Mirabeau informed the king that he had come to seek permission to study the great military manoeuvres, and that he hoped to push on to Russia. During this period he worked like a labourer all day at his writings. Part of his time he spent at supper parties of the most tiresome etiquette. The same laborious habits attended him everywhere, in prison and in freedom, in his own country and in other lands. It was in Germany that he conceived the idea of his treatise on "The Reform of the Jews," which is acknowledged to be one of his best works. Frederick the Great died on August 17, 1786. Feeling that he could do nothing useful, Mirabeau resolved at the close of 1786 to quit Berlin. He was urged also by a special motive in which he took pride, and which he thus described in a letter: "My heart has not grown old, and if my enthusiasm is damped, it is not extinguished. I have fully experienced this to-day. I consider one of the best days of my life that on which I received an account of the convocation of the notables, which no doubt will not long precede that of the National Assembly. In this I see a new order of things which may regenerate the monarchy. I should deem myself a thousand times honoured in being even the junior secretary of this assembly, of which I had the happiness of giving the first idea." Mirabeau was prodigiously occupied at Berlin. He often did not retire to rest till one in the morning, but regularly rose at five, even in the midst of severe winter. Without anything on but a simple quilted dressing-gown, without stockings or waistcoat, he worked away without even calling up his servant to light a fire. Besides his correspondence in cypher, which occupied him much, he worked assiduously at his "Prussian Monarchy," which was published in 1788. On departing from Berlin the count wrote a most eloquent letter of counsel to King Frederick William, appealing to him to cultivate peace, reminding him that his illustrious predecessor had conquered the admiration of mankind but never won their love, commending him not to extend the direct action of the royal power to matters which did not require it, advising him not to govern too much, and exhorting him to abolish military slavery; that is to say, the obligation then imposed on every Prussian to serve as a soldier from the age of eighteen to sixty or more, which forced men to go to the battle-field like cattle to the slaughterhouse.