From A Labyrinth of Kingdoms: 10,000 Miles through Islamic Africa, by Steve Kemper (W. W. Norton, 2012), Kindle pp. 211-213:
[Heinrich Barth] … began replies to his recent correspondents. One of them was William Desborough Cooley, the British historian and geographer. His book of 1841, The Negroland of the Arabs Examined and Explained; or, An Inquiry into the Early History and Geography of Central Africa, attempted to re-create the history and geography of the western Sudan through rigorous engagement with old travelers’ accounts and Arabic sources such as Al-Idrisi and Al-Bakri. Cooley sifted these sources for verifiable facts and cross-checked them against modern European travel accounts. Comparing all these sources, he believed, would yield a strong facsimile of truth about Central Africa’s past as well as the location of historical places and landmarks.
He was able to demonstrate that the half-legendary empires of Mali, Ghana, and Songhai had been real, and he roughly positioned them geographically for the first time. From old and new sources he extracted a detailed, complex history of black Africa that contradicted hazy European assumptions about the continent’s savagery. Cooley also avoided most of the era’s racial and cultural biases. He reminded readers that bloody executions by African leaders weren’t so different from English laws that burned women at the stake for counterfeiting money or that hanged hundreds of people for minor crimes such as pilfering.
Cooley’s book was immediately influential among Europe’s Africanists, but met its greatest resistance in Britain. Barth admired it so much that he carried it to Africa and often consulted it. On April 1851, a few days after he first arrived in Kukawa, he wrote Cooley an introductory letter that began, “Sir, It is from a warm love of science that I quite a stranger to you take the liberty of addressing you the following lines.” He expressed his esteem for The Negroland of the Arabs, “sincere as it is without the least prejudice and going on with a firm step from point to point”—a perspective and method like Barth’s own. Rereading the book in Africa, he told Cooley, increased his appreciation. He thought Cooley would like to know that on-the-ground observations were confirming the accuracy of the old Arab historians and many of Cooley’s speculations. “I am able to put truth in the place of conjectures,” wrote Barth, “and to give life to vague accounts of former times.”
Cooley’s response, written in January 1852, reached Bagirmi with the packet of letters in July. His tiny handwriting in pale ink contrasted strongly with Barth’s bold dark penmanship. The letter was a peculiar mixture of praise, advice, querulousness, bruised egotism, and condescension. Cooley regretted not meeting Barth in London and welcomed Barth’s compliments about his book, “as it has been received here with discouraging coldness,” despite “the revolution effected by me in the comparative Geography of Africa.”
He swatted away several of Barth’s suggested corrections to his speculations. Barth was right, but Cooley’s reaction was typical of him. He ridiculed any new information by explorers that contradicted his armchair conjectures. For instance, he mocked all the eyewitness reports of snow on Mounts Kenya and Kilimanjaro because they clashed with his theory about possible temperatures at the equator. This habit eventually undermined his influence and earned him the nickname “the stormy petrel.”
Cooley praised Barth for sending back “a larger amount of valuable information, then [sic] has been as yet appended to the narrative of any African traveller, Burckhardt alone perhaps excepted; and doubtless you now possess much the loss of which would be deplorable.”