In the relatedness of his explorations of water, air and movement, and weight, he worked out the similarity between the laws of equilibrium controlling solids and liquids. The equation between the motive force and resistance that makes for equilibrium or balance in solids can be compared to the equation between the upward pressure of liquids and the downward pressure exerted on them.
Far into the night Leonardo worked on his papers. He tired more easily now, and his eyes had grown weaker. To provide the increase in light that his failing eyesight demanded, he had improved on his original oil lamp by making the wick rise as the oil was burned away, and he had extra lamps fitted to the ceiling.
On January 9, 1515 Leonardo wrote in his notes, “Il Magnifico Giuliano de’ Medici set out on the ninth day of January 1515 at daybreak from Rome, to go and marry a wife in Savoy. And on that day came the news of the death of the King of France (Louis XII).” This meant that his new patron had left and his old patron had died. Leonardo’s note was a sad one and perhaps he felt, in the departure of his patron, more alone than ever in the crowded life of the Vatican. Giuliano, on the urging of his brother, was marrying Philiberta of Savoy, in an effort to strengthen the prestige of the Medici. Louis XII, before he died, had formed a league against Spain, and with the marriage of the Pope’s brother to a noble house of France, the league would be strengthened by keeping the Pope on the side of France. Actually Pope Leo was playing both sides, for at the time he was also friendly with Spain.
Shortly after Giuliano’s departure from Rome, Leonardo fell ill, presumably from a mild heart attack complicated by a touch of malarial fever. The doctor had been called. It was a warning, the doctor told Francesco de’ Melzi, and Leonardo must remain quiet for quite awhile.
By the end of the winter Leonardo was back on his feet and apparently feeling completely well again. Giuliano himself had fallen ill about the same time and the news that he had recovered and was finally returning to Rome cheered Leonardo. He sat down and wrote a long letter to his patron expressing his joy. This letter also included a long list of complaints against Georg and Johannes. Georg was now using his room in Leonardo’s apartment to do work for others. He lied to Leonardo and flew into such a rage when he was questioned that no one could go near him. Moreover, Johannes, the mirror-maker, was now moving back into the Vatican and turning out mirrors for everyone, even using Georg’s room as his own workroom. Johannes boasted of his skill and told everybody that Leonardo did not know what he was doing. Thus, it was not surprising that Leonardo, in his long complaint, was taking out the anger and frustration he felt against all the injustices of his life in Rome.