On rollers between wood 1/50


At each increase of knowledge, as well as on the contrivance
of every new tool, human labour becomes abridged. The man who
contrived rollers, invented a tool by which his power was
quintupled. The workman who first suggested the employment of
soap or grease, was immediately enabled to move, without exerting
a greater effort, more than three times the weight he could
before.(5*)

6. The economy of human time is the next advantage of
machinery in manufactures. So extensive and important is this
effect, that we might, if we were inclined to generalize, embrace
almost all the advantages under this single head: but the
elucidation of principles of less extent will contribute more
readily to a knowledge of the subject; and, as numerous examples
will be presented to the reader in the ensuing pages, we shall
restrict our illustrations upon this point.

As an example of the economy of time, the use of gunpowder in
blasting rocks may be noticed. Several pounds of powder may be
purchased for a sum acquired by a few days' labour: yet when this
is employed for the purpose alluded to, effects are frequently
produced which could not, even with the best tools, be
accomplished by other means in less than many months.

The dimensions of one of the blocks of limestone extracted
from the quarries worked for the formation of the breakwater at
Plymouth were 26 1/2 ft long, 13 ft wide, and 16 ft deep. This