124 



BENJ. PIKE S, JR., DESCRIPTIVE CATALOGUE. 



Fig. 611. 



inner side of which is fixed a thermometer. The reservoir 

 is inclosed in a brass case, having a portable screw beneath. 

 The barometer is suspended in a vertical position, by a brass 

 arm and gimbals, attached by thumb-screws to the side of 

 the case, just above the middle, which allows the barometer 

 to hang always in a vertical position, however the ship may 

 roll ; attached to the arm there is a stout circular plate, 

 having holes for screws, to fasten the instrument to any part 

 of the cabin of the ship ; the arm 

 is jointed at the plate for the pur- 

 pose of turning the arm and ba- 

 rometer up, that it may be out 

 of the way when not required in 

 use. Price, - - - $20. 

 fine finished, $25. 



Troughton's Mountain Barome- 

 ter. (Fig. 611.) The employ- 

 ment of the barometer for the 

 determination of heights, has 

 caused it to become an interesting 

 instrument to the philosopher and 

 traveller ; and many attempts 

 have been made to improve it, 

 and render it portable, that it 

 may be conveyed from place to 

 place, without much inconveni- 

 ence or risk. The adjoining figure 

 represents the portable barome- 

 ter, as constructed by Mr. Trough- 

 ton. In the brass box, A, which 

 covers the cistern of mercury near 

 the bottom of the tube, are two 

 slits made horizontally, precisely 

 similar and opposite each other, 

 the plane of the upper edges of 

 which represents the beginning 

 of the scale of inches, or zero of 

 the barometer. The screw, B, 

 at the bottom, performs a double 

 office ; first, it is the means of 

 adjusting the surface of the mer- 



