Percival Lowell, a 19th-century American businessman and astronomer, had a pet theory: that a careful look through a telescope revealed that intelligent life exists on Mars. Skeptics cried not enough evidence, but Lowell wouldn’t back down. Affected by what is known today as confirmation bias — the tendency to cherry-pick data that supports one’s prejudices and swat away the other kind — Lowell kept peering through his telescopes and seeing what he expected to see.

“The Martians: The True Story of an Alien Craze That Captured Turn-of-the-Century America,” By David Baron. 321 pages. Liveright. $29.99 (Liveright)

Like many other scientists of his day — he lived from 1855 to 1916 — Lowell had no formal training in his field. He did have plenty of money, though, which came largely from textiles on both sides of the family. Lowell, the Boston Brahmin at the center of David Baron’s engrossing new book, “The Martians,” studied mathematics at Harvard and aired his thoughts on how our solar system may have formed in a speech he gave on graduation day. After a few years of post-undergraduate dilettantism, he began financing his own investigations.

Lowell owed his sensational deduction about Mars to the Italian astronomer Giovanni Schiaparelli, who drew upon repeated sightings of the planet in his Milan observatory to make a map that, in Baron’s words, “baffled the astronomical community.” Schiaparelli’s map, Baron explains, “depicted not merely the dark-and-light regions that others saw [on the surface of Mars] – the features generally referred to as oceans and continents – but also an abundance of narrow streaks that appeared to connect the seas one to another. These delicate stripes extended for hundreds, even thousands, of miles with nary a bend, so straight and slender that they seemed to run with a sense of purpose.”

The name that Schiaparelli gave to the stripes inadvertently reflected that sense of purpose: canali, Italian for “channels.” A translator, however, seized upon an alternative meaning of the word, and a headline in the Times of London in 1882 shouted, “CANALS ON THE PLANET MARS,” the implication being that they were the brainchildren of Martian engineers.

Lowell in effect took a swan dive into those canals. He built his own observatory in Flagstaff, Arizona, and studied Mars with what Baron calls “hypnotic intensity.” From perceived changes in the stripes’ hue and their apparent clustering into networks, Lowell and his supporters inferred a gigantic irrigation system. Lowell was so convinced of his theory that, in 1896, he declared, “I have no doubt that there is life and intelligence on Mars.”

Baron attributes his antihero’s vainglorious self-deception to living “under the weight of expectations passed down from his accomplished ancestors and his demanding father,” and the scion’s periodic bouts of depression lend credence to that analysis.

Meanwhile, the popular culture of the era was awash in works such as H.G. Wells’s novel “The War of the Worlds”; Edgar Rice Burroughs’s series of novels on the adventures of John Carter among the Martians; a newspaper comic strip called “Mr. Skygack, From Mars,” created by A.D. Condo, also known for giving the world “Diana Dillpickles”; and countless other artists’ renditions of Martians with deformed heads, tentacles instead of hands and other “proboscis-like organs.” Their descendants are Kang and Kodos on “The Simpsons.”

Baron seasons his narrative with striking details. In the early days of the Mars craze, for example, nomenclature was up for grabs. “‘Marsians,’ ‘Marsonians,’ ‘Marsites,’ ‘Martials,’ … many fanciful names were given to the planet’s hypothetical inhabitants,” he writes, “before ‘Martians’ emerged as the consensus term.” (“Marsupials” was apparently never in contention.) One reason Lowell and his contemporaries had difficulty seeing Mars clearly was its image’s tendency to “wobble and blur, a problem due not to the telescope but to Earth’s atmosphere.” As Lowell himself admitted, “To look for the canals with a large instrument in poor air is like trying to read a page of fine print kept dancing before one’s eyes.”

Baron might have made more of the Martian fad as displayed in later pop culture. Orson Welles’s 1938 radio adaptation of “The War of the Worlds” gets only a couple of brief mentions, and Baron leaves out the intelligent-Martian renaissance of the late 1940s and early ’50s, when flying-saucer sightings were commonplace. I remember staring at an artist’s full-color impression of the Martian canals in a kids’ astronomy book at my hometown library, being thrilled by such movies as “The War of the Worlds” and “Invaders From Mars” (both released in 1953), and spending hours across the dining room table from my best friend as we drew homemade comic strips about interplanetary mayhem on Mars.

As for the canals, they disappeared when other scientists acquired more powerful telescopes. “The true appearance of the planet Mars is a natural one,” asserted the astronomer Eugène Michel Antoniadi in 1909, adding that, under good observation, “there is no trace whatever of a geometric network.” Subsequent missions to Mars have added little to that debunking, though Baron speculates that the young Mars “could well have been a nursery for life.” Until we learn more from future missions, his highly enjoyable book makes a strong case for the proposition that brainy Martians exist only in the imagination of Earthlings.