All the children, both boys and girls, were very carefully instructed in theology, according to the doctrine of Calvin, and, observed the candid Sophie, "knew the Heidelberg Catechism by heart, without understanding one word of it."[18] According to the curriculum arranged for them, the boys enjoyed four hours daily of leisure and exercise. They had to attend morning and evening prayers read in English; the morning prayer was followed by a Bible reading, and an application of the lesson. They were instructed also in the terrible Heidelberg Catechism, in the history of the Reformers, and in religious controversy. On Sundays and feastdays they had to attend church, and to give an abstract of the sermon afterwards. They learnt besides, mathematics, history, and jurisprudence, and studied languages to so much purpose that they could speak five or six with equal ease.[19] To their English mother they invariably wrote and spoke in English, but French was the tongue they used by preference, and amongst themselves; a curious French, often interpolated with Dutch and German phrases. Rupert early evinced his independence of character by revolting against the strict course laid out for him. "He was not ambitious to entertain the learned tongues.... He conceived the languages of the times would be to him more useful, having to converse afterwards with divers {12} nations. Thus he became so much master of the modern tongues that at the thirteenth year of his age he could understand, and be understood in all Europe. His High and Low Dutch were not more naturally spoken by him than English, French, Spanish and Italian. Latin he understood."[20] He showed, moreover, a passion for all things military. "His Highness also applying himself to riding, fencing, vaulting, the exercise of the pike and musket, and the study of geometry and fortification, wherein he had the assistance of the best masters, besides the inclination of a military genius, which showed itself so early that at eight years of age he handled his arms with the readiness and address of an experienced soldier."[21] Occasionally their mother would summon the children to the Hague, that she might show them to her friends; "as one would a stud of horses,"[22] said Sophie bitterly. The life at Leyden was also varied by the visits of the Elector Frederick, who was occasionally accompanied by Englishmen of distinction.