Each day is subdivided into 24 hours ' The pointer, going round once a week, indicates the exact day and hour, solar time. It also shows the sign of the zodiac for each day after which that day was originally named: Sunday, the Sun; Monday, the Moon, Tuesday, Mars, Wednesday, Mercury; Thursday, Jupiter; Friday, Venus; Saturday, Saturn.

Between the circumference and the centre of the day dial, a rectangular space has been cut which shows the year. On the 31st of December, about 4 p.m., the number of the year begins to move automatically: next morning the number of the new year appears in the right place.

At the end of every 22 years a disc bearing 22 new year numbers has to be painted.

Moon Dials

On the right hand side of the day dial on the ceiling are two more dials. The first indicates the position of the mounting or northern node (point of intersection) of the moon orbit and the signs of the zodiac. Photo 5 shows part of the wooden wall over the cupboard-bed and presses.

Here there are two more dials. One indicates the hour of the setting of the moon, the other the distance between the moon and the northern node.

The nodes are the points of intersection of the moon orbit and the plane of the earth orbit, One half of the moon orbit lies, so to speak, over the plane of the earth orbit, the other half under it. At two points the plane of the earth orbit is cut by the moon orbit. Those points of intersection, the nodes, are not stationary but move along the signs of the zodiac once every 18 years and 228 days.

Accordingly the pointer on the ceiling, indicating the place of the northern or mounting node among the signs of the zodiac, does one complete circuit in the same time. The monthly movement of the earth brings the moon twice a month into a node. The pointers of the dial on the pilaster indicate the distance of the moon from the northern node. This distance is expressed in zodiacal signs and degrees.

'The sky has risen or the earth descended'

'The sky has risen or the earth descended...' These words once must be exclaimed by Eise Eisinga, accompanied by a couple of students, on one of the bastions of the city. Eise Eisinga was sitting on a tabouret surrounded by the students when he was called away. The students decided to pull a joke on him, and they saw off all four legs of the tabouret. But Eise Eisinga presumably didn't go for it, because, when he returned to sit on his (shortened) tabouret, his diagnose was 'that the sky has risen or the earth descended'.

The big pointer indicates the degrees, the small one the signs. If both pointers stand at zero, then the moon is in the northern node; if the small pointer stands at six and the big at zero, than the moon is exactly six signs away from the northern node, i.e. in the southern node.

Should the moon be in one of the two nodes when the moon phase pointer indicates new moon, then that day there will be an eclipse of the sun somewhere in the world. But if they indicate full moon, then there will be an eclipse of the moon.

To get an exact indication of these phenomenal, Eisinga had to devise his mechanism in such a way that the pointers not only came round in the correct time, but that just like the real moon they moved with irregular speed. This he accomplished by interpolating eccentric cogwheels.

As in the previous reproduction, photo 6 also shows four dials. On one of the dials on the ceiling, the farthest point of the moon orbit, the apogee, in the sign of the zodiac has been marked. The moon follows an elliptic course round the earth in which the lat-