 In the period 1603–9, Galileo experimented with inclined planes and, most importantly, pendulums. These studies again exhibited to Galileo that acceleration and, therefore, time is a crucial variable. Moreover, the isochrony of the pendulum—the period depends only on the length of the cord, regardless of the weight of the bob—went some way towards showing that time is a possible term in the equilibrium (or ratio) that needs to be made explicit to represent motion. It also shows that, in at least one case, time can displace weight as a crucial variable.