In either case the distance through which the prongs move is very small and the period is very short, so that the eye can seldom detect the movement itself. 伯莎M.克拉克.科学通论.
If a light cork ball on the end of a thread is brought in contact with a sounding fork, the ball does not remain at rest, but vibrates back and forth, being driven by the moving prongs. 伯莎M.克拉克.科学通论.
The passengers slide off upon the prongs of the comb at the top and land without jar or shock. 佚名.神奇的知识之书.
The platform glides through the prongs of a comb at the lower level and journeys upward at a moderate speed. 佚名.神奇的知识之书.
That the prongs are in motion, however, is seen by the action of a pith ball when brought in contact with the prongs (see Section 250). 伯莎M.克拉克.科学通论.