tag="{http://www.w3.org/1999/xhtml}a">Locomotive Boilers.

CHAP. VIII.--CONSTRUCTIVE DETAILS OF ENGINES.

Pumping Engines.

Various forms of Marine Engines.

Cylinders, Pistons, and Valves.

Air Pump and Condenser.

Pumps, Cocks, and Pipes.

Details of the Screw and Screw Shaft.

Details of the Paddles and Paddle Shaft.

The Locomotive Engine.

CHAP. IX.--STEAM NAVIGATION.

Resistance of Vessels in Water.

Experiments on the Resistance of Vessels.

Influence of the size of Vessels upon their Speed.

Structure and Operation of Paddle Wheels.

Configuration and Action of the Screw.

Comparative Advantages of Paddle and Screw Vessels.

Comparative Advantages of different kinds of Screws.

Proportions of Screws.

Screw Vessels with full and auxiliary Power.

Screw and Paddles combined.

CHAP. X.--EXAMPLES OF ENGINES OF RECENT CONSTRUCTION.

Oscillating Paddle Engines.

Direct acting Screw Engine.

Locomotive Engine.

CHAP. XI.--ON VARIOUS FORMS AND APPLICATIONS OF THE STEAM ENGINE.

Governor.

Donkey Pumps.

Portable Steam Engines.

Stationary Engines.

Steam Fire Engines.

Steam Excavator.

CHAP. XII.--MANUFACTURE AND MANAGEMENT OF STEAM ENGINES.

Construction of Engines.

Erection of Engines.

Management of Marine Boilers.

Management of Marine Engines.

Management of Locomotives.

MECHANICAL PRINCIPLES OF THE STEAM ENGINE.

CLASSIFICATION OF ENGINES.

1. Q.--What is meant by a vacuum?

A.--A vacuum means an empty space; a space in which there is neither water nor air, nor anything else that we know of.

2. Q.--Wherein does a high pressure differ from a low pressure engine?

A.--In a high pressure engine the steam, after having pushed the piston to the end of the stroke, escapes into the atmosphere, and the impelling force is therefore that due to the difference between the pressure of the steam and the pressure of the atmosphere. In the condensing engine the steam, after having pressed the piston to the end of the stroke, passes into the condenser, in which a vacuum is maintained, and the impelling force is that due to the difference between the pressure of the steam above the piston, and the pressure of the vacuum beneath it, which is nothing; or, in other words, you have then the whole pressure of the steam urging the piston, consisting of the pressure shown by the safety-valve on the boiler, and the pressure of the atmosphere besides.

3. Q.--In what way would you class the various kinds of condensing engines?

A.--Into single acting, rotative, and rotatory engines. Single acting engines are engines without a crank, such as are used for pumping water. Rotative engines are engines provided with a crank, by means of which a rotative motion is produced; and in this important class stand marine and mill engines, and all engines, indeed, in which the rectilinear motion of the piston is changed into a circular motion. In rotatory engines the steam acts at once in the production of circular motion, either upon a revolving piston or otherwise, but without the use of any intermediate mechanism, such as the crank, for deriving a circular from a rectilinear motion. Rotatory engines have not hitherto been very successful, so that only the single acting or pumping engine, and the double acting or rotative engine can be