510 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



much speed of the pump. At a slower speed, the sand came up 

 with little more water than it contained as it lay on the bottom. It 

 therefore occurred to me that the speed of pumping, the size of 

 pipe and hose, and other proportions, could be so adjusted as to get 

 the right mixture of sand and water, which would neither clog 

 the hose, nor fail to sink where it is wanted. In answer to 

 questions from me, Mr. Johnson gave information which con- 

 firmed this view, and I have subsequently conversed with two 

 distinguished engineers, who have had experience in pumping 

 sand and gravel, who assure me that the}'^ have no doubt that 

 sand and silt may be moved in this way, at much less cost 

 than by any other known. 



It will be recollected that Dr. Stevens, in answer to a question 

 on this subject, stated that, south of New Jersey, there are no 

 boulders larger than eggs, — nothing that will not go through 

 a centrifugal pump. Oysters would be the greatest obstruc- 

 tion ; but conch shells can go through the pumps required for 

 this work. 



If, as I should have supposed, before witnessing Mr. John- 

 son's experiment, a mere suction pipe will not raise all kinds 

 of sand and mud, there is a dredging machine, invented by 

 Mr. Montgomery, ten years ago, which consists of an archime- 

 dian pump, drawing mud up through a cylinder, and discharg- 

 ing it into a scow. Mr. Montgomery told me, some years ago, 

 that this machine worked well, and would have come into use 

 had it not been for disagreement among those concerned with it. 

 It was built and stationed in a ship on the North river. The own- 

 ers met to witness its trial. Mr. Montgomery said it must be re- 

 moved for trial, because it would stop up the ship, if tried as it lay. 

 They laughed at him, and would see it tried, and were willing to 

 pay all damages, " if he were not afraid to try it.'' He was indig- 

 nant and took them at their word, and set the engine to work ; and, 

 in a short time, it made a pile of mud that reached above the 

 water, so that the dredging vessel could not back out. And, as 

 she could not turn round to bring her pumps to bear upon the 

 banks, she was blockaded. A quarrel ensued, and the whole inven- 

 tion was abandoned. 



This appears to me to be a promising experiment in hydraulic 

 blockading. The archimedean, or wren-pump, has the power to 

 slice the mud or sand, if the centrifugal pump requires that help. 



