40 Fig. 39
39 PARABOLIC TRAJECTORY % i8th C. . j f l é f l Fig. 38
By J. Kampman and Adam Steitz, Amsterdam
Overall length 640, height 400; ball diameter 15.
Constructed in mahogany, with the base of the track of boxwood. The adjusting
screws, plumb-bob and rings are of brass. There are two ivory balls.
The board is cut with a quadrant-shaped channel, so that a ball may be released
from the top, roll down, and be projected horizontally into the air. The resulting path
of fall is a parabola, and to demonstrate this four brass rings are fixed to another
board for the ball to pass through. The design of this apparatus!" appears to be
’s Gravesande’s.
’s Gravesande (1748) XIX, fig. 3; Nollet «764) leçon 5, III, fig. 11 ; libeling ( 1789;
29, lot 117 .
Inv. * iojy
40 REBOUND TRAJECTORY % 18th C. % i ) Fig.39
By J. Kampman and Adam Steitz, Amsterdam
Overall width 510, depth 230, height 710.
Made of mahogany, with boxwood inlay and adjusting screws, beech wedges, and
a marble slab.
This apparatus demonstrates elastic rebound when an ivory ball falls on a marble
slab. The slab can be supported at three angles by using two wedges cut for i ÿ l
and 30°, which in combination make up 450. At the top, a brass catch may be put
into one of three positions corresponding to the angle chosen, and one of the sets of
inlay show the path the ball should follow. A straight line is also included to show
that, initially, the angle of reflection equals the angle of percussion. In the Inventory,
Van M arum has attributed this apparatus to Steitz; it will have been bought at the
Ebeling sale, lot 124.
Nollet (1764), leçon 4, V, fig. 11 ; Ebeling (1789) 32.
Inv. *12/1
J54
41 PROJECTILE TROLLEY V4 18th C. (14) Fig. 40, 41
By J. Kampman and Adam Steitz, Amsterdam
Platform 380 x 115, overall height 180; diameter of wheels 134, of cup 70, of ball 15.
The mahogany platform is provided with a lead plate underneath to increase stability ;
it moves on mahogany wheels with brass hubs. The drive to this trolley is a spring
whose brass drum, fitted with pawl and ratchet, winds a cord attached to an ivory
fusee that is fixed to the front axle, so ensuring constant speed. The other axle winds
up a cord attached to a trigger, which releases a powerful, steel, leaf-spring to eject
an ivory ball from the cup on top of the trolley. When the ball returns to the ground
it is intended that it fall back into the cup to demonstrate that the uniform horizontal
motion of the trolley is imparted to the ball. With respect to an outside observer, the
ball follows a parabolic path.
Whiston had a moveable trolley with a high pole and a trigger mechanism that
released a ball from the top of the pole. This was to show: “ that all respective
Motions on the Earth must be the very same, while it self moves as if it were at
rest” .
Whiston H1714) Mechanicks VI, fig. 9; Nollet (1764) leçon 5, III, fig. 13, a
different mechanism to show the same effect; Ebeling (1789) 27, lot 109; Utrecht
(1968) M24, a closely similar model.
Inv. 8jj
*55