TO MISS CAY.  June 1845.

I have drawn a picture of Diana, and made an octohed-ron on a new principle, and found out a great many   things in geometry. If you make two circles equal, and make three steps with the compasses (of any size), and cut     them out in card, and also three equal strips, with holes at each end, and joint them with thread to the upper side  of one circle and the lower side of the other; then if you put a pin through the centre of one and turn the other, the  one will turn, and if you draw the same thing on both in the same position,—if you turn them ever so,—they will     always be in the same position.