"Well, well," I said laughing, "I found that out without your assistance, and I am not going to let you dodge the question by a play on words. What I want to know is, why these gaseous contents at the center, are opaque while the air at the surface is not?"
"Well I see," said MacNair, "that you are determined to compel me to reveal how little I know. The scientists of the early ages evolved the theory that the center of the concave is a gaseous globe composed of the very lightest materials which they knew by actual experience to be opaque to their vision."
"But why," I asked, "is it that this concave sphere does not shut off the light from the sun?"
"Because," said MacNair, "this opaque sphere is above our line of vision,—our position on the surface, being twelve degrees below the verges. Besides this, the central opaque sphere is conceived to be flattened at the poles and bulged at the equator, and some have contended that it is also hollow like the earth. But for this opaque sphere our nights would be as light as day by the reflection from the hemisphere above."
"I have thought of that," I replied, "and still I have so much wished that the opposite hemisphere could be seen with the telescope."
"Well, that is precisely what you will be able to do from this airship," said MacNair.
"How so?" I asked. "We certainly cannot rise above the opaque sphere, and if we could, and got a clear view of the opposite hemisphere, that would not be seeing from one side of the concave to the other."
"Not that surely," said MacNair, "but scientists knowing that magnetic currents often pass more readily through opaque than transparent substances, began to search for rays of this kind that would pass through dark bodies and be reflected by substances beyond. At last they succeeded in securing a photograph through wood and metal, and then, all that was required in order to enable us to see through opaque matter, was an optical instrument that would cast the reflection on the retina of the eye. This, in the course of time, was accomplished. And now, these wonderful discoveries are used by the medical profession, in order to enable them to look into the bodies of their patients and examine the internal organs. And, these electro-magnetic optical instruments have been so improved that they are in general use, in observations where opaque bodies obstruct the view."
"And do you tell me this as sober truth?" I asked.