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af Mr. Cuthbertfon, was iiivental, and, in f;ift, esccuteJ, 

 before tlic end of 1779. by Dr. Daniel Rutherford, after- 

 wards profclTor of botany in the vinivcrfily of Edinburgh. 

 He made a drawing of a pump, having u conioal metal 

 valve in the byttom, fiuni(hcd with a long (lender wire, 

 fliding in the infidc of the pillon rod with a gentle fridlion, 

 fufficitnt for lifting the valve, and fecured againft all cl'ance 

 of failure by a fpring at the top, which took hold of a 

 notch in the infide of the pillon-rod, about a quarter of an 

 inch from the lower end, fo as certainly to lift the valve 

 during the lall quarter of an inch of the pillon's motion. 

 He had executed a valve on this principle ; but his thoughts 

 were diverted from the further profecution of the bufincfs. 



In Phil. Tranf. (vol. Ixxiii. p. 43 J,) we have a defcrip- 

 tion by Mr. Cavallo, of an air-pump contrived and executed 

 by Melfrs. Haas and Hiutcr, inllrunient-niakers in London, 

 ill tlie conlli-uftion of vhich thefc artifts have revived 

 Guerieke's method of opening the barrel-valve during the 

 lall ftrokcs of the pump, by an external force ; of this piuup 

 Mr. Cavallo fays, that when it had been long ufed, it had, 

 in the courfe of fome experiments, rarefied 600 times. 



Tlie drawing and defcriptiou of a new air-pump, afting 

 by means of a quantity of oil in the barrel, and invented by 

 James Sadler, Efq. have been publilhed by Mr. Nicholfon, 

 in his Journal, vol. i. p. 441, &c. He fays, that it poirefics 

 the deiinible rcquifites of fmiplicity, cheapnefs, and power ; 

 though at the fame time he very properly fuggefts, that the 

 oil, in procefs of time, may become changed by the circu- 

 lation, and lefs fit for the purpofe, and probably carry 

 with it bubbles of air. He does not mention its pradlical 

 effects. 



A new air-puaip, fimilar in its principle to thofe of 

 Mr. Smeaton and Mr. Cutlibertfon, has lately been con- 

 ftniifted by the Rev. Mr. Little, of the county of Mayo in 

 Ireland. The princijial parts of this machine are one baiTcl 

 and pillon, one llop-cock, one valve, and two pipes of 

 communication. It is of a portable iize, and fo contrived 

 as to be confined in a very fmall fpace. The barrel is placed 

 horizontally, and the rack by wliich the pilton is moved 

 underneath the barrel, fo that the machine may be packed 

 in a box two feet long,. 18 inches wide, and feven in depth. 

 It is adapted to the purpofes of a condenfing as well as of 

 an exhauiling engine. As to the eflefts of this pump, the 

 author informs us, that in feveral trials of exhauflion, in 

 the months of July, Auguft, and September, 1795, the air 

 being generally very di-y, the rarefaClion produced, as (hewn 

 by the pear-gage, was, five times, between 3000 and 4000 : 

 the mercury in the barometer gage (landing at the fame times 

 always above -roTj^h part of an inch higher than it ilood in 

 a ftandard barometer of a wider bore, which was filled with 

 mercury made very hot and poured into a hot tube, and the 

 mercu;-y in the reduced barometer-gage funk below the level 

 of the furrounding mercury. In the other nine trials, the 

 rarefaflion, as (hewn by the pear-gage, was from 9000 to 

 26000 ; v.-hen the barometer-gage ftood at -;-= ^^ths of an 

 inch higher than thai in the (landard barometer, and fur.k 

 in the reduced barometer ftill lov.-er than before beneath the 

 ftagnant mercury'. For a particular defeription and draw- 

 ing of this inftrument, and a minute detail of its praclical 

 effecls ; fee Tranfaftions of the Royal Iii(h Academy, 

 vol. vi. p. 319 — 391. 



The portable or tulle atr-pump diEFers principally in fize 

 and the Itrufture of the gage from the common air-pump 

 defcribtd at the beginning of this article. It has two brafs 

 barrels, which are firmly retained in a perpendicular fitua- 

 tion to the fquare wooden table on which they reft by a 

 tranfverfe beam, which is prelTed upon them by fcrews at 



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the top of two pillars. From the hole in the center of tlitf 

 pump-plate, there is a perforation or canal in a bnifs piec^", 

 to the fore part of the frame of the pump ; and from thi-; 

 canal there is a perforation right-angular to the former, paf- 

 fing to the center of the balls of each barrel. At each of 

 thefe centers a valve is placed opening upwards to admit tlie 

 air into the barrels. To each barrel a piftoii is fo fitted that 

 the air cannot pafs between it and tlie (ides oi the barrel.. 

 Eacii pillon has a valve opening upwards, that the air in' 

 the lower part of the barrel may efcape through them Into . 

 the common air. They are alio coimefted with a rack, 

 and are railed tir depreffed by a haHclle, the lower part of 

 which is fixed to the axis of a cog-wheel, v,hofe teeth lay' 

 hold of the t-ack. One pillon is raifed and the other is de- 

 preffed, by the fame turn of the handle. The operation of 

 exhauiling is the fame as in the common pump. Two bar- 

 rels are advantageous, becaufe they perfonn the work more 

 fpcedily, and "alfo becaufe the weight of tl-.e atmofphere, 

 preffing upon the riling pillon, is counterbalanced by the 

 fame weight preffing upon the other pillon defcending. 



Behind the large receiver upon the pump-plate, there is a 

 fmall plate for fuilaining a fmall receiver. From the hole at 

 the center of this plate there is a canal communicating with' 

 that which paflTes from the large receiver to the barrels. 

 Under the receiver is a fmall bottle containing mercury, a 

 fmall tube filled with mercury and freed from air, and in- 

 verted with the open end in the mercury ; this is called the 

 (hort barometer-gage. As the air is taken out of the re- 

 ceiver on this fmall plate, it is taken at the fame time from 

 the larger one ; and the defcent of the mercury in the tube 

 v.ill point out the degree of rarefaftion in the receiver. 

 The mercury, however, does not begin to defcend in this 

 tube till near three-fourths of the air have been exhaufted % 

 and the air is faid to be as many times rarer than the atmof- 

 phere, as the column of mercury fullaincd in this tube is lefs 

 than the height at which the mercury (lands, at that time, 

 in a common barometer. The fyphon-gage, which is fome- 

 times ufed, is a glafs tube, bent in the form of a fyphon, 

 hermetically fealed at one end and open at the other. The 

 longell leg Is four inches, each of which is divided on an 

 adjoining fcale, into 20 equal parts. After confiderable ex»- 

 hauftion the gage begins to aft ; and whilft the mercury 

 falls in one leg, it rifes in the other ; and the quantity of 

 air remaining will be determined by the difference of the 

 height, at which it (lands in both tubes. This gage is 

 placed in the fame fituation with the (hort barometer gage. 

 See Gage. 



The fmall fingle-barrelled pump has two plates, one for 

 receivers, and the other for a (liort barometer-gage. Its 

 principle is the fame with that of the air-pump juft def- 

 cribcd ; excepting that it has only one barrel, and that its 

 pillon is merely worked by the hand. In general the fingle- 

 barrelled pump is made only with one rccciver-plate and a 

 mahogany bafis, to favc expences, and with its fmall appa- 

 ratus, to be packed in a portable mahogany cafe. 



Air-pump, la-uos nf rarefa3'i(jn in the receiver of it.^ 

 I. For the proportion of air remaining at any time in the 

 receiver, (fuppofing no vapour from moiihire, 5;c.) we have 

 the following geiicral theorem. — " In a velTel exhaufted by 

 the air-pump, the primitive or natural air contained therein, 

 is to the air remaining, as the aggregate of the capacity 

 of the veflel and of the pump, {t. e. the cylinder left vacant 

 in an elevation of the pillon, with the pipe and other parts 

 between t'he cyhnder and the receiver) raifed to a power 

 whofe exponent is equal to the number of ftrokes of the 

 pifton, to the capacity of the velTel alone raifed to the 

 fame power." M. 'Varignon gives ;m algebraical demon- 



ftratioa 



