cf blowing up Rods under Water. 269' 



ing. C. Coulomb, the author of this memoir, after dcTeribing 

 the method of conftructing the air-boat, fhows in what man- 

 ner it is to be ufed. He points out the means by which it 

 may be made to (ink at pleafure, of placing the workmen 

 under the box, of continually renewing the air, of removing 

 the rubbifh and laying a foundation of mafon-work at the 

 bottom of deep water. He then calculates the time necef- 

 fary for removing a metre in height from the bank of Quille- 

 boeuf, which interrupts the navigation of the Seine; and fore- 

 feeing the cafes in which mattocks or pick-axes would be in- 

 fufticient for clearing obstructions from the bottom of the 

 water, and where the hardnefs of the rock might require the 

 tile of gun-powder, he propofes two methods of blowing up 

 rocks under water. 



In one, the workman placed under the box bores the rock, 

 and introduces into the bottom of the hole a box of tin plate 

 filled with gun -powder, to which is foldered a fmall tube, 

 alio of tin plate, which rifes above the water at ebb-tides, 

 and which is {topped with fome greafy matter, after having 

 been filled with a very weak compofuion to ferve as a 

 train. The fea, as it rifes, makes the air-boat float; and 

 when its lower edge has rifen higher than the extremity of 

 the tube it is then removed, and when the ebb-tide uncovers 

 that extremity a perfon goes in a boat and lets fire to it. 



In the other method, which the author propofes fot 

 the Mediterranean, and rivers where the affiftance of the 

 tide cannot be employed, the tube of tin plate which con- 

 tains the train rifes only 3 decimetres above the rock, but 13 

 terminated by a leather pipe covered on the outfide with 

 fome water-proof fubfiance, and in the iniide with an in- 

 combuftible varnifh, and fecured from the pretfure of the 

 water by a fpiral winding made of wire. Its extremity mult 

 be carefully clofed, and a buoy attached to it carries it to 

 the furface of the water when the air- boat is afloat. 



4th, I (hall fay nothing further of theft methods, which 

 fuppofe, as may be feen, the affiftance of the air-boat. I 

 only withed to point them out, becaufe they may be ufeful 

 in many cafes, and may, befides, give rife to new ideas, 

 and ferve to modify the three particular methods which are 

 the object of this memoir. 



J. Method of blowing up Rocks at the Depth qf 1^ or 1 8 Cen- 

 timetres under Water. 



5th. This method confifts in the following operations; 

 Firft, bore the hole at the bottom of the water by the 

 help of borers, and initruments of proper length. 



3 Then 



