As we bicker over the merits of paper books versus ebooks, it's salutary to recall that widespread ownership of books is relatively new. Before industrial production, only the rich had books at home.
And before the 16th century, when works of literature were copied by hand, even the plainest tome was an article of such value that it could be used as collateral for loans.
The British Library's latest exhib- ition, The Genius of Illumination, concerns itself with the top end of publishing – the reading matter of kings. Drawing largely on its own holdings of lavishly illustrated manuscript books dating from the ninth to the 16th centuries, 154 volumes show the range of material that shaped monarchs' understanding of their role and the world at large.
Take the book, produced around 1480 for the library of Edward IV, that may well have been intended for his two young sons who later died in the Tower. Its author was a Norman knight whose tales of chivalric deeds and adventure only thinly disguise an instruction manual of military and social skills.
Or consider an earlier Edward's Secretum secretorum, produced in 1326, originally composed as a letter sent from Aristotle to his pupil Alexander the Great. Aristotle's idea was that, to rule successfully, a prince must first learn how to govern himself, and this theme runs through many of the royal books that are not bibles, prayer books or histories.
Predictably, Christian literature forms the backbone of the exhibition. Royal children would have been taught to read using Psalms – no friendly Gruffalos for them. And because psalters were used daily for personal devotion, copyists found ways of appealing to individual recipients. A psalter made for Henry VIII inserts, at a point where one would expect a picture of King David, a portrait of the middle-aged Henry, shown sitting engrossed in this very book. Taken by this conceit, Henry wrote in Latin in the margin "Note who is blessed" (ie his royal self), a casual jotting every bit as exciting to see as the exquisite workmanship of the book's anonymous artwork.
Sheer beauty, though, is the dominant reason for hurrying to this well thought-out show. The vibrant coloured inks and glowing gold leaf appear as if freshly applied, thanks to the care of successive royal librarians. And although it can feel like hard work perusing even the larger-format pages in a darkened room (how ever did the Tudors manage by candlelight?), close study pays off in fun discoveries, such as the twins Romulus and Remus, in a grandly illustrated French history of Rome, pictured as tiny babies suckling from a proud she-wolf, a passing peasant throwing up his hands in surprise.
Of course, it's only possible to show two opened pages of each volume, but here ebook technology rides to the rescue, touch screens on the wall allowing you to leaf through entire virtual books. It is here that you can spot, in an early 14th-century book of natural history, the image of a hyena (believed to live among the dead) feeding on a partially unwrapped corpse in a coffin whose lid has been mauled off. Usefully, too, you are offered the chance to compare the feel of parchment (made of unspecified animal skin) and vellum (calfskin), and watch on video a calligrapher prick out her blank page, trim her quill, and form letters in a blocky gothic font.
Over the road at the Wellcome Collection, a (free) show of low-budget Mexican votive art also comes with integral captions. Commissioned from local artists by ordinary Mexicans, these thank-yous to saints take the form of small anonymous paintings, sometimes executed on tin roof tiles, depicting the moment when an individual has called on a saint for help and been delivered from disaster. (Presumably the ones whose prayers went unanswered just kept quiet.)
The 100 or so paintings dating from the 1820s to the present are collected under the title Infinitas Gracias ("endless thanks") and the effect is the graphic equivalent of a bumper edition of a red-top newspaper. Personal stories of illness, accidents, gun fights, muggings and lightning strikes are recounted in lurid detail, typically picturing the appealed-to saint hovering protectively nearby.
In 1863, when two brothers were abducted by armed gangsters and marched into a forest, their appeal to a local saint resulted in their abductors letting them go. Amusingly, though, the artist's skill extends only to the most crucial details: the blindfold, the guns, the bosky scene. The expressions on the faces of gangsters and victims are uniformly mild, verging on blank. It's just as hard not to smile in front of a retablo showing the prone figure of a man who survived falling off a wall after watching a bullfight. Luckily for him, the Virgin of Solitude took his plight seriously.
'Genius of Illumination': to 13 Mar; 'Infinitas Gracias': to 26 Feb (entry free)
Charles Darwent totally catches up with Saatchi's Gesamtkunstwerk
The blockbuster Leonardo da Vinci: Painter at the Court of Milan at the National Gallery, is open, but good luck getting in before the New Year (it's on till 5 Feb). Or check out the arresting entries for the Taylor Wessing Photographic Portrait Prize, won by an image of a girl and her guinea pig, at the National Portrait Gallery (free, until 12 Feb).