hese systems
involved problems far greater than had been encountered in previous
elevator work anywhere in the world. The basis of these difficulties was
the amplification of the two conditions that were the normal determinants
in elevator design--passenger capacity and height of rise. In addition,
there was the problem, totally new, of fitting elevator shafts to the
curvature of the Tower's legs. The study of the various solutions to these
problems presents a concise view of the capabilities of the elevator art
just prior to the beginning of the most recent phase of its development,
marked by the entry of electricity into the field.

The great confidence of the Tower's builder in his own engineering ability
can be fully appreciated, however, only when notice is taken of one
exceptional way in which the project differed from works of earlier
periods as well as from contemporary ones. In almost every case, these
other works had evolved, in a natural and progressive way, from a
fundamental concept firmly based upon precedent. This was true of such
notable structures of the time as the Brooklyn Bridge and, to a lesser
extent, the Forth Bridge. For the design of his tower, there was virtually
no experience in structural history from which Eiffel could draw other
than a series of high piers that his own firm had designed earlier for
railway bridges. It was these designs that led Eiffel to consider the
practicality of iron structures of extreme height.

[Illustration: Figure 1.--The Eiffel Tower at the time of the Universal
Exposition of 1889 at Paris. (From _La Nature_, June 29, 1889, vol. 17, p.
73.)]

[Illustration: Figure 2.--Gustave Eiffel (1832-1923). (From Gustave
Eiffel, _La Tour de Trois Cents Metres_, Paris, 1900, frontispiece.)]

There was, it is true, some inspiration to be found in the paper projects
of several earlier designers--themselves inspired by that compulsion which
throughout history seems to have driven men to attempt the erection of
magnificently high structures.

One such inspiration was a proposal made in 1832 by the celebrated but
eccentric Welsh engineer Richard Trevithick to erect a 1,000-foot,
conical, cast-iron tower (fig. 3) to celebrate the passing of the Reform
Bill. Of particular interest in light of the present discussion was
Trevithick's plan to raise visitors to the summit on a piston, driven
upward within the structure's hollow central tube by compressed air. It
probably is fort