Molecular models for demonstration to the visually impaired, 20th century.
© Science Museum / Science & Society Picture Library
These are simple models showing the structure of various molecules. Designed for use by visually impaired people, the balls are of various sizes, each size representing a different element. For sighted people, the elements are usually differentiated by balls of different colours. The models represent (clockwise from top); benzene (C6H6), water (H2O), carbon dioxide (CO2) and oxygen (O2).