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LVIII. Defcnpt'ion of a portable Baroineter. By Dr. J. Gt;ii- 

 RIN, ojAvigv.on, ProfeJJhr nf Natural Hijlorj in the Ceti' 

 tral School of y'cuclujef and Member ojjeveral Societies *. 



N< 



O philnfophical inftruments are fo varied in their con- 

 ftru6lion as barometers, and efpcciallv the portable ones. But 

 if the latter leave no room for improvement in rejjard to ex- 

 aftnefs, they are exceedingly complex, and liable to be de- 

 ranged; fo that travellers are often obliged to renounce the 

 obfcrvations they depended on making during the courfe of 

 their journeys. 



It is very rare that the beft barometers are not either de- 

 ranged or broken in the courfe of a long journey. Nothing 

 however but a violent fall can break the one which I am about 

 to defcribe. It may be tranfportcd on any carriage, and along 

 the worlt roads, provided care be taken to keep it inverted; 

 that re, with the cup uppernioft. Naturalifts u ho travel flood 

 in need of this fimple inftrument, the only barometer really 

 portable being that of Deluc, the conllruftion of which is 

 more difTicult; and which, in regard to obfcrvation, is liable 

 to inconveniences which in mine I have endeavoured to 

 avoid. 



I fliall fay nothing of a great number of other barometers 

 more or lefs complex, as well as defcftive, and in general in- 

 convenient for tranfportation. They all have faults, which 

 it would be too tedious to enumerate. It has been propofed 

 to ufe for this purpofe iron tubes with glafs tubes cemented 

 to them; but it has not been remarked that the m.ercury at 

 length oxidates, lofes its brilliancy, and adheres partially to 

 the tube. 



My barometer, the fimpleft pofTible, will be attended with 

 this advantage, that it can be procured at a moderate price. 

 The defcription of it is as follows : A, B, C, (Plate IX, 

 fig. 2.) is a glafs tube about 33 inches in length, bent from 

 B to C in fuch a manner as to leave the di(tance of an inch 

 between its branches. 



D is a ftop-cock^ made of iron, ivory, box-wood, or any 

 other fubflancenol fufccptible of being attacked by mercury, 

 and which ferves for intercepting at pleafure its pafTage into 

 the cup. Box-vv'ood, dipped in boiling wax, appears to me very 

 proper for making a good llop-cock, as it can permit the mer- 

 cury to pafs between the cock and its key-liopper (if the mer- 

 cury contained in the tube Ihould dilate too much), without 



* Ftjin the Journal Je Phv/ique, Friiiiaire an. 10. 



faffering 



