Today, investigation and research (documenting evidence, compiling statistics and collecting eyewitness accounts) is a standard part of good journalism. This was not the case in the 18th and 19th centuries. In the campaign against slavery, however, it proved vital.
The movement faced tough opposition from those who had made great fortunes from the trade and had the power to lobby politicians. They depicted slavery as a legitimate employment and produced witnesses to testify that a slave's life was not harsh. They said the enslaved people benefitted from life on the plantations, as there was little society in Africa and no alternative to the trade. The abolitionists realised that they had to gather evidence, to show this was not true.
Thomas Clarkson, in particular, set out to gather as much evidence as possible. He travelled thousands of miles, visiting all the major ports in England. His style contrasted strongly with much of the work of the time. He relied on facts rather than religious and moral arguments. The evidence he unearthed included accounts from ships' doctors, traders and British sailors. His tone of writing was impartial rather than emotional and he presented information so that it gained the attention of many different groups. He showed, for example, that 20% of each crew died from disease or ill treatment, proving that the trade was bad for sailors as well as enslaved Africans.
The abolitionists also published eye witness accounts. These included John Stedman's description of the appalling treatment of Africans during the suppression of a slave rebellion in Surinam, South America. This work became a best seller, as did the detailed account of former Caribbean resident, James Ramsay. His essay, 'The Treatment and Conversion of African Slaves in the British Sugar Colonies', exposed the cruelty of life on the British sugar plantations. Also influential was the Reverend John Newton's 'Thoughts upon the African Slave Trade', which was filled with strong images of enslaved people packed as close as 'books upon a shelf'. Newton's testimony was very influential, as he was a well known Anglican preacher as well as a former slave trader.
Most important were the moving accounts by former slaves, such as Phyllis Wheatley and Olaudah Equiano. These personal testimonies were very powerful, as the people reading them saw the events through the eyes of a person they could relate to. Olaudah Equiano published his autobiography in 1789, detailing his kidnap from Africa, his voyage across the Atlantic and his life in slavery. He was an excellent writer and his book became a bestseller, challenging many of the widely held assumptions of the time, about Africans and the Transatlantic Slave Trade.
Thomas Clarkson also collected physical evidence on his travels. He bought shackles and thumbscrews, to provide evidence of abuse but he also collected items that showed the talents of the African craftsman, to show that there was an alternative to the slave trade. You can find out more about this in the section on Clarkson's Box.
Another abolitionist, Zachary Macaulay, in a remarkable feat of investigative reporting, crossed the Atlantic on a slave ship, taking notes. The vivid descriptions of the voyage were later used in a book published by John Riland in 1827.