ROT. 



long period, and in felefted fituations. And that wood 

 ufed for the general purpofes of man is cut down at different 

 periods ; and although it may be felled at the proper feafon, 

 or when molt free from fap or moifture, it is not always to 

 be effected. Nay, even admitting it to have been cut down 

 in the mod favourable fituation, it (till abounds with fuch an 

 extra proportion of moilture, as to require a regular expofure 

 to the air prior to its being applied to ufe, if we wilh to 

 guard againil that (hrinking which always takes place where 

 this precaution has not been taken. And although the fir 

 kind contains lefs of this watery portion, yet it affuredly 

 poflefl'es a confiderable lhare ; and it is in this fpecies, he 

 apprehends, that the evil called the dry rot mod generally 

 occurs, as from the facility of working the fame it is molt 

 generally applied in buildings. But fuppofing it to be fir, 

 or any other fpecies, wood felled when abounding with any 

 extra proportion of fap, and applied to ufe without the pro- 

 per feafoning or expofure to a free current of air, until fuch 

 extra moifture has had time to exhale, is moll liable to the 

 difeafe in queition ; and the cure, or principal prevention 

 againft it, would be the precaution of felling all wood only 

 at the proper feafon, or when the fap is not in circulation. 

 The next mode of prevention would be to ufe fuch wood 

 only as lias been for a confiderable period expofed to the 

 influence of a free current of air, or, where convenience will 

 admit, to that of air heated to a moderate degree ; fuch air 

 extracting with greater facility the enclofed moifture, and 

 in a more certain ratio than the irregularity of our atmofphere 

 will allow, under other circumftances. 



And it is fuggefted, that in all rapidly-improving countries, 

 this evil is likely to be an increafing one, as the current de- 

 mand for wood generally exceeds the fupplies laid by in 

 ftore, fo as to be applied to ufe in regular iucceflion, after 

 being properly feafoned. And that another caufe that 

 affects all wood molt materially, when not fully dried, is 

 the application of paint, the nature of which prevents all 

 exhalation, and confines the enclofed moifture, till it occa- 

 fions a fermentation through the whole fibrous fyftem of the 

 wood, and brings on a premature ftate of decompofition, or 

 the dry rot. It is likewife fuppofed that a fimilar evil may 

 be induced, in confequence of any newly finifhed building 

 having all the doors and windows fhut up, and that for 

 fome length of time, particularly in moift weather. The 

 wood, even though unpainted, is thus frequently placed 

 in our atmofphere more charged with vapour than in its 

 own internal contents, and it is confequentlv in an imbib- 

 ing inftead of an exhaling ftate, and tending to decay. 

 Wood placed in dampifh fituations, and the ends of timbers 

 near to moift walls, fuffer from fimilar caufes, but what par- 

 ticularly attracted his obfervation to the circumftances was 

 this, that both oak and fir polls were brought into this pre- 

 mature ftate of decay, from their having been painted prior 

 to the due evaporation of their moifture ; and then extending 

 the obfervation, and tracing the hiftory of other wood affected 

 in a fimilar manner, he is convinced that the evil fre- 

 quently thus originates, and its prevention would be in 

 ufing timber previoufly well dried and feafoned for fuch 

 purpofes. 



And it is added, that fince thefe obfervations were made, 

 having been bufily engaged in draining from 4000 to 5000 

 acres of ground, further ideas on the fubject of the dry rot 

 have occurred to him from the work he has been engaged in. 

 Where houfes are troubled with damp walls, near to the 

 earth's furface, it is generally, if not univerfally, occa- 

 sioned by the percolation of water from the higher adjoining 

 ground, which, thus intercepted in its current, attempts to 

 follow the general hydroltatic law, of elevating itfelf, by 



the fyphon line, to a height equal to that from whence it has 

 its origin. Thus in houfes differently fituated, we fee the damp 

 arifing to varying degrees of height on the walls, and thofe 

 are probably correfponding to the height at which the 

 moifture circulates in the adjoining ground. At its firft en- 

 trance to the building, and whillt the moifture is in fmall 

 quantity, the excavated part of the foundation wall, he 

 thinks, may abforb, and gradually quit fuch proporckm : but 

 the excefs, as is generally the cafe in moift weather, exceed- 

 ing that power, the foundation ftones are then faturated in a 

 more rapid proportion than the adjoining rarefied internal 

 atmofphere can evaporate : the watery particles then creep 

 up, in degrees proportionate to the afcent from which they 

 originally defcended, excepting when prevented, or driven 

 off by the fuperior heat of the adjoining rooms, when, in 

 addition to the difagreeable damp they caufe, they frequently 

 occafion confiderable damage to the pictures, furniture, 

 &c. Drains laid out athwart the afcending ground, with a 

 very flight defcent or fall, and made of the depth of one 

 yard for each yard of afcent, and from the foundation until 

 equal the height that fuch damp ever rifes, would, there is 

 little doubt, completely fecure the houfe and furniture from 

 the iuconveniencies hitherto fuftained, and would generally 

 prove an effectual prevention to molt cafes of the dry rot, 

 where it originates in extreme moifture. He is of opinion that 

 the fungus which pervades decaying wood is not the firft caufe, 

 but a dependent on the peculiar Hate to which fuch wood 

 has been reduced by prior caufes. The diffeminated feeds 

 finding a proper bed, or nidus, like to the mufhroom, toad- 

 ftool, &c. fix their abode, and pervade the whole fubftance, 

 thus accelerating the general law of Providence, which tends 

 to make all matter reproductive. 



Upon thefe grounds cellars, or fuch other places, fhould 

 be drained in the manner he has mentioned, by taking off 

 the percolating water prior to its gaining admifiion to or 

 contact with the walls : and it is probable that, in molt 

 cafes, a tingle drain will have complete effect ; it would 

 aliuredly, he thinks, do fo, if it was not for the variation of 

 the earth's internal llrata, which are not eafily difcernible. 

 And that if attention to this rule was paid prior to the build- 

 ing any new ftreets in towns, it would prove ellentially ufe- 

 tul in preventing fuch mifchief. 



And it has alfo been fuggefted to the above fociety, that 

 mortar made of lime from burnt chalk is much more deftruc- 

 tive to timber than ftone-lime, or that burnt from lime-ftonc. 

 Chalk-lime attracts moifture ; and communicating it to any 

 timber which it touches, occafions its decay. And further, 

 likewife, that fea-fand is prejudicial, if made into mortar, 

 from a fimilar quality of attracting moifture from the at- 

 mofphere : this, it is fuppofed, may in fome degree be cor- 

 rected by warning the fand well in frefh water, where good 

 fand cannot be procured. But that good mortar, where any 

 is required to be in contact with timber, may be made from 

 a mixture of ftone-lime frefh burnt, and river-fand, to which 

 a very fmall quantity of common brown, or yellow iron 

 ochre fhould be added, and well incorporated therewith in 

 the operation of making it up. See Quicklime. 



And it has been fuggefted by Mr. Johnfon of Ipfwich, in 

 the fame volume of the Tranfactions of the above fociety, that 

 fome time between 177 1 and 1773, he went, at the requeft 

 of a friend, to the chapel at the Lock hofpital, through 

 curiofity, to examine a pew there that had frequently been 

 repaired for damages by the dry rot. And that after a clofe 

 inveftigation, he found it was the operation of a plant, whofc 

 leaf refembled that of the vine. Wherever it had touched, 

 the effect of its poifonous quality got through the wood to 

 the paint, which he has feen a mere fkin. He propofed to 



cover 



