"I did," he assented after a prolonged interval. "But how did you do it? And how were you aware?"
"One question at a time, please. I am on the point of showing you a somewhat ingenious device; what it has already done I will inform you of in due course. This chequered board is divided, as you see, into eighty-one squares, each division representing one square mile. Thus a 'field,' meaning nine miles in either direction, is at my command. Now, supposing a hostile ship is sighted. Her position is determined by the ordinary range-finding instruments. By placing these two pointers on the square representing the ship's position--the pointers, as you will observe, being capable of alteration of length--I release a wireless current, which I prefer to term the Z-ray--upon the enemy's ship. Instantly the whole of her electrical gear is completely disorganised, and, knowing as you do the vital importance of electricity on board a modern man-of-war, you can realise what it means."
"Then you have already committed a hostile action against the ship of a friendly nation?"
"I suppose I have. It is necessary to experiment, and having good cause to try my device upon a German ship, I proceeded to do so. I am fully aware of the results it occasioned while I kept the _Zietan_ under the influence of the Z-rays."
"However did you manage to know that?" asked Tregarthen. "Have you put into any port since leaving the Tyne?"
"I have neither put into port nor have I entered into communication with any vessel excepting your yacht, so obtaining information by those means is entirely out of the question. How I did find out the results of my experiment I will inform you shortly. But to return to this device. You will doubtless have observed that there are two pairs of pointers? Those with a black disc are merely deterrents. Any vessel that persists in forcing an action after receiving the stern warning given by these pointers has only herself to blame for the consequences; for the moment the pointers with the red disc are superimposed upon the others the fate of the _Olive Branch's_ antagonist is sealed."
"How?" asked Gerald, with ever-growing interest.
"The conjunction of the red-disced pointers release a super charge of electricity--which I term the ZZ-rays--and her magazines are instantly exploded."
