New mode of constructing the Mercurial Barometer. 223 



Art. III. — New mode of constructing the Mercurial Barometer; 

 by J. L. RiDDELL, A. M., Lecturer on Chemistry. 



The design of this contrivance, is to render the indications of tlie 

 barometer more obvious and deUcate. 



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A C, is a vertical glass tube near thirty two or thirty three inches in length, as 

 in the common barometer. 



C D. An iron joint held together by screws. 



G I. A horizontal glass tube five feet long, or of any required length. 



A O. Torricellian vacuum. The mercury is continuous from O to P. 



M K. A plumb line pendent in a glass tube, for adjusting the instrument so 

 that CA shall be exactly vertical. 



H. A spirit level, for detecting any variation of G I, from a horizontal direction. 



The iron tubes serve in part as caps, into which the ends of the 

 glass tubes are cemented ; and at the places where the glass termi- 

 nates, the iron must be so drilled that the cori'esponding calibres will 

 be exactly equal and continuous. If the glass and iron are fitted ac- 

 curately in the first place by grinding, a little resinous cement appli- 

 ed by heat, (such as shellac,) will render the junctions perfectly 

 secure. That part of the iron tube which embraces the glass, may 

 be attached with common cap cement. The iron faces that are 

 pressed together by screws, should be accurately ground ; and if the 

 position of the instrument require it, pieces of thin leather may in- 

 tervene. If the calibre of the ascending tube be one fourth of an 

 inch, and that of the horizontal tube one fifteenth ; the rise or fall of 

 the mercury four fifths of an inch, will cause the horizontal column 

 to move nearly a foot. 



