intensity only if the cost of time was the same for all commodities. Presumably, however, it varies considerably among commodities and at different
periods. For example, the cost of time is often less on week-ends and in the
evenings because many firms are closed then,' which explains why a famous
liner intentionally includes a week-end in each voyage between the United
States and Europe.The cost of time would also tend to be less for commodities that contribute to productive effort, traditionally called " productive consumption.