214 
These experimeBts also prove conclusively that the 
coefficients which have hitherto been applied to the effiux 
of air below 151bs. effective pressure derive nearly the whole 
of their value from the phenomenal changes of resistance 
between the discharging and receiving atmospheres, and not 
from the forms of the orifices and lengths of the adjutages, 
as in the discharge of inelastic fluids. 
Applying the coefficient *937 to the velocity with which 
the atmosphere of 151bs. absolute pressure rushes into a 
vacuum, before expansion, as deduced in Table II. in my 
633 
former paper. We have V = = 677 feet per second, or 
approximately one half the velocity due to the height of 
the homogeneous atmosphere. 
The following approximate velocities with which atmos- 
pheres of several gases of I51bs. absolute pressure rush into 
a vacuum through an orifice of the best form, before 
expansion, have been calculated on the basis of Graham’s 
law of the velocities of effiux for equal pressures being 
inversely as the square roots of the specific gravities. 
Air 1*000 X 677 = 677 feet per second. 
Oxygen ... 0*950 x 677 = 643 „ „ 
Nitrogen ... TOlSx 677 = 687 „ ,, 
Hydrogen ... 3*800x 677 = 2572 „ „ 
Saturated steam T445 x 677 = 978 „ „ 
“ On the determination of the Calorafic power of fuel by 
direct Combustion in Oxygen,” by William Thomson, 
F.H.S. Ed., F.C.S. 
Having been engaged some time ago with determinations 
of the heating power of various samples of coal by the 
apparatus devised by Mr. Lewis Thompson, M.H.C.S., I was 
struck by the unsatisfactory nature of the process, which 
consists in mixing intimately 2 grammes of coal with 
22 grammes of a mixture of 3 parts of chlorate and 1 part 
