We get the word “mesmerize” from a doctor named Franz Anton Mesmer, who in Paris in the late 18th century posited the existence of an invisible natural force connecting all living things — a force you could manipulate to physically affect another person.

Mesmer’s work inspired the stage hypnotists of mid-19th-century America. Before rapt audiences, these “mesmerists” used carefully choreographed gestures to lull their subjects into a state of credulous obedience. As the practitioner John Bovee Dods wrote in the 1850s, a mesmerist could make an entranced volunteer see “that a hat is a halibut or flounder; a handkerchief is a bird, child or rabbit; or that the moon or a star falls on a person in the audience, and sets him on fire.”

In our historical moment, the mesmerists are worth considering, for they were frequently debunked but the debunkings rarely had much of an effect. Just as the repeated corrections of President Trump’s falsehoods have failed to discourage him or his supporters, so too the mesmerists escaped their exposés unharmed.

A critic named J. Stanley Grimes, for example, challenged the mesmerist J. R. Buchanan’s claim that he could alter people’s behavior by targeting an invisible substance toward organs of personality in their brains. Grimes showed that the same effects could be produced by what we today would call the power of suggestion, simply by intoning, “You cannot open your eyes.”