s centrally through the cylinder head. On the
outer end of this rod is screwed an adjusting nut, by means of which the
piston may be adjusted. This rod is bored longitudinally, establishing
communication between the compressor cylinder and the drum containing
the piston.

It will be seen that the upper face of the piston is exposed so as to be
subjected to atmospheric pressure only, and when the compressor is in
operation a portion of the air in the compressor cylinder passes through
the hollow rod into the space beneath the piston, and there exerts
sufficient pressure, in combination with the pressure on the inner face
of the valve, to open the valve against an equal pressure in the
receiver or conducting pipes, so that when the pressure in the cylinder
equals the pressure in the receivers the valve is opened and held in
place until the piston in the cylinder starts on the return stroke, when
the pressure under the piston is immediately relieved through the hollow
rod and the main valve closes.

The space between the valve and its seat is made as shallow as possible,
so that the space may be quickly filled and exhausted. The piston may be
adjusted to regulate this space. This invention was recently patented by
Messrs. Samuel B. Connor and Henry Dods, of Virginia City, Nevada.

* * * * *

IMPROVED SAFETY VALVE.

In the annexed cut we have represented a steam safety valve, which is
the invention of M. Schmidt, M. E., of Zurich, Switzerland. It consists
of a lever terminating in two prongs, one of which extends downward and
rests upon the cap, closing the top of the tube through which the steam
escapes. The other prong extends upward and catches under a projection
of the steam tube, and forms the fulcrum for the lever. The opposite end
of this lever is provided with an adjustable screw pressing upon a plate
that rests on the top of a spiral spring, which keeps the valve closed
by pressing the outer end of the lever upward. As soon as the pressure
of the steam overcomes the pressure of the spiral spring the valve will
be raised, permitting the steam to escape. The apparatus is contained in
a case having a central aperture for the escape of steam.

[Illustration: IMPROVED SAFETY VALVE.]

* * * * *

RAISING SUNKEN VESSELS.

An experiment recently took place in the East India Dock Basin,
Blackwall, London, by permission of Mr. J. L. du Pla