[This is part of a lecture delivered at the Annual Conference of the Association on 31st March 1967. It contains an elementary teaching approach to matrices.]

Let us look at this diagram and consider what it might depict. It might be a map of airline routes between airports in three countries; with two airports, x 1 and x 2, in the first country, three airports y 1, y 2 and y 3, in the second country, and two, z 1 and z 2, in the third. The numbers beside the lines in the diagram might indicate the number of alternative flights (perhaps planes departing at different times) along the routes.