(16.)

When water is evaporated under ordinary circumstances,—that is, when exposed to no other external pressure than that of the atmosphere,—it increases its volume about seventeen-hundred-fold. Thus a cubic inch of liquid [Pg030] water would form about seventeen hundred cubic inches of common steam. If, however, the water be confined by a greater pressure than that produced by the common atmosphere, then the increase of volume which takes place in its evaporation would be less in proportion.

These important physical circumstances are now only indicated in a general way. As we proceed with our account of the invention and improvement of the steam engine, they will be developed more fully and accurately.