which the gas engines of to-day are constructed, many years elapsing
before experience enough was gained to turn the proposals of the older
inventors to practical account.

The most important of these patents are:

No. Year.
Robert Street 1,983 1794 Direct-acting engine.
Samuel Buren 4,874 1823 Vacuum engine.
Samuel Buren 5,350 1826 Vacuum engine.
W.L. Wright 6,525 1833 Direct-acting engine.
Wm. Barnett 7,615 1838 Compression first proposed.
Barsante & Matteucci 1,072 1854 Rack & clutch engine.
Drake 562 1855 Direct-acting engine.
Lenoir 335 1860 D.I. engine, electric ignition.
C.W. Siemens 2,074 1860 Compression, _constant
pressure_.
Hugon 2,902 1860 Platinum ignition.
Millein 1,840 1861 Compression, both constant vol. and
_pressure_.
F.H. Wenham 1,873 1864 Free piston.
Hugon 986 1865 Flame ignition.
Otto and Langen 434 1866 Rack and clutch, flame ignition.

Leaving for the present the history of the gas engine, which brings us to
a stage comparable to the state of the steam engine during the Newcomen's
time, it will be advisable to give some consideration to the principles
concerned in the economical and efficient working of gas engines, in order
to understand the more recent developments.