"6 Defcription of a new Ventilator, 



them; to fay nothing of the inj.urious efFefts of fmoke received into delicate lungs. One 

 caufe cfpecially of fmoking chimneys it removes, for which no cffedual cure has been 

 before difcovered. 



Dr. Franklin, to whom the world is fo much indebted for his many ufeful difcoveries 

 in natural philofophy, and the arts, has given two very valuable papers on the 

 fubjeft of fmoking chimnies, in the Tranfa£tions of the Philadelphia Society. In thefe he 

 lias recited nine caufes, which occafion chimneys to fmoke, amongfl: which that of high 

 winds blowing the fmoke down the funnel is a chief one : for all which he has propofed 

 effe£lual remedies ; except for this laft mentioned alone, for which, he acknowledges that 

 there was no certain remedy difcovered ; we may therefore look on fuch a remedy as an 

 objefl the more valuable, as it compleats what the Doftor began : fuch a remedy is the in- 

 ftrument defcribed in this paper, which by removing this evil leaves no defe£l incident to 

 diimneys that cannot be obviated ; and it is fo efFeftual for this purpofe, that from the 

 very principles of its conftruftion, the ftronger the wind blows, the better will the chim- 

 ney draw, thus changing what was formerly an evil into an a£l:ual benefit. 



The manner in which the inftrument fliould be ufed for this purpofe, is one with which 

 we are already familiar. It fhould be placed on the top of the chimney, in the fame man- 

 ner in which the contrivance, (intended for the fame purpofe, but very inefFe£tual) called 

 the Boar's Head, is ufually put up : and (hould like it be fupported on a pivot, fo as to turn 

 round with its back to the wind, that the blaft might fully enter its conical opening. 



To prevent the external air from being drawn up between the turning tube and the fixed 

 one, when placed on the chimney, fome foft leather, or canvas, fliould be faftened round 

 the outfide of the lower end of the turning tube, which furrounds the fixed tube ; this lea- 

 ther or canvas, which fhould hang down two or three inches below the interval between the 

 tubes, will aft as a fpecies of valve to prevent the outer air from entering, and will thus 

 caufe the whole efFedt of the inftrument to operate in increafing the draft of the chimney. 



There is another method of efFetting this laft purpose, more certain in its m.ode of act- 

 ing, but which from its requiring a much greater expence, cannot be recommended for 

 general ufe ; this is reprefented in fig. 3. which figure is on a fmaller fcale than the other 

 two, and is only intended to (hew the beft method of fixing the inftrument on a chimney : 

 it is drawn in feftion to exhibit the internal ftrudure. In it A rcprefents the fixed part to 

 be bedded in mortar on the top of the chimney in the ufual manner. B reprefents the 

 moveable part, which turns with the wind, fo that the conical opening G fhall be always 

 oppofite to the blaft. E is the upright rod on whofe point B turns round ; it is faftened 

 below to the two bars DD, which are fixed acrofs in the lower immoveable tube A, and 

 pafles through a collar in the bar H, which is faftened at its extremities to the moveable 

 tube B. By this means the rod preferves its perpendicular pofition ; and the part of the 

 moveable tube, which furrounds the upper part of the fixed one, will revolve round it very 

 clofc without coming in contaft in any part. 



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