Messrs. Editors;—I submit the following solution of "Practical Problem" on page 147: Given AB, arm, C, arm, D, chord of half angle of oscillation of arm, D, and angles of arms, with line AB. To find angles, BAc', ABb, and length of link, E. As the length of arm, D, is to the chord of arc, ab, divided by 2, so is the radius to the sine angle oscillation of arm, D, divided by 4. 360° is to the whole circumference as the angle bBa is to the length of arc ab.

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