considerably, thereby acting with the Garston tide, like the cushion of a billiard table, causes it to cannon off towards Tranmere Bight on the Cheshire shore, leaving a slack of tide on the Lancashire side. It is not necessary to explain that whenever a large rise and fall of tide exists with water laden with detritus, the effect on any part of it which becomes still water is to drop its load, whereby a bank or shoal is created.

The Pluckington Bank thus formed has often been liable to fluctuations; it may be enough to mention those which have caused inconvenience to the passenger ferry steamers which cross the Mersey. In September, 1881, a series of twenty-two sluices, placed opposite the south end of the George's Stage, after the design of Mr. Lyster, the Dock Engineer, were ready for work. These sluices are each formed of large cylinders, four feet in diameter, projecting at right angles to the base of the pier wall, where they are in connection with a larger cylinder, seven feet nine inches in diameter, placed at the level of low water spring tides, and parallel with the wall. By a culvert of eleven feet diameter through the pier wall it is in communication with the George's Dock immediately behind, and with the series of southern docks. Whenever required, some of these sluice pipes are set to work to prevent an accumulation of sand under the stage and beyond it. Many here present will remember the alarming state of the south end of the Liverpool stage at the time the sluices were being constructed, whenever it was towards low water of a spring tide. The sluices have fought manfully against the north tail of the Pluckington Bank, and have driven it off, enabling a statutory depth of six feet to be maintained on the river side of the George's Stage at low water of spring tides. At such times the Woodside Ferry Steamers, drawing eight to nine feet of

water, have to be shifted occasionally from their proper berths to land their passengers at the ferry goods stage.

I will now say a few words on the subject of the upper estuary, as represented on the large plan of the Mersey. It will be noticed that the river expands considerably above Dingle Point, till abreast of Ellesmere Port it acquires a width of three nautical miles. This we call the tidal basin of the estuary. Every spring tide, twice a month, this fine expanse gets filled with sea water from shore to shore on the flood tide, and it can be readily imagined with what velocity it rushes out to sea on the ebb tide through the confined and narrow gorge abreast of the Landing Stage, thereby causing a scour which extends over the bar to the sea. To maintain this noble basin intact is surely of the utmost importance, and when it was threatened by the original proposal of constructing the Manchester Ship Canal through its centre, the Mersey Docks and Harbour Board, as the riparian authorities, opposed it most strenuously. Mr. Eads, the celebrated American Engineer, who had done so much for the improvement of the Mississippi, and Captain Graham Hills, R.N., who was Marine Surveyor at the time, and who had gathered an immense deal of information on the subject of the canalisation of rivers generally, were able to give such useful evidence during the parliamentary contests which followed, that the scheme was abandoned and another substituted, viz., that now brought to a successful issue, which locates the entrance to the ship canal along the Cheshire side of the River Mersey.

105

EXPLOSIONS IN CONNECTION WITH COAL DUST. BY EDWARD DAVIES, F.C.S.

THE causes which lead to explosions in coal pits are deserving of such careful consideration, whether we consider the serious loss of life which so often attends them, or the minor point of the additional cost of coal which the dangerous character of the work entails, that I feel no excuse is necessary for bringing the subject before you.

To many persons it will be a revelation that fire-damp, or light carburetted hydrogen, is not the only agent capable of spreading ruin and death in coal mines, and that in mines practically free from gas, or where every precaution in the way of ventilation and the use of the most improved safety lamps is taken, a badly tamped blast may give rise to an explosion in no way less destructive than a fire-damp explosion, either in its direct violence, or in the after suffocation which the gases generated by the explosion produce beyond the range of the actual flame and shock.

Yet, just 50 years ago, two of our most distinguished scientific men, Faraday and Lyell, in a report on an explosion in Haswell Colliery, in September, 1844, called attention to the action of coal dust in colliery explosions in the following words :—

"In considering the extent of the fire from the moment of the explosion it is not to be supposed that fire-damp was its only fuel; the coal dust swept by the rush of wind and flame from the floor, roof, and walls of the works would instantly take fire and burn, if there were oxygen enough

present in the air to support its combustion; and we found the dust adhering to the faces of the pillars, props, and walls in the direction of, and on the side towards, the explosion, increasing gradually to a certain distance as we neared the place of ignition. This deposit was in some parts half an inch, in others almost an inch, thick; it adhered together in a friable coked state. When examined with the glass it presented the fused round form of burnt coal dust; and when examined chemically and compared with the coal itself reduced to powder, was found deprived of the greater portion of the bitumen, and in some instances entirely destitute of it. There is every reason to believe that much coal gas was made from this dust in the very air itself of the mine, by the flame of the fire-damp which raised and swept it along, and much of the carbon of this dust remained unburnt only from want of air. At first we were greatly embarrassed by the circumstance of the large number of deaths from choke damp, and in the evidence that that had been present in very considerable quantities compared with the small proportion of firedamp, which in the opinion of those in and about the works just before, must have occasioned the explosion. But, on consideration of the character of the goaves and reservoirs for gaseous fuel, and the effect of dust in the mine, we are satisfied that these circumstances fully account for the apparent discrepancy."

Subsequently, at the Royal Institution, Faraday said, "The ignition and explosion of the fire-damp mixture would raise and then kindle the coal dust which is always pervading the passages, and these effects must in a moment have made the part of the mine which was the scene of the calamity glow like a furnace."

A better instance of the superiority of a thoroughly trained scientific mind over merely practical experience in