“A device which will show whatever is occurring outside, while the operator of the machine to which it is attached remains hidden,” said Jack.
“Correct. But this is an improved periscope. It gives the operator of the ‘gun carriage’ a wide view of the sky in every direction. But to explain my invention more fully I must invite you inside.”
So saying, the inventor opened a door in the side of the steel structure, which they had not previously noticed. Taking Jack by the arm, he gave him a half shove into the interior of the steel cigar.
As the space within was small, Mr. Peregrine explained that he would have to show the points of his invention to one of them at a time. When Jack was inside the inventor closed the door and, turning a switch, caused a flood of light to illuminate the interior of the wheeled cylinder. Jack found that they were standing within the conning tower. Through the slits he could see out into the shed, but his attention was speedily distracted by Mr. Peregrine.
The inventor indicated a seat, and invited Jack to occupy it. The boy was informed that he was seated in the operator’s position. In front of him was a sort of desk with a white top. This was divided into squares. The inventor explained that the white surface represented the expanse of sky commanded by the periscope.
“The instant an aëroplane is seen to enter one of those squares, each of which, as you see, is numbered,” he explained, “I press one of these buttons which are correspondingly marked.”
He reached up to a sort of switchboard above the periscope desk, and pressed one of the numbered buttons on it. A whirring sound followed.
“What’s that?” demanded Jack.
“That noise is caused by the cylindrical band which you observed on the fore part of the machine,” said Mr. Peregrine; “two guns, controlled by electricity, are set in that band. By pressing this button one of them is automatically aimed at the square of sky which the periscope shows is occupied by a supposedly hostile aëroplane.”
Jack nodded. It was plain to him that the band which they had noticed revolved on an axis, and that the muzzles of the ‘vanishing gun’ revolved with it.