Dear Father,

If the impact of a weight falling on a horizontal plane is unity—the following table will give it for the other inclinations²

This may be epitomised thus, less to 40^o the impact is about $\frac{9}{10}$ at 40^o it is $\frac{3}{4}$, 45^o it is $\frac{7}{10}$, at 50^o = $\frac{2}{3}$, at 60^o = $\frac{1}{2}$, at 70^o = $\frac{1}{3}$ at 80^o = $\frac{1}{6}$ & at 90^o of course 0^o

Your affectionate Son | G H Darwin