Some one inside the observatory had fired a gigantic rocket.
Morse gave a shout of surprise. He had a fresh cigar in his hand, and, unknowingly, he dropped it and mechanically bit the end of his thumb instead.
"What was that?" I cried, echoing his shout.
He didn't answer, but grew very white as he stepped up to the parapet, placed his hand upon the stone, and leant forward.
I did the same, and for nearly a minute we stared at the white, circular tower in silence.
Nothing happened. There was the black slit in the gold, enigmatic and undisturbed.
"Some experiment," I stammered at length. "Professor Chang is at work upon some problem."
Morse shook his head. "Not he! I'll swear that old Chang would never be letting off fireworks without consulting or warning Pu-Yi. Kirby, there is some black business stirring! We must look into this. I don't like it at all—hark!"
He suddenly stopped speaking, and put his hand to his ear. His whole face was strained in an ecstasy of listening, which cut deep gashes into that stern, gnarled old countenance.
I listened also, and with dread in my heart. Instinctively and without any process of reasoning, I knew that in some way or other the horror was upon us again. My lips went dry and I moistened them with the tip of my tongue; and, without conscious thought, my hand stole round to my pistol pocket and touched the cold and roughened stock of an automatic Webley.