MECHANICS AND USEFUL ARTS. 89 



and public enterprise is so well and widely known, subscribed five thou- 

 sand dollars for commencing operations. Assurances of aid were ob- 

 tained from other quarters as fast as there should be any evidences of 

 success, and the enthusiastic Frenchman went to work. His mode of 

 operation is to sink a tin canister of powder down upon the top of the 

 rock, and there ignite it through a wire by means of a galvanic battery. 

 This is performed during the few minutes of slack tide at high water, 

 for the deeper the water over the powder the better. By the expansive 

 force of the explosion, the large mass of water above and around must 

 be instantly removed, lifted. But the motion of all matter requires 

 time. The expansive force is created instantly by the explosion, and 

 exerts itself instantly in every direction. It will not willingly wait for 

 the slow rising of the mass of waters high enough to afford it relief. It 

 therefore makes its way at the same tune downward upon the solid 

 rock, crushing, crumbling, and grinding it to pieces. All matter, as 

 far as we know, is porous and compressible, and rocks are more com- 

 pressible than water. Philosophy should therefore teach us that a 

 sudden expansive force between a body of water and a body of rock, 

 while it requires time to remove the water, must necessarily to some 

 extent crush the surface of the rock, if it is too large or too much con- 

 fined to be removed in a body. And this has proved to be the fact by 

 every blast which M. Maillefert has made. At high water, the top of 

 Pot Rock is now eighteen feet below the surface. After a blast, it is 

 found to be covered with broken fragments, some of which are grap- 

 pled and taken up. One piece was taken up weighing two hundred 

 pounds. The next rushing tide sweeps the top of the rock clean, and 

 after the next blast it is again covered with fragments. 



The eflect of these blasts has been so successful, that little doubt 

 remains that the obstructions will be removed, and that the navigation, 

 hitherto dangerous, will be rendered safe and easy. 



A correspondent of the National Intelligencer describes the method 

 of blasting, as follows : " A large float is anchored in the channel about 

 eighty feet from the rock. Precisely at high water, there being but 

 three or four minutes' cessation of the current, the large tin canister is 

 carried from the float and sunk upon the top of the rock. The boat 

 returns to the float, bringing the end of the wire attached to the can- 

 ister. Mons. Maillefert attaches the wire to his battery and completes 

 the circuit. Instantly a report is heard, and the mass of waters over 

 the rock rise into the air. There seems to be a solid body of water, 

 perhaps twenty feet in diameter, rising to a height of fifteen or twenty 

 feet, and then towering up in broken fragments and jets twenty or thirty 

 feet hio-her." 



SUPPLY OF WATER TO BLACKWELI/S ISLAND BY MEANS OF A GUTTA 



PERCIIA PIPE. 



AMONG the engineering achievements of the past year, the supplying 

 of Blackwell's Island with water, by means of a gutta percha pipe, is 

 worthy of notice. In December, 1850, the proper preliminary exam- 

 ination having been made, it was determined to supply Blackwell's 



8* 



