Literary memoirs of Germany and the North : being a choice collection of essays on the following interesting subjects ... / Done from the Latin and High-Dutch, by a society of gentlemen.

Date:
1759
Catalogue details

Licence: Public Domain Mark

Credit: Literary memoirs of Germany and the North : being a choice collection of essays on the following interesting subjects ... / Done from the Latin and High-Dutch, by a society of gentlemen. Source: Wellcome Collection.

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    Plate I. Fig. 6. Jo. 'BerupttillPs ■Barometer. Thefecondehr* 7. Tills is one clafs of barometers: Others have fought to mend the ut'Barometers, matter by the figure of the barometers only, and that i t -i twofold man¬ ner: Some have applied themfelves to caufe greater variations in the mercury; others again to obferve at lead more accurately the ordinary va¬ riations. The former was effected by thofe who inclined the upper part of the tube from the perpendicular to the horizon: This is an ancient contrivance, whofe firft author I know not; but it is found to be propofed by an anonymous author in the Philofophical Tranfaïïions % and is generally deferibed by others: As it may be eaiily conftrufted, and as by inereafing the inclination, it may be render’d fomewhat more fenfible, it, therefore, deferves commendation; yet it does not attain to the higheft: degree of exaótnefs, and that on feveral accounts; as the incrcafed fridtions of the glafs, the cohefion of the mercury, which hinders its running in narrower tubes, and makes it irregular in wider ones; the inconveniencies from heat become more fenfible by the inclination, 8. The bell in this kind is undoubtedly that which we owe to John Bernouilli, and is explain’d in Hermann's Phoronomiab *, its upper part, Fig *• where the variations of altitude are made, confifts of a bubble of any de¬ gree of bignefs; the tube at its lower part is incurvated, that it may run out parallel to the horizon or which is more commodious in pradlice, it is reflected at pleafure upon a horizontal plane: The Parifians have hinted, that Jo. Dom. Caßni attempted fuch kind of barometers feveral years be¬ fore ; but that he afterwards laid afide this method, becaufe the air infi- nuates itfelf into the mercury in a horizontal tube, fomewhat widerc. 9* I made trial of this, and found it fucceed, when the diameter of the line I was at firft apprehenfive of the inconveniencies of friddion, that on account of the narrownefs of the tube it would hinder the minuter variations : But I have learned by experiment, that they are not fo confiderable in a barometer accurately conftrucled; for, when, according to De la Hire'?,Q diredtion, I fhook the barometer a little, I obferv’d that the places, at which the mercury Hood before and after the fhake, differ’d little or nothing. The lcale of the variations, in the one The Author’s I firft caus’d make, is feven times greater than the common feale. _ I fhall in a note e my method of conftrudting thefe kinds of barometers, becaufe Experiment on mef«r!i//?'s Bar°* horizontal tube did not exceed a Method of con- ertvp ilru&ing thele Barometers. a N° 236. p. 4. b § 324- c Pberen. I. c. p. 180. «1 Mem. de PAcad, da Sciences An. 1712. p. 4. Ed. Bat. e ‘ Take a portion of a wider tube, three inches long ; at one end let it be hermetically fealed ; and at the other, by means of the flame of a lamp, let it be join’d to a flenderer tube of 28 inches in length : My inftrument, it is true, on each fide of the wider C) lin-, der, has a fleuder tube ; but you may eaflly perceive, that the upper one is not necefiary: Let the tube, thus conftru&ed and inverted, be fill’d with mercury to the height of one or two inches, with the fame precautions with refpeft to the air, as are ufuallyobferv’d: After