140 Introduction to Boileau's [No. 147. 



would be obtained by the simple subtraction of two tabular numbers ; 

 but since p and/' are both variable, and the possible number of dif- 

 ferent readings of each within the limits of observation is very great, 

 the former being recorded in inches and thousandths, the latter in 

 degrees and tenths of Fahrenheit's scale, the adoption of such an ar- 

 rangement would not only have very much enhanced the labour of 

 computation, but would have swelled the table to a very inconvenient 

 size. Accordingly as regards this term, the table has been separated 

 into two parts; the first part (Table I) contains the values of .01147 

 (*—?) x fj which have been computed for all values of (t — t') to 

 tenths of a degree of Fahrenheit's Thermometer between 0° and 30° 

 and for a range of pressure between 20 and 3 1 inches, the full numeri- 

 cal values being given for whole inches of pressure, and the propor- 

 tional parts (which can be taken out to *001 of an inch) in separate 

 columns : the second part (Table II) contains the corrections necessary 

 on account of the quantity — /' omitted in the above computations, and 

 which being comparatively small, are given only for single degrees 

 for values of t — t' between 1° and 30°, and for a range of t' between 

 10° and 129° the numbers in this table were computed for depressions 

 of 1° Fahrenheit and for all the values of t' corresponding thereto, and 

 the numbers for higher depressions being simple multiples of the 

 value of t — t' = 1° have been obtained in this manner, t. e. by mul- 

 tiplication. Table III contains the elastic force of aqueous vapour or 



— « o "ho 



values of/' for every degree and tenth part between 03*9 and 145*9 



of Fahrenheit's Thermometer, and in this table each number has been 

 computed directly by the formula above-mentioned. 



It may at first sight appear, that the tables have been extended un- 

 necessarily, both as regards their range and the numerical value of the 

 entries, but the depressions at this station have compelled their exten- 

 sion to values of (t — *') = 30° Faht. and if the computed numbers 

 had been carried out in Table I, to less than 5 places of decimals, they 

 would not have exhibited, with sufficient precision, the variations of 

 the elastic force of vapour due either to the tenth part of a degree 

 of Fahrenheit's Thermometer, or to several thousandths of an inch of 

 pressure ; this number of figures in the decimal places has therefore 

 necessarily been retained : the range of temperature has been taken 

 to include all possible contingencies. 



