Page:On the economy of machinery and manufactures - Babbage - 1846.djvu/433

Rh traces in the sand; but if it is put in high above that point, the part in contact with the sand will have become solid before the temperature of the central parts has sunk to that at which it begins to expand, and thus the expansion will probably all take place in the direction of the jet by which the metal entered.

It is much to be regretted that this beautiful manufacture seems to be declining; a circumstance which is attributed mainly to the insufficiency of the protection afforded to new designs. These are originally produced at great expense to the manufacturers, and when once sold to the public are immediately copied by other manufacturers, who, not having contributed to that expense, can easily undersell the original introducers of them. The copies are frequently inferior to the original, and the successive copies becoming gradually deteriorated, have introduced a bad article amongst the smaller manufactures, which greatly injures the foreign trade.

(451.) The length of all the roads in the Prussian monarchy amounts at present (1833) to 6766 English miles. The length of all the navigable rivers, excepting those parts joining the sea, is about 2,800 English miles.