Later it was found that H₂O had 11% H and 89% O.

Hence the ratio of the wt of O to that of 2H was 89:11.

Thus the ratio of the wt of O to that of 1H was 89:5.5 or 16:1.

Since H was the lightest element that could be found, it is assigned an atomic wt of 1.

In this way, the ratio of the weights of the atoms of the various elements could be determined.

This method only determines relative weights and one atom must be assigned an arbitrary weight.