More about The A-Format & Silver Rectangle - page 2.

If we imagine that the construction in the preceding figure represents the smallest of the sizes, A-5, in rectangle ACDE, we move in the next illustration one size up to format A-4: Fig. 378. Here, with radius AG, we have constructed another square, AKLJ, the upper horizontal sacred cut in which is FH. Thus format A-4 is the rectangle contained by the latter sacred cut, rectangle FHJA.

This is the same geometric construction as we discussed earlier in Fig. 40 with three squares inside each other. It is also the same figure as mentioned by Plato in his account of Timaeus's speech. When we examine the diagram we find that the long side of the smallest format is identical in length to the short side of the next size. Thus we turn A-5 through 90 it fills exactly half of a sheet of A-4 format.

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