436 THE POPULAR SCIENCE MONTHLY. 



obstructions in Hell Gate recommended a plan wbich, as to its general 

 features, was substantially the same as that -which Lieutenant-Com- 

 manding Davis had proposed in 1848. Instead of Maillefert's process 

 of surface-blasting, they recommended that of drilling. This would 

 have had to be done from within a diving-bell, which was impractica- 

 ble because of the certain disturbance of the apparatus by currents, 

 and the liability to collisions from passing vessels. All of the plans 

 so far tried or proposed seemed to have been limited to removing the 

 smaller rocks lying in the channel ; the possibility of clearing away 

 the larger reefs was not yet conceived. 



In 18G6 the department instructed me to make an examination of 

 Hell Gate, and to present a plan and estimate of the operations neces- 

 sary to improve its navigation. A report was submitted in January, 

 1867, with an estimate for removing the reefs by blasting, after drilling 

 the surface from a fixed platform above the water. In this plan, or 

 in whatever plan might be decided upon, it was considered essential 

 that the drills, which, to avoid interference from currents, were to be 

 worked within ii'on tubes reaching from the platform to the rock, 

 should be attached to a framing kept absolutely fixed while the drill- 

 ing was going on ; and that the divers or the machinery necessary to 

 handle and remove from the bottom the rock blasted should be pro- 

 tected from violent currents. It was proposed to accomplish the latter 

 object by means of a system of floats and iron curtains so arranged 

 as to constitute a dam protecting a space of 160 feet long and 40 feet 

 wide, within which the work could go on uninterrupted. Another 

 machine was alternatively suggested, embodying the same principle, 

 to consist of an iron caisson or cylinder, pointed at the ends, open at 

 the top and bottom, and having self-adjustable legs to accommodate 

 themselves to the irregularities of the rock, and to support it and keep 

 it level. The top of this structure was to be above the level of the 

 highest tide, and to be framed over so as to form a platform, on which 

 the machinery could be placed, and from w^hich the operations could 

 be conducted. It was important in constructing the machine to have 

 it adaptable to all the rocks on which it was intended to operate, what- 

 ever their size and the shape of their surface, and that it be perfectly 

 stable against the action of the currents without being unwieldy in 

 size. It was furthermore considered necessary to furnish it with a 

 protection against collisions which were sure to occur from the fleets 

 of vessels passing daily, and certain to destroy it, with a loss of life 

 and much property, if it were not protected. 



These conditions were fulfilled in the steam-drilling cupola-scow 

 (Figs. 1 and 2). The scow is built very heavy and strong ; is provided 

 with an overhanging guard, faced with iron, surrounding it as a pro- 

 tection against collisions ; and has a well-hole 33 feet in diameter. 

 The caisson or dome is a hemisphere 30 feet in diameter, composed of 

 a strong iron frame covered with boiler-iron. It is open at the bottom 



