270 POPULAR SCIENCE MONTHLY 



more than two or three men would form the crew, and on that ground 

 have condemned the construction of these small submarines. They 

 would necessarily be of slow speed and very limited radius of action, 

 while their efficient working would depend upon the nerve and skill of 

 only two or three men working in a very confined space. 



Progress in mechanical engineering and in metallurgy has been 

 great since Bushnell constructed and used his first submarine in 1776, 

 during the war between the United States and this country. These 

 advances have made it possible to increase the dimensions, speed and 

 radius of action of submarines; their offensive powers have been en- 

 larged by the use of locomotive torpedoes ; and superior optical arrange- 

 ments have been devised for discovering the jiosition of an enemy while 

 they themselves remain submerged. But it cannot be claimed that any 

 new principle of design has been discovered or applied. From descrip- 

 tions left on record by Bushnell and still extant, it is certain that he 

 appreciated, and provided for the governing conditions of the design in 

 regard to buoyancy, stability, and control of the depth reached by sub- 

 marines. Indeed Bushnell showed the way to his successors in nearly 

 all these particulars, and — although alternative methods of fulfilling 

 essential conditions have been introduced and practically tested — in 

 the end BushnelPs plans have in substance been found the best. The 

 laws which govern the flotation of submarines are, of course, identical 

 with those applying to other floating bodies. When they are at rest 

 and in equilibrium they must displace a weight of water equal to their 

 own total weight. At the surface they float at a minimum draught and 

 possess in this ' awash ' condition a sufficient freeboard and reserve of 

 buoyancy to fit them for propulsion. When submarines are being 

 prepared for ' diving ' water is admitted to special tanks, and the addi- 

 tional weight increases immersion and correspondingly reduces reserve 

 of buoyancy. In some small submarines comparative success has been 

 attained in reaching and maintaining any desired depth below the sur- 

 face simply by the admission of the amount of water required to secure 

 a perfect balance between the weight of the vessel and all she contains, 

 and the weight of water which would fill the cavity occupied by the 

 submarine when submerged. For all practical purposes and within the 

 depths reached by submarines on service water may be regarded as 

 incompressible ; the submarine should, therefore, rest in equilibrium at 

 any depth if her total weight is exactly balanced by the weight of water 

 displaced. If the weight of the vessel exceeds by ever so small an 

 amount the weight of water displaced, that excess constitutes an ac- 

 celerating force tending to sink the vessel deeper. On the contrary, 

 if the weight of water displaced exceeds by ever so small an amount 

 the total weight of the vessel, a vertical force is produced tending to 

 restore her to the surface. Under these circumstances, it is obvious 

 that if the admission or expulsion of water from internal tanks (or the 



