successful, one may easily recall the French 'Le Plongeur,' the 'Gustav Zédé' the 'Morse' the 'Narval,' the Nordenfeldt boats and those of Goubet and Baker. Here also belong, of course, the latest and most successful boats of all, the 'Holland' and Mr. Lake's 'Argonaut,' of which some account will follow.
Turning now from the history of submarine navigation to a consideration of certain practical problems connected with it, we are brought at the outset face to face with a fact of fundamental significance, namely, that even with the aid of very powerful electric illumination it is not possible to see clearly through ordinary sea water for more than a few feet. According to Mr. Lake of the 'Argonaut,' about fifteen feet is the limit of visibility in our Northern waters, and about twice that in Southern. Submarine navigation is like navigation in the densest sort of a fog. High speed under water is just as possible mechanically as upon the surface. But the fact just stated is a death blow to high speed. Unless there shall be discovered some hitherto unsuspected means of perceiving at a distance invisible objects, high speed will unquestionably be fraught with great peril.
For the same reason it will probably be found impracticable to attempt very long journeys under water. There will probably never be trans-sub-atlantic lines, much less submarine greyhounds.
In fact, practical inventors of submarine craft, at least of late years, have ceased to attempt to provide more than a surface-going boat which shall be able at any time or place to dive beneath the surface to the depth desired, to remain under water for considerable periods of time, either stationary or moving, with both safety and comfort to the crew, and then, the purpose of the dive having been accomplished, to return speedily and safely to the surface. Even these requirements constitute a pretty large contract, but that they have been met satisfactorily appears sufficiently, so far as the 'Holland' at least is concerned, from the quotations given at the beginning of the article, and from the further fact that our government, ultra-conservative in adopting new devices for use in warfare, has purchased the 'Holland,' which is now at Newport in charge of Lieutenant Caldwell, Admiral Dewey's aid at Manila, and that Congress has authorized the building of six more 'Holland' boats of an improved type. Two of these are now being built at the Union Iron Works, at San Francisco, the rest at Elizabethport, N. J.
Obviously, a prime essential for any sojourn under water is an ample supply of pure air. When possible to make use of it there is but one rational source of pure air, and that is the exhaustless supply at the surface. Provided she herself secures it, a submarine boat does not in the least surrender her independence by utilizing this supply. This the 'Argonaut' does at ordinary depths by means of a pair of vertical tubes, one for inflow, the other for discharge.
