This he promised to do, telling me he would 'phone me the result to the
hotel at eight o'clock next morning.

Therefore I returned to the factory, and through the long night-hours
listened to their secret experiments.

At eight next morning the telephone rang, and Ray briefly explained that
Gessner, who had placed his apparatus upon the high flagstaff in his
garden, had been receiving messages all night!

"Have you seen anything of Fowler?"

"No. But Hartmann has spent the night with Gessner, apparently watching
his experiments. Couldn't you manage to watch your opportunity and get
inside the factory somehow? I'll come north at noon, and we'll see what
we can do."

At five o'clock he stepped from the London express, and together we
walked down to the Imperial Hotel, to which I had suddenly changed my
quarters, feeling that I had been too long in the close vicinity of the
spy Dubois.

"It seems that they carry out their experiments at night," I explained.
"For in the daytime the wireless apparatus is no longer in position. I
see now why they engaged a builder to examine the chimney--in order to
place a pulley with a wire rope in position at the top!"

"But Gessner and Dubois are expert electricians, no doubt. Members of
the Telegraphen-Abtheilung of the German army, most probably," remarked
my friend.

"And who is Fowler?"

"A victim, I should say. He appears to be a most respectable man."

"In any financial difficulty?"

"Not that I can discover."

"But why have they established this secret communication between Hull
and London?"

"That's just what we have to discover, my dear fellow," laughed Ray.
"But if we are to get a peep inside the place it's evident we can only
do so in the daytime. At night they are down there."

"At early morning," I suggested, "after they have left."

"Very well," he said; "we'll watch them to-night, and get in after they
leave. I've brought a few necessaries in my bag--the set of
housebreaking implements," he added, with a grin.

"Well," I said, "neither of us know much about wireless telegraphy.
Couldn't we get hold of an operator from one of the Wilson liners in
dock, and take him along with us? A sailor is always an adventurer."

Ray was struck with the idea, and by eight o'clock that evening we had
enlisted the services of a smart young fellow, one of the operators in
the Wilson American service, to whom, in strictest confidence, we
related our suspicions.

That