[ 9S ] 



at the other by a cover that is to be fitted on with a fcrew, Co 

 fine and true as to prevent the efcape of any quickfilver when 

 the inftrument is put together. 



A SOUND, clean and porous cork, of about three-fourths of 

 an inch in length, and one in diameter, fhould be very nicely 

 fitted to enter with a moderate preffure at the bottom of the 

 ivory cylinder, which fliould be turned fo truly throughout 

 that the cork may be pufhed up to the extremity of the open, 

 where there fhould be left a fmall fhoulder to ftop the farther 

 progrefs of the cork, and to retain it in its proper place. When 

 the cork is in this fituation it fhould be carefully bored with a 

 circular file to receive the end of the glafs tube tightly through 

 its axis, fo that the end of the tube may rife beyond it, and 

 projed about half an inch into the empty part of the cyhnder, 

 and that the axis of the tube, and of the cylinder, may be exadly 

 in the fame right line. 



The tube fliould be then carefully filled in the ufual manner, 

 and the mercury poured over the end into the ivory cylinder till 

 fuch a quantity is admitted as may be fufiicient, when the lid 

 is fcrewed down tight, to cover the end of the glafs tube in any 

 poffible pofition of the inftrument : to wit, when held either 

 parallel, oblique, or perpendicular to the horizon, a bored maho- 

 gany ftafF with a brafs fcale and vernier, a thermometer cafe, 

 and caps of brafs to Aide or fcrew on each end, is to be prepared 

 to receive the barometer and its attached thermometer, which 

 being firmly and carefully introduced and fitted to their places, 

 the whole is completed and fit for ufe. 



FIGURE 



