Men had grown accustomed to Karellen’s imperceptible rule-but they were becoming impatient to know who ruled them.
You will live to see its completion-but the change will be so imperceptible that few will notice it when it comes.
Karellen made an imperceptible gesture with his hand.
There are no more uses of "imperceptible" in the book.
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...and he let the line slip down, down, down, unrolling off the first of the two reserve coils. As it went down, slipping lightly through the old man’s fingers, he still could feel the great weight, though the pressure of his thumb and finger were almost imperceptible.