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Crossover puzzle
Above:Front view
Click a thumbnail to see its larger version and description.
A puzzle back from the early 1980s produced by Nintendo. It works with intersecting plunges and polarised light.

The crossover puzzle was invented by Gupei Yokoi (R&D Manager at Nintendo) in 1981. It is described in USA pattern 4,402,510.

The Crossover puzzle uses polarisation filters. If 2 identical polarisation filters are positioned behind each other, light passes through these filters and the filters appear transparent or light. When applying 2 different filters, light is blocked and the filters appear nontransparent or dark.

The Crossover puzzle contains two planes with such polarisation filters. One plane consist of 16 square filters. These filters are placed at the inside of the transparent top of the puzzle. They form a 4x4 pattern and are fixed in position. So, they remain at their positions also when the sliders of the puzzle are moved. These 16 filters are orientated such that for every filter, all neighbouring filters in horizontal and vertical direction have a different polarisation filter (so the 2 kinds of filters are alternating).
For the second plane, the polarisation filters are attached to the 8 sliders (4 rows, 4 columns) which each can be moved between 2 positions. Each slider contains 5 of such filters of which 4 are visible and 1 is hidden when the sliders are in the end positions.
So, there are 24 polarisation tiles in this second plane of which 8 are of the one polarisation type and 16 of the other type.
When moving a slider from one end to the other end, 1 filter of the second plane disappears, 1 filter of the second plane becomes visible and 3 filters remain visible but will move one position along with the direction of the movement of the slider. Due to the alternating polarisation direction of neighbouring filters in the fixed first plane, the 3 filters in the moving second plane that remain visible will change colour (from light to dark or vice versa). This can be rather confusing.

This is explained in the pictures:
In picture #3, the 3rd row from above displays 4 positions. Let�s call these positions 1, 2, 3 and 4 (from left to right).

When moving the slider of this row from left to right, the moving filter (of the second plane) that is initially in position 1 (creating a dark field in position 1) moves to position 2 and changes colour to become light.
The second moving filter, that is initially in position 2 (creating a light field) moves to position 3 and changes colour to become dark.
The third moving tile, that is initially in position 3 (creating a light field) moves to position 4 and changes colour to become dark.
The result is shown in picture 4.

In the halfway position, it can be observed that each of the 3 moving filters is changing colours. This halfway position is shown in picture 5.

The aim of the puzzle is to create certain patterns, e.g. all positions dark, all positions light, a checker pattern or a line pattern.
There are 3 kinds of Crossover puzzles, with all purple tiles, all green tiles or all red tiles (as displayed here).

The initial selling price of the puzzle in Japan in 1981 was Yen 1000.
Due to the low quantities that were produced the puzzle is extremely rare and rather costly (if one can find a sample at all).

About the polarisation principle.
Light is a transverse electromagnetic wave. Natural light is generally unpolarised, meaning that all planes of propagation are possible.
Light that passes a polarisation filter becomes linearly polarised which means that the light propagates as a flat plane wave in space.
When two polarisation filters are placed behind each other that allow the same plane of light to be passed, light will pass through both filters.
When one of these filters is rotated 90 degrees, the light is blocked.
This is the principle used in the Crossover puzzle. It contains polarisation filters that are polarised in the same direction as well as filters that are rotated 90 degrees with respect to these filters.

This principle can also be observed in practical life. Blue sky light (from directions not too close to the sun) e.g. is linearly polarised and can be blocked with a polarisation filter. Rotating such a filter 90 degrees will allow the light to pass again and rotating the filter once more 90 degrees will again block the light. The principle is also applied in certain sun glasses making use of the fact that reflected light (e.g. from shinny, reflecting surfaces) is often linearly polarised.

Width: 90 mm
Height (including lid): 32 mm
Weight: 150 grams

Photo #9 is copyright by Nick Baxter. All rights reserved.

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Thank you to the following people for their assistance in helping collect the information on this page: Geert Hellings.

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