22 Dr. Hudson on an Error in Dr. Apjohn’s Formula. 
ing = 1168—¢ (capacity of water being = 1), it follows that 
1168—t eas Up NEA | oaths 
ery x f x 327958 of water in falling 1° will give out 
the quantity of heat necessary to produce this cubic inch of 
vapour. But in the experiments with dry gases an equal 
volume (i. e. one cubic inch) of the gas falling V° produces this 
same effect; consequently (S being the weight of a cubic inch 
of the gas at ¢°) VxS gives the weight of the gas which 
would produce this effect in falling 1°; from whence it is 
obvious that 1 (the capacity of water): C (the capacity of 
1168—¢ 1168—¢ 
“ J; —____ 27 dO ae 
the gas)::S x \ 748 Lt x f x 3°27958, and C 44840: 
x a x 3:27958; or (since S’,the weight of a cubic inch of 
S x 508 MALES 
. fe} ( RSs 
the gas at 60°, = ade we have by substitution 
1168—t x f 
Gy eS Se ° 456. 
Vx’ x 006456 
Now, if V (the depression of wet thermometer) in hydro- 
gen gas be = 20° (/’, the temperature of wet ball being 48°), 
and if V in atmospheric air be = 25° (¢ being = 43°), and 
Gr. 
taking weight of cubic inch of hydrogen at 60° = 0:02153, 
Grs. 
and weight of cubic inch of air at 60° = 0°3099*; conse- 
quently, 
1120 x 34875 _ ee 
20 xc02153 © 006456 = 5°856, 
, 2 A D185 % 99848). Wow hag 
and capacity of air = STU a is 006456= 2751. 
Dr. Apjohn appears to have used ( for every gas) the weight 
of a cubic inch of air, instead of S, the weight of the particu- 
lar gas. Accordingly, the experiments (except with hydrogen) 
rather favour my view that the capacities of gases are equal 
in equal volumes. 
The same I believe to be true with hydrogen, and that 
V will be found the same in every gas (with an improved 
apparatus for trying the experiments) under similar circum- 
stances of temperature and pressure, if the current of gas be 
sufficiently powerful. 
capacity of hydrogen = 
* J have supposed P (the pressure) = 30. ‘The requisite alteration in 
1168 —t x f 
the value of S! gives C= —Vxsxp ™ 006456 x 30. 
