Following the death of General Advisor in Foreign Affairs Gustave Rolin-Jaequemyns in 1902, Phya Suriyanuwat, the Siamese Minister in Paris, was instructed to find a replacement. Phya Suriya was unable to find a suitable candidate in Europe, and notified Phya Akaraj Varathon, the Siamese Minister in Washington, that under the circumstances, he had decided to engage an American. In 1903, former US diplomat Edward Henry Strobel took a leave of absence from his position as the Bemis Professor of International Law at Harvard School of Law to represent the Kingdom of Siam in The Hague at the International Peace Court—which Rolin-Jaequemyns had been instrumental in founding. In 1906, Strobel moved to Bangkok to take the position of general advisor, where he died January 15, 1908. Among his successors were Jens Westengard, 1909-14, Wolcott Pitkin, 1915-17, Eldon James, and Francis B. Sayre—all but for Pitkin former Harvard law professors. "The Siamese government trusted the American Adviser in Foreign Affairs to act in the best interests of Siam. Authority and responsibility were delegated to him. He was permitted a considerable degree of freedom in his work. It was in his capacity as a lawyer, a jurist, an advocate, and a policy counselor that the American adviser contributed significantly to the successful conclusion of the treaty negotiations with the West." An agreement on relations between the two countries was signed in Washington D.C. on December 16, 1920.. How many years did Wolcott Pitkin serve as general advisor?