In 1797 the doctor, chemical experimentalist and political campaigner Thomas Beddoes (1760-1808) was treating, in Clifton, Bristol, two young men who were his friends as well as his patients. James Watt Jr (1769-1848) was the son of the engineer and chemist James Watt. Like Beddoes, he had been a radical reformer who admired the French Revolution. After travelling to Paris in 1792 to present to the Club des Jacobins an address from the Manchester Constitutional Society, he was denounced in parliament byEdmund Burkeas a traitor. He left Paris in the wake of the massacres there for Italy, and returned to Britain later in 1794 as it became apparent that the prosecution of leading radicals for treason would fail. Thereafter, he became a manager of the family engineering firm, Boulton and Watt. With James Watt Sr, he helped Beddoes to found, in Clifton, a Pneumatic Institution designed to test whether the recently discovered gases oxygen and hydrogen might be effective in curing diseases (chiefly consumption/TB and palsy/paralysis). Watt advised on the subscription drive and supplied breathing apparatus invented by his father. The Institution opened in 1799. Watt spent much of 1797 in Clifton, under treatment by Beddoes with nitrous acid for what he suspected was a sexually transmitted disease. Suffering from a rash of red and yellow spots, and internal pains, he was, however, well enough to dine with friends in Bristol and Bath. One of these friends was another of Beddoes's patients, Thomas Wedgwood (1771-1805), the son of the pottery magnate Josiah Wedgwood. Having inherited part of Josiah's enormous wealth, Thomas, a scientific researcher who worked on the light emitted by heated bodies and on photography, became a major financial supporter of the Pneumatic Institution. He was also a philosopher who investigated the role in perception of emotion. In 1797 he visited Alfoxden in Somerset, hoping that Wordsworth and Coleridge would put into practice his ideas about the emotional education of young children. He was unable to take this project forward himself because he was afflicted by a serious stomach complaint that left him unable to digest food and caused bouts of depression. On Beddoes's recommendation, he and Watt Jr would spend the winter of 1797-98 recuperating from their illnesses on the Cornish coast. From there, in January 1798 Wedgwood wrote offering a lifetime annuity to enable Coleridge to take forward the kind of philosophical researches that he himself had to lay aside.

The tour of Wales was rapidly conceived and relatively brief. It was, however, unusual in that it did not follow the already standard tourist route along the lower section of the River Wye – either on horseback or foot from Chepstow to Tintern Abbey or by pleasure boat from Monmouth downstream to the river's mouth. Instead, the three men went along the valley of the Usk to Abergavenny and Brecon, then crossing the hills to Builth Wells and following the upper Wye upstream to Rhayader, from where they crossed the inland moors and mountains to the well-known tourist site, Devil's Bridge. Stopping at Hafod, the house of Beddoes's patient Thomas Johnes, with its picturesque grounds, the travellers then returned to Usk and back to Clifton.

The tour was undertaken for three reasons. First, Beddoes wanted to alleviate his patients' depressed state with a change of scene whilst himself enjoying a break from his busy medical practice. Second, Beddoes and Watt were keen geologists, involved in the controversy of the time – whether the strata that compose the earth's surface are of marine or igneous origin. They knew that the distribution of rocks and order of strata in Wales had been little studied. Third and most significant, Beddoes wanted information about the health of Welsh cottagers that might confirm or disprove his theory about the relationship of lifestyle and disease. A pioneer of statistically-based preventive medicine, Beddoes viewed the dramatic increase in the prevalence of consumption as a result of the modern, urban habit of living in warm, poorly-ventilated rooms. He suspected that a less luxurious outdoor life such as that pursued by farm labourers was likely greatly to lessen the chance of contracting consumption. He also suspected that exposure to effluvia from animals – fumes from their dung, or from their carcasses – might confer some protection against the disease (he interviewed butchers and noted that consumption was uncommon amongst them; he also placed consumptive patients in cowhouses in the hope that the manure would benefit their lungs). The Welsh tour was an opportunity to question the rural poor about their illnesses and to view their living conditions.