At the time the Eiffel Tower elevators were under consideration, water
under pressure was, from a practical standpoint, the only agent capable of
fulfilling the power and control requirements of this particularly severe
service. Steam, as previously mentioned, had already been found wanting in
several respects. Electricity, on the other hand, seemed to hold promise
for almost every field of human endeavor. By 1888 the electric motor had
behind it a 10- or 15-year history of active development. Frank J. Sprague
had already placed in successful operation a sizable electric trolley-car
system, and was manufacturing motors of up to 20 horsepower in commercial
quantity. Lighting generators were being produced in sizes far greater.
There were, nevertheless, many obstacles preventing the translation of
this progress into machinery capable of hauling large groups of people a
vertical distance of 1,000 feet with unquestionable dependability.
The first application of electricity to elevator propulsion was an
experiment of the distinguished German electrician Werner von Siemens,
who, in 1880, constructed a car that successfully climbed a rack by means
of a motor and worm gearing beneath its deck (figs. 17, 18)--again, the
characteristic European distrust of cable suspension. However, the effect
of this success on subsequent development was negligible. Significant use
of electricity in this field occurred somewhat later, and in a manner
parallel to that by which steam was first applied to the elevator--the
driving of mechanical (belt driven) elevator machines by individual
motors. Slightly later came another application of the "conversion" type.
This was the simple substitution of electrically driven pumps (fig. 21)
for steam pumps in hydraulic installations. It will be recalled that pumps
were necessary in cases where water main pressure was insufficient to
operate the elevator directly.
In both of these cases the operational demands on the motor were of course
identical to those on the prime movers which they replaced; no reversal of
direction was necessary, the speed was constant, and the load was nearly
constant. Furthermore, the load could be applied to the motor gradually
through automatic relief valves on the pump and in the mechanical machines
by slippage as the belt was shifted from the loose to the fast pulleys.
The ultimate simplicity in control resulted from permitting the motor to
run continuously, drawing current only in proportion to its loading. The
direct-current motor of the 1880's was easily capable of such service, and
it was widely used in this way.
[Illustration: Figure 15.--Rope-geared hydraulic freight elevator using a
horizontal cylinder (about 1883). (From a Lane & Bodley illustrated
catalog of hydraulic elevators, Cincinnati, n.d.)]
[Illustration: Figure 16.--English direct plunger hydraulic elevator
(about 1895). (From F. Dye, _Popular Engineering_, London, 1895, p. 280.)]
Adaptation of the motor to the direct drive of an elevator machine was
quite another matter, the difficulties being largely those of control. At
this time the only practical means of starting a motor under load was by
introducing resistance into the circuit and cutting it out in a series of
steps as the speed picked up; precisely the method used to start traction
motors. In the early attempts to couple the motor directly to the winding
drum through worm gearing, this "notching up" was transmitted to the car
as a jerking motion, disagreeable to passengers and hard on machinery.
Furthermore, the controller contacts had a short life because of the
arcing which resulted from heavy starting currents. In all, such systems
were unsatisfactory and generally unreliable, and were held in disfavor by
both elevator experts and owners.
[Illustration: Figure 17.--Siemens' electric rack-climbing elevator of
1880. (From Werner von Siemens, _Gesammelte Abhandlungen und Vortraege_,
Berlin, 1881, pl. 5.)]
There was, moreover, little inducement to overcome the problem of control
and other minor problems because of a more serious difficulty which had
persisted since the days of steam. This was the matter of the drum and its
attendant limitations. The motor's action being rotatory, the winding drum
was the only practical way in which to apply its motive power to hoisting.
This single fact shut electricity almost completely out of any large-scale
elevator business until after the turn of the century. True, there was a
certain amount of development, after about 1887, of the electric
worm-drive drum machine for slow-speed, low-rise service (fig. 19). But
the first installation of this type that was considered practically
successful--in that it was in continuous use for a long period--was not
made until 1889,[7] the year in which the Eiffel Tower was completed.
Pertinent is the one nearly successful attempt which was made to approach
the high-rise problem electrically. In 1888, Charles R. Pratt, an elevator
engineer of Montclair, New Jersey, invented a machine based on the
horizontal cylinder rope-geared hydraulic elevator, in which the two sets
of sheaves were drawn apart by a screw and traveling nut. The screw was
revolved directly by a Sprague motor, the system being known as the
Sprague-Pratt. While a number of installations were made, the machine was
subject to several serious mechanical faults and passed out of use around
1900. Generally, electricity as a practical workable power for elevators
seemed to hold little promise in 1888.[8]
[Illustration: Figure 18.--Motor and drive mechanism of Siemens'
elevator. (From Alfred R. Urbanitzky, _Electricity in the Service of Man_,
London, 1886, p. 646.)]
[Illustration:
_Morse, Williams & Co._,
BUILDERS OF
PASSENGER
AND
FREIGHT
ELEVATORS.