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POPULAR SCIENCE MONTHLY. 



sure is about fifteen pounds to the squrre inch, or more than a ton to 

 the foot. Solid construction is naturally in order for a submarine 

 boat. But power to resist pressure depends also upon shape. A cir- 

 cular section, because it involves the principle of the arch, is the strong- 

 est. With a given thickness of metal, therefore, a spherical boat 

 could safely dive deeper than one of any other form. But the ex- 

 terior of such a boat is ill-adapted to propulsion, and the interior for 

 the arrangement of machinery. 



Since the days of Captain Nemo and the fabulous 'Nautilus' the 

 cigar shape has doubtless been associated with submarine navigation in 



&&5E^ 



Fig 4. The 'Holland' in Dry I j. 



the minds of ninety-nine out of every hundred persons who have 

 thought of the matter at all. And it is equally a matter of sober his- 

 tory that this form has been almost universally adopted. Some in- 

 ventors in the earlier days, with the vision of high speed in mind, have 

 trimmed down the lines to almost needle-like fineness, as in the 'Gustar 

 Zede.' Now that attempts at high speed have been abandoned, the 

 elongated spheroidal or egg-shape is the favorite, as illustrated both 

 by the 'Holland' and the 'Argonaut.' 



But what of power for locomotion under water? Obviously steam 

 power, at least as ordinarily produced elsewhere, will not do. Even 

 supposing the necessary draft to be secured, how shall the smoke be 



