he air of England is too pure for a slave to breathe in.'' This phrase, with slight variations, recurs through long years in the rhetoric of movements to abolish first African slavery within England, then the Atlantic traffic in African people that England dominated for more than a century and then the institution of slavery in the British Empire, whose populations included hundreds of thousands of slaves. It is an axiom traditionally believed to have been invoked in 1772, in principle if not verbatim, by Lord Mansfield, the judge in Somerset v. Steuart, which Steven M. Wise in ''Though the Heavens May Fall'' calls the ''trial that led to the end of human slavery.'' Somerset was an African who accompanied Steuart, his owner, to England. He escaped, was recaptured and sued successfully for his freedom.

Both Wise and Adam Hochschild celebrate this trial and the events and personalities that brought it about. No doubt they should. It is a melancholy fact, however, that the phenomenon of African slavery loomed as it did over the Atlantic world because, from the reign of Elizabeth I to the reign of George III, England assumed that the air of its colonies, or of any other colony ready to buy, was impure enough to accommodate slavery very nicely.

Wise, the president of the Center for the Expansion of Fundamental Rights, traces with reverent care how the question of the legality of slavery developed within England, culminating in this famous trial. The hero of his narrative is Granville Sharp, a minor government clerk who educated himself in the law in the course of defending the rights of Africans brought into England as slaves. He devoted himself and his slender resources to this work over decades with the object of finally putting an end to slavery itself. The trial, which is said to have abolished slavery within England by legal precedent, was centered on the question of Steuart's right to sell Somerset into the West Indies. Lord Mansfield ruled in favor of Somerset on the grounds that slavery ''is so odious that nothing can be suffered to support it but positive law.'' There being no such law in England, ''the black must be discharged.'' This decision freed an estimated 15,000 Africans then held as slaves in England.

Wise follows Sharp and the lawyers sympathetic to him through a series of trials in which they attempt to obtain rulings to vindicate the argument that English law does not countenance slavery. He has an eye for evocative detail and an interest in the trappings and procedures of an 18th-century courtroom that do as much to engage the reader as the drama of the trials themselves. And he has a good lawyer's love of those moments in which the true poetry of humane justice finds its voice. More insight into the actual operations of the law would have been useful -- some discussion, for example, of the yawning gulf between the principle of the right to trial and the fact that in early-19th-century England, an average felony trial lasted less than nine minutes, sometimes ending so quickly that the accused did not know he had been tried. In practice, common law seems only a little too supple to be called a rope of sand. Yet Wise assumes, more or less, that by means of it England pulled itself out of the abyss of slavery and pulled America and the world after it.

In this instance, though the purport of the Mansfield judgment was taken to be that ''as soon as any slave sets foot on English ground, he becomes free,'' the emancipated black population fell into a wretchedness so extreme as to justify their expulsion to -- such paradoxes are endless -- the region of Sierra Leone that was also the center of the British slave trade and from which Africans were shipped into the West Indies. Their destitution was exploited and exacerbated by none other than Granville Sharp, who ''distributed handbills asking London's gentlemen to cease dispensing charity to poor blacks in order to nudge them toward Africa.'' This coercion was apparently not at odds with the high view of English liberty with which he had swayed public and judicial opinion. Sharp, Wise says, ''believed wild tales of how mild and fertile'' Sierra Leone was -- surely a remarkable feat of credulity, given England's long experience with the place. In any case, in 1787 several hundred former slaves sailed to Sierra Leone ''with dozens of white prostitutes whom the English authorities, anxious to rid themselves of as many undesirables as possible, black and white, had married to the settlers while the women were drunk'' -- if true, a further light on English liberty. The population of the colony promptly fell by two-thirds largely because of famine and disease.

This is not to give away the end of the story, which for Wise is in fact the triumph of law and the beginning of the abolition of human slavery. He acknowledges anomalies like this one in a late chapter but, he concludes, ''Somerset's chief legacy'' was that human slavery ''was so odious the common law would never support it.'' And he continues: ''Mansfield's proved just the opening salvo in a legal barrage that, within a century, splintered all of human slavery's bulwarks.'' That century brought the world to 1872, when colonialism was at its height and its depredations were only accelerating. Colonialism disrupted and destroyed far more African lives than did slavery. Indeed, the distinction between the two seems no more than convenient.

Yet the Atlantic slave trade was an enormity stunning in its scale and its duration. In ''Bury the Chains,'' Adam Hochschild says: ''So rapidly were slaves worked to death, above all on the brutal sugar plantations of the Caribbean, that between 1660 and 1807, ships brought well over three times as many Africans across the ocean to British colonies as they did Europeans. And, of course, it was not just to British territories that slaves were sent. From Senegal to Virginia, Sierra Leone to Charleston, the Niger delta to Cuba, Angola to Brazil, and on dozens upon dozens of crisscrossing paths taken by thousands of vessels, the Atlantic was a vast conveyor belt to early death in the fields of an immense swath of plantations that stretched from Baltimore to Rio de Janeiro and beyond.'' The subject of this interesting and valuable book is the tiny cadre of reformers that undertook to arouse public feeling against this great abuse. Hochschild says: ''For 50 years, activists in England worked to end slavery in the British Empire. None of them gained a penny by doing so, and their eventual success meant a huge loss to the imperial economy.'' Vast, entrenched and profitable as the slave trade was, how did they manage to bring it to an end?

That they did end it is assumed by Hochschild rather than proved by him. It seems a little odd in a historian to use the improbability of a movement's success as grounds for heightened admiration, rather than for heightened attention to other contributing factors. Given that the whole infernal enterprise was sustained by the immense wealth it generated, one might, without cynicism, look to the economic considerations in play. When the British outlawed the exportation of Africans to the colonies for sale in 1807, they had had almost 20 years' notice that the Americans intended to ban the importation of Africans in 1808. And it was just about this time that Napoleon, cut off by the British Navy from French colonies in the Caribbean, began looking into the domestic cultivation of the sugar beet.

And there were the rebellions in the West Indies, particularly the Haitian rebellion. The sections of the book that deal with them bring to light an astounding, and forgotten, episode in Western history. Since Haiti alone produced as much foreign trade at that time as the whole of the 13 colonies of North America, it was potentially a great loss. It belonged to France, but Britain supplied it with slaves, a valuable trade since the slaves were intentionally worked to death -- it was cheaper to replace them than to sustain them -- so the market for Africans was very brisk. Uprisings had long been frequent in the West Indies, but at long last rage in Haiti converged with the tactical brilliance of Toussaint L'Ouverture and others and the slaves seized the island. This part of the story is familiar. But there is more.

First the British and then the French under Napoleon sent huge forces against the Haitians. The British sent a larger army against Haiti than it had dispatched to fight in the American Revolution. And it buried 60 percent of those soldiers in Haiti. The two greatest powers on earth went up against a population of half-starved, desperate people and were utterly defeated. It is no surprise that these two abysmal wars of empire have fallen out of history. One cannot read about them without concluding that the Haitian Africans contributed mightily to making the Caribbean slave system untenable. All in all, in 1807 the prospects of the traffic in human beings were not good. It is perhaps coincidental that in adopting the abolitionist stance Britain was able to seize the moral high ground and attempt (together with the United States) to suppress the slave trade among its economic rivals. Certainly this posture was gallant enough to make a great part of the world forget that Britain was for so long pre-eminent among the despoilers of Africa.

Hochschild has written eloquently about the importance of this kind of historical forgetting in ''King Leopold's Ghost,'' his account of the policies of the Belgian King Leopold II in the Congo in the early 20th century, which are estimated to have taken 10 million lives. There he writes, ''The world we live in -- its divisions and conflicts, its widening gap between rich and poor, its seemingly inexplicable outbursts of violence -- is shaped far less by what we celebrate and mythologize than by the painful events we try to forget.'' How consistently and with what lethal effect we choose not to be aware.

Nevertheless, Hochschild interprets the success of the British abolitionist movement as a triumph of empathy, a humane response to horrors of which the public only gradually became conscious. His heroes are Thomas Clarkson, William Wilberforce, Granville Sharp and the former slave Olaudah Equiano, among others. These men did indeed work patiently and passionately for emancipation. Certainly it is uplifting to find empathy and law together championing justice, as they do in the narratives of both Hochschild and Wise. The intention of the writers is clearly the honorable one of finding an instance in history in which justice has prevailed and the world has been changed, and of finding as well a model of the kinds of activism by which present enormities are, or might be, addressed. Yet, again to the credit of both writers, these narratives include elements incompatible with this kind of interpretation, indeed consistent with the opposite and very bleak conclusion that movements based on empathy and law, when proceeding from exalted tributes to the essential decency of a population, can flatter indifference or complicity.

In fact, the slave trade was at home in a world where the appropriation of lives and the extortion of labor were astonishingly commonplace. Hochschild describes the virtual abductions by which slave ships were manned, and tells how these sailors were subject to flogging and starving, and died in numbers as great as did the abducted Africans they helped to transport. And the British Navy was manned in the same way. None of this was at all exceptional, as it would have to have been if there were indeed a presumption of freedom embedded in English culture, as both books assert. No consensus in support of freedom can be demonstrated. The industrialist Robert Owen, writing in 1813, years after the Mansfield decision, describes the transfer to factories of the children of British paupers by the hundreds, 6-, 7- and 8-year-olds who worked 13 hours a day through seven-year apprenticeships. These little workers died quickly and were replaced by other pauper children. They were not slaves in the strictest sense. The system did resemble Caribbean slavery, however, in that it set a negative value on their well-being.

The literature on such practices is immense because they were pervasive and long lived and of interest to many generations of activists. Indeed, if there were not economic motives behind British abolition, then the speed with which that reform came about is miraculous compared with the laggardly pace of reforms affecting the laboring classes who were the great majority of the British population. Owen asks, ''Shall the well-being of the poor, half-naked, half-famished, untaught and untrained . . . not call forth one petition, one delegate, one rational effective legislative measure?'' Just at the time of the emancipation of the British West Indies, a reform bill passed by Parliament created the ''Poor Law Bastilles,'' a system of punitive incarceration for the indigent. Hochschild describes how the Parliament paid the West Indian slaveholders extravagant sums for their emancipated slaves, who then became their oppressed and wretchedly paid employees, driven to frequent rebellion just as the slaves had been. If Britain taught the world by ending actual slavery, it gave the world a second lesson in establishing virtual slavery. As Hochschild remarks in ''King Leopold's Ghost,'' empathy is fickle.

The primacy of England in these narratives slights the fact that a consensus against slavery had been building for a generation in New England, and longer in Quaker Philadelphia. The role of England in sustaining slavery in its colonies is demonstrated in the abolition of slavery immediately after the American Revolution, in Vermont in 1777 and in Massachusetts in 1780. The institution of human bondage became truly peculiar to the South only after the Revolution, because it was legal everywhere in the colonies while they were under British law. And years after the emancipation of slaves in the empire, Britain came near intervening in the American Civil War on the side of the slave states. The arguments in Somerset v. Steuart treat the laws of the colonies as alien to England, though members of the royal family were major stockholders in the slave trade, and what is more English than the Church of England, which was a great slaveholder in Jamaica? While every good effect of an important precedent must be welcomed, the fact remains that the claim to an exclusive English purity that is the basis for the legal arguments associated with Steuart v. Somerset was and is a denial of history, a part of the great forgetting.

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