of Barometrical Mensuration. 91 



Temp, of air at lower station 55 Dew point 40 

 Do. upper station 51 i Do. 38 



Mean 53^ 

 Expansion of air, per Table, at 53« .04374 

 1.00000 

 - 04374 



.95626 Specific gravity oi' air corrected for temperature. 

 Expansion of air for vapour at 40^ per Table, .00876 



- Increase of density for ditto j!!f!l .00345 



Expansion of air for vapour, at 38° . . . .00816 



_ Increase of density -^^^^^ ^^^^^i 



.00666 



Mean .00333 



.95626 

 — .00333 



.95293 correct specific gravity of atmosphere. Then 



Approx. Correct 

 height. height. 



.95293 : 1.00000 :: 1214 : 1273 



Art. VIII. Account of a Steam-Engine Indicator. 



[In a Letter to the Editor.] 



Glasgow, UthFeb. 1822. 

 This instrument which has been long known to engineers, 

 thoughlbelieve never publicly described, originated with our 

 illustrious countryman, the late Mr. Watt. That which was 

 employed in our works was made from a description of the 

 instrument given to us by Mr. Field, of London, and was ap- 

 plied with the view of ascertaining in what part the extraordi- 



