35 2 Dr. Ure's new experimental researches 
Or by common arithmetic, multiply or divide 28.9, accord- 
ing as the temperature is above or below 210°, by the mean 
ratio, involved to a power denoted by the number of terms. 
The product or quotient is the tension required. 
Example 1st. The temperature is 140°. What is the corres- 
ponding elasticity of the vapour from water heated to that 
point ? 
140° is 7 terms of io° each under 210°; 1.26 is the 
mean ratio = — and, consequently, r = 1.26 ; n = 7. 
Log. 28.9 = 1.46090 
Log. 1.26 x 7 = 0.10007 x 7 = — 0.70259 
0*75831, which is 
the logarithm of 5*73 2 inches. 
Experiment gives - - 5*77 > difference .04, 
inconsiderable. 
Example 2. What is the tension of steam at the tempera- 
ture of 290° ? 
„ 1.23 4 - 1.16 
r = 3 . J - - = 1.195 
Log. 28.9 
8. Log. r = 8 x 0.07737 
n = 8 
= 1.46090 
= -f- 0.61896 
Log. of 120.02 inches 2.07986 
At 290° by experiment = 120.15 
Example 3. Temperature 250°. Force of steam in contact 
with water ? 
r = 12 3 + 130 
1.215 
Log. 28.9 
4 Log. r = 4 x 0.08458 
n = 4 
= 1.46090 
= + °-i 
Log. of 62.98 
At 250° Experiment 61.90 
1.79922 
