Jackson occupied and amused himself with literary compositions. His Thirty Letters touched on many interesting points of art, literature, and philosophy.

In The Four Ages he put together a collection of various articles and stories. The volume took its title from the leading essay, in which he showed that the opinion of the Ancients as to a sequence of Golden, Silver, Brass, and Iron Ages should be inverted—that early man began in the Iron Age, and that society and culture were rapidly progressing to the Golden Age.

Dr. Burney said with severity, yet not without some truth, of Jackson: “He has never been remarkable for sailing with the tide of general opinion on any occasion. He would, perhaps, suppose the whole universe rather than himself to be in the wrong, in judging of any of the arts.” The critic ascribed his perverse ingenuity to “prejudice, envy, a provincial taste, or perhaps all together, which prevented his candid attention.”

He possessed a certain amount of wit, but it was of a cumbrous nature. On one occasion, being called upon at a public dinner for a toast, he said: “I have great pleasure, Mr. Chairman, in complying with your command, and give you the opening words of the third Psalm.” The chairman, astonished at the inappropriateness of the idea, stopped the musician short by exclaiming: “Oh, fie, Mr. Jackson! the beginning of a Psalm as a convivial toast?”

“Yes, sir, unless you can suggest a better. I give you Lord How.”

But what humour he had acidulated into sarcasm, as he could not move musically with the times. He could not advance out of the restricted circle of his own ideals, which was very narrow. To such a mind, Gothic architecture could only exhibit “an incongruous mass of absurdities—it is a false style, only showing the want of skill in the builders in mixing forms which cannot accord.”

He was greatly incensed that the public appreciated the music of Haydn, Mozart, and even Handel, whose strains were “an imposition of the feelings drawn from illegitimate sources.” Why could not English ears rest satisfied with Greene and Boyce and Blow? He affected to smile on “musical expression,” which he considered so contemptible that fantastic Germans were only capable of attempting it. Did the poet ask, “What passion cannot music raise or quell?” I ask in turn, What passion can music raise or quell? Poets or musicians can only produce different degrees of pure pleasure, and when they have produced this last effect they have attained the utmost in the power of poetry or music. Jackson published his Observations on the Present State of Music in London in 1791, in which he gave vent to his spleen. Dr. Burney replied, “And must we go to Exeter to ask Mr. Jackson how to please and be pleased? Are we to have no music in our concerts but elegies and balads? Mr. Jackson’s favourite style of music has been elegies, but what is an elegy to a tragedy or to an epic poem? He sees but one angle of the art of music, and to that all his opinions are referred. His elegy is no more than a closet in a palace.”

The great Handel Commemoration in Westminster Abbey in 1784 affected the organist of Exeter Cathedral with an attack of the spleen, from which he seems never to have recovered. At first, when that gigantic project was announced, he declared it to be impracticable, for that so stupendous a band, composed of many hundred instruments, could produce only a universal and deafening clash. When, however, the miracle succeeded, he took exception at the selection of pieces that had been performed. Lest Handel should obtain an exclusive triumph, he protested that there were other musicians beside Handel who deserved to be heard, and merited as high honours as were accorded to him. In 1790 came Haydn to London, and the cup of Jackson’s wrath overflowed. His ear could not endure the lively melodies and gorgeous effects of The Creation. It was then, in the rage of his heart, that he published his Observations. Artists and amateurs, according to him, who welcomed the ravishing music of Haydn were taking “their present musical pleasure from polluted sources.” And on his accustomed principle and in his usual style he declared that, “judging of the sensations of others by his own, the public is not pleased with what it applauds with rapture.”

Jackson entertained the greatest contempt for the physicians of his day, and perhaps not unjustly. He imagined that all the diseases to which man is heir are produced by misconduct and intemperance, and that they could be resisted by sobriety; and prevention, said he, was better than cure. His decision, persevered in, of using only abstinence, when his constitution was broken, precipitated his end. He died of asthma on 5 July, 1803, and was buried in S. Stephen’s Church, Exeter, where is a tablet to his memory, with a eulogistic description of his talents and attainments, written by his friend, William Kendall. The tablet also records the death of his widow, his daughter Mary, and four sons. One of his sons was ambassador to the King of Sardinia, and afterwards to Paris and Berlin. His eldest son, William, at an early age entered the service of the East India Company, and was secretary to Lord Macartney in his embassy to China. He amassed a considerable fortune in India, and married Frances, the only plain daughter of Charles Baring, of Courtlands, near Exmouth. One of the other daughters married Sir Stafford Northcote, Bart., of Pynes, another Sir Samuel Young, Bart., of Formosa Place, on the Thames. William purchased Cowley Barton, where he built Cowley House. The design is said to have been suggested by his father, as bearing some resemblance to an organ front. He was High Sheriff of Devon in 1806. He died in 1842, without leaving any issue.