The Rolling Ball Web
An Online Compendium of
Rolling Ball Sculptures, Clocks, Etc.
By David M. MacMillan et. al.
The distinction between the use of a rolling ball in an actual scientific experiment and its use in a salon or classroom demonstration device is difficult. In part, this is because the use of rolling balls in science predates the establishment of modern criteria for experiment. Much of the early history of rolling balls is obscured both by time and by legend, especially in the case of Galileo. The divisions here should not be considered firm.
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The demonstration of scientific and mechanical principles by means of lectures accompanied by demonstration apparatus reached a high point in the 18th. century. At this time, it became an accepted part of the training of a well-educated person. Since the 18th. century, popular scientific demonstration of this sort has been in decline. ( Stafford has written an excellent book on the subject of 18th century scientific demonstration.)
In this type of device, a ball rolls down a short incline or curve so as to gather speed; it then exits into free space in a horizontal direction. The path followed by such a ball is a parabolic trajectory. Often, this trajectory is indicated by rings arranged along the parabola, through which the ball travels.
Morton and Wess, in
Public and
Private Science,
attribute the invention of this device to
's Gravsende,
and cite its appearance in:
Morton and Wess illustrate two examples from the King George III collection at the Science Museum (London).
The first example, "D24," "Path of Projectile Apparatus," on page 156, is an apparatus thought to be from the collection of S.C.T. Demainbray, George III's science tutor. It is 630mm long x 220mm wide (200mm at one end) x 370mm high, and made of wood with metal hardware. Science Museum (London) Inventory No. 1927-1112.
The second example, "M75," Path of Projectile Apparatus," on page 348, is thought to have been made by G. Adams for King George III. It is 615mm long x 430mm high x 198mm high. It uses a ball whose diameter is alternately given as 25mm and 3/4 inch. Science Museum (London) Inventory No. 1929-114. Curiously, Turner illustrates this same apparatus (1927-1127) and attributes it to the early 19th century (Turner 77).
The cycloidal curve is, in general, a curve generated by a point on a circle when that circle is rotated on another curve. An epicycloidal curve is generated by a circle rolling on the outside of another circle; a hypocycloidal curve is generated by a circle rolling on the inside of another circler. A cycloidal curve has the property of being isochronous; a pendulum bob swinging in a cycloidal arc will take the same time to complete an oscillation whatever the amplitude of that oscillation. [Is this true of all cycloidal curves? I need some assistance from a physicist here.] Similarly, two balls released at different points on identical cycloidal curves will reach the bottom of the curve at the same time.
Morton and Wess, in
Public and
Private Science,
attribute the invention of this device to
's Gravsende,
and cite its appearance in:
Morton and Wess illustrate two such devices from the King George III collection at the Science Museum (London).
The first of these, "M69," "Cycloidal Channels," on page 344, was constructed by G. Adams for the King. It is 760mm long, 315mm high, and 245mm wide; it uses 33mm ivory balls. It consists of two parallel cycloidal channels with scales along them and movable stops. Science Museum (London) Inventory No. 1927-1127. Curiously, Turner illustrates this same apparatus (1927-1127) and attributes it to the early 19th century (Turner 78).
The second of thes, "M72," "Straight and Cycloidal Channels," on page 346, was also constructed by G. Adams. It is 880mm long, 310mm high, and presumably 190mm wide (there seems to be a typographical error here). It uses 1/2 inch ivory balls. This apparatus consists of a single channel which begins and ends at the same level, together with a straight channel which may be adjusted to a variety of angles. Both channels have movable stops. The ball in the cycloidal channel will reach its stop more quickly. Science Museum (London) Inventory No. 1927-1128.
Although these are legitimate scientific demonstration devices, I've filed them on the "Toys and Games" page under the heading of model roller coasters.
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2.3, 1998/06/18.
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