"Did you ever observe a bubble resting on a bubble?"
"Yes."
"Did you ever place a pipe-stem in a partly filled bowl of soap water, and by blowing through it fill the bowl with bubbles?"
"Yes."
"Did you ever calculate the tensile strength of the material from which you blew the bubble?"
"No; for soap water has no appreciable strength."
"And yet you know that a bubble made of suds has not only strength, but elasticity. Suppose a bubble of energy floating in space were to be covered to the depth of the thickness of a sheet of tissue paper with the dust of space, would that surprise you?"
"No."
"Suppose two such globes of energy, covered with dust, were to be telescoped or attached together, would you marvel at the fact?"
"No."