Early America was also a much, much wetter place than it is now, modern frat culture notwithstanding. Instead of binge-drinking in short bursts, Americans often imbibed all day long. “Right after the Constitution is ratified, you could see the alcoholic consumption starting to go up,” said Bustard. Over the next four decades, Americans kept drinking steadily more, hitting a peak of 7.1 gallons of pure alcohol per person per year in 1830. By comparison, in 2013, Americans older than 14 each drank an average of 2.34 gallons of pure alcohol—an estimate which measures how much ethanol people consumed, regardless of how strong or weak their drinks were. Although some colonial-era beers might have been even weaker than today's light beers, people drank a lot more of them.

In part, heavy alcohol consumption was a way to stay hydrated: Often, clean water wasn’t always accessible. Hard liquor, on the other hand, was readily available, Bustard said; farmers frequently distilled their grain into alcohol. Rush “may have been observing what's going on on the frontier,” Bustard said, “thinking, you know: What's the country going to come to?”

Along the way, Rush helped shape American medical thinking on alcohol. At the time, hard liquor was widely viewed as medically beneficial, and Rush “cautioned against the then-common use of spiritous liquors to guard against the effects of heat or cold, or to relieve the effects of fatigue,” wrote the researcher Brian S. Katcher in the American Journal of Public Health in 1993. One of his major scientific contributions was describing alcoholism as a progressive disease, Bustard said. And “he was one of the first people, certainly in this country, to propose some sort of place where the drinker could go away to get sober.”

Rush was a Christian, like most early (and current) Americans. Throughout the country’s history, religion has been closely intertwined with attitudes toward alcohol: For example, American drinking began to decline in the middle of the 19th century largely thanks to the evangelical protestants who led the temperance movement. As Bustard wrote in an email, the Women’s Christian Temperance Union got its start in 1874 “when a group of socially prominent women decided to pray outside a saloon in the hopes of embarrassing the owner into ending alcohol sales.” Rush didn’t believe in total abstinence from alcohol: In his chart on the morality of different kinds of drink, he gave cider, wine, and beer a “health and wealth” seal of approval. But his religious beliefs definitely shaped his thinking on alcohol. As he wrote in a 1784 letter, “I wish it was thought compatible with the duties of the pulpit to teach our Presbyterian farmers how much the credit of religion and the honor of society were concerned ... in abolishing whiskey distilleries and converting them into milkhouses.”

* For those curious about the other morally threatening beverages on Rush’s “thermometer”: A “flip” is like egg nog, but without the cream. The colonial American “shrub” usually included a vinegar-based syrup mixed with liquor and other ingredients. Grog involves the classic “mix your alcohol with more alcohol” move, usually combining rum with beer or water and citrus juice.

** Capitalization choices all Mr. Rush’s.

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