By means of a lens, a watchmaker gets an enlarged image of the dust which clogs the wheels of his watch. 伯莎M.克拉克.科学通论.
The watchmaker, unassisted by the magnifying glass, could not detect the tiny grains of dust or sand which clog the delicate wheels of our watches. 伯莎M.克拉克.科学通论.
The large wheel at the left is the main wheel, called by watchmakers the barrel. 佚名.神奇的知识之书.