Western engines, on which he lays such stress, is 2,300 square feet,
and the table which he gives of the heating surface of various English
engines really means very little. It is quite true that there are no
engines working in England with much over 1,500 square feet of
surface, except those on the broad gauge, but it does not follow that
because they manage to make an average of 53 miles an hour that an
addition of 500 square feet would enable them to run at a speed higher
by 20 miles an hour. There are engines in France, however, which have
as much as 1,600 square feet, as, for example, on the Paris-Orleans
line, but we have never heard that these engines attain a speed of 80
miles an hour.

Leaving the question of boiler power, M. Nansouty goes on to consider
the question of adhesion. About this he says:

Is the locomotive proposed by M. Estrade under abnormal conditions as
to weight and adhesion? This appears to have been doubted, especially
taking into consideration its height and elegant appearance. We shall
again reply here by figures, while remarking that the adhesion of
locomotives increases with the speed, according to laws still unknown
or imperfectly understood, and that consequently for extreme speeds,
ignorance of the value of the coefficiency of adhesion f in the
formula

d 2 I
fP = 0.65 p ------- - R
D

renders it impossible to pronounce upon it before the trials earnestly
and justly demanded by the author of this new system. In present