Its convenience arises not merely from saving the servant or
workman useless journeys to receive directions, but from
relieving the master himself from that indisposition to give
trouble, which frequently induces him to forego a trifling want,
when he knows that his attendant must mount several flights of
stairs to ascertain his wishes, and, after descending, must mount
again to supply them. The distance to which such a mode of
communication can be extended, does not appear to have been
ascertained, and would be an interesting subject for enquiry.
Admitting it to be possible between London and Liverpool, about
seventeen minutes would elapse before the words spoken at one end
would reach the other extremity of the pipe.
8. The art of using the diamond for cutting glass has
undergone, within a few years, a very important improvement. A
glazier's apprentice, when using a diamond set in a conical
ferrule, as was always the practice about twenty years since,
found great difficulty in acquiring the art of using it with
certainty; and, at the end of a seven years' apprenticeship, many
were found but indifferently skilled in its employment.
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