During the 1760s, he gained recognition as a scientist and, through mutual interests, he met and became an intimate friend and correspondent of Benjamin Franklin.

He represented Kingston upon Hull in parliament from 1774 to 1780, and from 1782 to 1784, and attained considerable reputation as an opponent of the war with America, and of the African slave trade.

Although a liberal on American policy, Hartley was a long-time friend of Lord North and strongly disliked the Prime Minister, Shelburne.

Nathaniel William Wraxall says that Hartley, "though destitute of all personal recommendation of manner, possessed some talent with unsullied probity, added to indefatigable perseverance and labour".

He adds that his speeches were intolerably long and dull, and that "his rising always operated like a dinner bell" (Memoirs, iii.

the object was to establish an influential dominion of the crown by means of an independent American revenue uncontrolled by parliament".

Six volumes of letters and other documents relating to the peace went to America and passed into the collection of Levi Leiter of Washington, D.C.; others are in the British Museum.

An obelisk was built on the heath, adjacent to Tibbet's corner, 1776 marking the Lord Mayor of London's decision to give Hartley £2,500 for work on his fire plates.

The RECORD of which EXPERIMENTS and also of his admission into the FREEDOM of the said CITY of LONDON is entered in the BOOK signed with the letter R["¦?

That a sum not exceeding Two Thousand Five Hundred Pounds be granted to His MAJESTY to be paid To DAVID HARTLEY, ESQR.

Towards enabling him to defray the Charge of Experiments in order to ascertain the practicability and Utility of his INVENTION for securing buildings from FIRE and that the same be paid without Fee or Reward

the late LORD MAYOR of this CITY having laid a Foundation Stone for erecting an Obelisk on Putney Common to commemorate the invention of FIRE PLATES for securing buildings from FIRE By DAVID HARTLEY ESQ The Committee of City Lands be empowered to erect and complete the same.