e exception (that at Carron),
had adopted the improvement; while it was also employed in half the
furnaces of England and Wales, and in many of the furnaces on the
Continent and in America. In course of time, and with increasing
experience, various improvements were introduced in the process, more
particularly in the shape of the air-heating vessels; the last form
adopted being that of a congeries of tubes, similar to the tubular
arrangement in the boiler of the locomotive, by which the greatest
extent of heating surface was provided for the thorough heating of the
air. By these modifications the temperature of the air introduced into
the furnace has been raised from 240 degrees to 600 degrees, or the
temperature of melting lead. To protect the nozzle of the air-pipe as
it entered the furnace against the action of the intense heat to which
it was subjected, a spiral pipe for a stream of cold water constantly
to play in has been introduced within the sides of the iron tuyere
through which the nozzle passes; by which means the tuyere is kept
comparatively cool, while the nozzle of the air-pipe is effectually
protected.[4]

This valuable invention did not escape the usual fate of successful
patents, and it was on several occasions the subject of protracted
litigation. The first action occurred in 1832; but the objectors
shortly gave in, and renewed their licence. In 1839, when the process
had become generally adopted throughout Scotland, and, indeed, was
found absolutely essential for smelting the peculiar ores of that
country--more especially Mushet's Black Band--a powerful combination
was formed amongst the ironmasters to resist the patent. The
litigation which ensued extended over five years, during which period
some twenty actions were proceeding in Scotland, and several in
England. Three juries sat upon the subject at different times, and on
three occasions appeals were carried to the House of Lords. One jury
trial occupied ten days, during which a hundred and two witnesses were
examined; the law costs on both sides amounting, it is supposed, to at
least 40,000L. The result was, that the novelty and merit of Mr.
Neilson's invention were finally established, and he was secured in the
enjoyment of the patent right.

We are gratified to add, that, though Mr. Neilson had to part with
two-thirds of the profits of the invention to secure the capital and
influence necessary to bring it into general use, he realize