of air, and even a partial abstraction of heat and humidity, will arrest the decay of all substances for a great length of time.

These conclusions seem to be sanctioned by all I have seen, and by every sensible observation I have read or heard, on the subject of dry rot in houses and in ships.

In houses, we continually observe, that the decay commences first, where the change from one to the other of these states is most frequent. The ends of joists inserted into damp walls, for instance, and the upper and lower timbers of a house, are most liable to decay the latter, arising from the evaporation of moisture from the ground, and the former, by the breaking in of the elements from above.

The same laws are uniformly obeyed in the decay of ships: for, in their upper works, where moisture, heat, and evaporation, follow each other in excess, the timbers run sooner to destruction than in their holds: this is owing, 1st, to the almost constant application of water to the decks, by rain or washing; 2dly, to the higher range of temperature produced there by animal and solar heat; and, 3dly, to the greater subsequent evaporation. Whereas, in the hold of a ship, the exclusion of solar and animal heat, and the low temperature maintained there by the iron ballast and ambient salt water, usually, in a great measure, preserve her timbers from decay.

These observations are further corroborated, by the yet more rapid decay.of ships in warm and tropical climates, where moisture is more abundant, and heat more powerful, than in the temperate

zone.

Much controversy has taken place, of late, respecting the causes and difference between the dry and wet rot in ships. I believe it consists simply in this; the former is accompanied by vegetation, and the latter is not; or, in other words, air, heat, and humidity (besides their usual destructive qualities in dry rot), call the dormant seeds of fungi into life: while, in the wet rot, the same agents only hasten the decomposition of the woody fibre.

But these distinctions are little necessary, owing to the remedy for both being the same; for, admitting this spongy vegetation to possess the power of absorbing moisture, and maintaining a higher range of temperature than the surrounding dead matter, still, as we have no means of preventing the diffusion of the seeds, all we can do, is to endeavor to starve them, by expelling the sap, before the timber is put into a ship, and keeping her as free from moisture as possible afterwards; by which means the pollen will remain in a dormant state, and by the same measures, the wet rot, occasioned by air, heat, and humidity, will also be arrested. Indeed, our means of preserving a ship from decay, will be in exact

proportion to the powers we possess of freeing the timber of its natural sap and moisture, and keeping it dry afterwards.

Is it not a little remarkable, that some of the most able writers on dry rot should have fastened on causes which are hardly hypothetical; while those laws which are well established, and continue in perpetual activity, in the vegetable kingdom, should have been passed unnoticed by them?

Morrison" attributes the production of this vegetation (dry rot) to the mixture of salt and sulphur, mixed with oils from the dung of quadrupeds." While Mr. Bowden, at page 82 of his Treatise, says, "The cause of dry rot is heat acting on the vegetable juices; by which," says he, at page 87," they (the juices) will rise from their dormant state into life and action, and the timber will be consequently destroyed."

Had these gentlemen not been sufficiently acquainted with the physiology of the seeds of plants to know that all vegetables perpetuate their species through the medium of seeds, suckers, slips, &c. they ought at least to have known, that when the great Author of nature separated the sea and earth from the chaotic mass, and called animals and vegetables into existence, he set certain limits to their sphere of action, by giving them the faculty only to multiply" after their kind." And although man has dominion over, and is invested with power to kill, and drive back ferocious animals to the desert, and root out certain noxious weeds from the garden; yet he has never been able to exterminate a single species of either from the face of the earth. Power, therefore, has never been given to the most exalted in the class of animated existence to produce the vilest insect; nor is the stately oak, the king and pride of the forest, (during life or after death,) capable of generating even a mushroom. But, under decay, this wood yields a suitable nourishment to that species of fungi, whose seeds had been previously disseminated by the wind, or otherwise.

I have here to mention, by the way, that although vegetables have not the power of locomotion, yet the diffusion of many of them is not less certain, by wings, spines, hooks, and scales; for instance, the downy appendages by which the dandelion wafts itself through the air is familiar to every one. Moreover, Nature seems less tenacious in the preservation of animal and vegetable life themselves, than she is in giving to the one a strong desire to propagate its species, and to the other the power of retaining life until that object is accomplished.'

1

Ray rapporte qu'à la suite d'un incendie arrivé à Londres, peu de temps après, les murs furent couverts de sisymbrium irio. Il ajoute que cette plante étoit rare et éloignée de cette ville. Les graines s'étaient sans doute

VOL. XXVI.

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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.2

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 Elémens 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.1

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."