What does the heaviside layer mean in Cats?

Could you please clarify what you mean by "heaviside layer" in the context of the play "Cats"? As far as I'm aware, "Cats" is a musical written by Andrew Lloyd Webber based on T.S. Eliot's poetry collection "Old Possum's Book of Practical Cats." There is no direct mention of a "heaviside layer" in the musical or the original poetry. Could you perhaps be referring to a specific scene, character, or metaphor that you've interpreted as a "heaviside layer"? If so, I'd be happy to discuss it further with you.