second response Robert said: a. It is non-material. i.e. [has no physical properties normally expected of matter.] Over the top, I think. The aether will only be observable to us by its effects on matter (and radiation/light) . Analogs are ways of building knowledge bridges between the known and unknown. Ruling out properties of matter that are equal to or similar to matter - like density, compressibility, viscosity - is a bit premature. Won't you please reconsider, Philip? response: I have elsewhere acknowledged analogy, and analogical properties like density etc.. but we cannot say an immaterial entity has the same properties exactly, which the word "normally" was meant to say.. You are welcome to rephrase it.. Phil Thanks, Phil. Here's my rephrase: a. Its composition is unknown - now. Robert B