D.
So it can be shown that 2 other eyes would see F in positions F and F''.
.'. 4 eyes focused on R see F as F, F, F' and F''.
D.
FIG. 11. THE PATH OF A TACK. WORK DONE BY D AT AGE 11 YEARS.
Discussion
of the determination of the course of a freed tack, T, connected with other tacks by rubber bands.
A. Fig. 1.
[Diagram including points T, T'; band B; and ray L.]
When connected to a tack T' by band B.
Draw T[,] T'[,] or L.
T freed will travel along L, answer.