252 | 24 TURING, lOVElACE, AND BABBAGE
figure 24.1 Difference Engine No. 1 demonstration piece, 1832 (top). View from above showing crank
handle (Bottom).
Photographs by Doron Swade.
between y (the dependent variable) and x (the independent variable) and the equation defines
the value of y for each value of x. By convention the ‘solution’ (also called the ‘root’) of the
equation is the value (or values) of x for which y is zero. In our example there are two roots:
+1 and –1. In Babbage’s engine the value of y appears on the last column and each cycle of the
engine increases the value of x by a fixed increment, usually 1, and produces the correspond-
ing new value of y. When the value of x coincides with a root, the result on the last column is all