. 
92 REPORT—1845. 
of calculation laid down, on each of which statistical criticism found cause for objec- 
tion and correction. 1. Taking the number of houses, and an average to each house : 
the fallacy of result from this mode was illustrated by reference to various countries, 
at their various stages in the progress of civilization, and by the different ‘habits of 
persons in the same district of the same country which affected the average number 
of persons in each house. 2. The estimate of population from the records of deaths, 
births, and marriages was still more fallacious, Among other illustrations, he men- 
tioned his having known of five marriages between six people, with only three chil- 
dren as a result; and such perturbating influences are frequent. 3. Comparing a 
certain part of the population,—as, for instance, those capable of bearing arms, an 
element often occurring in history; to which he believed that more value was to be 
attached than any of the preceding methods. 4. Actual enumeration; of course the 
the most perfect method, but one requiring a more complete machinery than had been 
hitherto applied, 
MECHANICAL SCIENCE. 
On Nasmyth’s Steam Hammer for Pile-driving. By Ricuarv Greene, M.D. 
Turs machine consists of a steam cylinder, closed at the bottom, but with openings 
in the top to allow the passage of air: a piston works in it, having its rod passing 
through a steam-tight aperture in the bottom, To this piston-rod the monkey or 
driver, which weighs 23 tons, is attached, and is thus suspended. The machine is 
worked by high-pressure steam, which, being admitted at the bottom of the cylinder 
by the induction-pipe, raises the piston, and with it the monkey attached to it. The 
instant it arrives at the height required it closes the induction-pipe, and opening 
the eduction-pipe (also at the bottom of the cylinder), the steam escapes, and the 
piston with the monkey attached to its rod falis freely upon the head of the pile. 
A large heavy cap of iron, with a hole to allow the bead of the pile to pass through, 
slides between two upright standards and guides the direction of the pile. The mon- 
key and cylinder also follow the course of the pile, guided by the same uprights, be- 
tween which they slide. 
Dr.’Greene then added, on the authority of the inventor, the following report of the 
performance of the machine :— 
In the first trial with a part of the machine at the manufactory, it drove a pile 
fourteen inches square and eighteen feet in length, fifteen feet into the ground with 
twenty blows of the monkey, the machine then working seventy strokes a minute 
(the ground was a coarse gravel imbedded in a strong tenacious clay), and performed 
this work in seventeen seconds. The entire machine is now in full action at Devon- 
port for the embankment to be erected there to keep out the sea, and forms an im- 
mense wet dock to contain the royal steam navy. ‘he operations required to be 
performé@ on each pile from the time it is floated alongside of the stage, until it is 
imbedded in the solid foundation of slate-rock, occupy only 45 minutes. ‘The great 
stage which carries the machine, boiler, workmen, and everything necessary, trots 
along on its railway like a wheelbarrow. Having driven one pile it moves onward, 
the space of the diameter of another; it picks the pile up out of the water, hoists it 
high in the air, drops it into its exact place, then covers it with the great iron cap, 
which follows it as it sinks into the ground: then thump goes the monkey on its head, 
jumping away seventy-five jumps a minute. At the first stroke the pile sunk six feet, 
its advance gradually diminishing, until in the hard ground above the solid slate-rock 
it was reduced to nine inches. 
Nothing can better prove the superiority of the principle of this invention, of em- 
ploying a heavy weight moving with small velocity, instead of a light weight moving 
with great velocity, than the state of the heads of the piles as driven by the two 
methods. 
Dr. Greene called attention to a sketch of two heads of piles. One was fifty-six feet 
long, driven by a monkey of 12 cwt., falling from a great height, and making only one 
blow in five minutes, and requiring twenty hours to drive it; this, though protected 
