Table XVII. 



The following Table, calculated after that of Schumacher, has been adopted by the 

 Committee of Physics and Meteorology of the Royal Society of London. It gives 

 immediately the correction for every degree of Fahrenheit, and for every half-inch 

 from 20 up to 31 inches. The scale of the barometer is supposed to be of brass, 

 extending from the cistern to the top of the mercurial column. The difference of ex- 

 pansion of brass and mercury is taken into account. The standard temperature of 

 tlw yard being 62° Fahr., and not 32° Fahr., the difference of expansion of the scale 

 and of the mercurial column carries the point of no correction down to 29° Fahr. 

 Therefore, from 29° up the correction must be subtracted from, from 29° down it must 

 be added to, the observed height. 



Examples of Calculation. 



Barometer, observed height, 30.231 



Attached thermometer 82° Fahr. 



See in the last page the column of 30 inches ; go down as far as the horizontal 

 hne corresponding with 82° in the first vertical column, which contains the tempera- 

 tures ; you will find there the correction — .143. We have thus : — 



Barometer, observed height, 30.231 



SwJiracfiue correction for 82° Fahr., . . . — 0.143 



Barometer at 32° Fahr., . . . 30.088 



Barometer, observed height, ..... 29.743 



Attached thermometer 25° Fahr. 

 The column of 29.5 inches opposite to 25° Fahr. gives an 

 additive correction of, ....... . -|~^'^^^ 



Barometer at 32° Fahr., . . . 29.752 



It will be easy to apply also the correction for fractions of a degree Fahrenheit ; 

 for example : — 



Barometer, observed height, ..... 28.358 



Attached thermometer 71.3 

 In the column of 28.5 inches, we find that the difference between 

 the correction for 71° and that for 72° is .003; dividing this differ- 

 ence proportionally to the fraction, we have for three tenths of a de- 

 gree a correction of — .001, which added to — .108, the correction 

 for 71°, makes a total correction of, .... — .109 



And barometer at 32* Fahr., . . . 28.249 

 65 



