H'Q ON PREV1:NTING the dry-rot in W009. 



which is de- heat. If a sufficiently cold substance conies into contact 

 V^iir-oWe""^ ^'^^ vapour, the superabundant heat, which was necessary 

 tl'.ai'ftho air. to its existence in that form, passes into that cold substance, 

 and the vapour is then immediately condensed or changed 

 into water. Thus if in the hottest day in summer, when 

 the vapour in our breath is totally invisible, we breathe on 

 a looking-glass or plate of polished metal, which is colder 

 than opr breath, the suriace is immediately dimmed ; and 

 if we continue to breathe on it, small drops of liquid appear, 

 vhich gradually become larger and larger, and many of 

 them at length uniting, run down the surface in a stream. 

 The same thing takes place on the outside of a glass of 

 water drawn in summer from a deep well, and of a bottle 

 brought up into a warm room out of a cool cellar; and on 

 the inside of our windows in frosty weather. On the other 

 hand, we could not dim with our breath a plate of metal or 

 glass of 100 degrees of heat, which is greater than that of 

 our breath, and no mist is observable on the inside of our 

 windows'^during the heat of a summer's day; nor is there 

 any condensation of moisture on the outside of a glass of 

 cold water fresh drawn from the well, or of a bottle out of ^ 

 cellar, wljen either is brought into the open frosty air. 

 Manycircum- These circumstances will explain many appearances, by 

 oiainedlhus, ^'^''i*'^'' ^or want of due examination, we are often greatly 

 puzzled. We are frequently mortified by seeing in our 

 houses, especially in tlie country, the walls become stained, 

 or the paper separated and hanging down, and often perish- 

 Dampness of ing; and as this usually happens on the side or corner which 

 cr^ruin -vriiUs. jg j^ost exposed to the weather, we conclude that the damp 

 comes through the wall, and tax our faculties to the utmost, 

 in order to prevent th:§ penetration. The measur.es whicl^ 

 we employ sometimes succeed. But it often happens, that 

 casing, and plastering, and painting the devoted angle fails; 

 and then, as the last resource, we take off the paper and at- 

 tach it to canvass at the distance of one or more incheg 

 from thje wall, and thus, for the present at least, effect the 

 The wet does desired purpose. Now in this case it is just qs absurd to 

 :.ot come supposje, that the wet comes through the wall, as that it 

 vau)^ * comes through the glass window in a frosty day, or the glas§ 

 or bottle from the well or cellar. The fact is, that in an e:x^ 

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