Note 90 — Chapter VI · THE AGE OF MODERN CHEMISTRY

In order that these laws may hold good, it is, of course, necessary that the substances are weighed under precisely similar conditions. To state these laws in a more absolute form, we can replace the term “weight” by “mass,” or in preference, “inertia”; for the inertias of bodies are proportional to their weights, providing that they are weighed under precisely similar conditions. For a discussion of the exact significance of these terms “mass” and “inertia,” the reader is referred to the present writer’s Matter, Spirit and the Cosmos (Rider, 1910), Chapter I., “On the Doctrine of the Indestructibility of Matter.”