A third complication caused by the Industrial Revolution is that technologies that serve the same function at different times often cannot be readily compared in economic terms.

In the nineteenth century housework was done by hand or by servants (hired hands). Today washing machines, food processors, dryers, Scotchgard, dishwashers, vacuum cleaners, wash-and-wear clothes, and a host of other inventions have changed matters completely. Although the real cost of a maid has increased greatly over the last hundred years, the need to have one has drastically diminished.

A hundred years ago private transportation was by horse and carriage; today the automobile fills that role. Both are expensive in terms of the percentage of average annual per capita income required to buy them, although the automobile much less so. But a horse and carriage is very much more expensive to run than a car. A car can be parked on the street, but a horse must be stabled and cared for. A car burns gasoline only when it is running; a horse burns oats day in and day out. Furthermore, a horseless carriage’s capacities are so much greater, its comforts so much more extensive, and the skills required to operate it safely so much less difficult to master, that the two means of transportation can hardly be compared at all in money terms.

Consider an extreme example of technology on the march, for here, really, is the most difficult problem faced by the historian in translating money over time in the modern era. In the mid-eighteenth century Prince Nikolaus Esterhêzy, a Hungarian nobleman, had a passion for music. Being one of the richest men in Europe, he could afford to indulge this passion with a state-of-the-art music reproduction system, and indulge it he did. He maintained his own private orchestra, chorus, and five-hundred-seat theater. Presiding over this vast musical establishment was the great composer Haydn.

While Esterhêzy still lived, however, the mechanization of music reproduction began with the invention of the music box, and today anyone with the price of a portable cassette player can possess a system that would astound Esterhêzy. The two systems are not the same, of course. The fidelity of Esterhêzy’s was, by definition, perfect, while that of the Walkman is only superb. And Esterhêzy’s system could compose original masterpieces on request, no mean feature. But the Walkman has advantages of its own that Esterhêzy would have greatly admired. It is a lot easier to take to the beach; it does not need to be fed, clothed, and housed; and one needn’t worry about its getting the upstairs maid pregnant.

And the Walkman has one capacity that would boggle Esterhêzy’s mind: It can summon the dead. Do you want to hear Judy Garland sing “Over the Rainbow”? Just insert a cassette, push a button, and the voice of an artist who has been dust for twenty years fills your head with music.