s we have seen, had to retrace his steps, in the case
of expansion.

The other improvement is the cross-head of Haswell, an American, a
decided advance, giving the piston rod a smooth and straight bed to rest
upon and freeing it from all disturbance. The drop valve is now
displacing the slide valve as a better form of excluding or admitting
steam.

Watt of course knew nothing of the thermo-dynamic value of high
temperature without high pressure, altho fully conversant with the value
of pressures. This had not been even imagined by either philosopher or
engineer until discovered by Carnot as late as 1824. Even if he had
known about it the mechanical arts in his day were in no condition to
permit its use. Even high pressures were impracticable to any great
extent. It is only during the past few years that turbines and
superheating, having long been practically discarded, show encouraging
signs of revival. They give great promise of advancement, the hitherto
insuperable difficulties of lubrication and packing having been overcome
within the last five years. Superheating especially promises to yield
substantial results as compared with the practice with ordinary engines,
but the margin of saving in steam over the best quadruple expansion
engine cannot be great. Lord Kelvin however expects it to be the final
contribution of science to the highest possible economy in the steam
engine.

In the January (1905) number of "Stevens Institute Indicator,"
Professor Denton has an instructive resume of recent steam engine
economics. He tells us that Steam Turbines are now being applied to
Piston Engines to operate with the latter's exhaust, to effect the same
saving as the sulphur dioxide cylinder; and adds

that the Turbine is a formidable competitor to the Piston Engine
is mainly due to the fact that it more completely realizes the
expansive principle enunciated in the infancy of steam history
as the fundamental factor of economy by its sagacious founder,
the immortal Watt.

Watt's favorite employment in Soho works late in 1783 and early in 1784
was to teach his engine, now become as docile as it was powerful, to
work a tilt hammer. In 1777 he had written Boulton that

Wilkinson wants an engine to raise a stamp of 15 cwt. thirty or
forty times in a minute. I have set Webb to work to try it with
the little engine and a stamp-hammer of 60 lbs. weight. Many of
these _battering rams_ will be wa