This inventor is, however, an enthusiast about the future awaiting the submarine as a social factor. His boat has been tested by long voyages on and below water with complete success. The _Argonaut_ also upon one occasion travelled a thousand miles with five persons, and proved herself “habitable, seaworthy, and under perfect control.” Mr. Holland confidently anticipates in the near future a Channel service of submerged boats run by automatic steering-gear upon cables stretched from coast to coast, and eloquently sums up its advantages. The passage would be always practicable, for ordinary interruptions such as fog and storms cannot affect the sea depths. An even temperature would prevail summer and winter, the well-warmed and lighted boats being also free from smoke and spray. No nauseating smells would proceed from the evenly-working electric engines. No motion cause sea-sickness, no collision be apprehended--as each line would run on its own cable, and at its own specified depth, a telephone keeping it in communication with shore. In like manner a service might be plied over lake bottoms, or across the bed of wide rivers whose surface is bound in ice. Such is the submarine boat as hitherto conceived for peace or war--a daring project for the coming generation to justify. ANIMATED PICTURES. Has it ever occurred to the reader to ask himself why rain appears to fall in streaks though it arrives at earth in drops? Or why the glowing end of a charred stick produces fiery lines if waved about in the darkness? Common sense tells us the drop and the burning point cannot _be_ in two places at one and the same time. And yet apparently we are able to see both in many positions simultaneously. This seeming paradox is due to “persistence of vision,” a phenomenon that has attracted the notice of scientific men for many centuries. Persistence may be briefly explained thus:-- The eye is extremely sensitive to light, and will, as is proved by the visibility of the electric spark, lasting for less than the millionth part of a second, _receive_ impressions with marvellous rapidity. But it cannot get rid of these impressions at the same speed. The duration of a visual impression has been calculated as one-tenth to one-twenty-first of a second. The electric spark, therefore, appears to last much longer than it really does. Hence it is obvious that if a series of impressions follow one another more rapidly than the eye can free itself of them, the impressions will overlap, and one of four results will follow. (_a_) _Apparently uninterrupted presence_ of an image if the same image be repeatedly represented. (_b_) _Confusion_, if the images be all different and disconnected. (_c_) _Combination_, if the images of two or a very few objects be presented in regular rotation. (_d_) _Motion_, if the objects be similar in all but one part, which occupies a slightly different portion in each presentation.