Memorials of the lineage, early life, education and development of the genius of James Watt

JAMES WATT. 225
interesting, and may be given at length, simply altering the ortho-
graphy, as it has not hitherto been quoted in this country.
" The expense of a patent in France is 300 livres for three years,
800 do. for ten years, and 1500 do. for fifteen years. There can be
no difficulty in obtaining a patent for the mode of propelling a boat,
which you have shown me. But if the author of the model wishes to
be assured of the merits of his invention, before he goes to the expense
of a patent, I advise him to make the model of a boat in which he can
place a clock-spring which will give about eight revolutions. He can
then combine the movements so as to try oars, paddles, and the leaves
which he proposes. If he finds that the leaves drive the boat a greater
distance in the same time than either oars or paddles, they consequently
are a better application of power. About eight years ago the Earl of
Stanhope tried an experiment on similar leaves, in Greenland Dock,
London, but without success. I have also tried experiments on similar
leaves, wheels, oars, paddles, and flyars, similar to those of a smoke
jack, and found oars to be the best. The velocity with which a boat
moves is in proportion as the sum of the surfaces of the oars, paddles,
leaves, or other machine, is to the bow of the boat presented to the
water ; and in proportion to the power with which such machinery is
put in motion. Hence if the sum of the surfaces of the oars is equal
to sum of the surfaces of the leaves, and they pass through similar
curves in the same time, the effect must be the same. But oars have
this advantage, — they return through air to make a second stroke,
and hence create very little resistance ; whereas the leaves return
through water, and add considerably to the resistance, which is in-
creased as the velocity of the boat is augmented. No kind of
machinery can create power ; all that can be done is to apply the
manual, or other power, to the best advantage.
" If the author of the model is fond of mechanics, he will be much
amused, and not lose his time by trying the experiments in the manner
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