[ 44 ] 



Now to fill the tube up to tlie top, and thereby render the 

 inftrument portable, you muft proceed as follows : 



By means of the crank, Fig. 2d, turn the ftop-cocks C and F, 

 (Pi. I ft and 2d) until the communication be open through them 

 to the air, as marked in PI. 2d, Fig. ift, in which you muft 

 conceive the fcparated pieces lowered down, and firmly fcrewed 

 into their places, as reprefented in PI. ift. Then the piece H, 

 which is alfo tubular, being fcrewed down into its place in 

 the piece F, pour in mercury at the top T until the refervoir 

 be intirely filled, and continue pouring in until the mercury 

 (having afcended through longitudinal grooves cut for this pur- 

 pofe through the threads of the fcrew M, parallel to its axis) 

 appears in the piece C at S ; then turn the ftop-cock C, and 

 all communication with the external air is cut off". 



The mercury now ftands in the tube H at the level of S ; 

 continue to pour in at T as before, and the mercury will rife 

 in the tube of the barometer by the preffure of the column 

 in H, and at length compleatly fill it ; when this is cftcded, 

 turn the ftop-cock F, and, inverting the barometer, pour back 

 what little remains in the tube H, which piece you may then, 

 if you think proper, unfcrew. 



The inftrument thus filled, if carried in an inverted fitua- 

 tidli, is fo freci from agitation, that a fmart trot on horfeback 

 will not caufe it to play fo as to be heard or felt againft the end 

 of the tube. 



Every 



