Mr. Thompson was taken into Lord George Germain’s office, and he was appointed Secretary of the Province of Georgia.
In the autumn of 1777 Thompson was at Bath for his health, drinking the waters. Whilst there he made some experiments on the cohesive strength of different substances. These led to no great results, but he communicated them to Sir Joseph Banks, the new President of the Royal Society.
Sir W. Howe was at this time asking for large reinforcements. He thus wrote to Lord G. Germain from Philadelphia:
‘From the little attention, my Lord, given to my recommendations since the commencement of my command, I am led to hope that I may be relieved from this very painful service wherein I have not the good fortune to enjoy the necessary confidence and support of my superiors, but which I conclude will be extended to Sir Henry Clinton, my presumptive successor.’
In 1778 Mr. Thompson was with Lord G. Germain at his house, Stoneland Lodge, Sussex. Whilst there Thompson made experiments on testing gunpowder, and on a new method of determining the velocity of projectiles. The results were sent to the Royal Society, in 1781, and were published at great length in the ‘Philosophical Transactions.’ One good observation is now of great interest. ‘Being much struck with the accidental discovery of the great degree of heat that pieces acquire when they are fired with powder without any bullet, and being desirous of finding out whether it is a circumstance that obtains universally, I was very attentive to the heat of the barrel after each of the succeeding experiments, and I constantly found the heat sensibly greater when the piece was fired with powder only than when the same charge was made to impel one or more bullets.’
In order to pursue these experiments he went in 1779, on board of the ‘Victory,’ of 110 guns, commanded by his friend Sir Charles Hardy. He passed the whole of the campaign on board of the fleet, and the result of the observations that he then made furnished the materials for a chapter which he contributed to Stalkart’s ‘Treatise on Naval Architecture.’ He added to it a code of signals for the navy, which was not published. In his paper on gunpowder, read in 1797 to the Royal Society, he says:
During a cruise which I made, as a volunteer, in the ‘Victory,’ with the British fleet, under the command of my late worthy friend Sir Charles Hardy, in the year 1779, I had many opportunities of attending to the firing of heavy cannon; for though we were not fortunate enough to come to a general action with the enemy, as is well known, yet, as the men were frequently exercised at the great guns and in firing at marks, and as some of my friends in the fleet, then captains (since made admirals), as the Honourable Keith Stewart, who commanded the ‘Berwick,’ of 74 guns,—Sir Charles Douglas, who commanded the ‘Duke,’ of 98 guns,—and Admiral Macbride, who was then captain of the ‘Bienfaisant,’ of 64 guns, were kind enough, at my request, to make a number of experiments, and particularly by firing a greater number of bullets at once from their heavy guns than ever had been done before, and observing the distances at which they fell in the sea,—I had opportunities of making several very interesting observations, which gave me much new light relative to the action of fired gunpowder.
In 1778 Mr. Thompson was elected a Fellow of the Royal Society.
Great must have been the trouble in his office this year. In October 1778, Sir H. Clinton wrote to Lord G. Germain from New York that he was about to send, as he was ordered, ten thousand men to the West Indies and St. Augustine. ‘After a wound in my humble opinion so fatal to the hopes of any future vigour in this army, I trust, my Lord, you cannot wish to keep me in the mortifying command of it.’ ‘You cannot, I am confident, my Lord, desire that I should remain a mournful witness of the debility of an army at whose head, had I been unshackled by instructions, I might have indulged expectations of rendering serious service to my country.’