46 Description of the Mountain Barometer *. 



tcrs should be considered relatively to tlic soaps as the inso- 

 luble metallic salts are relative to the alkaline salts. 



I am convinced that the defect in the consistency of the 

 soaps of potash by no means depends upon the state of the 

 oil, but rather upon the kind of combination ; for I never 

 obtained any thing but a soft soap on treating by potash 

 some oil proceeding from a very dry soap of soda. 



Xf. Description of the Mountain Barometer , invented ly 

 Sir Henkt C. Englefield, Bart, F,R,S, and made hy 

 Mr, Thomas Jones, of Mount Street, Berkley Square, 



To Mr, TillocL 



X HE various advantages which are likely to be derived 

 from taking altitudes of every description, in a short time, 

 with very little trouble, and at a small expense, gives me 

 every reason to suppose the curious and enlightened mind 

 will be pleased with a description of a new portable moun- 

 tain barometer, contrived, and most peculiarly adapted, for 

 that useful purpose, by a gentleman well known in the phi- 

 losophical world. Its great simplicity in use, as well as 

 portability, renders it superior to any barometer yet made. 



The celebrated experiment devised by Pascal (says the 

 French National Institute, in their Transactions of 1S05,) 

 and which proved, that a column of mercury decreased in 

 proportion as the barometer was carried to a greater height, 

 after having proved the gravity 6f the air, must have made 

 the mercury be considered as a scale capable of measuring 

 the height to which it is carried. But this scale being very 

 small, in comparison of the heights which it ought to mea- 

 sure, it was soon perceived, that it would be necessary to 

 improve the construction of the barometer, so far as to 

 render sensible and appreciable the smallest changes in the 

 heiirht of the mercurv. The ncccssit v of avoiding: or of cal- 

 culating the continued variations which the barometer ex- 

 periences, even without changing its place, presented an- 

 other obstacle, much more formidable, and which seemed 



. to 



