"The first point to decide," said I, "is obviously the physical properties of our visitor. Mr. Egerton, will you kindly allow us to feel your hand?"
"You may try to feel it if you like," said the phantom quietly, "but I doubt if you will succeed to any brilliant extent." As he spoke, he held out his arm. Harry and I endeavoured successively to grasp it: our fingers slipped through the faintly luminous object as though it were air or shadow. The phantom bowed forward his head; we attempted to touch it, but our hands once more passed unopposed across the whole face and shoulders, without finding any trace whatsoever of mechanical resistance. "Experience the first," said Harry; "the apparition has no tangible material substratum." I seized the pen and jotted down the words as he spoke them. This was really turning out a very full-blown specimen of the ordinary ghost!
"The next question to settle," I said, "is that of gravity.—Harry, give me a hand out here with the weighing-machine.—Mr. Egerton, will you be good enough to step upon this board?"
Mirabile dictu! The board remained steady as ever. Not a tremor of the steelyard betrayed the weight of its shadowy occupant. "Experience the second," cried Harry, in his cool, scientific way: "the apparition has the specific gravity of atmospheric air." I jotted down this note also, and quietly prepared for the next observation.
"Wouldn't it be well," I inquired of Harry, "to try the weight in vacuo? It is possible that, while the specific gravity in air is equal to that of the atmosphere, the specific gravity in vacuo may be zero. The apparition—pray excuse me, Mr. Egerton, if the terms in which I allude to you seem disrespectful, but to call you a ghost would be to prejudge the point at issue—the apparition may have no proper weight of its own at all."
"It would be very inconvenient, though," said Harry, "to put the whole apparition under a bell-glass: in fact, we have none big enough. Besides, suppose we were to find that by exhausting the air we got rid of the object altogether, as is very possible, that would awkwardly interfere with the future prosecution of our researches into its nature and properties."
"Permit me to make a suggestion," interposed the phantom, "if a person whom you choose to relegate to the neuter gender may be allowed to have a voice in so scientific a question. My friend, the ingenious Mr. Boyle, has lately explained to me the construction of his air-pump, which we saw at one of the Friday evenings at the Royal Institution. It seems to me that your object would be attained if I were to put one hand only on the scale under the bell-glass, and permit the air to be exhausted."
"Capital," said Harry: and we got the air-pump in readiness accordingly. The spectre then put his right hand into the scale, and we plumped the bell-glass on top of it. The connecting portion of the arm shone through the severing glass, exactly as though the spectre consisted merely of an immaterial light. In a few minutes the air was exhausted, and the scales remained evenly balanced as before.
"This experiment," said Harry judicially, "slightly modifies the opinion which we formed from the preceding one. The specific gravity evidently amounts in itself to nothing, being as air in air, and as vacuum in vacuo. Jot down the result, Jim, will you?"
I did so faithfully, and then turning to the spectre I observed, "You mentioned a Mr. Boyle, sir, just now. You allude, I suppose, to the father of chemistry?"