SCALE OF THE BAROMETER* 105 



communicated to Lord Melville, when Treasurer of the 

 Nayy, in 1792: whether the lifeboat were borrowed from it 

 is more questionable. 



Mr. Bremner also takes this opportunity of asserting hia *"* of locate 

 claim to the invention of applying locks to cannon, >vhich he 

 communicated to the lale ^ir Charles Douglas so long ago 

 as the year 1768. 



III. 



On the Scale ofth^ Barometer, and the Consiruction of an ♦ 



Airptimp for procuring a perfect Vacuum, In a Letter 

 from a Correspondent, 



To Mr. NICHOLSON, 

 SIR, 



JL FEEL much obliged by the insertion of ray paper on 

 the Airpump, in your very valuable Journal. Should the ^, ^^ *-* 

 following hint, respecting the construction of the barometer, 

 (which is at least new to myself,) appear to be worthy the at- 

 tention of your readers, it is much at your service. 



In Mr. Dalton's Meteorological Observations, page 7, obser^ationsof 

 where he is speaking of the barometer, I find the following the scale of tke 

 remark: *'The scale in strictness ought not to be full *'*^™^®'' 

 ** inches, but something less, owing to the rising and falling 

 «< of the surface of the reservoir. If the tube have a bulb, 

 ** then the area of the surface at the top of the column, di« 

 " vided by the sum of the areas of the top and reservoir, 

 *' will give the part to be dedufted; but if the tube be 

 ** straight, then the whole area of the reservoir, lessened by 

 ** the area of the glass annulus, made by a horizontal sec- 

 ** tion of the erected tube, must be used as the denomi- 

 " nator of the fraction ; hence, if the fraction be ^V* then 

 •* the scale of 3 inches must be diminished by half a tenth." 

 At page 9 the following observation occurs. "With re- 

 «* spect to the barometers at Kendal and Keswick, they 

 " were both clear of air and moisture, and exhibited the 

 •* electric light in the dark. The scales were both full 

 ** inchesj and therefore the variations were somewhat greatef 



♦Vthai^ 



