He hummed to himself deeply and thoughtfully, but Merry and Pippin caught no proper words: it sounded like boom, boom, rumboom, boorar, boom, boom, dahrar boom boom, dahrar boom, and so on with a constant change of note and rhythm.
for this new passage twisted and turned constantly; but he thought he was catching the two Orcs up: their voices were growing nearer again.
There are no more uses of "constant" in the book.
Show samples from other sources
The history of computers is a history of constant technological advancement.