APPENDIX C. 



CALCULATION OF LOG. FACTORS. 



Let AV be the weight of mercury which would take the place of the liquid in 

 the piezometer, w that of the mercury which fills a length I of the stem. Then a 

 compression read as x on the stem is 



X w 



rw 



This assumes the stem to be uniform ; in general it must be corrected from the 

 results of the calibration : — unless, as in the example given on p. 16 of the text, / be 

 chosen very nearly ecpaal to x, as found by trial for each value of the pressure. 



Also if y be the reading of the gauge, and if a on the gauge correspond to an 



atmosphere, the pressure is 



-i aim. 

 a 



Hence the average apparent compressibility per atmosphere is 



x wa 



lj Tw- 



its logarithm is 



log. x - log. y + (log. w - log. W - log. I) + log. a. 



The last four terms', of which log. a is the "gauge log.," form the log. factor as 



oiven in the text 



C3 



