|By Hieronymus Bosch (circa 1450–1516) - Galería online, Museo del Prado., Public Domain, https://commons.wikimedia.org/w/index.php?curid=45147809|
It is mainly about a musical notation painted on the posterior of a naked body in the right hand panel of the triptych. The music was transcribed in 2014 by Amelia Hamrick, a music student at Oklahoma Christian University. Here is the music (played by Jim Spalink):
The convention among art scholars and critics is that the three panels of the triptych are read from left to right as Paradise; this world; a vision of hell. The music is in the panel showing hell but it doesn't sound hellish to me... quite the opposite in fact. But there is another, choral version of the same music which sounds much darker:
I have stood or sat in front of that painting many times in the Prado and it is baffling and fascinating. So what do I know about it? Well, I know that Phillip II acquired the painting at auction in 1591. He also owned this painting by Bosch:
|By Hieronymus Bosch (circa 1450–1516) or follower - www.museodelprado.es : Home : Info : Pic, Public Domain, https://commons.wikimedia.org/w/index.php?curid=1170708|
What does it all mean? Well, nobody seems to know. The medieval mind inhabited a very different universe. There are many theories; alchemical references, biblical references, hermetic references as well as the idea that Bosch was on a 'psychedelic trip' because at that time a great deal of the bread was contaminated with the ergot fungus. LSD is distilled from ergot so eating such bread could possibly induce similar effects. I am not entirely convinced by that last one.
Alchemical? Lots of books devoted to the idea but Adam McLean is less than convinced:
Christianity? Certainly Bosch was a devout Christian and the painting is believed to have been commissioned by Engelbrecht II of Nassau, in or shortly after 1481, when he attended the Chapter of the Order of the Golden Fleece, this Order being a Roman Catholic Order of Chivalry
Another link from the BBC page is to art critic Kelly Grovier who points to the existence of an egg at the centre of the painting:
"To find it, one’s eyes need merely draw an ‘X’ from the four corners of the work and an egg marks the spot, smack before us at the dead centre of the painting. Suddenly, the tempestuous vision collapses into a mystical vanishing point. Through the timeless symbol of the unhatched egg, Bosch offers us a way out of his troubled work: the hope of a birth that’s evermore about to be."
There are many instances of ostrich eggs hanging from the ceilings of cathedrals as well as in Mosques or Temples of other religions both east and west. There were still two hanging in Durham Cathedral as late as 1780.
The second painting mentioned above is called "The seven deadly sins" and is very explicitly Christian. It is painted in the form of an eye with the 'sins' arranged on the periphery. In the centre, in the pupil is a small painting showing Christ rising from the tomb. Around it are written the words 'Cave Cave Deus Videt' - "Take care, God is watching!" Note also the significance of placing Christ in the pupil of the eye. There are several Biblical references along those lines including Deuteronomy 32:10, Zechariah 2:8, Psalm 17:8, Proverbs 7:2.
Hermetic? Phillip and his two principal architects of the Escorial were very well versed in The Hermetica. The new palace of El Escorial was designed to be a replica of Solomon's temple so he and they would see something in the paintings which is now hidden to us with our different perceptions, education and experience.
It is worth pointing out that Phillip, like Bosch, was a devout Catholic but at that period people would not differentiate between Christianity and magic. Phillip's nemesis, Elizabeth of England, was of like mind. One of her most trusted advisors was the Magus John Dee.
I have been looking again at one of my books called "The Mercurian Monarch" and it occurred to me that this was an age when both Phillip of Spain and Elizabeth of England believed in the divine right of Kings as being very real. They believed in a divine succession through Adam, Moses and Solomon to themselves and thus had a direct connection to God which is why they felt able, even obliged, to defy ecclesiastical authority. (The king and queen on the chessboard rank higher than the bishops.)
The established Church itself was extremely hostile to any such heresy although looking at the Gothic Cathedrals or much of Renaissance art one wonders if such hostility was genuine.
I bought this book in the bookshop at El Escorial and it is extremely informative- https://www.amazon.com/Arquitectura-Magia-Biblioteca-Sumergida-Spanish/dp/8478441344 (Originally published in English but I have never seen an English version.) The book is dedicated to Rudolf Wittkower, which brings me to another book I have with the title "Allegory and the Migration of Symbols" by Wittkower: http://thamesandhudson.com/Allegory_and_the_Migration_of_Symbols/9780500274705
I looked through the last chapter "Interpretation of Visual Symbols" and it echoed the thoughts of Ernst Gombrich in his "Art and Illusion." What we see depends on perception and interpretation. Wittkower refers to the chronicles written by Marco Polo after his travels. He was widely denounced as a liar and a fantasist because those who read his stories had no concept of the things he described, they were unable to interpret his descriptions in any meaningful way because such descriptions were outwith their own experience. If you have never seen an elephant or a camel for example then you will regard a drawing of such as pure imagination or fantasy - or the product of a hallucination.
You might like to look at the illustrations from the "Livre des Merveilles", several of which are reproduced in Wittkower's book:
As you can see the landscapes are very stylised in the manner of Bosch and there are some very strange looking creatures in there too. Some of the images shown are of Marco Polo's book but, as the Wiki entry says, they should not be confused with Jean de Mandeville's book- https://fr.wikipedia.org/wiki/Livre_des_merveilles_du_monde
There is also the way in which the accepted meaning of symbols changes over time. The most obvious example is the swastika which is a symbol of good fortune in Tibet and parts of India but is now a symbol of evil in the western world.
Another and probably more serious handicap in trying to interpret and understand the painting came with the invention by Brunelleschi of single point perspective in architectural drawings and in paintings. This changed painting forever and also altered how we now look at not just paintings but the world around us. Via photography, cinema and television we have been subtly and unintentionally brainwashed into looking without seeing. We see paintings now as if through a window, it is 'framed' and therefore we are some how set apart from the scene; peeping through a keyhole as it were.
Over the years a few painters tried to highlight the absurdity of perspective; Piranesi, Hogarth, Picasso and Escher among them. Velazquez turned it around with his painting "Las Meninas" and El Greco ignored it altogether. So it is now very difficult and almost impossible to 'see' the painting in the way that Bosch and his contemporaries saw it.
Your best guide to what it all means comes from the American painter Frank Stella who said "What you see is what you see." In other words it depends on your own perception and an interpretation based on your own experience of life which is where education becomes a handicap rather than a help - anything other than the orthodoxy of received wisdom is regarded as heresy.
Make of it all what you will but always remember the famous phrase from the Tao Te Ching: "Those who know, do not speak. Those who speak, do not know" (Lao Tzu). That includes me, so what I have written above should be taken with a grain of salt. Ignore any and all experts. The best way to understand anything, anything at all is to work it out for yourself. Start with your intuition and filter that through your reason and you will arrive at something approximating to the truth.
Note: There is currently in the Prado, Madrid an exhibition of the paintings of Bosch. It ends on 25th September. Go and see it if you can!
References (other than those cited in the text):
1) "Architecture, Mysticism and Myth" by W.R. Lethaby,  http://www.sacred-texts.com/earth/amm/amm03.htm
2) "the apple of his eye" http://biblehub.com/zechariah/2-8.htm
3) "Hermetica" - by Walter Scott (Translator) https://www.amazon.co.uk/Hermetica-Trismegistus-Hermes/dp/0877733384
4) The Mercurian Monarch" by Douglas Brooks-Davies https://www.amazon.com/Mercurian-Monarch-Magical-Politics-Spencer/dp/0719009545
5) Symbolism in chess http://enchantedmind.com/html/creativity/techniques/creative_chess.html
6) "Art and Illusion" - by E H Gombrich https://www.amazon.co.uk/Art-Illusion-Psychology-Pictorial-Representation/dp/0714842087
7) Tao Te Ching http://taotechingdaily.com/tao-te-ching-chapter-56-essay/
8) "The Mysteries of Chartres Cathedral" by Louis Charpentier https://www.amazon.co.uk/Mysteries-Chartres-Cathedral-Louis-Charpentier/dp/0902103164
9) "That's the Way I see It" - by David Hockney https://www.amazon.co.uk/Thats-Way-See-David-Hockney/dp/0500280851
10)"The Object Stares Back" - by James Elkins https://www.amazon.co.uk/Object-Stares-Back-Nature-Seeing/dp/0684800950