ition of cast iron at their lower
ends, to overbalance the weight of a capacity load in the lower car. The
second condition demanded simply that the system be powerful enough to
lift the unbalanced weight of the plungers plus the weight of passengers
in the upper car.

As in the other systems, safety was a matter of prime importance. In this
case, the element of risk lay in the possibility of the suspended car
falling. The upper car, resting on the rams, was virtually free of such
danger. Here again the influence of Backmann was felt--a brake of his
design was applied (fig. 38). It was, true to form, a throwback, similar
safety devices having proven unsuccessful much earlier. Attached to the
lower car were two helically threaded vertical rollers, working within
the hollow guides. Corresponding helical ribs in the guides rotated the
rollers as the car moved. If the car speed exceeded a set limit, the
increased resistance offered by the apparatus drove the rollers up into
friction cups, slowing or stopping the car.

[Illustration: Figure 35.--Detail of links in the Roux system. (From
Gustave Eiffel, _La Tour de Trois Cents Metres_, Paris, 1900, p. 156.)]

[Illustration: Figure 36.--Section of guide trunks in the Roux system.
(From Gustave Eiffel, _La Tour de Trois Cents Metres_, Paris, 1900, p.
156.)]

The device was considered ineffectual by Edoux and Eiffel, who were aware
that the ultimate safety of the system resulted from the use of supporting
cables far heavier than necessary. There were four such cables, with a
total sectional area of 15.5 square inches. The total maximum load to
which the cables might be subjected was about 47,000 pounds, producing a
stress of about 3,000 pounds per square inch compared to a breaking stress
of 140,000 pounds per square inch--a safety factor of 46![16]

[Illustration: Figure 37.--Schematic diagram of the Edoux system. (Adapted
from Gustave Eiffel, _La Tour de Trois Cents Metres_, Paris, 1900, p.
175.)]

[Illustration: Figure 38.--Vertical section through lower (suspended)
Edoux car, showing Backmann helicoidal safety brake. (Adapted from Gustave
Eiffel, _La Tour Eiffel en 1900_, Paris, 1902, p. 12.)]

A curiosity in connection with the Edoux system was the use of Worthington
(American) pumps (fig. 40) to carry the water exhausted from the cylinders
back to the supply tanks. No record has been found that might explain why
this particular exception was made to the "for