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XV. DcfcriptioJi ofRvwEO-LT^ New Portable Barometer* i. 



X. O have a barometer compofed of feveral parts whicK 

 could be eafily put together, and which {hould correal itfclf 

 ;it each obfcrvation hke an aftronomical inltrument, were 

 the reafons which induced M. Humbolt to devife the pre- 

 fcnt conftru6lion. Tralles, the learned aftronomcr of Berne*., 

 has judiciouflv obferved, that all barometers are liable to be 

 broken when the tube is fixed to the fcale which belongs to 

 it. la Humbolt's barometer the tube is diftinft from the 

 fcale ^ and when the tube breaks, its place cari be fupplied 

 by another even on the top of a mountain. The tube, the 

 lower part of which is reprefented by abc (fig. i. pi. VII.) is 

 cemented into an iron one be, two inches long, terminating 

 ia a nut c, which receives a fcrew to the depth of 2|- lines : 

 the end of the fcrew is fquare. When the tube is filled with 

 mercifrv, and fcrewed clofe, it is put into a tube of copper 

 lined with flannel, and covered on the outfide with leather. 

 Tills cafe may be carried as a cane 5 the head d of the fcrew 

 being kept, as far as pofllble, in a vertical pofition. If the 

 eiUrance of air be apprehended, it will lodge itfelf under d. 

 In that cafe turn the fcrew and pour a drop of mercury upon 

 it before it is (liut. The whole tube may be examined to 

 fee that the mercury is not fcparatcd by air bubbles j an ad- 

 vantage wanting in the Englifli barometers, in which the 

 tubes are half concealed. The mahogany pillar cgf (fig. 2.) 

 contains the mercur}'^, to be poured into it after it has beca 

 fcrewed into its rtand ^^ iS'^g-^-), fupported by three feet 

 that fold over each other. The interior part of the column 

 forms a hollow parallelopipedon, the fquare aperture of 

 which is exaftly equal in fize to the fquare of the fcrew cd^ 

 In pufliing the tube klma (fig. 4.) into this aperture until 

 cd be above the level of the mercury, you turn the tvibe to 

 the right, by laying hold of it with one hand between Intt 



, * From the Jaurnal dc Phyjique, an. 7. 



As 



