Co Description of the Mounta'm Barometer. 



again, and note the time. IF the baromelcr has altered in 

 the interval, a simple proportion eoirects cither oi" the three 

 observations, and reduces the height to what would have 

 (>ccn observed had the nicrenry been stationary. . It is true 

 that this method supposes the motion of the mercury to have 

 been uniform during the interval of observation ; but except 

 in very variable weather, wliich does not often occur, par- 

 ticularly in summer, when the greater numl)er of these ob- 

 servations will naturally be made, this supposition is liable 

 to but small error. It is also true, that a traveller has often 

 jio opportunity of making a second observation at the spot 

 he sets out from. Even in this case, a near ap[)roximatiou 

 ^nay oflen be made by observing, for example, at a stream 

 on eueh side of the hill to be measured. Jf also he observes 

 the barometer repeatedly in the morning before he sets out, 

 and sets its tendency, and does the same at every halt, during 

 the day, he will have data whereon to found a nearly accu- 

 rate correction. But if all tliis should be out of his power, 

 even under the most unfavourable circumstances, barome- 

 trical obi«crvations will give a much more accurate idea of 

 the outline of a country than any we now ptjssess; and it 

 should be ever remembered, that observations though defec- 

 tive, if carefully made, and faithfully recorded, are valua!)le, 

 and if repeated by diflerent travellers the errors vvill, in most 

 cases, compensate each other, and from the whole very ac- 

 curate conclusions may be drawn. 



I have entered into a greater detail than would be neces- 

 sary for a greater part of your readers, in the liope of being 

 intelligible to those who are less acquainted wiih the sub- 

 ject, and who may wish to employ any instrument-maker 

 for the construction of barometers sinular to that which I 

 have described. 



Injustice to a very ingenious young artist, permit me.to 

 add, that I h:i,ve employed in making those which 1 have, 

 Mr. Thomas Jones, of No. li?4, Mount-street, Berktlcy- 

 fcqnare (pupil of the late Mr. Kamsden), and who makes 

 them complete at the price of three iz;uineas and a half, wiih 

 ^ short scale reading from 25 to 31 inches 3 and four gui- ' 

 'i neas 



