Page:Barbour--For the freedom from the seas.djvu/175

 propeller, having wings that caused it to turn in the water and so release the locking gear of the firing pin. A second safety device was a bolt passing from the outside of the war head to the firing pin to prevent the latter being moved back against the percussion cap. Behind the war head was the compressed air tank by which the propeller at the tail was rotated. When Martin remarked that the air chamber was at the moment charged with 2,250 pounds of air Nelson began to wonder if the war head was, after all, the more dangerous part of the thing! He sincerely hoped that the steel wells were equal to that pressure of over a ton to each square inch! The balance chamber mechanism was a bit too much for Nelson, although Martin patiently tried to make him understand the functions of the gyroscope and the pendulum control. In the end Nelson mastered the reason for those devices, but he was hazy as to why they performed the remarkable stunts attributed to them!

Martin stopped lecturing before he became tiresome and the two boys talked of less technical things, one of them being home. Perhaps it would be more exact to say that Martin talked about his home and Nelson listened. Nelson's home just then had few attractions for him as a matter for 150