he was allowed to put a bend in the blast-main. After many
years of perseverance, he was, however, at length enabled to work out
his plan into a definite shape at the Clyde Iron Works, and its
practical value was at once admitted. At the meeting of the Mechanical
Engineers' Society held in May, 1859, Mr. Neilson explained that his
invention consisted solely in the principle of heating the blast
between the engine and the furnace, and was not associated with any
particular construction of the intermediate heating apparatus. This,
he said, was the cause of its success; and in some respects it
resembled the invention of his countryman, James Watt, who, in
connection with the steam-engine, invented the plan of condensing the
steam in a separate vessel, and was successful in maintaining his
invention by not limiting it to any particular construction of the
condenser. On the same occasion he took the opportunity of
acknowledging the firmness with which the English ironmasters had stood
by him when attempts were made to deprive him of the benefits of his
invention; and to them he acknowledged he was mainly indebted for the
successful issue of the severe contests he had to undergo. For there
were, of course, certain of the ironmasters, both English and Scotch,
supporters of the cause of free trade in others' inventions, who sought
to resist the patent, after it had come into general use, and had been
recognised as one of the most valuable improvements of modern times.[3]

The patent was secured in 1828 for a term of fourteen years; but, as
Mr. Neilson did not himself possess the requisite capital to enable him
to perfect the invention, or to defend it if attacked, he found it
necessary to invite other gentlemen, able to support him in these
respects, to share its profits; retaining for himself only three-tenths
of the whole. His partners were Mr. Charles Macintosh, Mr. Colin
Dunlop, and Mr. John Wilson of Dundyvan. The charge made by them was
only a shilling a ton for all iron produced by the new process; this
low rate being fixed in order to ensure the introduction of the patent
into general use, as well as to reduce to a minimum the temptations of
the ironmasters to infringe it.

The first trials of the process were made at the blast-furnaces of
Clyde and Calder; from whence the use of the hot blast gradually
extended to the other iron-mining districts. In the course of a few
years every furnace in Scotland, with on