Both Uses of

ebb
in
Barn Burning, by Faulkner

the spell of this peace and dignity rendering even the barns and stable and cribs which belong to it impervious to the puny flames he might contrive ...this, the peace and joy, ebbing for an instant as he looked again at the stiff black back, the stiff and implacable limp of the figure which was not dwarfed by the house, for the reason that it had never looked big anywhere and which now, against the serene columned backdrop, had more than ever that impervious quality of something cut ruthlessly from tin, depthless, as though, sidewise to the sun, it would cast no shadow.†

ebbing = declining -- typically gradually as with the height of the tide

But it ebbed only for a moment, though he could not have thought this into words either, walking on in the spell of the house, which he could even want but without envy, without sorrow, certainly never with that ravening and jealous rage which unknown to him walked in the iron like black coat before him.†
*

ebbed = declined -- typically gradually as with the height of the tide

Definition:

decline -- typically gradually as with the height of the tide