there had been any tendency
to rupture. In the other cases, the concrete arches being turned
between iron beams, the strength of the floor was limited by that of
the beams, so the extreme load could not be put on; but the curious
fact was established that a section of concrete flat on top, and
forming a regular segmental arc beneath, was far stronger than one in
which a portion of the under surface was parallel to the upper;
showing, apparently, that the arched form, even with homogeneous
concrete, causes the conversion of a large part of a vertical pressure
into lateral thrust, reducing by so much the tendency of the load to
break the concrete transversely. This observation is important
theoretically as well as practically. It has been of late generally
maintained that a concrete arch is not an arch at all, but a lintel,
without thrust, and that the common form, flat above and arched
beneath, is objectionable, as it gives least material at the centre,
where a lintel is most strained. The Erfurt experiments directly
contradict this view, and it remains for some students of architecture
to render the profession a service by repeating them, and, at the same
time, actually determining the thrust, for a given load, of arches of
particular forms. Until this is done, the concrete construction, which
is likely, we may hope, to become before many years the prevailing one
in our cities, will be practised with difficulty and uncertainty, if
not with danger. Incidentally, a trial was made of the effect of
freezing on the concrete. The floor of a room arched in four bays,
between iron beams, had just been finished when the weather became
cold, and on the morning after its completion the thermometer stood at
twenty above zero. The concrete had not been protected in any way, and
the contractor was notified that it had been frozen, and must be
removed. This was early in December, and it was about the first of
April before the work of removal, preliminary to replacing the
concrete with new material, was begun. Three bays had been wholly or
partly removed when the hardness of the concrete under the workmen's
tools attracted attention, and the arch remaining intact was tested
with a load of three hundred pounds per square foot, which it bore
perfectly.

* * * * *

The question how far an architect can be held responsible in damages,
in cases where the cost of work exceeds the estimates, is examined in
a