There is nothing like a recession to throw economists into a despondent mood. Much as happened in the late 1930s—when there was a fear of so-called secular stagnation, or the absence of growth due to a dearth of investment opportunities—many of my colleagues these days seem to believe that "sad days are here again." The economic growth experienced through much of the 20th century, they tell us, was fleeting. Our children will be no richer than we are. The entry of millions of married women into the workforce and the huge increase in college graduates that drove post-1945 growth were one-off boons. Slow growth is here to stay.

What is wrong with this story? The one-word answer is "technology." The responsibility of economic historians is to remind the world what things were like before 1800. Growth was imperceptibly slow, and the vast bulk of the population was so poor that a harvest failure would kill millions. Almost half the babies born died before reaching age 5, and those who made it to adulthood were often stunted, ill and illiterate.

What changed this world was technological progress. Starting in the late 18th century, innovations and advances in what was then called "the useful arts" began improving life, first in Britain, then in the rest of Europe, and then in much of the rest of the world.

Why did it happen? In brief: Science advanced. One reason science advanced so rapidly is that technology provided the tools and instruments that allowed "natural philosophers" (as they were known then) to study the physical world. An example is the barometer. Invented by a student of Galileo's named Torricelli in 1643, it showed the existence of atmospheric pressure. That scientific insight spurred the development of the first steam engines (known as atmospheric engines).

In 1800 another Italian, Alessandro Volta, invented the "pile"—the first battery. It served primarily as a tool for chemical research, allowing chemists to map out the newly discovered world of elements and compounds that unleashed the chemical industries of the 19th century.