B. FRANKLIN.
TO THE SAME.
[Magical Circle.]
Sir,
I am glad the perusal of the magical squares afforded you any amusement. I now send you the magical circle. ([See Plate XII.])
Its properties, besides those mentioned in my former, are these.
Half the number in any radial row, added with half the central number, make 180, equal to the number of degrees in a semi-circle.
Also half the numbers in any one of the concentric circles, taken either above or below the horizontal double line, with half the central number, make 180.
And if any four adjoining numbers, standing nearly in a square, be taken from any part, and added with half the central number, they make 180.