PONDERABLE • E-FREE TRANSLATION.COM • Definition of Ponderable

... diminishing with the latter. The enormous velocity of light in stellar space is attainable because the ether is at the same time of infinitesimal density and of enormous elasticity. Now the ether surrounds the atoms of all bodies, but it is not independent of them. In ponderable matter it acts as if its density were increased without a proportionate increase of elasticity; and this accounts for the diminished velocity of light in refracting bodies. We here reach a point of cardinal importance. In virtue of the crystalline ...

— Six Lectures on Light - Delivered In The United States In 1872-1873 • John Tyndall