Archduchess helped Wolfgang when he slipped on the polished floor; she is supposed to have received a proposal of marriage in return. As the Mozarts began to be noticed by the Viennese aristocracy, they were often required to give several performances during a single day. They were well rewarded for this activity—at the end of their first hectic week in Vienna, Leopold was able to send home the equivalent of more than two years' salary. Their schedule was interrupted when Wolfgang fell ill with scarlet fever, and their former momentum was not regained. Nevertheless, the visit left Leopold eager to pursue further opportunities for social and financial success. On their return to Salzburg, Wolfgang played the harpsichord and violin at a birthday concert for the archbishop, to the evident astonishment of those present. Grand tour Preparations In a letter to his friend and landlord Johann Lorenz Hagenauer (1712–1792), a prominent Salzburg merchant, written after the tour, Leopold quotes the German diplomat Friedrich Melchior, Baron von Grimm, who after hearing the children play had said: "Now for once in my life I have seen a miracle: this is the first". Leopold believed that it was his duty to proclaim this miracle to the world, otherwise he would be "the most ungrateful creature". He was said to have described Wolfgang as "The miracle which God let be born in Salzburg." Mozart biographer Wolfgang Hildesheimer has suggested that, at least in the case of Wolfgang, this venture was premature: "Too soon, [the] father dragged [the] son all over Western Europe for years. This continual change of scene would have worn out even a robust child..." However, there is little evidence to suggest that Wolfgang was physically harmed or musically hindered by these childhood exertions; it seems that he felt equal to the challenge from the start. Leopold wanted to begin the tour as soon as possible—the younger the children were, the more spectacular would be the demonstration of their gifts. The route he intended to take included southern Germany, the Austrian Netherlands, Paris, Switzerland and possibly northern Italy. The London leg was only added after urgings during the Paris visit, and the eventual Dutch trip was an unplanned detour. The plan was to take in as many princely European courts as possible, as well as the great cultural capitals—Leopold was relying on his professional musical network and on his more recent social contacts