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The practical usefulness of puzzles is a point that we are liable to overlook.  Yet, as a matter of fact, I have from time to time received quite a large number of letters from individuals who have found that the mastering of some little principle upon which a puzzle was built has proved of considerable value to them in a most unexpected way.  Indeed, it may be accepted as a good maxim that a puzzle is of little real value unless, as well as being amusing and perplexing, it conceals some instructive and possibly useful feature.  It is, however, very curious how these little bits of acquired knowledge dovetail into the occasional requirements of everyday life, and equally curious to what strange and mysterious uses some of our readers seem to apply them.  What, for example, can be the object of Mr. Wm. Oxley, who writes to me all the way from Iowa, in wishing to ascertain the dimensions of a field that he proposes to enclose, containing just as many acres as there shall be rails in the fence?

The man wishes to fence in a perfectly square field which is to contain just as many acres as there are rails in the required fence.  Each hurdle, or portion of fence, is seven rails high, and two lengths would extend one pole (161/2 ft.):  that is to say, there are fourteen rails to the pole, lineal measure.  Now, what must be the size of the field?

118.—­CIRCLING THE SQUARES.

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The puzzle is to place a different number in each of the ten squares so that the sum of the squares of any two adjacent numbers shall be equal to the sum of the squares of the two numbers diametrically opposite to them.  The four numbers placed, as examples, must stand as they are.  The square of 16 is 256, and the square of 2 is 4.  Add these together, and the result is 260.  Also—­the square of 14 is 196, and the square of 8 is 64.  These together also make 260.  Now, in precisely the same way, B and C should be equal to G and H (the sum will not necessarily be 260), A and K to F and E, H and I to C and D, and so on, with any two adjoining squares in the circle.

All you have to do is to fill in the remaining six numbers.  Fractions are not allowed, and I shall show that no number need contain more than two figures.

119.—­RACKBRANE’S LITTLE LOSS.

Professor Rackbrane was spending an evening with his old friends, Mr. and Mrs. Potts, and they engaged in some game (he does not say what game) of cards.  The professor lost the first game, which resulted in doubling the money that both Mr. and Mrs. Potts had laid on the table.  The second game was lost by Mrs. Potts, which doubled the money then held by her husband and the professor.  Curiously enough, the third game was lost by Mr. Potts, and had the effect of doubling the money then held by his wife and the professor.  It was then found that each person had exactly the same money, but the professor had lost five shillings in the course of play.  Now, the professor asks, what was the sum of money with which he sat down at the table?  Can you tell him?