[ 33S ] 



filled in the moft perfect manner with mercury, and immerfed 

 into a pool of mere" in the bottom of the glafs vefTel, The 

 interval between the tube and the neck of the vefTel is clofed 

 by cement, which, as the neck muft be a good deal wider 

 than the tube, is efFedled by a deep ring (I) fitted to the tube, 

 having a round plate at the bottom of it ; which being let 

 down on the tube, after it has been immerfed in the ciflern, 

 is joined with cement to the top of the cap. The tube was 

 eaiily immerged in the mercury within the vefTel, by covering 

 its open end, and fuflaining the mere" in it by a little plate or 

 fcale of iron (P) fig. 7. having two threads tied to it through 

 two holes made near its edges ; which threads were grafped 

 together with the top of the tube between the fingers, and the 

 tube was inverted and let down into the mere'' in the vefTel : 

 the little plate was then pulled up by one of the threads, it 

 being made fo fmall as to pafs through the neck of the glafs 

 while the tube was within it and remained immerfed in the 

 mere" * : the vefTel was then clofed at the top with melted ce- 

 ment ; and as it communicates by the pipe E with the con- 

 duit pipe, it is exhaufled with the receiver, and the merc^ 

 in the tube will fink as the rarefadion advances : if a per- 



fed 



♦ I thouglit this the beft way of fixing the reduced barometer, for if there were 

 a feparate veflel, as a ciftern, for the merc^, and a receiver placed over it and 

 the tube, the eye, when on a level with the furface of the ftagnant mere'', could 

 not fee the altitude of thnt in the tube, with precifion, through two glafles. 



