arc
of earthenware, embedded in concrete, and are said to be still in a
good state of preservation. There is, therefore, no novelty in the
construction of this kind of water-conduit ; but the use of
wrought-iron pipe for this purpose was very limited until adopted in
California, where it has been very largely employed, and where there
have been obtained valuable data of the strength of materials and
methods of construction, as well as of the flow of water through long
pipes, essentially modifying theories and formulas previously accepted.
Thickness of Iron.—The
thickness of the iron is determined by the pressure of the water and
the diameter of the pipe, allowance being made, of course, for the
quality of the material and the method of riveting. The factor of
safety against damage from accident is regulated by the importance of
the line. On account of variations in plates marked as being of the
same size and number, it would be well, as a precautionary measure, to
