100 Improvement of the Barometer. 



The screw-joint at o may appear simple and useless, but the want 

 of it occasioned a delay of many days, and caused the breaking of 

 several tubes, while trying to fasten the globe. The person em- 

 ployed on this part, twice threatened to abandon the work as im- 

 practicable, when fortunately the idea occurred to me of disconnect- 

 ing the cistern in that part to afford ample space to work 'dtp. 



q is the mercurial column, f of an inch in diameter, except the 

 part inside of the cistern, which is diminished, in order to leave the 

 more vacant space for the column to fall in high altitudes, and like- 

 wise to lessen the large orifice in the globe through which the tube 

 enters. 



Other proportions than those here given, may serve equally well 

 to construct a barometer on this principle, but these are the dimen- 

 sions of the one which I have now completed, and for distinction, 

 will call the Globe Portable Barometer. It has been inspected by 

 several scientific gentlemen, who with ray request, exposed it to all 

 the causes which usually derange barometers, such as jaring, shaking, 

 concussions, inverting and reinverting its positions, without causing 

 the least perceptible derangement. I invite all who are so inclined, to 

 call and see it ; and to those who desire to make one, I will cheerful- 

 ly give any information in my power, to aid them in its construc- 

 tion. 



Since the invention of the barometer by Torricelli, many learned 

 men have devoted their attention to the improvement of this valua- 

 ble instrument, and among the most useful, is probably M. Gay Lus- 

 sac's " Improved Marine Portable Barometer,''^ wherein, at a certain 

 point, the column of mercury is contracted to prevent the sudden 

 rise and fall of the mercury by the undulating motion of the ship, 

 while the remainder of the column retains sufficient diameter to 

 avoid a very sensible effect from the temperature of the atmosphere. 

 But this, as well as other forms of the barometer, whether secured 

 by the screw and cushion pressing on the bottom, or by the stop- 

 cock as employed by Mr. J. F. Daniels, is liable, by sudden turn- 

 ing or concussion, to admit air into the tube ; for although the 

 cushion and stop-cock renders the instrument portable, it never 

 can be employed as a barometer, until the entire column is open 

 from the hermetical seal to the cistern or atmosphere below. It 

 is in this situation, (the only one of practical use,) that the instru- 

 Hien't is deranged. First, by suddenly inverting and re-inverting 

 ihe position, so that, (while passing from the bottom to the top of 



