For the first evil, two
remedies were adopted; a sole of slate, of wood, or of its own
material, was sometimes placed under the tile, but the more usual
practice was to form them with club-feet. To meet the case of
longitudinal fracture, the tiles were reduced in size, and very
much thickened in proportion to their area. The first of these
remedies was founded on an entirely mistaken, and the second on no
conception at all of the cause of the evil to which they were
respectively applied. The idea was, that this tile, standing on
narrow feet, and pressed by the weight of the refilled soil, sank
into the floor of the drain; whereas, in fact, the floor of the
drain rose into the tile. Any one at all conversant with
collieries is aware that when a _strait_ work (which is a small
subterranean tunnel six feet high and four feet wide or
thereabouts) is driven in coal, the rising of the floor is a more
usual and far more inconvenient occurrence than the falling of the
roof: the weight of the two sides squeezes up the floor. We have
seen it formed into a very decided arch without fracture. Exactly
a similar operation takes place in the drain. No one had till
recently dreamed of forming a tile drain, the bottom of which a
man was not to approach personally within twenty inches or two
feet. To no one had it then occurred that width at the bottom of
the drain was a great evil.
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