If the force were not sufficient to pull the boat out of the water, but were just enough to bring its bottom to the surface, it would be carried along with a kind of gliding motion with great rapidity; for at every point of its course it would require a certain time before, it could sink to its usual draft of water; but before that time had elapsed, it would have advanced to another point, and consequently have been raised by the reaction of the water on the inclined plane at its forepart.

40.  The same fact, that bodies moving with great velocity have not time to exert the full effect of their weight, seems to explain a circumstance which appears to be very unaccountable.  It sometimes happens that when foot-passengers are knocked down by carriages, the wheels pass over them with scarcely any injury, though, if the weight of the carriage had rested on their body, even for a few seconds, it would have crushed them to death.  If the view above taken is correct, the injury in such circumstances will chiefly happen to that part of the body which is struck by the advancing wheel.

41.  An operation in which rapidity is of essential importance is in bringing the produce of mines up to the surface.  The shafts through which the produce is raised are sunk at a very great expense, and it is, of course, desirable to sink as few of them as possible.  The matter to be extracted is therefore raised by steam-engines with considerable, and without this many of our mines could not be worked velocity, with profit.

42.  The effect of great velocity in modifying the form of a cohesive substance is beautifully shown in the process for making window glass, termed “flashing”, which is one of the most striking operations in our domestic arts.  A workman having dipped his iron tube into the glass pot, and loaded it with several pounds of the melted “metal”, blows out a large globe, which is connected with his rod by a short thick hollow neck.  Another workman now fixes to the globe immediately opposite to its neck, an iron rod, the extremity of which has been dipped in the melted glass; and when this is firmly attached, a few drops of water separate the neck of the globe from the iron tube.  The rod with the globe attached to it is now held at the mouth of a glowing furnace:  and by turning the rod the globe is made to revolve slowly, so as to be uniformly exposed to the heat:  the first effect of this softening is to make the glass contract upon itself and to enlarge the opening of the neck.  As the softening proceeds, the globe is turned more quickly on its axis, and when very soft and almost incandescent, it is removed from the fire, and the velocity of rotation being still continually increased, the opening enlarges from the effect of the centrifugal force, at first gradually, until at last the mouth suddenly expands or “flashes” out into one large circular sheet of red hot glass.  The neck of the original globe, which is to become the outer part of the sheet, is left thick to admit of this expansion, and forms the edge of the circular plate of glass, which is called a “Table”.  The centre presents the appearance of a thick boss or prominence, called the “Bull’s-eye”, at the part by which it was attached to the iron rod.