The Day the Universe Changed - James Burke [23]
The early medieval view of life is shown (above) in a crucifix of the late twelfth century. The face is expressionless, stereotyped. The walrus ivory carving below, from the same date, already shows the new realism in the suffering depicted on Christ’s face.
In church activities too, the life of this world began to make itself felt. At the end of the twelfth century Christ was brought to the worshipper in a new way. The new cult of the Eucharist, the elevation of the Host, the dogma of transubstantiation (the changing of the bread and wine to the body and blood of Christ while it is consumed at the altar) and the Feast of Corpus Christi, inaugurated in 1264, all manifested the new desire to ‘see and touch’. The brief dramatic interludes in the liturgy which had appeared in the tenth century moved out of the church into the porch, where they took the form of public plays. On the doors of his abbey at St Denis, in the northern suburb of Paris, the first building in the new Gothic style, Abbot Suger wrote: ‘The windows will lead you to Christ.rsquo;
This concern with the metaphysical properties of light brought to its logical conclusion the change in European thought begun by Aristotle and the Muslim philosophers. During the first half of the thirteenth century Bishop Grosseteste, who was teaching Aristotelian logic in the newly established university at Oxford, took the view that light was the raw material of Creation because of the way it behaved. Starting as an immeasurably small point, it expanded instantaneously to form a perfect sphere. With the aid of Aristotle, Grosseteste began to observe the phenomenon of radiation. From Arab writers like Al Hazen he culled information about optics, lenses, reflection and refraction. He came to the conclusion that the understanding of nature had to be based on the use of mathematics, optics and geometry, saying: ‘All the causes of natural effects should be reached by lines, angles and figures; otherwise it is impossible to know their cause.’ Grosseteste realised, however, that there were several apparent causes of the phenomenon. He suggested comparison of repeated observations as the best method of verifying or disproving the true cause. He also reasoned that if light really were the fundamental material, there were two kinds of light-generated phenomena to analyse: the primary manifestations propagated by light, and the secondary ones which were sensed. Grosseteste concluded that to understand what caused something to happen it was necessary to go beyond what was revealed by observation to the mechanism of the phenomenon itself.
His younger contemporary Roger Bacon tried to solve the problem by the use of mathematics, arguing that the truth could only be found through experimentation. Where his predecessors had talked hopelessly of’standing on the shoulders of giants’, Bacon said: ‘We of later times should supply what the ancients lacked, since we have become involved in their works. And unless we are fools, those works of theirs should arouse us to do better.rsquo;
At some time between 1301 and 1310, this new approach was given true experimental form by a German Dominican called Theodoric of Freiburg. The phenomenon of light Theodoric chose to examine was the rainbow. Using a hexagonal crystal, a spherical glass filled with water, a crystal ‘droplet’ and a piece of parchment with a pinhole through it, Theodoric discovered what caused the rainbow.
One of Theodoric of Freiburg's sketches showing how the rainbow was formed, which clearly demonstrates his understanding of reflection and refraction. The sun shines, from the left, on to the droplets, and the eye perceives the colours, in