We had come over to the periscope, the “eye” of the submarine when she is running just under the surface, but of no use that we were below.  “Yes,” he remarked, in answer to my half-spoken question, “that is the periscope.  Usually there is one fixed to look ahead and another that is movable, in order to take in what is on the sides and in the rear.  I have both of those.  But, in addition, I have the universal periscope, the eye that sees all around, three hundred and sixty degrees—­a very clever application of an annular prism with objectives, condenser, and two eyepieces of low and high power.”

A call from one of the crew took him into the stern to watch the operation of something, leaving me to myself, for Kennedy was roaming about on a still hunt for anything that might suggest itself.  The safety devices, probably more than any other single thing, interested me, for I had read with peculiar fascination of the great disasters to the Lutin, the Pluviose, the Farfardet, the A8, the Foca, the Kambala, the Japanese No 6, the German U3, and others.

Below us I knew there was a keel that could be dropped, lightening the boat considerably.  Also, there was the submarine bell, immersed in a tank of water, with telephone receivers attached by which one could “listen in,” for example, before rising, say, from sixty feet to twenty feet, and thus “hear” the hulls of other ships.  The bell was struck by means of air pressure, and was the same as that used for submarine signalling on ships.  Water, being dense, is an excellent conductor of sound.  Even in the submarine itself, I could hear the muffled clang of the gong.

Then there were buoys which could be released and would fly to the surface, carrying within them a telephone, a light, and a whistle.  I knew also something of the explosion dangers on a submarine, both from the fuel oil used when running on the surface, and from the storage batteries used when running submerged.  Once in a while a sailor would take from a jar a piece of litmus paper and expose it, showing only a slight discolouration due to carbon dioxide.  That was the least of my troubles.  For a few moments, also, the white mice in a cage interested me.  White mice were carried because they dislike the odour of gasoline and give warning of any leakage by loud squeals.

The fact was that there was so much of interest that, the first discomfort over, I was, like Kennedy, beginning really to enjoy the trip.

I was startled suddenly to hear the motors stop.  There was no more of that interminable buzzing.  The Z99 responded promptly to the air pressure that was forcing the water out of the tanks.  The gauge showed that we were gradually rising on an even keel.  A man sprang up the narrow hatchway and opened the cover through which we could see a little patch of blue sky again.  The gasoline motor was started, and we ran leisurely back to the dock.  The trip was over—­safely.  As we landed I felt a sense of gladness to get away from that feeling of being cut off from the world.  It was not fear of death or of the water, as nearly as I could analyse it, but merely that terrible sense of isolation from man and nature as we know it.