5) One hollow, boxwood cylinder (length 42) with four brass hooks embedded, into
which lead weights may be fitted and on the end of which a cap can be screwed to
contain clay. Four boxwood end-caps to screw onto the cylinder, for holding clay to
receive the indentations from the heads; op. cit. fig. 10, 11.
6) Two cylindrical lead weights with a brass hook at one end, to fix into the boxwood
cylinder; op. cit. fig. 5.
7) Two ivory balls (diameter 39) with a pair ofbrass hooks embedded, for Newton’s
impact experiment; ’s Gravesande (1748) XXVI, fig. 7G.
8) Six ivory balls (diameter 25.5) with a brass hook, for showing the transmission
of momentum by impact from ball to ball along the row of six; ’s Gravesande (1748)
XXXVII, fig. 7 - 1 1.
9) Three ivory cylinders (two of length 58, and one of length 40), flat at one end
and domed the other, with four brass hooks embedded, for ballistic pendulum;
’s Gravesande (1748) XXVI, fig. 7C, B; see also Cat. 53.
Inv. *12/2
53 PERCUSSION PENDULUM APPARATUS s/4 18th C. Jnii) Fig* j f c P |X
A shaped mahogany board (width 650,:) is held vertically by a bracket that fits into
the slot in the column. It carries in a groove two sliding boxwood scales (each of length
335) marked 0-23, divided into tenths. The top edge of the board carries two brass
pointers. This board also has two holes for fixing the clay tray described under
Cat. 52/4. ,r.
The percussion bodies are suspended from a frame that attaches to the top of the
column. An iron, square-sectioned rod (length 430) projects from the column and
bears, crossways, two brass bars (length 260) that carry cord attfljhment points with
turn-keys. By means of this frame, four cords, are attachable to each percussion body,
and the arrangement endeavours to allow the impact force to be solely in the
horizontal direction.
On 11 March, 1790, Van Marum attended an auction sale of instruments jield
in Amsterdam. He bought there a percussion apparatus for ƒ 34-10-0, and this
probably comprised the items listed under Cat. 52 and 53.
’s Gravesande (1748) XXVII, fig. 1; XXVIII, fig. 2, 3; sec also Cat. 52,
Inv. *i^ji
54 THE WEDGE ' % 18th C. ;f| 1105/1 ,2) Fig. « 5 7
1) Two adjustable wedges of boxwood. One is a se«-wedgeab<iairds: width 63,
length oflonger 310) marked with its weight, 8 oz. The Other is a symmetrical wedge
(boards 160 x 62) marked with its weight, 7 oz. Both wedges are adjusted by a locking
screw acting on an arc ofbrass.
2) Ten boxwood triangles for setting the angles between the boards that constitute
the wedge. The triangles are marked with the horizontal and vertical forces appropriate
to the angle of the wedge, that is, the weights that have to be used between the
rollers and at the bottom of the wedge. Five are for the semi-wedge: 2*816, 3*'/2:i6,
4*/2:i6, 5*/2:i6, 6*/2 : i 6 ; and five are for the symmetrical wedge: 5:16, ®:t6> 9: 16,
11:16, 13:16.
3) " Two boxwood rollers (length 152, operational diameter 45.7) provide the reaction
to the wedge. Two brass hooks with two small pulleys attached to each, carry the
weights acting on the rollers.
4}; Mahogany board (155 x 115) with six turn-pegs to adjust the cords supporting
the rollers. This board mounts on the top of the column.
5|f,i Mahogany frame (160 x 144 x 30) with three boxwood rollers. Central roller as
above; two side rollers (operational diameter 25.7) rotating in brass strips that can
move about the axis of the central roller. This frame mounts in the slot in the
column. It is used in conjunction with one of the large rollers and the semi-wedge.
The long, vertical side of the wedge slides past the fixed set of rollers while the angled
board forces the other roller away. Two pulleys in brackets to attach to the frame
carry the weights acting on the roller.
The experiment with the symmetrical wedge is shown in fig. 53. The arrangement
is derived from that illustrated in Whiston.
Whiston (1714) Mechanicks IV, fig. 5 ; ’s Gravesande ( 1748) X, fig. 2 ; Musschenbroek
{i 762) VII, fig. 8, illustrates the roller frame and semi-wedge.
Inv. 4I1
55 BALANCE BEAM »/4 18th C. (nil)
f il A mahogany bar (655 x 50 x 2ô| faced with boxwood and engraved with a centre
zero scale. Along the centre line runs a slot into which pulley brackets may be pressed.
This bar mounts in the slot in the column.
igfl ^ thin boxwood beam (length 655) marked with a centre zero scale as above, with
two brass hooks attached. -
With these two pieces of equipment, the beam may be kept in horizontal equilibrium
by attaching weights directly to the beam to act downwards, and other weights over
pulleys pressed in the bar acting upwards.
’s Gravesande Ét 748) VIII, fig. 3, 4.
Inv. js f/ jv '
56 LEVELLING BOARD Éjjgi8th C. (63;
A mahogany board (1,040 x 250«upported on two fixed feet at one end and on an
adjusting screw at the other. From the centre rises a bar (length 230) to carry a
plumblinc (missing). On the top edge are two moveable brass projecting stops to mark
the extreme positioifptof a pendulum bob.
’s Gravesande^||i 748) XV, lig. 6, shows the levelling board in use with the bar in
Cat. 55.
Inv, u/g P
57 HAMMER 18th C. (1103) Fig. 57
Mahogany block '450 x 65 x 30) with an ivory, cylindrical hammer-head (height 75,
diameter 38) mounted on a thin iron rod. At one end isg ibrass strip, hinged and notched
to support the rod in a flexed position, with a hole for a pull-cord to release the rod.
Below the hammer-head are two slightly overlapping circular holes in the block, with
É metal strip between them. A ball located in one of the holes can be ‘fired’ by
pulling the trigger cord. A second ball is lightly attached to the first with wax, and
is dislodged when the first is struck. This is to demonstrate the difference between falling
under gravity alone, and with an added impulse.
Nollet !)i;764[»eçon 3, I, fig* g, illustrâtes the hammer.
58 INERTIAL CYLINDERS 3/4 18th C. (1110/1,2)
a Mahogany cylinder (height 265^ diameter 47) supportable by two cords,
b Maho gany cylinder (height 265, diameter 23) supportable by two cords, which
is weighted at each end by two screw-on disks of lead. The inertia of the cylinders can
be investigated by oscillating the cylinders in a horizontal plane.