the main and quarter decks will be seen in that chapter.

The measures recommended to prevent drunkenness will, I hope, be found useful, and the method of ascertaining the air's capacity for moisture, and the consequent injury sustained by individuals exposed to washing decks at the time, will be valuable in a practical point of view.

I think I have, also, satisfactorily proved, that the decay of timber is never premature unless exposed to the alternate action of impure air, a high temperature, and humidity; and, that the only power we possess in retarding it, is by endeavoring to abstract one of its destructive agents: and water and the juices of timber being the most tangible, I have recommended that the timbers should be well seasoned before they are put into a ship, and that the decks be protected from the excess of washing, and well ventilated afterwards; by which means, the men's health will be much benefited, and the decay of wood greatly retarded. Moreover, from the windsails now in use being incapable, on many occasions, of dislodging the ponderous gases, generated in the lower department of a ship, I have recommended that they should be pumped out by certain ventilators.

To the few officers in the royal navy who keep the hold clean, dry holy stone the lower deck, and select a mild period for washing the main and quarter decks, the foregoing observations cannot apply and, by the many equally zealous officers, who come within


their limits, I hope they will not be taken amiss: "my object is not to give offence, but to convince ;-not to attack in person, but in principle ;-not to interfere with motives, but point out the abuse of them."

The above conclusions on the baneful effects of humidity on our seamen, have been the result of ten years' observation in actual service, during which period I had almost daily reason to lament the abuse of washing decks, and with this strong conviction on my mind, I was induced to throw my observations together in manuscript, and show them to some of the most eminent physicians of this great metropolis, who so completely accorded with me in sentiment, that I have been encouraged to lay them before the public.

« 上一頁繼續 »