d was firmly bolted to the
stone wall. Practical fixed endedness could be attained, of course, by
means such as these, but the value of such tests is only theoretical.

Mr. Mensch says:

"The elastic theory was fully proved for arches by the remarkable
tests, made in 1897 by the Austrian Society of Engineers and
Architects, on full-sized arches of 70-ft. span, and the observed
deflections and lateral deformations agreed exactly with the
figured deformation."

The writer does not know of the tests made in 1897, but reference is
often made to some tests reported in 1896. These tests are everywhere
quoted as the unanswerable argument for the elastic theory. Let us
examine a few features of those tests, and see something of the strength
of the claim. In the first place, as to the exact agreement between the
calculated and the observed deformations, this exact agreement was
retroactive. The average modulus of elasticity, as found by specimen
tests of the concrete, did not agree at all with the value which it was
necessary to use in the arch calculations in order to make the
deflections come out right.

As found by tests on blocks, the average modulus was about 2,700,000;
the "practical" value, as determined from analysis of a plain concrete
arch, was 1,430,000, a little matter of nearly 100 per cent. Mansfield
Merriman, M. Am. Soc. C. E., gives a digest of these famous Austrian
tests.[Y] There were no fixed ended arches among them. There was a long
plain concrete arch and a long Monier arch. Professor Merriman says,
"The beton Monier arch is not discussed theoretically, and, indeed, this
would be a difficult task on account of the different materials
combined." And these are the tests which the Engineering Profession
points to whenever the elastic theory is questioned as to its
applicability to reinforced concrete arches. These are the tests that
"fully prove" the elastic theory for arches. These are the tests on the
basis of which fixed ended reinforced concrete arches are confidently
designed. Because a plain concrete bow between solid abutments deflected
in an elastic curve, reinforced concrete arches between settling
abutments are designed with fixed ends. The theorist has departed about
as far as possible from his premise in this case. On an exceedingly
slender thread he has hung an elaborate and important theory of design,
with assumptions which can never be realized outside of the schoolro