May's appeal had only quickened a little the sure work of Channing's conscience. A few months later, in December, 1835, he published his short treatise on _Slavery_. No weightier word on the subject was ever spoken. If mankind were moved by their higher reason the North would not have waited twenty years to be converted to anti-slavery by _Uncle Tom's Cabin_. And if the South had been wise in her day, she would have listened to this noble and persuasive utterance. No passion sullied its temper; slave and slave-holder were held in equal regard; the case was pleaded on irresistible grounds--of facts beyond question and rooted in the very constitution of human nature. The needed, the righteous, the inevitable reform, was shown as part of the upward movement of humanity, and as appealing to every consideration of practical wisdom and of justice. The little book of 150 pages deserves to be held as a classic in American history. Channing never lost the sense of proportion in his own work. He went on giving inspiration and leadership to religious thought and to social advance. It was neither necessary nor possible for him to be in close sympathy or habitual alliance with the extreme Abolitionists. But he vindicated the right of free speech when it was denied them, and he was recognized by the best of their number as a friend of the cause. Mrs. Lydia Maria Child,--like Mr. May, one of the finest spirits among the Abolitionists--wrote: "He constantly grew upon my respect, until I came to regard him as the wisest as well as the gentlest apostle of humanity. I owe him thanks for preserving me from the one-sidedness to which zealous reformers are so apt to run. He never sought to undervalue the importance of anti-slavery, but he said many things to prevent me from looking upon it as the only question interesting to humanity."