Richard Bussian, age 11 of West Allis, Wis., for is question:

How do they weigh an atom?

One little atom is too small to be weighed and even too small to be seen. There are various methods for finding the weight of atoms of a certain kind in bulk ‑ and each method calls for a lot of tedious and painstaking work. Furthermore, we cannot weigh atoms in bulk and then give a specific weight for each single atom. The weight of an atom can be calculated only in relation to the weight of other atoms.

For this reason, one atom had to be chosen and given a unit of weight before other atoms could be compared with it and with each other. The atom selected was oxygen, mainly because it combines with most other elements and one of the best ways to weigh atoms involves a complicated ,fob of weighing them in combination with other atoms. Oxygen was given the arbitrary weight of 16 units. One by one the other atoms were weighed in terms of their relationship to the weight of oxygen.