What makes blood clot? (Vol. 4, p. 81.)
Are there any red-haired human races? (Vol. 12, p. 823.)
Why does a cut apple turn brown? (Vol. 21, p. 756.)
What makes negroes black? (Vol. 25, p. 190.)
Are men or women oftener colour-blind? (Vol. 28, p. 139.)
Why do stars twinkle? (Vol. 23, p. 29.)
What happens in your throat when you sob? (Vol. 23, p. 195.)
What change in water, as it freezes, makes ice float? (Vol. 14, p. 227).
Why is the shadow cast by an electric light sharper-edged than the shadow cast by the sun? (Vol. 24, p. 758).
Why does fright make people faint? (Vol. 27, p. 942).