1846, but in the following June again embarked for North America, having been selected with Captain Pipon of the royal engineers as commissioner to make an exploring survey in order to fix a boundary between Canada and New Brunswick in the territory ceded by the United States to the crown under the Ashburton treaty, and to determine the practicability of a line of railway of some seven hundred miles between Halifax and Quebec to connect the three provinces of Canada, New Brunswick, and Nova Scotia.
The eastern half of New Brunswick was allotted to Pipon, who lost his life late in the autumn of 1846 by the upsetting of a canoe in a rapid of the Restigouche river in the endeavour to save one of the crew. The western half fell to Henderson, who, forty years after, wrote an account in 'Murray's Magazine' (March 1887) of an adventure on this service, which proved a very difficult one, as the interior was unknown except to lumbermen. His skill as a draughtsman enabled him to illustrate his official report with a panoramic sketch of the country, which attracted the attention of Earl Grey, then secretary of state for the colonies. Henderson married at Halifax, Nova Scotia, and, having successfully completed the duty entrusted to him, returned to England in November 1848, and was quartered at Gravesend.
Early in 1850 he accepted from Earl Grey the appointment of comptroller of convicts in Western Australia, where it had been decided, with the approval of the colonists, to establish for the first time a penal settlement, on account of the opposition from the flourishing colonies of the eastern and southern parts of Australia to continue to receive convicts from home. Western Australia had not so far been a successful colony, and as the government undertook to send out as many free emigrants as convicts the increased supply of labour was welcomed. At the same time a new development of the convict system was to be tried. The prisoners were to be selected with reference to their fitness for colonial life, and, after passing a certain time in a public works prison, were to be sent out to private employment under police supervision, or else employed in public works in various parts of the colony.
Henderson arrived at Freemantle with the first party of convicts and a guard of sappers in June 1850. No preparations had been made for their reception in the colony, and, after making temporary arrangements, he set to work to build a complete establishment. He obtained from England the services of the 20th company royal engineers, commanded by Captain (afterwards Major-general) Henry Wray, with two subaltern officers, Lieutenant (afterwards Colonel Sir) William Crossman and Lieutenant (afterwards Colonel Sir) Edmond Du Cane, to furnish instructors and artisans to conduct the work, and with its assistance not only the convict prison and quarters but a barrack and officers' quarters also were erected. Hiring depots were formed in different parts of the colony, while the ticket-of-leave men who could not obtain private employment were maintained by government and employed in making roads and building bridges.
At the end of 1855 Henderson lost his wife and went home on leave of absence. He married again two years later, and returned to Western Australia in the beginning of 1858. He spent another five years there, during which he was most active in his duties and in all that contributed to the well-being of the colony, in which, after the governor, he was the principal public officer. He resigned the appointment in 1863, and returned to England.
Henderson arrived in England while a royal commission, presided over by Earl Grey, was inquiring into the systems of penal servitude and transportation. Sir Joshua Jebb [q. v.] had recommended Henderson for a seat on the prison board, and in the meantime he gave evidence before the committee. The sudden death of Jebb left vacant the offices of chairman of directors of prisons and surveyor-general, and also the inspector-generalship of military prisons. Lord Grey's commission represented the especial fitness of Henderson for these posts, and he was appointed to them on 29 July 1863. He retired from the army on 1 Oct. 1864. He carried out the changes in the administration of prisons made in consequence of the report of the royal commission, and was ably assisted in the work by his former subaltern in Australia, who afterwards succeeded him, Sir Edmond Du Cane. Henderson was made a companion of the order of the Bath, civil division, in 1868.
In 1869 Henderson reluctantly accepted the post of chief commissioner of metropolitan police on the death of Sir Richard Mayne [q. v.] For the second time he found himself at the head of a public department over the heads of, and new to, all serving in it, some of them at the outset not too well pleased with his appointment. That in both cases he succeeded in winning the confidence