287 



TABLE XX . 



This table has been calculated by using the same coefficients of dilatation as in the 

 preceding table, viz. : — 



Brass, linear dilatation, from LaplacG a*id Lavoisier for 100°C. = 0.0018782. 



Mercury, dilatation in volume, from Dulong and Petit for 100°C.= 0.0180180. 



Dilatation of the mercurial column for 100° C. . . . = 0.0161398. 



Dilatation of the mercurial column for 1°C. . . . = 0.0001614. 

 This table, calculated for the reduction of long series of meteorological observa- 

 tions, gives immediately the value of the correction for each tenth of a degree up to 

 35° C. above, and down to 35° C. below, the freezing point, and for mercurial columns 

 extending from 605 to 800 millimetres. 



Examples of CalcuJafion. 



mm. 



Barometer, observed height, ..... 754.17 



Temperature of the attached thermometer, -f-17°.8. 

 For finding the correction, seek in the horizontal column, headed haromeier, at the 

 head of the pages, the corresponding height of the barometer; it will be found, p. 31, 

 barometer 755""" (from 752.50 to 757.50) ; next seek in the first vertical colmrm, 

 containing the temperatures, 17°, follow then horizontally this line as far as the col- 

 umn of 8 tenths, and you find there 2.17 millimetres, which is the correction, or the 

 quantity to be subtracted for reducing the observed height to zero. We have thus : 



mm 



Observed height, ..... 754.17 



Subtr active correction for -\-\7°. 8 = . . . — 2.17 



Barometer at zero, 752.00 



If the temperature is below zero, the correction will be additive. 



mm. 



Observed height, 729 72 



Temperature of the attached thermometer, — 8°. 4. 

 Additive correction. ...... -j-0.99 



Barometer at zero, 730.71 



r1 



