A great part of the Eiffel Tower's worth and its _raison d'etre_ lay in
the overwhelming visual power by which it was to symbolize to a world
audience the scientific, artistic, and, above all, the technical
achievements of the French Republic. Another consideration, in Eiffel's
opinion, was its great potential value as a scientific observatory. At its
summit grand experiments and observations would be possible in such fields
as meteorology and astronomy. In this respect it was welcomed as a
tremendous improvement over the balloon and steam winch that had been
featured in this service at the 1878 Paris exposition. Experiments were
also to be conducted on the electrical illumination of cities from great
heights. The great strategic value of the Tower as an observation post
also was recognized. But from the beginning, sight was never lost of the
structure's great value as an unprecedented public attraction, and its
systematic exploitation in this manner played a part in its planning,
second perhaps only to the basic design.
The conveyance of multitudes of visitors to the Tower's first or main
platform and a somewhat lesser number to the summit was a technical
problem whose seriousness Eiffel must certainly have been aware of at the
project's onset. While a few visitors could be expected to walk to the
first or possibly second stage, 377 feet above the ground, the main means
of transport obviously had to be elevators. Indeed, the two aspects of the
Tower with which the Exposition commissioners were most deeply concerned
were the adequate grounding of lightning and the provision of a reliable
system of elevators, which they insisted be unconditionally safe.
To study the elevator problem, Eiffel retained a man named Backmann who
was considered an expert on the subject. Apparently Backmann originally
was to design the complete system, but he was to prove inadequate to the
task. As his few schemes are studied it becomes increasingly difficult to
imagine by what qualifications he was regarded as either an elevator
expert or designer by Eiffel and the Commission. His proposals appear,
with one exception, to have been decidedly retrogressive, and, further, to
incorporate the most undesirable features of those earlier systems he
chose to borrow from. Nothing has been discovered regarding his work, if
any, on elevators for the lower section of the Tower. Realizing the
difficulty of this aspect of the problem, he may not have attempted its
solution, and confined his work to the upper half where the structure
permitted a straight, vertical run.
[Illustration: Figure 22.--Various levels of the Eiffel Tower. (Adapted
from Gustave Eiffel, _La Tour de Trois Cents Metres_, Paris, 1900, pl.
1.)]
The Backmann design for the upper elevators was based upon a principle
which had been attractive to many inventors in the mid-19th century period
of elevator development--that of "screwing the car up" by means of a
threaded element and a nut, either of which might be rotated and the other
remain stationary. The analogy to a nut and bolt made the scheme an
obvious one at that early time, but its inherent complexity soon became
equally evident and it never achieved practical success. Backmann
projected two cylindrical cars that traveled in parallel shafts and
balanced one another from opposite ends of common cables that passed over
a sheave in the upperworks. Around the inside of each shaft extended a
spiral track upon which ran rollers attached to revolving frames
underneath the cars. When the frames were made to revolve, the rollers,
running around the track, would raise or lower one car, the other
traveling in the opposite direction (fig. 23).
[Illustration: Figure 23.--Backmann's proposed helicoidal elevator for the
upper section of the Eiffel Tower. The cars were to be self-powered by
electric motors. Note similarity to the Miller system (fig. 20). (Adapted
from _The Engineer_ (London), Aug. 3, 1888, vol. 66, p. 101.)]
In the plan as first presented, a ground-based steam engine drove the
frames and rollers through an endless fly rope--traveling at high speed
presumably to permit it to be of small diameter and still transmit a
reasonable amount of power--which engaged pulleys on the cars. The design
was remarkably similar to that of the Miller Patent Screw Hoisting
Machine, which had had a brief life in the United States around 1865. The
Miller system (see p. 19) used a flat belt rather than a rope (fig. 20).
This plan was quickly rejected, probably because of anticipated
difficulties with the rope transmission.[9]
Backmann's second proposal, actually approved by the Commission,
incorporated the only--although highly significant--innovation evident in
his designs. For the rope transmission, electric motors were substituted,
one in each car to drive the roller frame directly. With this
modification, the plan does not seem quite as unreasonable, and would
probably have worked. However, it would certainly have lacked the
necessary durability and would have been extremely expensive. The
Commission discarded the whole scheme about the middle of 1888, giving two
reasons for its action: (1) the novelty of the system and the attendant
possibility of stoppages which might seriously interrupt the "exploitation
of the Tower," and (2) fear that the rollers running around the tracks
would cause excessive noise and vibration. Both reasons seem quite
incredible when the Backmann system is compared to one of those actually
used--the Roux, described below--which obviously must have been subject to
identical failings, and on a far greater scale. More likely there existed
an unspoken distrust of electric propulsion.
That the Backmann system should have been given serious consideration at
all reflects the uncertainty surrounding the entire matter of providing
elevator service of such unusual nature. Had the Eiffel Tower been erected
only 15 years later, the situation would have been simply one of
selection. As it was, Eiffel and the commissioners were governed not by
what they wanted but largely by what was available.