of blowing up Modes under Water . 124 
Observation . 
12th, This method, the success of which is proved, 
deserves, no doubt, to be known by all those engaged in 
great undertakings, and who have frequent occasion to 
apply it.* It is, perhaps, susceptible of being modified ; 
and it appears to me that, without employing the imper- 
meable tube, a varnished cartridge might be used, with 
a flexible tube proceeding from it, lodged in the groove 
between the two wedges, and then rising above the 
Water. 
Fire also might be conveyed to the powder below the 
water by means of a strong discharge of electricity ; but 
little can be expected from this method in the hands of 
workmen. 
In the last place, the lower wedge might be made of 
hard and very dry wood. 
13th, But, in whatever manner this method may be 
employed, it will not require great expense, and it may 
be used with great advantage for deepening ports, ren- 
dering certain harbours more convenient and safe, and 
for freeing rivers and streams from those rocks which 
obstruct their course and impede the navigation of them. 
* Mr. Daniel Thunberg employed the same means to raise large blocks of 
stone from the bottom of the water. For this purpose a hole is bored in the 
block with a miner’s borer to the depth of twenty or twenty-five centimetres. 
Two wedges are introduced into it, forming by their junction a cylinder so as 
to fill the hole. Several blows are then struck on the iron bar which adheres to 
the upper wedge : the two wedges are then closely squeezed together, and the 
block is raised out of the water by means of a windlass and a cord attached to a 
ring fixed in the lower wedge 
You T. 
a 
