_--The force necessary to move a stone along
the roughly-chiselled floor of its quarry is nearly two-thirds of its
weight; to move it along a wooden floor, three-fifths; by wood upon
wood, five-ninths; if the wooden surfaces are soaped, one-sixth; if
rollers are used on the floor of the quarry, it requires
one-thirty-second part of the weight; if they roll on wood,
one-fortieth; and if they roll between wood, one-fiftieth of its weight.
At each increase of knowledge, as well as on the contrivance of every
new tool, human labour becomes abridged.
_Economy of time._--Several pounds of gunpowder may be purchased for a
sum acquired by a few days' labour; yet, when this is employed in
blasting rocks, effects are produced which could not, even with the best
tools, be accomplished by other means in less than many months.
_Economy of Materials._--The worn-out saucepans and tin-ware of our
kitchens, when beyond the reach of the tinker's art, are not utterly
worthless. We sometimes meet carts loaded with old tin kettles and
worn-out iron coal-scuttles traversing our streets. These have not yet
completed their useful course; the less corroded parts are cut into
strips, punched with small holes, and varnished with a coarse black
varnish for the use of the trunkmaker, who protects the edges and angles
of his box with them; the remainder are conveyed to the manufacturing
chemists in the outskirts of the town, who employ them, in conjunction
with pyroligneous acid, in making a black dye for the use of calico
printers.
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