Arriving in Jamaica, he in 1774 became assistant to an eminent general practitioner at Savana-la-Mar, Dr King, who was also in medical charge of a detachment of the first battalion of the 60th regiment. This latter he consigned to Jackson's care; and well worthy of the trust did our young adventurer, though but twenty-four years of age, approve himselfvisiting three or four times a day the quarters of the troops to detect incipient disease, and studying with ardour and intelligent attention the varied phenomena of tropical maladies. Four years thus passed profitably away, and they would have been as pleasant as profitable, but for one circumstance. The existence of slavery and its concomitant horrors appears to have made a deep impression on Jackson's mind, and, at last, to have produced in him such sentiments of disgust and abhorrence, that he resolved on quitting the island altogether, and, as the phrase is, trying his luck in North America, where the revolutionary war was then raging. This resolutiondue perhaps, as much to his love of travel as to the motive assignedwas not altogether unfortunate, for shortly after his departure, October 3, 1780, Savana-la-Mar was totally destroyed, and the surrounding country for a considerable distance desolated, by a terrible hurricane and sweeping inroad of the sea, in which Dr King, his family and partner, together with numbers of others, unhappily perished.
The law of Jamaica forbade any one to leave the island without having given previous notice of his intention, or having obtained the bond of some respectable person as security for such debts as he might have outstanding. Jackson, when he embarked for America, had no debts whatever, and was, moreover, ignorant of the law, with whose requirements therefore he did not comply. Nor did he become aware of his mistake until, when off the easternmost point of the island, the master of the vessel approached him and said: 'We are now, sir, off Point-Morant; you will therefore have the goodness to favour me with your security-bond. It is a mere legal form, but we are obliged to respect it.' Finding this 'legal form' had not been complied with, the master then, in spite of Jackson's protestations and entreaties, set him on shore, and the vessel continued on her voyage. What was to be done? Almost penniless, landed on a part of the coast where he knew not a soul, Jackson well-nigh gave himself up to despair. There was a vessel for New York loading, it was true, at Lucea; but Lucea was 150 miles distant, on the westernmost side of the island, and not to be reached by sea, whilst our adventurer's purse would not suffer him to hire a horse. No choice was left him but to walk, and that in a country where the exigencies of the climate make pedestrianism perilous in the extreme to the white man. Having reached
Kingston, which was in the neighbourhood, in a boat, and obtained the necessary certificate, he started on his dangerous expedition, and on the first day walked eighteen miles, being sheltered at night in the house of a benevolent planter. The next day he pushed on for Rio Bueno, which he had almost reached, when, overcome by thirst, he stopped by the way to refresh himself, and imprudently standing in an open piazza exposed to a smart easterly breeze, whilst his lemonade was preparing, contracted a severe chill that almost took from him the power of motion, and left him to crawl along the road slowly and with pain, until he reached his destination.
Having finally arrived, friendless and moneyless, in New York, then in the occupation of the British, he endeavoured first to obtain a commission in the New York volunteers, and afterwards employment as mate in the Naval Hospital. In his endeavours, he was kindly assisted by a Jamaica gentleman, a fellow-passenger, whose regard during the voyage he had succeeded in conciliating by his amiable manners and evident abilities; but his efforts were all in vain, and poor Jackson, familiar with poverty from childhood, began now to experience the misery of destitution. In truth, starvation stared him in the face, and a sense of delicacy withheld him from seeking from his Jamaica friend the most trifling pecuniary assistance. In this, his state of desperation, he determined upon passing the British lines, and endeavouring to obtain amongst the insurgents the food he had hitherto sought in vain; resolving, however, under no circumstances to bear arms against his native country. Whilst moodily and slowly walking towards the British outposts to carry into execution this scheme, having in one pocket a shirt, and in another a Greek Testament and a Homer, he was met half-way by a British officer, who fixed his eyes steadily on him in passing. Jackson in his agitation thought he read in the glance a knowledge of his purpose and a disapprobation of it. Struck by the incident, he turned back, and, after a moment's reflection, resolved on offering himself as a volunteer in the first battalion of the 71st regiment (Sutherland Highlanders), then in cantonment near New York. Arriving at the place, he presented himself to the notice of Lieutenant-Colonel (afterwards Sir Archibald) Campbell, who, having first ascertained that he was a Scotsman, inquired to whom he was known at New York. Jackson replied, to no one; but that a fellow-passenger from Jamaica would readily testify to his being a gentleman. 'I require no testimony to your being a gentleman,' returned the kind-hearted colonel. 'Your countenance and address satisfy me on that head. I will receive you into the regiment with pleasure; but then I have to inform you, Mr Jackson, that there are seventeen on the list before you, who are of course entitled to prior promotion.' The next day, at the instance of Colonel Campbell, the regimental-surgeon, Dr Stuart, appointed Jackson acting hospital or surgeon's matea rank now happily abolished in the British army; for those who filled it, whatever might be their competency or skill, were accounted and treated no better than drudges. Although discharging the duties that now devolve on the assistant-surgeon, they were not, like him, commissioned, but only warrant-officers, and therefore had no title to half-pay.