Here’s a little bit of an excerpt on somthing like intelligence - wit, perhaps, or speeds of thinking - from George Cheyne, an 18th century physician to the stars (everyone from literary folk like Samuel Richardson, James Boswell and Alexander Pope to minor aristocracy like the Countess of Huntingdon, who was apparently a very pious lady). Cheyne was renowned in his day for numerous medical treatises, including most famously The English Malady, or, a treatise on nervous diseases of all kinds (1733). The book was a hit, going through six editions in six years, and addressing all kinds of nervous disorders. In it, he claimed that some people were more likely to experience nervous disorders than others: specifically, quick-witted folk were more likely to be afflicted by diseased nerves, on account of their more highly attuned sensitivity. “The common Division of Mankind, into Quick Thinkers, Slow Thinkers, and No Thinkers, is not without Foundation in Nature and true Philosophy. Persons of slender and weak nerves are generally of the first Class: the Activity, Mobility and Delicacy of their Intellectual Organs make them so, and thereby weakens and relaxes the Material Organs of the Intellectual Faculties; and therefore ingenious flattering, easy and agreeable Amusements, and Intervals of No-thinking and Swiss-Meditation, (as it is maliciously called) is as necessary for such, as Sleep to the Weary, or Meat to the Hungry, else the Spring will break, and the Sword wear out the Scabbard.” Your quick wit, says Cheyne, is a sign that you may also be a bit on the high-strung side. In fact, he also likes to compare good mental health to the proper tuning of an instrument, so that “the Intelligent Principle, or Soul, resides somewhere in the Brain, where all the Nerves, or Instruments of Sensation terminate, like a Musician in a finely fram’d and well-tuned Organ-Case; that the Nerves are like Keys, which, being struck or touch’d, convey the Sound and Harmony to this sentient Principle, or Musician”.
I couldn't say off hand what "Swiss meditation" refers to.. and for the rest, I'm not convinced how common Cheyne's Quick/Slow/No-thinking division might have been back in the day... but that's a question, isn't it? Was this really a common division? And were the quick-witted really liable to great mental distress, thanks to their inner musician being over-burdened with keeping the instrument in tune?