The subjects of Mackay's debunking include alchemy, crusades, duels, economic bubbles, fortune-telling, haunted houses, the Drummer of Tedworth, the influence of politics and religion on the shapes of beards and hair, magnetisers (influence of imagination in curing disease), murder through poisoning, prophecies, popular admiration of great thieves, popular follies of great cities, and relics.

[4] In later editions, Mackay added a footnote referencing the Railway Mania of the 1840s as another "popular delusion" which was at least as important as the South Sea Bubble.

[7] Mackay's accounts are enlivened by colorful, comedic anecdotes, such as the Parisian hunchback who supposedly profited by renting out his hump as a writing desk during the height of the mania surrounding the Mississippi Company.

Mackay notes that many of these cases were initiated as a way of settling scores among neighbors or associates, and that extremely low standards of evidence were applied to most of these trials.

Mackay notes that many of these practitioners were themselves deluded, convinced that these feats could be performed if they discovered the correct old recipe or stumbled upon the right combination of ingredients.