This toy was designed in 1987 by Werner Bartmes, and sold by the NAEF company. It was not available for very long, probably because it was quite expensive.
It is water filled, and each side has a pattern of black and white lines, and also a disc which also has a pattern of lines on it. In one case the disc is slightly denser than water, and you need to angle the toy so that it rolls downwards. The disc on the other side is slightly lighter than water, so in this case you angle the toy so that this disc rolls upwards.
In either case though, the straight lines in the background, and the slowly revolving lines on the moving disc interact, and create an ever changing array of moiré patterns.
Like many water filled toys, this one has lost a bit of water over the years, but luckily it had a very smart filler at one end, that could be opened with an Allen key, so Tim was able to top it up and restore it to it’s original condition. Quite often, when Tim gets out one of his cases of toys that is thirty or more years old, we have quite a bit of fun (if that is the right word) getting things working. Sometimes a bit of oil is all that is needed, or topping up the water. Other times, Tim takes the whole thing apart, in order to effect major repairs.
