The advocates for the Slave-Trade endeavour to advance, that the mortality of the seamen is entirely to be attributed to the nature of the climate—but this assertion, is founded neither in veracity nor experience. The climate comes in for its share in _heightening_ the horrid scene, but it is the previously wretched situation of the poor victims that gives it that effect. I heard our doctor, an able intelligent man, declare, that if the trade, with the same concomitant circumstances, was carried on at the Canary Islands, the same mortality would be the consequence. And I am fully convinced, that if a commerce was carried on to the coast of Africa of any other kind than that of slaving, and the captains treated their people with as much humanity as they are treated in other employs, not one of the causes of the great mortality, I have been witness to, could exist. Among the many causes of destruction, which originate from the trade, and not from the climate, the bulk-heads between the decks, excluding a salutary circulation of air, have been insisted upon as producing these effects. But there is another which has not claimed such notice, and which yet is a terrible assistant to African mortality. This is the fabricating of an house over the vessel for the security of slaves, while on the coast. This enclosure helps the stagnation of air, and is, in that point of view, dreadful: but it is more fatal in the act of its preparation. I know nothing more destructive than the business of cutting wood and bamboe, for the purpose of erecting and thatching this structure. The process is generally by the riverside. The faces and bodies of the poor seamen are exposed to the fervour of a burning sun, for a covering would be insupportable. They are immersed up to the waist in mud and slime; pestered by snakes, worms, and venomous reptiles; tormented by muskitoes, and a thousand assailing insects; their feet slip from under them at every stroke, and their relentless officers do not allow a moment's intermission from the painful task. This employment, the cruelty of the officers, and the inconceivably shocking task of scraping the contagious blood and filth, at every opportunity, from the places where the slaves lie, are, in my opinion, the three greatest (though by no means the sole) causes of the destruction of seamen, which this country experiences by the prosecution of the trade in slaves. LETTER IV. As I wish to meet and to answer every possible question that may be asked about this simple enumeration of facts, I find two plausible interrogations that may with no great impropriety be stated in the present place.