BAROMETRICAL, TABLES. XVll 



28.°5 Fahrenheit, and this is therefore the standard temperature to which 

 all readings are reduced. For temperatures above 28°5 Fahrenheit, the 

 correction is subtractive, and for temperatures below 28°. 5 Fahrenheit, the 

 correction is additive, as indicated by the signs ( + ) and ( — ) inserted 

 throughout the table. 



The table gives the corrections for every half degree Fahrenheit from 

 0° to 100.° The limits of pressure are 19 and 31.6 inches, the corrections 

 being computed for every half inch from 19 to 24 inches, and for every 

 two- tenths of an inch from 24 to 31.6 ipches. 



Example : 



Observed height of barometer = 29.143 



Attached thermometer, 54^5 F. 



Reduction for temperature = — 0.068 



Barometric reading corrected for temperature = 29.075 



TABLE 11. 



Table 11. Reduction of the barometer to standard temperature — Metric 

 measures. 



For the metric barometer the formula for reducing observed readings to 

 the standard temperature, 0° C, becomes 



I + mt 



in which C and B are expressed in millimetres and / in Centigrade 



degrees. 



m = 0.00018 18 ; / = 0.0000184. 



In the tables, the limits adopted for the pressure are 440 and 795 mil- 

 limetres, the intervals being 10 millimetres between 440 and 600 milli- 

 metres, and 5 millimetres between 600 and 795 millimetres. 



The limits adopted for the temperature are 0° + and + 35°8, the 

 intervals being o.°5 and ifo from 440 to 560 millimetres, and o°2 from 560 

 to 795 millimetres. 



For temperatures above 0° Centigrade the correction is negative, and 

 hence is to be subtracted from the observed readings. 



For temperatures below 0° Centigrade the correction is positive, and 

 from 0° C. down to — 20° C. the numerical values thereof, for ordinary baro- 

 metric work, do not materially differ from the values for the corresponding 

 temperatures above 0° C. Thus the correction for — 9° C. is niunerically 

 the same as for + 9° C. and is taken from the table. In physical work of 

 extreme precision, the numerical values given for positive temperatures may 

 be used for temperatures below 0° C. by applying to them the following 

 corrections : 



