Download An Introduction to the Gravity-driven Clocks in the Forbidden City

The 14th IFToMM World Congress, Taipei, Taiwan, October 25-30, 2015
DOI Number: 10.6567/IFToMM.14TH.WC.OS6.007
An Introduction to the Gravity-driven Clocks in the Forbidden City
Y.-H. Chen 1
National Cheng Kung University
Tainan, Taiwan
K.-H. Hsiao 2
National S&T Museum
Kaohsiung, Taiwan
T.-Y. Lin3
Southern Taiwan University of S&T
Tainan, Taiwan
H.-S. Yan4
National Cheng Kung University
Tainan, Taiwan
Abstract— Ancient timepieces are combinative products of
science and technology, and they were communicated to China
through importation during the 17 to 19 centuries. Clocks collected
by Chinese emperors are elegant works and show the highest
manufacture level. Regarding the gravity-driven clocks, the methods
to apply gravity as a power source are ingenious. The development
of power sources in timepieces and the communication of technology
from Europe to China are introduced briefly. Four typical gravitydriven clocks are presented and divided into two types, driven by an
outer force and by its own weight. Furthermore, structural analyses
regarding the mechanisms of typical gravity-driven clocks are
provided.
Keywords: Clocks and watches, Forbidden City, Structural analysis,
History of machinery
I. Introduction
The Forbidden City in Beijing took a part of imperial
palace from the Ming Dynasty (1368-1644) to the end of
Qing Dynasty (1644-1911). It was the residence for
emperors, and the political center of ancient Chinese
government. In 1925, the role of Forbidden City was
changed from palace to museum. Emperors’ collections
became exhibitions, including jewels, calligraphies,
paintings, and timepieces. These clocks and watches reflect
the development of timepieces and the highest manufacture
levels of the period from the 17 to 19 centuries. Some
timepieces came from countries in Europe, and others were
made in China. The former ones were contributed by Jesuit
missionaries, purchased by the government, or ordered by
the emperors; and the latter ones were manufactured by the
clock workshop in the palace, with over one hundred
artisans under guidance of missionaries worked in.
Timekeepers collected by emperors were made of
expensive material, resplendent adornment, and exquisite
mechanical structure. Not only the ancient Europe artistic
style is shown, but also Chinese cultural elements are
combined, Fig. 1 [1]. Hundreds years passing, people are
still amazed by these ingenious antique timepieces. These
clocks and watches are evidence to provide communication
between China and Western countries in that period [1, 2].
Fig. 1. A Chinese style clock [1]
These gravity-driven clocks were made in the palace and
France. This paper focuses on the historical and mechanical
studies of the gravity-driven clocks in the Forbidden City. In
what follows, the development of power source applied to
timepieces is briefly introduced. Then, the communication of
the technology and science in ancient China during the Qing
Dynasty is expressed. Finally, the classification and the
structural analysis of typical gravity-driven clocks are
presented.
II. Power Sources in Mechanical Clocks
People have got sense of “time” since thousands years ago.
Many kinds of timekeepers such as gnomons, sundials,
clepsydras, sandglass, and mechanical timepieces were
invented. Mechanical clock is one of the most important
inventions that greatly affect the development of science and
technology in the history of mechanical inventions. Figure 2
shows the evolution of power source in mechanical clocks,
including water, gravity, and coiled spring.
Thousands of mechanical timepieces were collected in the
Forbidden City. Coiled spring is the main power source of
these timepieces, but a small number of clocks are driven by
gravity of weight [3].
1 [email protected]
2 [email protected]
3 [email protected]
4 [email protected]
Fig. 2. Power sources in ancient timepieces
In the 11th century, a water-driven astronomical tower
clock was built in ancient China. Two spherical instruments
in the upper floors show celestial phenomena, and the
devices at the base floor are power and time-telling systems,
Fig. 3 [4]. Water trickles out of the tank and constantly
flows into a bucket attached to the water wheel. To make the
wheel revolute in a uniform speed, a set of steelyardclepsydra device was applied. Unfortunately, the exquisite
work was destroyed in the end of the 12th century, and the
achievement was not inherited and developed.
Although coiled spring had been applied to drive
machines since the 14th century, it was hard to power
timepiece because of its various force. The tighter a spring is
wound, the larger force is released. To the 15th century, a
regulated device, fusee, was invented. It makes output
torque of the coiled spring uniformly. Clocks driven by
coiled spring and adjusted by fusee were created, Fig. 5.
Obviously, the size and weight of spring-driven clock is
smaller than the former types, so portable timepieces were
developed since the 16th century [6].
Fig. 5. A spring-driven clock [8]
III. Communication of Technology and Science
through Timepieces in Qing Dynasty
Fig. 3. Su-Song’s water-driven clock in ancient China [4]
During the period of 13 to 14 centuries, with the invention
of escapement device, the mechanical clocks driven by
weight were presented in Europe. It is said that the first
gravity-driven mechanical clock was built at a cathedral in
British [5]. Figure 4 shows a similar movement of clock
tower. The power source coming from a device consisting of
a heavy weight tied to a rope activates gears through a ropewrapping pulley. The earliest gravity-driven clock tells time
by striking since there is neither dial nor hands in the clock.
Many years later, hour hand and minimum hand were
attached step by step. Weight is a good power source for
clock because the heft of each weight is fixed and a stable
force is applied to the movement. Nevertheless, gravitydriven clocks were not only heavy but huge, and were
usually set at churches, towers, or city halls in that period.
Until the 15th century, the dimension of gravity-driven
clocks was reduced for domestic use and people continued
to make timepiece portable [5, 6].
Fig. 4. A gravity-driven clock [7]
Jesuit missionaries went to China from Europe after the
Age of Discovery. They not only disseminated the religion,
but also brought Western science and technology. Since the
Italian missionary Matteo Ricci ( 利 瑪 竇 , 1552-1610)
introduced mechanical chime clocks to China in 1601, a
large numbers of timepieces were sent to the Forbidden City
as gifts, tribute, or purchases. Chinese Emperors were
interested in Western clocks, watched, mechanical toys, and
instruments. In order to maintain, manufacture, and refit
timepieces, Kangxi Emperor (康熙, 1662-1722) of Qing
Dynasty set a clock workshop in the palace in 1677.
Foreigner missionaries, technical personnel, and local
artisans were hired. According to the archives of imperial
workshop, emperors gave detailed instructions on form and
manufacturing process, including how to disassemble,
combine, and refit. Also, when craftsmen finished the madeto-order clock, emperors checked their work and provided
comments for modifying. Chinese style such as architecture,
decoration, symbol of myths, and folk ritual is shown in
these timepieces. Except for the workshop in the palace,
timepiece industry was developed in coastal cities such as
Guangzhou (廣州) and Suzhou (蘇州). Most importation
from Europe was through the trading ports in these areas.
The timepiece industry in China started in the 17th century,
reached its height during the period of Qianlong Emperor
(乾隆, 1711-1799), and decayed in the 19th century because
of the decline of the Qing Dynasty [1, 2, 9-15].
The clock brought by Matteo Ricci was driven by weight
and regulated by foliot and verge escapement, Fig. 6. It did
not work accurately that the error was more than one quarter
per day. In 1658, most imported clocks were with pendulum
and cycloidal cheeks, and the error is less than 1 minute per
day, Fig. 7. Clepsydra, the most important device for
keeping time in ancient China before the 17th century, was
also erred in 20 seconds to 1 minute a day. Until 1681, the
timepieces with coiled spring and balance wheel were
imported from the West, and the error was just a few
seconds per week. That is to say, the clepsydra was replaced
progressively when the accuracy of mechanical timepieces
improved. Clocks were regarded as elegant art work, rather
than instrument, by Chinese emperors in the early 17th
century [16, 17].
滴水, 水乃漸減, 遂以為輪之運轉, 是水由重而漸減為
輕也; 自鳴鐘以鐵為捲, 置銅鼓之中, 捩之使屈其力,
力由屈求伸, 亦由重而減為輕也。…綜其理, 皆由重以
減輕, 故曰重學也。[19] )
Even though we did not read the definite physical
principle in the article, it shows that contemporary Chinese
got a little sense of potential energy from the power source
of timekeeper [14, 15].
Some series and journals about science knowledge were
published in China during 19 century. Chinese scholars and
foreign missionaries not only translated European literature,
but also selected to compile series, including the book “Shi
Wu Tong Kao” (時務通考, Collected Edition of Western
Science Continued) and the text of “Zhong Xue Qian Shuo”
(重學淺說, Popular Treatise on Mechanics). Subjects such
as machinery, force, gravity, and kinematics were introduced.
However, the communication of mechanics knowledge in
Qing Dynasty is just on conceptual level, and the relation
between theory and its application is not reflected [20].
IV. Classification of Gravity-driven Clocks
Fig. 6. Gravity-driven clock with the verge escapement [17]
Within the collections of the Forbidden City, the number
of gravity-driven clocks is much less than that of springdriven. Nevertheless, the way that a coiled spring drives the
clock is the same, but the methods to apply gravity as a
power source are various [3]. Gravity-driven clocks in the
Forbidden City can be classified into two types, powered by
outer forces and by their own weights, and this classification
is depended on whether there is a relative motion between
the movement and the weight, Fig. 8. The adding weights
are attached to the movements of the gravity-driven clocks.
If the movement is fixed but the weight is falling, there is a
relative motion between the two parts, and it is driven by an
outer force, Fig. 9(a). If the movement and the weight are
fixed together, there is no relative motion between the two
parts, so it is driven by its own weight, as shown in Fig. 9(b).
Each type of gravity-driven clocks is described in the
following sections, along with four gravity-driven clocks
collected in the Forbidden City as examples.
Fig. 7. Huygens clock with a pendulum and cycloidal cheeks [18]
Although Chinese could imitate the Western timepieces in
the Qing Dynasty, most of contemporary people did not
learn relevant science knowledge. Nevertheless, some
people got sense about the physical principle through
observing how clocks work and each component inside. For
example, an article written by Juan Yuan (阮元, 1764-1849)
told about mechanics as following:
The water clock in ancient time works on the following
principle: First, people fill water into a leaking tank. As the
water leaks, the quantity of the water in the tank decreases
and becomes the motive power of the clock. As for the
chime clock in recent days, there is a coiled spring in its
bronze barrel. When one turns the coiled spring, it bends,
gradually stretches, and therefore generates motive power.
Both methods display an application of energy consumption,
which falls in the field of mechanics. (古漏壺盛水, 因漏
Fig. 8. Classification of gravity-driven clocks in the Forbidden City
(a)
(b)
Fig. 9. Relative motion between the movement and the adding weight
A. Clocks driven by an outer force
As shown in Fig. 8, an outer force driven clock is divided
into two types, hanging weight and rolling balls. The detail
of each type is as follows:
A.1 Clocks with a hanging weight
The size of a clock with a hanging weight is usually
bigger than others [5]. Figure 10(a) shows the chime clock
on a sandalwood tower with carved floral patterns. As the
largest timepiece collected in the Forbidden City, it is 585
cm tall and 262 cm in width and thickness, made in the
clock workshop of the Forbidden City during Qianlong
period (乾隆, 1736-1795) in the Qing Dynasty [1]. Figure
10(b) shows how the adding weight is attached to the
movement. The power source is the gravity of a weight
hanging by a rope or chain, and the other end of the
rope/chain wraps a pulley. With the weight falling down, the
pulley turns and transmits force through gear trains to the
movement.
The power-system is a mechanism with four members
and four joints, including the frame (member 1, KF), a pulley
with a pinion (member 2, KGU), a rope/chain (member 3, KR),
and a gear attached to the movement (member 4, KG2). Since
there is no relative motion between the pulley and the pinion,
they are considered as the same member. The pulley with a
pinion is connected to the frame, the gear, and the rope/chain
with a revolute joint (JR), a gear joint (JG), and a wrapping
joint (JW), respectively. The gear is connected to the frame
with a revolute joint (JR). Figure 10(c) shows the structural
sketch.
A.2 Clocks with rolling balls
A clock driven by steel balls is shown in Fig. 11(a). It is
53 cm tall, imported from France during the 19th century. A
large wheel with 12 sections is behind the movement. A box
contains 18 balls is on the clock, and a drawer is at the
bottom for receiving the fallen balls. When 4 balls enter the
divided parts on the wheel and make torque to the shaft, the
clock starts working. With the wheel turning, a ball finishes
half-circle turning and falls into the drawer at the bottom
every 16 hours. At the same time, another rolling down ball
enters the wheel from the box at the top story. The wheel
driven by balls rotates clockwise and transmits torque to the
movement through gears, Fig. 11(b). The users have to move
balls from the bottom drawer to the top box when no ball left.
It is the only one clock with rolling ball mechanism in the
Forbidden City [2, 3].
The power-system is a mechanism with three members
and three joints, including the frame (member 1, KF), a
pinion with a wheel (member 2, KG1), and a gear attached to
the movement (member 3, KG2). The pinion is connected to
the frame and the gear with a revolute joint (JR) and a gear
joint (JG), respectively. The gear is connected to the frame
with a revolute joint (JR). Figure 11(c) shows the structural
sketch.
(a) External [1]
(a) External [1]
(b) Diagram of power-system
(c) Structural sketch of power-system
Fig. 11. Gilded copper clock with a rolling ball mechanism
B. Clocks driven by its own weight
There are two types of clocks that are driven by its own
weight in the Forbidden City, Fig. 8. The detail of each type
is as follows:
B.1 Clocks with falling movement
(b) Diagram of power-system
(c) Structural sketch of power-system
Fig. 10. Chime clock on tower with carved floral patterns
The clock with falling movement was made in France in
the 19th century. It is 53 cm tall, 30 cm wide and 20 cm
thick, Fig. 12(a). The clock consists of four pillars with slots
standing on the base, and pins on the casing of movement
are in the slots. It makes the movement be slid up and down
along pillars. A rack is fixed between pillars on the right side,
and engaged with a gear connected to the movement, Fig.
12(b). The weight and the movement are fixed together. The
clock is “winded” through raising the movement to the top
of pillars every six days. When it falls down by gravity, the
gear turns, transmits power to the movement and makes the
clock work.
The power-system is a mechanism with three members
and three joints, including the frame (member 1, KF), a
pinion with outer sleeve (member 2, KG1), and a gear
(member 3, KG2). The movement remains plumb, so it is
considered as the frame. The pinion is connected to the
frame and the gear with a revolute joint (JR) and a gear joint
(JG), respectively. The gear is connected to the frame with a
revolute joint (JR). Figure 13(d) shows the structural sketch.
The power-system is a mechanism with three members
and three joints, including the frame with a rack (member 1,
KF), a gear (member 2, KG), and a slider (member 3, KP).
Since there is no relative motion between the rack and the
frame, they are considered as the same member. The slider
is connected to the frame and the gear with a sliding joint (JP)
and a revolute joint (JR). The gear is connected to the frame
with a gear joint (JG). Figure 12(c) shows the structural
sketch.
(a) External [1]
(b) Inner [21]
(a) External [1]
(c) Diagram of power-system
(d) Structural sketch of power-system
Fig. 13. Gilled copper clock with a rolling sleeve
(b) Diagram of power-system
(c) Structural sketch of power-system
Fig. 12. Cooper clock with a falling movement
B.2 Clocks with rolling sleeve
Figure 13(a) and (b) show a clock with rolling sleeve,
with 13 cm in diameter and 9.5 cm in thickness. It was also
imported from France in the 19th century. The clock is
driven by its own weight through rolling down a 55 cm long
and 10° sloping board. It is the combination of an outer
sleeve and a movement fixed with weight. When the clock
rolls down the board, a line from 6 to 12 o’clock on the dial
attached to the movement remains plumb because of the
weight. It takes 24 hours for the clock to roll down the board
[21]. A gear attached to the outer sleeve and engages with
another gear that is fixed with the movement. It transforms
gravity potential energy of weight into power for driving the
clock, Fig.13(c).
V. Conclusions
It is necessary to keep a stable and sustaining power
source in timepieces. In the process of searching, many
kinds of power sources were applied to drive timepieces,
including water, gravity, and coiled spring. Timepieces
become smaller and smaller with evolution of power sources,
and the portable timekeepers, watches, were also invented.
Mechanical timepieces not only changed people’s life, but
influenced the development of science and technology.
Importation is a way to communicate. When Jesuit
missionaries brought science instruments and introduced
Western technology in the 17th century, Chinese started
timepiece industry at imitating and improved their products
progressively. With Chinese emperors’ enthusiasms for
Western timepieces, the most exclusive products were sent
to the Forbidden City, and outstanding artisans were
gathered in the imperial clock workshop during the Qing
Dynasty. As the result, timepieces collected in the palace
show the highest level of manufacturing during 17 to 19
centuries, and they cover all kinds of mechanical devices.
Even though the number of gravity-driven clocks is much
less than that of spring-driven in the Forbidden City, the
ways to apply gravity are diversified. Hanging weight is a
typical case to drive clock by gravity, therefore this type of
clocks are familiar. Nevertheless, clocks with rolling balls,
falling movement, and rolling sleeve are rare. They were
imported from France during the 19 century, with artful
designs and unique shapes. Nowadays, these clocks are not
only elegant work of technology, but reflect the
development of timepieces and the highest manufacture
levels in that period.
Acknowledgement
The authors are grateful to the Ministry of Science and
Technology (Taipei, Taiwan) under Grant MOST 103-2221E-006 -040 - for the financial support of this work.
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