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It has been urged by the advocates for spontaneous germination from the juices of the timber, that the dry rot is an internal disease, from the vegetating fungi always inclining towards the exterior. But I have never seen a specimen of fungus growing from the centre, where a fissure could not be detected sufficiently large for the previous admission of seeds and moisture.' Ignorance of the well-known circumstance of seeds, wherever they may be placed, growing always towards the air and light, on that side where they are most powerful, has induced them to believe that the dry rot is an internal disease. "A plant, in a shady place, inclines all its branches to that side where the action of the air and light is most powerful; and plants, confined in a hot-house, turn all their leaves and branches towards that side from which the light proceeds."
As nothing, therefore, can be more ridiculous than the supposed germination of fungi from the juices in the heart of oak, I shall only make another quotation from a very able author, pointing out the means by which fungi are propagated.
Of the Prevention of the Dry and Wet Rot in Ships.
The success that we may expect to arrive at in arresting the decay of ships, will be in proportion to the power we possess in performing the three following operations, viz.
conservées dans le mortier, puisque la génération spontanée est une chimère, et que tout ce qui a vie, provient d'un œuf ou d'une graine.-Nouveaux Elemens de Botanique.
The living principles of seeds, eggs and vegetables also enable them to resist congelation: this is said to be owing to their peculiar attraction for caloric.
1 "Ex nihilo, nihil; in nihilum nil posse reverti."
2 Que cette poussière que l'on trouve entre les feuillets de ce champignon, lorsqu'il a acquis un certain développement, n'est autre chose que sa graine, qui, vue au microscope, ressemble assez à des graines de pavot. J'ajouterai que ces graines, semées avec profusion par-tout, sont en si grand nombre, que celles d'un seul individu de cette espèce suffiroient, à en juger par leur extrême finesse, pour couvrir de champignons des terrains immenses; mais que, malgré qu'il faille peu de circonstances réunies pour favoriser leur développement, il en faut encore auxquelles l'art a souvent moins de part que le hasard, et que c'est par cette raison que ces graines ne lèvent pas partout où elles sont semées. J'ajouterai encore que, semées naturellement sur de terrains convenables, elles produisent ce qu'on appelle blanc de champignon; c'est-à-dire, des petits plantes enracinés, que les maraîchers trouvent tout formés sur du fumier ou sur d'anciennes couches, et qu'ils sèment sur de nouvelles couches préparées pour cet effet ; que ces mêmes couches, sans qu'on y eût mis du blanc, auroient pu produire à la longue des champignons de cette espèce, mais que le cultivateur fait en bien moins de temps, avec ces plantes enracinés, ce que la nature auroit fait avec les graines.-Louis Chaude Richard, Professeur de Botanique à l'Ecole de Médecine de Paris.
1st, Freeing the wood of its natural sap and moisture, before it is put into a ship; 2dly, keeping her perfectly dry during the time she is on the stocks; and, 3dly, protecting her, as much as possible, from the alternate action of impure air, heat, and humidity, after she is put in commission, or sent into ordinary.
Now, as the power we possess over the different states of the atmosphere is very limited, the methodus medendi, on that account, must be always defective; for we can set no limits to ever-varying and diffusible caloric, and have very little more influence over "thin air." But, fortunately, humidity is more tangible, and equally formidable with any of the other destructive agents; and, on that account, I have fastened upon it, as being the only means left of stopping the march of destructive action in timber; always keeping in mind, that it is the united action of these three which produces the premature decay of ships, and that the abstraction of either will arrest the vegetation of fungi, and the destruction of timber.
In order to fulfil the above injunctions, the trees of which His Majesty's ships are to be built, should always be felled in winter, (December and January,) for the following important reasons :-because, at this season, there is least sap in the wood, and hibernal felled timber is of greater specific gravity than that cut in summer, (when the ligneous vessels are filled with sap and air ;) and, owing to this greater density, it is not only stronger, but its contracted pores are less pervious to present and subsequent moisture. Winter felled timber will also require shorter time to season than that cut in summer, from there being less sap in it to evaporate.
The following operations now practised in our great naval dockyards, of building ships under cover, and housing them over in ordinary, after having been well caulked and painted, are very complete external means, and admit of little improvement. But the internal measures, with regard to drying and ventilating ships, (in my opinion,) are, in many respects, defective.
I have been informed, by many intelligent carpenters, that the pump in the well of a ship's hold does not dry her of water by nearly a foot, even when newly sucked. Now, however necessary this arrangement may be in sea-going ships, no excuse can be made for it in ordinary, where ships are always on an even keel, and in no danger of having their pumps choked.
By remedying this defect, and enjoining greater punctuality with regard to keeping ships clean pumped out, that evaporation would be prevented from the well, &c. which keeps the under surface of the decks in a half-dry state; and this condition I consider to be most destructive to a ship's timbers.
Of Ventilating Ships.
That great care and attention which used formerly to be paid to ventilation in the British Navy, has been rather on the decline of late years, amidst the exigencies of a long and arduous war; for, so early as the year 1756, the Lords Commissioners of the Admiralty issued an order for the ventilators of the celebrated Dr. S. Hales to be used in the Royal Navy. This order was followed by the most happy results in our men of war, and its salutary effects were yet more eminently felt in transports and store-ships.
On active service, however, those ventilators were found to take up much room, and require more time than could well be spared to work them; and for this reason they gradually gave way to the common windsail now in use. But, for the peace establishment, at any rate, and for ships in ordinary and guard ships, they are very superior to the windsail of the present day.
In ventilating a ship, we ought to have three objects in view :1st, supplying her with a current of pure air, for the purpose of animal respiration; 2dly, air is wanted to dry the decks and timbers of a ship; and, 3dly, we must draw upon the atmosphere for diminishing the temperature of the interior of a man of war, by which her timbers, provisions, and stores, will be longer preserved. Now, it is evident, from what has been stated, that the common windsails, in this variable climate, cannot be used with advantage more than one day out of three, and during the remainder of the time their operation will often be null, and sometimes even detrimental.
But, under all changes of weather, Dr. Hales' ventilators were useful in pumping out the vitiated air from the hold of a ship, while the atmospheric pressure supplied its place with that of a cold and pure quality; by which means the atmosphere of the lower deck, &c. could be renovated at pleasure. It ought to be remarked here, that, owing to air becoming specifically lighter by being heated, it will continue to ascend from the interior of a ship, through the different apertures, while its place will be supplied by colder air from the exterior. This, to a certain extent, is true, and in continual operation; yet, when we recollect the great quantity of carbonic acid gas which is thrown off by animal respiration during the night, and the proportion in which this ponderous air
Dr. Hales says; "The Earl of Halifax has often informed me of the benefit they found by the use of ventilators in Nova Scotia transport ships; twelve to one more having been found to die in unventilated, than in ventilated ships."
enters into chemical combination with the atmosphere, we are compelled to admit (from its greater specific gravity) that the holds and store-rooms, &c. will become the receptacles of this pestiferous gas. But the evil does not end here; for fixed air furnishes a natural and luxurious nourishment for fungi; carbon being part of the food and the base of all the vegetable kingdom. Indeed, this is a process which Nature employs for the double purpose of norishing plants and renovating our atmosphere.1
'The method I would recommend for ventilating ships is as follows. During the continuation of wind, and while there is considerable motion in a ship, the windsail now in use and Mr. Perkins' ventilator will answer the purpose most completely: but when neither wind nor motion is present, we must have recourse to manual strength and machinery to pump out the vitiated air; and the atmospheric pressure will supply its place with that of a cold and pure quality.
The windsail and Mr. Perkins' ventilator will be best suited to sea-going ships; while an engine for pumping out the foul air, (after the manner of ventilating the Session House at the Old Bailey,) will be better adapted for ships in ordinary and guard ships, where the rolling is inconsiderable.
Mr. Perkins' method of ventilating the hold of a ship will at once be understood, by referring to the plate-the Frontispiece.
A SECTION OF THE VENTILATOR.
a a, tanks, or water butts.
bb, hose for conducting the foul air into the tanks. cc, hose for conducting the foul air from the tanks. d, connecting water pipe.
e e, valves for admitting the foul air into the tanks. ff, valves for allowing the foul air to escape.
The operation of this self-acting ventilator is as follows: Each tank or butt is half filled with water, which flows freely from one to the other through the pipe d. The quantity of water running alternately from each depends upon the motion of the ship. When one of the tanks is elevated by the ship's motion, the water will run through the pipe d into the depressed tank, and thereby discharge as much foul air through the valve ƒ as the additional water displaces. The elevated tank at the same time is receiving
I once saw the hold of a ship so filled with fixed air, that a candle would not burn in it; and a dog, which was thrown in, instantly became convulsed. The hold of a ship may thus be rendered as hostile to the canine tribe as the famous "Grotto del Cane" in Italy.
the foul air through valve e, from the hold of the ship, to supply the vacuum that would otherwise be made by the escape of the water. If the tanks are fixed at right angles with the keel of the ship, the ventilator will operate only with the roll of it; but, if placed diagonally, both the pitch and roll of the vessel will discharge the foul air. It would be most economical to fill the tanks at the beginning of the voyage. The first water for the ship's use should be taken from the ventilating tanks, leaving, however, half of it behind for operation. If the remaining water should ever be wanted for the ship's use, it can be drawn off, and replaced by salt water. It will be seen that, by this mode of ventilating, nothing but the hose and valves are to be added to what must necessarily be on board every ship.
Any improvement in the arts generally becomes valuable in exact proportion to its strength and simplicity; for when an implement is complicated or easily deranged, it is only useful in the hands of the inventor and the scientific. Mr. Perkins' ventilator not only combines those properties in a most eminent degree, but, from its principle, works hardest when most wanted. In a gale of wind, when the hatchways are on, and when there is much straining and rolling in a ship, the noxious gases are then generated to the greatest extent; then, also, the operations of the ventilator become most powerful, both in admitting fresh, and expelling foul, air. If another ventilator be placed parallel with the keel of a ship, it would, on many occasions, be useful in forcing out the gases, when she is pitching deep at anchor. I will venture to say, if ships were built of well-seasoned timber, protected from the excess of washing decks, and ventilated after the principle here laid down, their decay would never be premature.
The application of heat, by means of stoves, to dry the holds and under-works of a ship, is as useless as kindling a fire in a parlor to dry the cellar. Besides, combustible heat is altogether a very doubtful remedy; for when a ship shall happen to have been built of wood containing part of its natural sap and moisture, heat, applied short of expelling them completely, will unquestionably do harm, by calling into vegetation the seeds of the fungi, which, under a lower range of temperature, would have remained in a quiescent state.
As the juices of the oak are known to abound with tannin and gallic acid, those individuals who imagine vegetation proceeds from the sap of the timber, have recommended it to be drenched in solutions of the alkalies and alkaline earths, in order to decompose them; and speak of the union of the acid with the alkali in the ligneous fibre with the same confidence as if it were in the mortar of an apothecary. For my own part, I would as soon believe soda