192 
On Hygrometnj. 
To apply these to the experiments in question, we must consider, that as the a. 
was dry /= 0. The values of A and e must be determined from the observations 
themselves ; to do this the formula will become 
±=h (E) 
e D‘- 233 B 
We will now take one of the results in page 80 to determine the numerical value 
of this equation. The temperature of the air was 60°, surface of evaporation 39°, 9, 
Depression 20,1 Barometer 29.27*. 
Now in the above equation 
B (Barometer) = 29, 27. 
D (Depression) = 20, 1. 
F (Force of vapour due to temperature of evaporating surface) for 39°, 9 = 
,2635 inch. 
L (proportion of mass of water to the vapour required to be evaporated to 
produce a fall of 1°.) for 39. 9 =895,9 f 
The calculation will now stand thus 
Log. of F' (,2635 inch) 9,42078 
Log. of 30 1,47712 
Log. of L ( 895,9) 2,95226 
Log. of D > • 2 3 3 Log. of 20", 1 X 1,233) Ar. Co. 8,40619 
Log. of B. (29,27) Ar. Co. 8,53358 
Log. of — = sum 0,78993 
e 
In this manner the value of the constant logarithm was found for each obser- 
vation; these values are as follows. 7899, 7732, 7763, 7840, 7859, 7872, 7837, 
7771 and 7505, the index being 0. 
These agree sufficiently well, with the exception of the last, and there appears to 
be some anomaly in that observation. The mean of the first eight is 0.7822 and of 
the whole 0.7787. The first answers to the N. N. 6 056 and the latter 6.008. The 
formula (C) divided by A and multiplied by e will then become 
- L (P-/) 30 - 
6.056 B 
And extracting the root, 
= / (L fF'-/) 30 W.,, 
\ 6.056 B / 
Taking/= 0, B = 30, and substituting for F' and L the values due to each of 
the temperatures 40°,45,50,55,60,65,70,75, 80, 1 find the following series. 
Temperature of air. 
Temperature of evapo- 
rating surface. 
Depression. 
Deg. of Fah. 
142.10 
129.11 
117,05 
105,86 
95,40 
85,62 
76,42 
67,57 
59,60 
Deg. of Fah. 
80 
75 
70 
65 
60 
55 
50 
45 
40 
Deg. of Fah. 
62°, 10 
54,11 
47,05 
40,86 
35,40 
30,62 
26,42 
22,57 
19,60 
* Mean of all the observations, page 79. 
t As the publication referred to in my former paper for the value of L may not 
be at hand, 1 subjoin a few values which will lie sufficient for verifying these calcu- 
lations, or making new ones : 40°898, 50°919, 6o°941, 70°962, 80°983, 90°1005. 
