A I R 



hcntcJ to i-arcfv llic impending column of air, the cqiiili- 

 briiim will be maintained by the pntiid air iVom the bultom 

 ol the tube, which being thuj drawn out, will be luocttdcJ 

 by a fupply of frefh air from the other parts of the (liip ; 

 and by continiiiiif^ the operation, the air will be clianged in 

 all parts of the (hip. Upon this principle, Mr. tjutton pro- 

 pofed to purify thebad air of a (hip, by means of the (ire 

 uftJ for the coppers, or boiling places, willi which cveiy 

 fliip is provided. Under eveiy fuch copper or boiler there 

 n:e two holes feparated by a grate, one for the (ire and the 

 other for the aflies ; and there is alfo a flue, communicat- 

 ing with the fire-place, for the difcliarge of the fmokc. 

 Tile fire, after it is lighted, is prefervcd by the conltant 

 draught of air through thele two iioles and the flue ; and if 

 the two holes are clofed, the fire is extiiiguiilicd. But 

 when thefe are clofed, if another hole, communicating 

 with any other airy place, ar.d alfo witli the fire, be opened, 

 the fire will of courfe continue to burn. In order to clear 

 the holds of the fliips of the bad air, Mr. Sutton propufed 

 to clofe the two holes above mentioned, I'/is. the fire-place 

 and alh-plac£, with fubllantial iron doors, and to lay a 

 copper or leaden pipe of fufficicnt i'r/x from the hold intjj 

 the alh-place, and thus to fupply a drauglit of air tin- feed- 

 ing the fire ; a conltant difcharge of air from the hold will 

 be thus obtained, and frelh air will be fupplied down tlie 

 hatches, and by fuch other communications as are open into 

 the hold. If other pipes are connected with this principal 

 pipe, communicating eitiier with the wells or lower decks, 

 the air that fervcs to feed tlie fire will be drawn from fuch 

 places. 



In large (hips, there is not only a copper, but a fire- 

 grate, like thofe ufed in kitchens ; behind tliis grate an iron 

 tube might be fixed, and inferted quite through the brick- 

 work and through the deck, fo that one end of it might 

 ftand alwut a foot, or fomewhat more, in the chimney above 

 the brick-work, and the other made to enter into the hold 

 or any otiier part of the (hip. When the upper end of this 

 tube is heated, the draught of air will be fupplied from be- 

 low, as in the other cafe. Mr. Sutton's pratlicable and 

 ufeful contrivance was much oppofed at its firll propofal ; and 

 though his pipes were recommended by Dr.Mead and Mr. W. 

 "Watfon, after feveral trials of their effect, they were very 

 flowly introduced, and in procefs of time very much neglefted. 

 Mr. Sutton, after eonfiderable delay, and with no fmall 

 difliculty, obtained a patent for his invention. 



Mr. Watfon recommends the ufe of thefe pipes for the 

 circulation of trefii air in houfes, prifons, hofpitals, wells, 

 &c. And they have undoubtedly this obvious advantage, 

 that by caufing the putrid and noxious air to pafs into the 

 fire, they not only diflipate but deftroy it. Phil. Tranf. abr. 

 vol. viii. p. 628. 630. Mead's Works, p. 397 — 437. 



For other inventions adapted to the fame purpofe, fee 

 AiK-trunk, Bellows, iSA/^'j-LUNGs, Ventilator, Blonu- 

 t«j'-wnEEL, and WiND-/2;;/r. 



A\v.-pump, a machine, by means of which the air may be 

 fxhauiled out of proper vefTels. 



The ufe and effect of the air-pump is to make what we 

 popularly call n nmcmim ; but this, in reality, is only a degree 

 of rarefaction fufficient to fufpcnd the ordmaiy effefts of the 

 atmofphere. 



By this machine, therefore, we learn in fomc m.eafnre, 

 what our earth would be without an atmofphere ; and how 

 much all vital, generative, nutritive, and ;Jterative powers, 

 depend upon it. 



The principle on which the air-pump is conftrufted, is 

 the eladicity of the air ; as that on which the common, or 

 water-pump is founded, is the gravity of the fame air. 

 7 



A I R 



The ftniAure of the air-pump jvi" itfelf, more fimpEe 

 even than that of the water-pump.— The latter fnppofes two 

 principles, gravity and elaflicity liliewife : fo that ttie water- 

 pump inufl iirfl be an air-pump, /. c. it muft rartty the air 

 before it can rail'e the water. — In effeft, water being 3 

 dormant unelallic fluid, needs fonje external agent to make 

 it alcend ; whereas air afeends in virtue of its own elaftic 

 adtivity : its natural tendency is to feparate and leaye a 

 vacuum ; and all that remains for art is to prevent the am- 

 bient air from fupplying the place of that which thus fpon- 

 taneoudy efcapcs. I'o make water afcend, the force 

 wlierewith it is prefied dovvnwaj-ds is either to be diminiflied 

 or increafed in one part more than another ; like a balance 



in ivquihi 



hr'io, one of whofe fcales may be made to rife, cither 

 by diminifiiing its own weight, or increafing that of the 

 other ; the water, therefore, recedes from the common centre 

 of gravity by the veiy power with which it tends towards it 

 indireetly or fecondarily applied ; becaufe, two fimilar cen- 

 tripetal forces being made to ai£l contrary to each other, 

 wiiat in the one over-balances the other muft have the effeft 

 of a centrifugal force — Whereas, the principle whereby air is. 

 rarefied or diminilhed, does not refpeiSt the centre of the earthy 

 but the centres of its own particles ; being no other than a 

 certain implanted power, whereby they immediately tend 

 to recede from each other. 



The invention of this noble inilrumcnt, to which the 

 prefeut age is indebted for fo many fine difcoveries, is af- 

 cribed to Otto dc Guericke, the celebrated conful of Magde- 

 burg, who exhibited his firll public experiments with it,, 

 before the emperor and the ftatts of Germany, at the break- 

 ing up of the imperial diet at Ratlfbon, in the year 1654;. 

 but hisdefeription of the inilrumcnt, and of the experiments 

 performed with it, is contained in his " Experimenta nova 

 Magdeburgica de Vacuo Spatio," and was not publifltcd 

 before the year 1672, at Amfterdam. 



Dr. Hooke and M. Duhamel, indeed, afcribe the invention 

 of it to Mr. Boyle ; but that ingenious autlior frankly con- 

 fefTes de Guericke to have been beforehand with him. la 

 a letter which he wrote to his nephew, Lord Dimgarvan, 

 at Paris, about two years after Schottus's book was pub- 

 lilhed, he introduces the acknowledgment of his obligation, 

 for the difcovery of this ufeful machine, to what he had 

 heard of it, though he had not then perufed it, by that 

 wcll-appllcd paflage of Pliny, kcmgnuin ijl el plenum higcnui 

 puiloris fat:rl per qiios profeeeris. Some attempts, he afiures 

 us, he had made upon the fame foundation, before he knew 

 any thing of what had been done abroad : but the infor- 

 mation he afterwards received from Schottus's Mcchanica 

 Hydraulico Pneumatica, publiflied in 1657, wherein was an 

 account of de Guericke's experiments, firft enabled him to 

 bring his deiign to any thing of maturity. From hence, 

 with the affiftance of Dr. Hcol;e, after two or three un- 

 fuccefsful trials, arofe a new air-pump more eafy and ma- 

 nageable than the Gennan one ; and hence, or rather fi-om 

 the great variety of experiments that illullrious author 

 applied it to, the engine came to be denominated mach'ina 

 B'jyl'mna, and the ■vacuum produced by it, -vaciiui/i Boy~ 

 liamim. 



A\K-p!imp, Jirudure and ufe of the. The bauf or eflential 

 part in the air-pump, is a metalline tube, anfwering to the 

 barrel of a common pump, or fyringe ; having a valve at the 

 bottom, opening upwards ; and a moveable piiton or em- 

 bolus, anfwering to the fucker of a pump, furnifhed hkewife 

 with a valve opening upwards. The vshoie muil be duly 

 fitted to a veffel as a recipient or receiver. 



The refl, being only circumftances chiefly refpefting 

 convenieacy, have been diverfified aud improved from time 



to 



