On the Duke of Weymar's death, Reigersberg advised Cornelius to write that Prince's history. Young Grotius mentioning this project to his father, he pressed him to execute it, because it would give him an opportunity of expressing his gratitude to a Prince who had laid him under great obligations, and done such important services to Sweden. Besides, this work would be of use to the author, by obliging him to study the Art of War, in order to speak of it properly. Cornelius contented himself with projecting this design[743]: he changed his service, and entered into the Marshal de Chatillon's army, in which he continued not long: he made the campaign of 1640, in quality of Cornet in the Colonel's company of a German regiment of horse in the French service. Soon after he got a company: however he wanted to serve in the Valtoline[744]. He had not been long there before he took a fancy to enter into the Venetians service; and, without consulting his father, went to Venice to make his contract with them: but it is probable they could not agree; for Grotius writes[745], July 16, 1644, "Cornelius will return from the Antenorides without doing any thing." This fickleness of temper much displeased Grotius[746], who in the latter part of his life spoke of his son with great indifference. In the sequel, when the States of Holland wanted to indemnify such as were unjustly persecuted during the overgrown power of the Stadtholders[747], they gave Cornelius Grotius a company in the guards; to Peter, a troop of horse; and to Mombas, their brother-in-law, a regiment; with leave to dispose of them, or sell them to the best advantage: which was contrary to custom and law. It was in 1633 that the States thus sought to repair the injuries which Grotius had formerly suffered. Cornelius died unmarried. Peter, Grotius's second son, was more like his father. In his infancy he was very sickly: having received a hurt in his leg[748], the Surgeons and Physicians treated it so ill, that he remained lame all his days. His father, thinking his education would be cheaper in Holland than at Paris, sent him to his native country. The young Grotius gave great satisfaction to his parents, as we learn by a letter from Grotius to his brother William[749], Oct. 4, 1630, "Your accounts of my son give me great pleasure: if he goes on in the same manner, he will have reason to be satisfied with me." Gerard Vossius directed his studies; and by a letter[750] of thanks from Grotius to him, we learn that he was of an indolent turn. "The exhortations you give Peter are worthy of the friendship you have always entertained for me and mine. I cannot think why my children should be so idle; perhaps it is because they see their father's diligence has turned to so little account."