20 Introduction. [Jan. 
can well be added, is itself susceptible, popularly speaking, of a 
further development, and what is known amongst engineers as super- 
heating, is now daily acquiring a greater amount of favour. The pro- 
cess and its effect are simple and easily understood. 
In its passage from the boiler to the cylinder, where its work has 
to be performed, the steam loses a certain amount of heat ; in other 
words, a portion of it becomes condensed into water ; and in addition 
to this, a certain proportion of partially vaporized water passes from 
the body of that liquid in the boiler along with the current of steam 
into the cylinder. The steam thus deteriorated is, according to the 
more recent plan, “superheated” in its passage, the result being an 
improvement in its quality: for owing to its more perfect vaporization 
and its increased temperature on its arrival in the cylinder, it possesses 
more elasticity, and necessarily a greater impelling power. 'The super- 
heating process is performed by allowing the steam to pass through an 
apparatus of tubes, around which the flame or heated gases and 
atmospheric air circulate in their passage from the boiler to the chim- 
ney, thus converting the water-charged steam into elastic vapour, or 
what is technically called dry steam ; and utilizing an amount of heat 
which would otherwise have been wasted. 
Another equally simple, useful, and interesting improvement in 
engineering science, is “surface condensing.” The ultimate effect is 
the same as that of the foregoing process, namely, an acquisition of 
power without any additional expenditure of fuel. No doubt our 
readers will have frequently observed a jet of steam passing into the 
sea from the hulls of steam-vessels. This is the partially condensed 
steam, after it has done its work in the cylinder; and in order to supply 
its place, a fresh stream of cold sea-water is admitted into the boiler. 
The object of surface-condensing is to save the steam by converting it 
into warm water and returning it to the boiler. The apparatus 
somewhat resembles the last-named ; but cold water for condensing 
takes the place of steam for superheating. Instead of the cold sea- 
water passing into the condenser, there to be mixed with the steam and 
pumped off again along with it, the steam alone passes through tubes 
in the condenser, and around these, there flows a current of cold sea- 
water, which is subsequently pumped out, without having come in 
direct contact with the steam. The latter is returned into the boiler, 
and thus, instead of cold water charged with saline matter, that vessel 
is supplied with distilled water at a temperature of 100° to 120°. The 
foregoing observations apply to the condensation of waste steam from the 
ordinary low-pressure engine, but a still further improvement has been 
added, inasmuch as the steam usually ejected into the atmosphere from 
the high-pressure engine is now conducted into the vacuum in the 
