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.
1. 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.
2. 360° is to the whole circumference as the angle bBa is to the length of arc ab.
3. Now arc ab is equal to arc a'c'.
4. The whole circumference is to 360° as the length of arc a'e' is to the angle oscillation of C divided by 2.
5. Half angle oscillation, C, taken from angle BAa' is equal to angle BAc'.
6. Half angle oscillation, D, taken from angle ABa is equal to angle ABb.