Sir John threw his personal energy into every work in which he engaged, rousing the inert, stimulating the idle, encouraging the hopeful, and working with all. When a French invasion was threatened, he offered to Mr. Pitt to raise a regiment on his own estate, and he was as good as his word. He went down to the north, and raised a battalion of 600 men, afterwards increased to 1000;and it was admitted to be one of the finest volunteer regiments ever raised, inspired throughout by his own noble and patriotic spirit. While commanding officer of the camp at Aberdeen he held the offices of a Director of the Bank of Scotland, Chairman of the British Wool Society, Provost of Wick, Director of the British Fishery Society, Commissioner for issuing Exchequer Bills, Member of Parliament for Caithness, and President of the Board of Agriculture. Amidst all this multifarious and self-imposed work, he even found time to write books, enough of themselves to establish a reputation. When Mr. Rush, the American Ambassador, arrived in England, he relates that he inquired of Mr. Coke of Holkham, what was the best work on Agriculture, and was referred to Sir John Sinclair's; and when he further asked of Mr. Vansittart, Chancellor of the Exchequer, what was the best work on British Finance, he was again referred to a work by Sir John Sinclair, his 'History of the Public Revenue.' But the great monument of his indefatigable industry, a work that would have appalled other men, but only served to rouse and sustain his energy, was his 'Statistical Account of Scotland,' in twenty-one volumes, one of the most valuable practical works ever published in any age or country. Amid a host of other pursuits it occupied him nearly eight years of hard labour, during which he received, and attended to, upwards of 20,000 letters on the subject. It was a thoroughly patriotic undertaking, from which he derived no personal advantage whatever, beyond the honour of having completed it. The whole of the profits were assigned by him to the Society for the Sons of the Clergy in Scotland. The publication of the book led to great public improvements; it was followed by the immediate abolition of several oppressive feudal rights, to which it called attention; the salaries of schoolmasters and clergymen in many parishes were increased; and an increased stimulus was given to agriculture throughout Scotland. Sir John then publicly offered to undertake the much greater labour of collecting and publishing a similar Statistical Account of England; but unhappily the then Archbishop of Canterbury refused to sanction it, lest it should interfere with the tithes of the clergy, and the idea was abandoned.
A remarkable illustration of his energetic promptitude was the manner in which he once provided, on a great emergency, for the relief of the manufacturing districts. In 1793 the stagnation produced by the war led to an unusual number of bankruptcies, and many of the first houses in Manchester and Glasgow were tottering, not so much from want of property, but because the usual sources of trade and credit were for the time closed up. A period of intense distress amongst the labouring classes seemed imminent, when Sir John urged, in Parliament, that Exchequer notes to the amount of five millions should be issued immediately as a loan to such merchants as could give security. This suggestion was adopted, and his offer to carry out his plan, in conjunction with certain members named by him, was also accepted. The vote was passed late at night, and early next morning Sir John, anticipating the delays of officialism and red tape, proceeded to bankers in the city, and borrowed of them, on his own personal security, the sum of 70,000L., which he despatched the same evening to those merchants who were in the most urgent need of assistance. Pitt meeting Sir John in the House, expressed his great regret that the pressing wants of Manchester and Glasgow could not be supplied so soon as was desirable, adding, "The money cannot be raised for some days.""It is already gone! it left London by to-night's mail!" was Sir John's triumphant reply; and in afterwards relating the anecdote he added, with a smile of pleasure, "Pitt was as much startled as if Ihad stabbed him." To the last this great, good man worked on usefully and cheerfully, setting a great example for his family and for his country. In so laboriously seeking others' good, it might be said that he found his own - not wealth, for his generosity seriously impaired his private fortune, but happiness, and self-satisfaction, and the peace that passes knowledge. A great patriot, with magnificent powers of work, he nobly did his duty to his country; yet he was not neglectful of his own household and home. His sons and daughters grew up to honour and usefulness; and it was one of the proudest things Sir John could say, when verging on his eightieth year, that he had lived to see seven sons grown up, not one of whom had incurred a debt he could not pay, or caused him a sorrow that could have been avoided.