|North-Western | 6 6 | 17 x 24 | " | +--------------------+------------------+-----------+-------
------+ |Lancashire and | | | | |Yorkshire | 6 0 | 171/2 x 26 | " | +--------------------+------------------+-----------+-------
------+ |North British | 6 4 | 17 x 24 | " | +--------------------+------------------+-----------+-------
------+ |Nord | 7 0 | 17 x 24 | " | +--------------------+------------------+-----------+-------
------+ |Paris-Orleans, 1884 | 6 8 | 17 x 231/2 | outside. | +--------------------+------------------+-----------+-------
------+ |Ouest | 6 0 | 171/4 x 251/2| " | +-----------------------------------------------------------
------+

This table, the examination of which will be found very instructive, shows that there are already in use:  For locomotives with single drivers, diameters of 9 ft., 8 ft. 1 in., and 8 ft.; (2) for locomotives with four coupled wheels, diameters 6 ft. to 7 ft.  There is therefore an important difference between the diameters of the coupled wheels of 7 ft. and those of 8 ft. 3 in., as conceived by M. Estrade.  However, the transition is not illogically sudden, and if the conception is a bold one, “it cannot,” says M. Nansouty, “on the other hand, be qualified as rash.”

He goes on to consider, in the first place:  Especial types of uncoupled wheels, the diameters of which form useful samples for our present case.  The engines of the Bristol and Exeter line are express tender engines, adopted on the English lines in 1853, some specimens of which are still in use.[1] These engines have ten wheels, the single drivers in the center, 9 ft. in diameter, and a four-wheeled bogie at each end.  The driving wheels have no flanges.  The bogie wheels are 4 ft. in diameter.  The cylinders have a diameter of 161/2 in. and a piston stroke of 24 in.  The boiler contains 180 tubes, and the total weight of the engine is 42 tons.  These locomotives, constructed for 7 ft. gauge, have attained a speed of seventy-seven miles per hour.

   [Footnote 1:  M. Nansouty is mistaken.  None of the Bristol and
   Exeter tank engines with. 9 ft. wheels are in use, so far as we
   know.  ED. E.]

The single driver locomotives of the Great Northern are powerful engines in current use in England.  The driving wheels carry 17 tons, the heating surface is 1,160 square feet, the diameters of the cylinders 18 in., and that of the driving wheels 8 ft. 1 in.  We have here, then, a diameter very near to that adopted by M. Estrade, and which, together with the previous example, forms a precedent of great interest.  The locomotive of the Great Northern has a leading four-wheeled bogie, which considerably increases the steadiness of the engine, and counterbalances the disturbing effect of outside cylinders.  Acting