I.down1[美 daʊn, 英 daʊn]副down often appears as the second element of certain verb structures in English (back down, clamp down, tone down, etc). For translations, see the relevant verb entry (back, clamp, tone, etc).
This created a giant bifocal system which allowed him to see the blackboard through the right side, then use the left side to write down what he had seen.
Although the theory is typically formulated in four dimensions, one can write down the same equations for the gravitational field in any number of dimensions.