GKEEN'S STANDARD BAROMETER. 



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The following is an account 

 of Green's improved standard 

 barometer, adopted by the 

 Smithsonian Institution, for 

 observers of the first class. 



The barometer consists of a 

 brass tube, (Fig. 1) terminat- 

 ing at top in a ring A, for sus- 

 pension, and at bottom in a 

 flange B, to which the several 

 parts forming the cistern are 

 attached. 



The upper part of this tube 

 is cut through so as to expose 

 the glass tube and mercurial 

 column within, seen in Fig. 5. 

 Attached at one side of this 

 opening is a scale, graduated 

 in inches and parts; and inside 

 this slides a short tube c, con- 

 nected to a rack-work arrange- 

 ment, moved by a milled head 

 D; this sliding tube carries a 

 vernier in contact with the 

 scale, which reads off to ^^^ 

 (.002) of an inch. 



In the middle of the brass 

 tube is fixed the thermometer 

 E, the bulb of which being ex- 

 ternally covered, but inwardly 

 open, and nearly in contact 

 (54) 



