Add 0 and 3. Add 2 and the negative of 1. Find which result is greater. Select 3 if this result equals 2; otherwise select 2. To work out the coding for this and like problems would be a good exercise. Simon, in fact, is a rather clever little mechanical brain, even if he has only a mentality of 4. It may seem that a simple model of a mechanical brain like Simon is of no great practical use. On the contrary, Simon has the same use in instruction as a set of simple chemical experiments has: to stimulate thinking and understanding and to produce training and skill. A training course on mechanical brains could very well include the construction of a simple model mechanical brain as an exercise. In this book, the properties of Simon may be a good introduction to the various types of more complicated mechanical brains described in later chapters. The rest of this chapter is devoted to such questions as: How do transfers of information actually take place in Simon? How does the computer in Simon work so that calculation actually occurs? How could Simon actually be constructed? What follows should be skipped unless you are interested in these questions and the burdensome details needed for answering them. SIMON’S THINKING—TRANSFERRING INFORMATION The first basic thinking operation for any mechanical brain is transferring information automatically. Let us see how this is done in Simon. [Illustration: FIG. 4. Scheme of Simon.] Let us first take a look at the scheme of Simon as a mechanical brain (see Fig. 4). We have 1 input, 8 storage, 5 computer, and 1 output registers, which are connected by means of transfer wires or a transfer line along which numbers or operations can travel as electrical impulses. This transfer line is often called the _bus_, perhaps because it is always busy carrying something. In Simon the bus will consist of 2 wires, one for carrying the right-hand digit and one for carrying the left-hand digit of any number 00, 01, 10, 11. Simon also has a number of neat little devices that will do the following: When any number goes into a register, the coils of the relays of the register will be connected with the bus. When any number goes out of a register, the contacts of the relays of the register will be connected with the bus. For example, suppose that in register _C_5 the number 2 is stored. In machine language this is 10. That means the left-hand relay (_C_5-2) is energized and the right-hand relay (_C_5-1) is not energized. Suppose that we want to transfer this number 2 into the output register _O_, which has been cleared. What do we do?