PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 513 



and there must be managers and secretaries. If we organize 

 aright, talent and capital will come in. 



Dr. Stevens drew a diagram of the teredo navalis or ship-worm. 

 There extends through it a double tube, through one branch of 

 which it draws in a current of water, and sends it out through 

 the other. When the animal is born it is almost microscopical, 

 but when full grown has the size of a man's thumb. It is very 

 prolific, bringing forth several millions, and it is exceedingly vora- 

 cious. They will penetrate several feet into sand, wherever there 

 is water. That little animal is capable of eating up, in a few 

 weeks, all the vessels we have sunk in Charleston harbor. 



Mr. Johnson exhibited the operation of pumping sand under 

 water, repeating the experiments made by him at a former 

 meeting. He proposed to do all the work under water, thus sav- 

 ing the power required in other machines to lift the sand above 

 the water. He proposed merely to lift the difference between the 

 weight of the sand and the water, while other machines lifted 

 the whole weight of the sand, saturated with water. A vessel 

 being built with an air-tight deck, and furnished with suitable 

 apparatus for taking in the sand below the water line, may be 

 worked in dredging out docks, by a steam engine on shore. The 

 air is exhausted from below the deck by this pump, and its place 

 is supplied by sand and water raised from the bottom. The sand is 

 then prevented from escaping, and the vessel is towed to the 

 point for discharging its load, where, upon opening a trap door 

 in the bottom, the sand, being heavier than water, will fall out, 

 and its place will be supplied with water. Returning to the 

 dock this water is removed by pumping, and its place supplied 

 by sand and water, as before. It is found that in most cases the 

 sand will be taken up with a small proportion of water. Care 

 must be taken that the sand should not become dry in the tube ; 

 and, to avoid this, it is only necessary, before taking it from the 

 water, to draw enough of water through it to wash it out. The 

 laws regulating the deposit of solids held in mechanical suspension 

 by flowing water, show at what velocity it is necessary that the 

 water should flow to prevent a deposit. If that speed is attained 

 there will be no tendency of the sand to subside and clog the 

 tube. To remove a vessel, the tube can be placed below it so 

 as to draw out the sand, and cause the hull to keel over. 



Mr, Enos Stevens suggested that the same principle might be 

 applied to removing sand without the intervention of a floating 



Am. Inst.] GG 



