Yesterday, you may have read, Benvenuto Cellini and I were both in Paris. As for me, I shall return to Germany tomorrow evening, but by the early summer of 1545 Cellini, too, had had his fill of the French capital. He decided it was time to return to his native Italy, and he planned to enjoy en route the renowned hospitality of the Cardinal of Ferrara at Lyons. A short distance from the abbey of His Eminence, however, Cellini had a memorable experience. He recounts the story in his autobiography.
"It was close upon the hour of twenty-two when the heavens began to thunder with sharp rattling claps. They made a sound so great and horrible that I thought the last day had come." Then came the hailstones - small at first but later "the size of big lemons". He and his friends took refuge in a nearby wood. Rather uncharacteristically, Benvenuto began to "sing a Miserere, and while I was uttering this psalm to God there fell a stone so huge that it smashed the thick branch of the pine under which I had retired for safety". After the storm abated, he continues, "all the trees were stripped of their leaves and we observed large quantities of hailstones which could not have been grasped with two hands."
Despite his reputation for tall stories, Cellini was not necessarily exaggerating. Hailstorms in continental regions are often quite different in scale to the kind we are accustomed to in Ireland. Hailstones are not solid ice through and through, but rather, when cut in half, they are found to consist of concentric layers of ice and snow, formed as they bob up and down for some considerable time within a thundercloud.
Having collected a layer of water in the nether regions of a cloud, an embryonic hailstone is carried upwards again by powerful updrafts; this layer of water freezes, and it then acquires an additional coating of snow before falling earthwards again. This process may be repeated many times. Indeed the size to which a hailstone can grow depends only on the extent to which the upward winds inside a cloud are strong enough to prevent it falling to the ground.
A hailstone which needed to be grasped by both hands, left to its own devices, would fall through the air at about 60 m.p.h. In order for it to reach this size, therefore, the cloud in which it was formed must contain upward gusts in excess of this figure - which is an indication of the ferocity of the storm encountered by Benvenuto on his way to Italy.