_A._–It is an elongation of the valve face to a certain extent over the
port, whereby the port is closed sooner than would otherwise be the case.
This extension is chiefly effected at that part of the valve where the
steam is admitted, or upon the _steam side_ of the valve, as the technical
phrase is; and the intent of the extension is to close the steam passage
before the end of the stroke, whereby the engine is made to operate to a
certain extent expansively. In some cases, however, there is also a certain
amount of lap given to the escape or eduction side, to prevent the eduction
from being performed too soon when the lead is great; but in all cases
there is far less lap on the eduction than on the steam side, very often
there is none, and sometimes less than none, so that the valve is incapable
of covering both the ports at once.

A. In starting an oil burning engine the oil should gradually be brought
up as the throttle is opened and the movement and amount of oil should
be kept slightly in advance of the action of the engineer in order to
prevent an inrush of cold air as the engine is working, which would
result in injury to the fire-box and flues. When the throttle is to be
closed, the fire should be reduced very slightly in advance of the
closing of the throttle. This is to prevent the engine from popping off
and black smoke drifting back over the train.

_A._–Marine engines are of two kinds,–paddle engines and screw engines.
In the one case the propelling instrument is paddle wheels kept in rotation
at each side of the ship: in the other case, the propelling instrument is a
screw, consisting of two or more twisted vanes, revolving beneath the water
at the stern. Of each class of engines there are many distinct varieties.

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A. A combination boiler check is fitted with a valve similar to a globe
valve and can be closed at will. Its advantage is that the boiler
pressure can be shut off from the check and the valve repaired without
cooling the boiler. This hand-operated valve can be closed to prevent
the boiler water passing back in case the check valve sticks up and
allows the boiler water to pass back to the injector when not working.

the angle of the plane? It is no wonder that
aviators have not been able to make the theoretical
considerations and the practical demonstrations
agree
Such being the case, why take into account only
the angle of the plane? It is no wonder that
aviators have not been able to make the theoretical
considerations and the practical demonstrations
agree.

sections that are comparatively free from life-endangering reefs are
provided with refuge houses where supplies are stored and where wrecked
survivors may find shelter
The dangerous coasts are more thickly studded with stations, and the
sections that are comparatively free from life-endangering reefs are
provided with refuge houses where supplies are stored and where wrecked
survivors may find shelter.

THE ANEMOMETROGRAPH.–This device for recording,
as well as indicating the speed, pressure
and direction, is called an Anemometrograph,
The two important parts of the combined
apparatus, for the speed and pressure, are illustrated,
to show the principle involved. While the speed
will give the pressure, it is necessary to make a
calculation to get the result while the machine does
this for you.

ftp> get newthisweek.Z
200 PORT command successful.
150 Opening ASCII mode data connection for newthisweek.Z (42390 bytes).
226 Transfer complete.
local: newthisweek.Z remote: newthisweek.Z
42553 bytes received in 6.9 seconds (6 Kbytes/s)
ftp>

_A._–If a weight be placed on a long and slender beam propped up in the
middle, and the prop be suddenly withdrawn, so as to allow deflection to
take place, it is clear that the deflection must be greater than if the
load had been gradually applied. The momentum of the weight and also of the
beam itself falling through the space through which it has been deflected,
has necessarily to be counteracted by the elasticity of the beam; and the
beam will, therefore, be momentarily bent to a greater extent than what is
due to the load, and after a few vibrations up and down it will finally
settle at that point of deflection which the load properly occasions. It is
obvious that a beam must be strong enough, not merely to sustain the
pressure due to the load, but also that accession of pressure due to the
counteracted momentum of the weight and of the beam itself. Although in
steam engines the beam is not loaded by a weight, but by the pressure of
the steam, yet the momentum of the beam itself must in every case be
counteracted, and the momentum will be considerable in every case in which
a large and rapid deflection takes place. A rapid deflection increases the
amount of the deflection as well as the amount of the strain, as is seen in
the cylinder cover of a Cornish pumping engine, into which the steam is
suddenly admitted, and in which the momentum of the particles of the metal
put into motion increases the deflection to an extent such as the mere
pressure of the steam could not produce.