matic 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 upper