98 JOVARIUM *792 (724 ) Fig’ 111
By George Adams, London
Signed on the face plate: G. Adams Mathematical Instrument Maker to his
MAJESTY N°6o Fleet Street LONDON
Height to face plate 312, diameter of face plate 223; length of umbraical tube 345.
The construction follows that of the planetarium (Cat. 95). The face plate is engraved
with a calendar scale, and at the 31 December side of centre is a 24-hour clock
face and a single pointer. Inside the clock face is marked on one side DAY and on
the other NIGHT. When the crank is turned, the four ivory Jovian moons rotate in
their orbits and so pass through the black-painted tin-plate tube representing the
planet’s shadow as seen from the earth. This model can be used to demonstrate the
method of finding the longitude by noting the positions of the moons, as it gives
their relative angular velocities.
The discovery of the moons of Jupiter was made by Galileo Galilei in 1609, by
means of his new telescope.
The decision to buy two pieces of apparatus from Adams to show the planets Jupiter
gnd Saturn was taken on 14 October, 1791, and they were to cost between f 300 and
ƒ 400. Adams announced their despatch in a letter of 16 March, 1792; their combined
price was 32 guineas.
Adams|i79« 539.
Inv. 74/3
99 SATURNIUM 1792 (721) Fig. 112
By George Adams, London
Signed on the face plate: G Adams Mathematical Instrument Maker to his
MAJESTY N° 60 Fleet Street LONDON
Height to face plate 317, diameter of face plate 223; Saturn sphere diameter 23,
Saturn ring outer diameter 55, orbital radius of outermost moon 590.
The construction is similar to that of the planetarium (Cat. 95). The face plate is
inscribed with a calendar and zodiac scale only, apart from the signature. On this
model there are seven moons, whereas on the planetarium there are, oddly enough,
eight. William Herschel discovered nos,, six and seven in 1789, and the eighth was first
observed in 1848. Adams was almost certainly anticipating that Herschel would soon
discover an eighth moon for the benefit of his sales.
On 14 October, 1791, the decision was taken to buy this model together with a
Jovarium (Cat. 98) for between ƒ 300 and ƒ 400. Each instrument probably cost
16 guineas.
Adams (1790) 539.
Inn. 74:4