Description of the Mountain Barometer. 47 



to take away all hope of approaching the truth, or coming 

 near it : these difficulties, however, philosophers have been 

 able to surmount; so that barometric measures, properly 

 employed, may vie in exactness with the trigonometrical 

 measures, to which they are superior, on account of their 

 facility and generality of the method. 



On this subject it is not necessary that I should add any- 

 thing further, the inventor of the instrument, of which a 

 drawing is herewith sent, having satisfactorily and correctly 

 detailed every thing connected with it, in the paper, of 

 which, by his desire, I send you a copy subjoined. 



The paper alluded to appeared in a respectable periodical 

 work * nearly two years ago, but it has since been revised 

 and received some considerable improvements from the au- 

 thor, which renders its republication desirable. 



I flatter myself, that the section which I have likewise 

 sent, of the principal and most essential improvement, will 

 not be unacceptable to the gentleman, nor the person who 

 may wish to make such an instrument, a, a, a, a, (Plate I) 

 represents the cistern, made of box -wood ; — c, c, c, the cover, 

 made of brass, which screws on, and is prevented from 

 being unscrewed (by idle curiosity,) by four small screws, 

 t. — e e represents the stem of the cistern, into which the 

 glass tube, n w, is firmly glued ;-— R R represents the ma- 

 hogany tube, in which is inserted the stem of the cistern, 

 where it is secured by the screws, t t, passing into it. 

 I am^ sir, your very humble servant, 



Thomas Jones. 



An expeditious Method of determining Altiitides, of every 

 Denomination, ivith a new portable Mountain Barometer ; 

 with a Description of the Instrument, 



The mensuration of heights by the barometer has been, 

 by the labours of M. Dc Luc, sir George Shuckburgh, 

 general Roy, and several other scientific men, brought to 

 such perfection, and affords so much an easier mode of as- 

 certaining the elevations of the different parts of the surface 



* Nicholson*s Journal. 



of 



