Description of the Mountain Barometer: 53 



bodv, or, ir no such occurs, by kneeling on one knee. The 

 cistern sliould be let down so as to touch the ground, the 

 left hand holding the barometer in a vertical position, which 

 a little practice will render very easy. The index must then 

 be moved by the knob till its under surface, as before stated, 

 is tangent to the mercury. A few light taps should be given 

 to the tube, to ascertain that the mercury has fallen as low 

 as it can. The height being then read off and registered, 

 together with that of the attached thermometer, tiie brass 

 tube is turned back, so as to cover the slits ; the instrument 

 gently inverted, and the whyle is finished. All this may be 

 done in two minutes. 



It may not he improper here to add, that I have found 

 by experience that it is not necessary to quit the chaise in 

 order to make observations with this b-trometer; it is only 

 requisite for the horses to stand still. The thermometer, if 

 held at arm's length out of the chaise window, v»-ili give the 

 temperature exactly, before the order is given to slop the 

 carriasfe: and the delav to the traveller will not much ex- 

 ceed a minute, as the observation may be read off and writ- 

 ten down while the carriage is again going on. 



The most convenient mode for deducino; the heiizhts from 

 the barometrical observations is, certainly, by the common 

 logarithmic tables ; and it is unnecessary here to detail tlie 

 method, wliieh may be found in nunjcrous hooks. It is, 

 however, necessary for this method to carry the tables of lo- 

 garithms, which is sometimes inconvenient. Tlie engraved 

 table formed by Mr. Ramsden is on a single narrow sheet, 

 and extremely portable, besides being very easy in its use; 

 but it may be lost or mislaid when wanted. Several inge- 

 nious formulce have been devised, which 'niciy either be en- 

 graven on the instrument itself, or committed to memory. 

 Of the former, sir Georgx; Shuekburgh has given a very con- 

 cise one, in his second paper on the measurement of heights 

 by the barometer, in the (3Sth volume of the Philosophical 

 Transactions ; and Mr. Professor Leslie has invented a very 

 elegant one of the latter sort ; but these, though very simple 

 in form, require a considerable number of figures in the ope- 

 ration, and are, on that account, inconvenient. For the 



D 3 purpose. 



