VENTILATOR. 



the crofs-trees reft on the blocks a, a, and are fixed to the 

 floor by ftrong iron bolts. The mill-poft J, being hollow, 

 admits the iron rod b to pafs through from the crank of the 

 iron axle-tree « ; the turning-frame g n moves on the girdle/, 

 on which lies a broad circular iron plate, where is the bear- 

 ing of the brafs fridlion-wheels, whofe iron axle-trees move 

 in brafs collars : the turning-frame g n carries the axle-tree 

 i i, and the fails /, /f, which are turned, fo as always to face 

 the wind, by the vane h ; the frame is kept from wrack- 

 ing by iron braces q, r, reprefcnted by the double pricked 

 lines. The crank z is fix inches and a half long, and there- 

 fore gives a (Iroke of thirteen inches ; but the lower end of 

 the rod .r is fixed to the lever of the ventilator {Jig. 4- ) at 

 fuch a diilance from the centre of its motion, as to raife and 

 fall the midriffs fifteen inches. The iron axle-tree extends 

 forward, about two feet and a half beyond the face of the 

 fails ; from the extremity of which, s, eight iron braces, /, /, 

 go to eacli arm, to which they are failened by iron fcrevv- 

 9)olts, which bind them and the iron circle of pricked lines 

 -mm [jig. 7.) faft together: the diameter of this circle is 

 dix feet, and the fweeps or arms of the mill k k are feven 

 cfeet three inches long, and they are mortifed into the drum 

 y y. A void fpace of about fix inches breadth is left be- 

 tween the fails, as reprefented in the figure, that the direft 

 current of the wind, as it paffed through, might give a turn 

 to the courfe of the wind ; which otherwife, being driven 

 obliquely from the face of the preceding fail, would be 

 forced to aft on the back of the following fail, and thereby 

 abate the force, and retard the motion of the mill. The 

 brake-pole [fg. 6. ) is n ; and the fingle pricked line / at 

 the end of it is the fword which is to clafp round the nave 

 to ftop the mill, by pulling the rope iw : is the bottom 

 ftiear-tree of the turning-frame ; and p exprefles the manner 

 of fcrewing the brafs collars of the axle-tree nearer and 

 nearer, as they wear away. For a farther account of this 

 machine, fee Hales's Treatife of Ventilators, part ii. 1758, 

 p. 32, &c. 



Dr. Hales farther fuggefts, that ventilators might be of 

 life in making fait, in order to which there fhould be a 

 flream of water to work them, or they might be worked 

 by a windmill, and the brine ftiould be in long narrow ca- 

 nals, covered with boards or canvas, about a foot above the 

 furface of the brine, in order to confine the ftream of air, fo 

 as to make it aft upon the furface of the brine, and carry 

 off the water in vapours. Thus it might be reduced to a 

 dry fait, with a faving of fuel, in winter and fummer, or in 

 a rainy or dry ftate of the air. Ventilators, he apprehends, 

 might alfo ferve for drying linen hung in low, long, narrow 

 galleries, efpecially in damp, rainy weather, and alfo in dry- 

 ing woollen cloths, after they are fulled or dyed, and in this 

 cafe they might be worked by the fulling water-mill. Ven- 

 tilators might alfo be an ufeful appendage to malt and hop- 

 kilns ; in which cafe it would be beft to have the air-trunk 

 enter the kiln about eighteen or twenty-four inches from 

 the ground, and juft oppofite to the fire ; but in order to 

 prevent the air's blowing too ftrongly on the fire, a (kreen 

 of brick-work might be formed about a yard diftant from 

 the hole of the air-trunk, and a yard fquare ; for thus the 

 air from the ventilators would be better diffufed through 

 the whole kiln. 



Dr. Hales is alfo of opinion, that a ventilation of warm 

 dry air from the adjoining ftove, with a cautious hand, 

 might be of fervice to trees and plants in greenhoufes ; 

 where it is well known that an air full of the rancid vapours, 

 which perfpire from the plants, is very unkindly to them, 

 jas well as tlie vapours from human bodies are to men. 



For frefh air is as neceflary to the healthy ftate of vegetables 

 as of animals. 



The larger kinds of ventilators ufed by the doftor, are 

 ten feet long, five feet broad, and two feet high in the 

 clear witliin. Thofe he ufed by way of experiment on 

 board the Captain, a feventy-gun fliip, were ten feet long, 

 four feet three inches wide in the clear within, and thirteen 

 inches deep ; one inch of which being occupied by the 

 midriff, there remained a foot depth for it to rife and fall 

 in. A ventilator of thefe dimenfions will, through a trunk 

 of a foot fquare, drive the air at the rate of twenty-five 

 miles in an hour, which is double of what Mai'iotte afligns 

 for the velocity of a pretty ftrong wind. 



But befides thefe large ventilators, the doftor made a 

 fmaller fort, four feet in length, fixteen inches in breadth, 

 and thirteen inches deep, all in the clear within. This 

 fmaller ventilator may be very ufeful in preferving the 

 bread, in the bread-room of a fhip, fweet and dry. Peafe 

 alfo, and oatmeal, which are apt to heat and fpoil in 

 caflvs, may be preferved, by putting them into a large 

 bin, with a falle bottom of hair-cloth laid on bars, by which 

 frelh air may be blown upwards through them with thefe 

 fmall ventilators. 



Ventilators are alfo of excellent ufe for the drying of 

 corn, hops, and malt. See Granary. 



Gunpowder may be thoroughly dried, by blowing air up 

 through it by means of ventilators. 



What advantage dry gunpowder has over that which ia 

 damp, may be feen by the experiment mentioned in the 

 article Gunpowder. 



Thefe fmall ventilators will alfo ferve to purify moft eafily 

 and effeftually the bad air of a fhip's well, when there is 

 occafion for perfons to go down into it, by blowing air 

 thi-augh a trunk, reaching within a yard of the bottom of 

 the well, both for fome time before, and during their ftay 

 there. They may be alfo made ufe of at fea to fweeten 

 ftinking water, &c. See 5ea-WATER. 



Dr. Hales made alfo feveral trials for curing ill-tafted 

 milk by ventilation. 



For thefe and other ufes to which they might be ap- 

 plied, as well as for a particular account of the conftruftion 

 and difpofition of ventilators in Ihips, hofpitals, prilons> 

 &c. and the benefits attending them, fee Hales's Treatife 

 on Ventilators, part ii. paffim ; and Phil. Tranf. vol. xlix. 

 p.332, &c. 



The ventilators in large Ihips, fince the order for venti- 

 lating the fleet, iffued by the lords of the Admiralty in 1 756, 

 are fixed in the gunner's fore-ftore-room, and generally 

 a-head of the fail-room. The foul air is carried up through 

 the decks and fore-caftle, near the fore-maft, fometimes 

 afore it, and fometimes abaft it, but more frequently on its 

 ftarboard fide ; the lever, by which the ventilators are 

 worked, is under the fore-caftle in two-deck fhips, and 

 between the upper and middle decks in three-deckers ; 

 fometimes the lever is hung athwart-fhips ; in fome fhips 

 afore and aft ; and in others oblique. The iron rod, which 

 communicates the motion from the lever, partes through 

 the partners of the fore-maft, and is connefted with another 

 lever, fufpended at or near the middle ; in fome fhips over 

 the ventilators ; in others under them, when it is found 

 neceffary to fix them up to the deck. The beft method to 

 fave room is to place the ventilators over one another, with 

 their circular ends together ; the air-trunk fhould be fu 

 high above deck, that the men on deck may not be incom- 

 moded by the foul air which blows out of it ; and tliereforo 

 the trunk comes through the upper deck, near and behind 



the 



