of the Moist-bulb Hygrometer. 291 
caiculated dew-points, instead of being lower, should be higher than the truth. In 
order, in fact, to account for the discrepancy in question, supposing it to be well 
established, it would be necessary to conclude either that m, the co-efficient of our 
hygrometric formula, is assumed somewhat too great, or that the observed depressions 
are a little too small. The first, I believe, to be the true solution, and am, at pre- 
sent disposed to consider m as more correctly represented by the fraction = than 
= This point, however, I have not as yet been able fully to satisfy myself upon, 
nor can the more exact determination of the value of the constant be considered a 
matter of much practical importance, since the formula, in its present state, conducts, 
as we have seen, to results which harmonize admirably with each other and with 
observation. 
I shall conclude by su}joining a couple of tables, by the aid of which the applica- 
™ nt to ‘ . . s = 
tion of my formula f”=f ~ a Xa to the determination of the dew-point, is 
greatly facilitated. Table (A), which I have taken from the Edinburgh Encyclo- 
pedia, article hygrometry, gives the elastic force of the vapour of water for every 
: ne : d 1 
degree Fahrenheit between 0° and 100" inclusive. Table (B) gives ea for every 
( U 
value of d between | and 10. This quotient, as is obvious from a glancez at the 
formula, is, in calculating an observation, to be multiplied by p the existing pressure, 
and the product, when deducted from J’, as given by table (A), will afford f”, or the 
tension of vapour, at the dew-point. Should the depression exceed 10° the value of 
d : ona : 1 
a7xgo May still be got from table (B) by addition. Thus if d= 13°, s7e30= 
-00383 + .00114= .00497. 
Taste (A.) 
+ 
~ 
~> 
~ 
. 
Ss 
” 
if ap Ff 
-06121 | 21 | -13408 | 41 | .27376 | 61 | .54089 | 81 | 1.03350} 
-06359 | 22 | -13906 | 42 | .28346 | 62 | .55913 | 82 | 1.06656 | 
06605 | 23 | .14421 | 43 | .29848 | 63 | .57795 | 83 | 1.10058 | 
06861 | 24 | .14954 | 44 | .30384 | 64 | .59735 | 84 | 1.13559 
.07126 | 25 | .15506 | 45 | .31453 | 65 | .61734 | 85 | 1.17161 
07401 | 26 | .16076 | 46 | .52557 | 66 | .63795 | 86 | 1.20867 | 
07685 | 27 | .16667 | 47 | .33684 | 67 | .65919 | 87 | 1.24680 
.07980 | 28 | -17277 | 48 | -34875 | 68 | .68108 | 88 | 1.28602 
| .08286 | 29 | -17908 | 49 | -36090 | 69 | .70364 | 89 | 1.32636 | 
| .08603 | 20 | -18561 | 50 | -37345 | 70 | .72688 | 90 | 1.36785 | 
10 | .c8931 | 31 | -19237 | 51 | -38640 | 71 | .75083 | 91 | 1.41059 
11 | .09270 | 32 | -19934 | 52 | -39977 | 72 | .77551 | 92 | 1.45438 | 
12 | .09622 | 33 | -20658 | 53 | -41356 | 73 | .80092 | 93 | 1.49948 | 
3 | .09987 | 34 | -21404 | 54 | -42779 | 74] .82710 | 94 | 1.54585 
14 | .10364 | 35 | -22175 | 55 | -44249 | 75 | .85407 | 95 | 1.59352 
15 | .10755 | 36 | -22972 | 56 | 45764] 76 | .88184 | 96 | 1.64251! 
16 | -11160 | 37 | -23796 | 57 | 47328 | 77 | .91042 | 97 | 1.69286, 
17 | .11579 | 38 | -24647 | 58 | *48940 | 78 | .93987 | 98 | 1.74461 
18 | .12013 | 39 | -25527 | 59 | *50604 | 79 | .97017 | 99 | 1.79778 
19 | .12462 | 40 | -26436 | 60 | °52320 | 80 | 1.00137 | 100 | 1.85241 
20 | .12927 | 
VOL. XVII. 3M 
SoOortnankwworeo 
