part 17

160 Air travel would have seemed very strange two or three thousand years ago, to men keeping their sheep on the mountainsides. All these changes are the outcome of the great step taken in the invention of numbers. Before men could count, how did anyone know which were his sheep and which were another man's? He put his mark on his sheep. He was their owner. They were his own sheep. He owned them. Sometimes he gave his sheep names, and then he would go through all the names—with his sheep—to see if they were all there.

161 Before the invention of writing how did people keep records? They made pictures on soft earth or sand. But rain and wind and waves quickly washed away such records. Smooth stone or wood was better, and best of all, the smooth stone walls of caves whose roofs kept the rain and wind away. It may be that the drawings copied on page 142, or others like them, were records made by early humans. (Someone recording animals on a cave wall may have taken pleasure in the drawing for itself and become the first artist.)

162 How did a man know how many sheep he owned? Sometimes he used small stones or sticks, putting one of them into a bag or pocket for each sheep he had. When he came to the end of his sheep, the number of stones in the bag was the same as the number of his sheep. The stones and the sheep were equal in number. The stones gave him a record of how many sheep he owned. When a sheep died he could take a stone out of the bag. And when lambs were born he could put in another stone for each lamb.

163 Sometimes a record was made by taking a sharp, hard stone and making cuts on a stick. The number of cuts in the stick equaled the number of things to be recorded. Then the stick was cut in half down the middle so that each half had half of every cut on it. The two half sticks were tallies. If they were put side by side, the halves of the cuts came together. They tallied. One man took one tally and another the other, and both then had the record.

164 Tallies are some of the earliest and simplest records of the numbers of things. They tell how many things have been counted. Even today in a bank a person who takes money in and gives it out is sometimes named a teller. The shelf or table where the teller works is a counter. On it the teller does the counting of the money coming in and going out, and keeps a record of all this in an account book. A person who makes a statement tells something. Most banks make a statement every month to each person banking with them to tell them what their account is. The statements tell them how much money they have in the bank at that date. Then both they and the bank have the record straight. To get these statements ready, the banker has to take the amount of money given out (for any one person) from the amount of money put in.

165 Bank tellers must keep a complete record of the money they take in and give out. This is their way of making certain that their accounts are in order. Banking is a very important sort of business. A bank must keep all its accounts in good order and the statements which the bank makes must be true statements.