366 Editorial.

21.- -What is the proper allowance of belt for cog-gear in order that each may be equal to the other in durability ; the belt enveloping half the pulley, of single leather, andall the parts in good working proportions and condition ?

22.--Ifpossible~ give the values of w in inches, in the formula: w ~ p f ; in which w ~ width of single leather belt in inches, and p and f ~ pitch and face of gear in inches. All the terms should be derived from machinery in use~ and particulars given~ observing also that w gives the effective belt width at the pitch line of the teeth.

23.--Give the particulars of any high-speed belts with which you may be fami- liar, more especially of the loss of driving-power due to velocity.

24.--Give any other facts and figures in relation to belts with which you may be acquainted ?

Removal of the Hell Gate Obstructions.--The work of re- moving these noted obstructions to navigation is continued unre- mittingly night and day. Eight "galleries' ' or chambers have been commenced. These run in various directions--under the reef--all converging to a common centre at the point of beginning. They are named after distinguished men. Those furthest advanced arc "Grant," "Sherman,' ' "Humphries." They all front the great ex- cavation, which is 60 by 100 feet in size, and 30 feet from the mean low-water mark to the floor line. "Grant" gallery has been pierced to a distance of 32 feet directly under the most formidable spur of the reef. These tunnels are to be extended a distance of 200 feet, and are from eight to ten feet in diameter. The rock is very hard-- mostly gneiss. The blasting charges are one-quarter, one-half, one and two pounds respectively, contained in paste-board tubes well wrapped in glazed gutta-percha cloth, tarred at the ends, with safety- fuse, all water-proof. Thirty or forty of these are discharged at the same time, a gong being previously sounded to draw off the workmen.

Huge logs, interlaced with iron bands, form "curtains," which are hung at the opening of each tunnelling to prevent the detached rock from being hurled into the air without. The force is so terrific, how- ever~ that these ponderous curtains are often swung out eight or ten feet. Great steam derricks elevate the refuse, and steam pumps lift out the water. Daily observations are taken to guide the work. A miniature levee keeps off the water on the river side. A tem- porary platform extends out over the reef, from which a fine view of the wild, rushing tides is afforded. Even when but about a depth of two feet of water is flowing over the "hog's back," its force is so great as to sweep a strong man instantly off his feet. This gigantic enterprise must proceed very slowly, and require years for its successful consummation.