The Problem with eBook Readers
The rule isn't exact, of course. The Collected Works of Dame J. K. Rowling might be only six centimeters deep, in your opinion, but you must recognize a certain subjectivity in your estimation. You may be one of those aficionados who could drown in Odyssey of a Cockroach and other such flighty, filmy, flimsy dewinesses of Yoko Ono, although every woman in America who was under 40 in 1969 automatically reaches either for her pearl-handled revolver or her Dramamine™ and silently repeats the age-old mantra — Why her?...Why her?...Why...HER...? Really. How thick is thick? We're talking literature here!
Don't get me started on Mickey Spillane, Isaac Asimov, Ursula Leguin or Yevgeny Yevtushenko.
Maybe a set of sliding weights, like solid copper playing cards. Normally distributed inside the case, they could all slide together toward the bottom edge of the reader, giving an illusion of sudden insurmountable inertia if you load up an old author like Bulwer-Lytton, say.
Or you could simply unscrew a cap and pour a variable amount of some heavy brown liquor, Irish Mist, for example, into your reader's internal reservoir. The better the book, the deeper the gurgle, the drowsier the reading.
On the other hand, thanks to back-lit LED screens, light reading was never brighter.
†American publishers have realized this for years, of course, printing all their recent stuff on thick, ragless pulp with high acid content — bound, to boot, in cheap unornamented cardboard — making their books likely to wear out in four years rather than 400.