Desci'iptidn of the Moimtain Barometer. 5 i 



level : this defect might be remedied by dividing the scale ac- 

 cordingly ; but it is much more convenient to divide the scale 

 to real inches, and make the necessary allowance in the result* 



The tube and cistern being thus prepared, are mounted iil 

 a mahogany tube or frame of the size of a common walking- 

 f?tick. The stem of the cistern goes into the mahogany 

 tube, and is there secured by a piece of brass tube, which 

 fits to the cistern and mahogany frame to which it is screw- 

 ed ; or the stem may be on the outside, cut into a malti 

 screw, and so be screwed into the mahogany tube. The 

 tube is secured in the mahogany case by passing through per- 

 forated corks in the usual way. 



For the observation of the height of the mercury, two 

 Opposite slits are cut in the mahogany tube, reaching from 

 about 32 to 20 inches for the long scales; /and 32 to 25 

 inches for the short ones ; which are sufficiently long for 

 any purpose in this country. The front slit has its sides 

 bevelled, and is, exteriorly, about three- fourths of an inch 

 wide 3 on one side is fixed a brass scale, divided as usual to 

 inches, tenths, and twentieths. On this scale a nonius 

 slides, moveable by a small knob, which reads off, as in 

 other barometers^ to 500th of an inch. To this nonius a 

 small portion of brass tube is attached, which embraces 

 the barometer tube, and its ld\ver edge is, in observation, 

 made a tangent to the convex surface of the mercury, as 

 in other well -constructed barometers ; and the very narrow 

 slit behind gives abundant light for observation. 



On the bevelled side of the front slit, opposite the scale, 

 a thermometer is placed for taking the heat of the instru- 

 tnent ; and there is room for the scale of correction, placed 

 on Ramsden's attached thermometers, as wellas Fahrenheit^ 

 scale. This thermometer is so contrived as to take out of its 

 place, and answers the purpose of the attached and detached 

 thermometer. 



A thin brass tube, \Vith slits in it, turns half round, on 

 two pins, in the usual manner, and covers the apertures 

 above described in the mahogany tube when the barometer 

 is not in use. 



The mahogany tube is made rathet tapering, and with a 

 i> 2 ferrule 



