1844.] Hygrometric Tables. 141 



A single example will suffice to render the use of the Tables fa- 

 miliar. 



Example. — Required the elastic force of vapour in the atmosphere 

 and the temperature of dew-point, the observed temperature of a dry 

 bulb Thermometer being 49° 58 F. of a wet bulb Thermometer 36° 65, 

 F. and the height of the Barometer 23*278 inches. 



Here (*— *') = 49°58— 36°65 == I2°93 

 Enter Table I, and under the nearest depression 12°9 take out the 

 numbers corresponding to the height of the Barometer; viz. 



for 23000 ins. 011344 

 •200 „ 99 



070 „ 34 



008 „ 4 



whichgivesthe valueof -01147 {t—t')y^ = ioY 23*278 ins.=01148I 

 Correction for/ Table II, for 12°9 and 36*6 (always negative)— 115 



(a) 01147 (*—OX^-'= -. diff. 0-11366 



(b) /' from table III for 36°6 023444 



(a-b) =/" =/'— -01 147 (t— *') X ^p = • • • - diff. 0*12078 



which gives for t" the temperature of dew-point 18° 17, F. 



By Anderson's Table, going through the computations for this 

 example, we should have obtained/" = 0*12106 



and *"= 18°20Fahrt. 



When however the wet bulb Thermometer stands below 32° Fahrt. 

 the quantity a in the foregoing example requires to be corrected for 

 the difference of the co-efficient above and below the freezing point ; 

 it will suffice for all practical purposes, to subtract from the number a, 

 obtained as above, its 10 3 ~th part, the remainder taken from the 

 tabular value of/' will give the tension of atmospheric vapour and 

 deduced temperature of the dew-point as before : to prevent misappre- 

 hension an example is given. 



Example 2nd. — Required the tension of the atmospheric vapour 

 and the deduced temperature of the dew-point for the following ob- 

 servations of a dry Thermometer 28°5 F. wet bulb do. 23°7, Fahrt. 

 and Barometer 23*104 inches. 



