"It's the sensograph!" exclaimed Mr. Ironsides, with what Tom fancied was one sharp flash of alarm.
"What does it mean?" began Tom. "Are we——"
"It means that we are in dangerous proximity to a submerged wreck!" was the disquieting reply.
The words had hardly left Mr. Ironsides' lips before there was a jarring crash.
The submarine quivered throughout her structure. Her swift motion ceased as if she had been dealt a mortal blow.
As if he had been the victim of some ugly nightmare, Tom felt the diving boat begin to sink. She seemed to be lying over on her side—helpless beneath the waters of the lake.
CHAPTER XVI.
IN THE GRASP OF CALAMITY.
Once before Tom had faced death in the depths. This was when he had battled with the octopus in the wreck of a sunken treasure ship in the tropic seas. But then he had been fighting for his uncle's life, and his success had been dependent on his own efforts.
Imprisoned in the stricken submarine, however, the experience was far different, and vastly more alarming. In the first place, none of them could do anything but await the result of Mr. Ironsides' hasty efforts to right his craft, and the inaction was as hard to endure as the actual peril.