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TIIE STEAM-ENGINE.

the illumination of modern science. Of so large a sub-ject, one part only can be studied at a time, and thatsuccession of parts by which they enter into the mind ineasiest transition is the very succession in which historypresents them to us.

We shall therefore divide this subject into two parts:the first containing a description of the steam-engine, andthe elucidation of its principles, in historical order ; thesecond forming a description of the functions and parts ofthe modern steam-engine.

Part I_Historical Description of the Steam- Engine.

1. The Era of the Ancients. 2. The Eraof Worcester. 3. Tiie Era of Watt.

1. The Era of the Ancients.

The knowledge which some of the ancients possessedof the constitution of steam is remarkably in accordancewith the most recent modern conclusions on this speciesof matter. Steam is now known to be only one of thecommon airs or gases whose particles at one degree ofheat and of pressure assume a liquid form, and at anothertemperature and pressure become solid ice.

The modern doctrine concerning matter may be thusstated ; that matter is known to exist in four conditions—solid, liquid, aerial, and etherial. Earth and stone areexemplars of solid matter ; water and mercury of liquidmatter ; the atmosphere, and smoke, and steam, of aerialsubstances ; caloric, light, and electricity, of etherial mat-ter. It is further the doctrine of modern physics that nokind of matter exclusively possesses one of these condi-tions as its distinguishing property, but that all may, in