At the present time, physical science recognizes the following divisions of matter: masses, molecules, atoms, electrons and protons. Matter appeals to us directly in the form of masses. We can readily sense a mass of water, a mass of air or a mass of iron; but it is quite different with the other divisions of matter. Molecules are so small that it takes about seventy billion billion of them laid side by side to extend through the length of one inch.
©1929 by Iowa State Teachers College
"The Structure of Matter,"
Science Bulletin: Vol. 1:
5, Article 4.
Available at: https://scholarworks.uni.edu/science_bulletin/vol1/iss5/4