If it tends to thicken the crust of ice on which, as it were, we are
skating, it is all right. If it tries to find, or professes to have
found, the solid ground at the bottom of the water, it is all wrong. Our
business is with the thickening of this crust by extending our knowledge
downward from above, as ice gets thicker while the frost lasts; we should
not try to freeze upwards from the bottom.