At Chatham, with the warm approbation of Major-General Hewett, commanding the depôt, he introduced that system of hospital reform form which had elsewhere operated so successfully. The changes he effected, as soon as they were made, became known to the Medical Board, and were publicly approved of by one of its members. However, shortly afterwards, an epidemic broke out in the depôt (then removed to the Isle of Wight), arising from the fact, that the barracks were overcrowded with young recruits, but which the medical board ascribed to Jackson's innovations, and reported so to the Horse-Guards. The commander-in-chief directed an inquiry to take place before a medical board impannelled for the purpose, and the result of that inquiry may be guessed from a communication made by the War-Office to the commandant of the depôt. This states "the unanimous opinion of the board to have exculpated Dr. Jackson from all improper treatment of diseases in the sick," and the commander-in-chief's gratification, "than an opportunity has thus been given to that most zealous officer of proving his fitness for the important situation in which he is placed." The result of this wretched intrigue, however, was that Jackson, disgusted with the whole affair, requested to be placed on half-pay, to which request the Duke of York, with marked reluctance, at last (March 1803) acceded. In his retirement at Stockton, Jackson put forth two valuable works, one on the medical economy of armies, and another on that of the British army in particular, and was much gratified by an offer to accompany, as military secretary, General Simcoe, just appointed commander-in-chief in India. The general's sudden death, however, put an end to this plan; and Jackson continued at Stockton, addressing frequent representations to government on the defective medical arrangements in the military service--representations the very receipt of which were not acknowledged by Mr. Pitt, to whom they were forwarded. The Peninsular war commencing, Dr. Jackson was again named Inspector of Hospitals, but was not, thanks to the persevering enmity of the Medical Board, sent on foreign service, although he volunteered to sink his rank, and go in any capacity. The Board even succeeded, by calumnious statements, that he had purchased his diploma--statements he readily confuted--in preventing his appointment to the Spanish liberating army; although the British government had formally requested him to accept such an appointment, and agreed to give credentials testifying to his capacity and trustworthiness. This last appointment led him, in an unguarded moment--peppery to the last--to inflict a slight personal chastisement on the surgeon-general, for which he was imprisoned six months in the King's Bench.