32 Mr. Davies Gilbert on the expediency of assigning 
gallons of water each minute in the form of steam, unassisted 
by centrifugal force, while the pressure amounts to no more 
than 14,66 pounds. The other factor (velocity) must therefore 
be made proportionably great to produce an adequate effect. 
Now, since air rushes into a vacuum with the velocity of 
1295 feet in a second _ - _ log. 3.1122698 
And steam at 212® is said to have a specific 
gravity compared to air of 0.6235 
Log. 9.7948365 -r 2 = 9.8974183 arith. comp. 0,1025817 
A velocity of 1640 feet in a second 3.2148515 
Three quarters of this velocity in rotation will be requisite 
for imparting an efficiency to the machine of about one 
half of the efficiency expended. But such a velocity nearly 
equals that of a cannon shot, and the effect of centrifugal 
force on the arms (-^) would produce a strain equal to the 
weight of 41776 feet of the material composing them, inde¬ 
pendently of the strain arising from centrifugal force of the 
fluid they contain. And as the modulus of tenacity for iron is 
estimated at 14800 feet, the centrifugal force will exceed that 
tenacity almost three times. But independently of this insu¬ 
perable obstacle, any velocity adequate to the production of 
an useful efficiency must be utterly unmanageable in every 
other respect; nor is it easy to imagine the possibility of any 
expedient, similar to the air pump of Mr. Watt, for maintain¬ 
ing the vacuum in which their arms are to revolve. 
The Steam Engine. 
To estimate the efficiency of steam acting uniformly with 
its entire force, at a power corresponding to 30 inches of 
barometrical pressure, in reference to the consumption of one 
bushel of coal, I assume, from repeated experiments, that 
