Page:Inland Transit - Cundy - 1834.djvu/54

 place in an immensely rapid proportion. Even if the resistance of a fluid were not increased, the effect of a horse's power, by the condition of his nature, would be materially reduced by every increase of speed; and, on the other hand, even were a horse capable of working with the same effect at an increased speed, the resistance of a fluid, increasing in a greater proportion than the square of the speed, would impair the total effect. But, in fact, these two causes cooperate; and both theory and experience agree in the result, that horse power at greater speed than about three miles an hour, is altogether incompatible with any useful effect upon canals; and ten miles an hour on turnpike roads, for any useful purpose.

To render intelligible the advantages which attend the use of steam as a moving power in the transit of loads over land, whether by canals or roads, it will be necessary to premise a few observations respecting the steam-engine. It is a universal property of matter, that by the application of heat, so as to raise its temperature, it suffers an increase in its magnitude. Also in different substances, when certain temperatures are attained by the application of fire or other methods of heating, they undergo a change of form. Solids, at certain temperatures, are converted into liquids; and liquids, in like manner, when heated to certain degrees, become aeriform fluids or gases. These changes are familiar to every one in the ordinary phenomena attending water. Below the temperature of 32° of the common thermometer, that substance exists in the solid form, and is called ice. Above that temperature, it passes into the liquid state, and is called water; and when raised to the temperature of 212°, under ordinary circumstances, it passes into the aeriform state, and is called steam.