The Clockwork 

The room has a double ceiling. The original ceiling, composed of beams and joists, is not visible from below. From this original, Eisinga suspended a second ceiling in which he cut the orbits of the planets. These appear in the second ceiling as flat circles, fixed with strong iron rods to the joists of the original ceiling. The circles can be removed by unscrewing the nuts. Moreover, by lifting hatches in the original ceiling, access can be gained to the clockwork between the two ceilings and to the space over the cupboard-bed and presses.

The cogwheels are mostly made of oak discs and hoops, with wrought iron pins serving as cogs. Only the central clock work, placed over the cupboard- bed, as shown on photo 8, had metal wheels similar to those in more up-to-date works. This clockwork, which Eisinga had made by a clockmaker, is not the main motor: it merely serves to regulate the movement. The whole mechanism is driven by eight weights hanging in the presses on either side of the cupboard-bed. The principal axis has its own weight. so t at power is evenly distributed over all the clockwork. This is how the greater part of the backlash,

which might be considerable with this type of cogwheel, is overcome, practically all the parts being under load. The central clockwork is also driven by a weight. The pendulum swings eighty times a minute and is therefore not a second-pendulum. As it is not self-compensating, its length has to be adjusted whenever there is a big change in the temperature.

The Planet Wheels

The wheels (photo 9) actuating the planets and date pointers are

oak hoops, supported and kept in position by pockwood rollers.

There is a hoop over each groove (the orbits) in the ceiling. The largest and outside wheel moves the date pointer, and rotates once a year. The second in size is the one that brings the planet Saturn round the sun in 29 years 164 days. The third one, just visible in our photo, moves Jupiter. On the side of the date pointer wheel a white pin can be seen.

This is the year cog, which brings into action the mechanism to change the year every 31st of December. The vertical wheel is moved by the date pointer wheel: this transmits the year movement by a long wooden axle to the wheel to which the earth is fixed.

Eccentric Cogwheel

Various moon-pointers turn round at an irregular speed. Eisinga obtained these irregular movements by interpolating ec- centric cogwheels. These eccen- tric wheels mesh into the pins of a so-called rin-wheel so that there is no break in the gearing (photo 10).