226 



KNOWLEDGE. 



[OCTOBEK 1, 1896. 



brought to an advanced stage of efficiency. An idea of the 

 improvement in this direction may be gathered from the 

 fact that in the early decades of this century, the currents 

 of air, in what were then considered well-ventilated mines, 

 travelled at a rate of about five feet per second, or a mile 

 in seventeen and three-fifth minutes, whilst in our days, 

 currents travelling thirty feet per second, or at a rate of a 

 mile in less than three minutes, are found in parts of 

 mines. Obviously currents of such high velocity are neither 

 required nor sustained throughout a mine — in fact, the 

 miners would probably disapprove of working in a stiff 

 breeze — but such currents are nevertheless encountered, 

 whilst some notion of the immense quantity of air that 

 modern fans are capable of dealing with will be obtained 

 by reference to examples furnished m a recent number of 

 the Tninsactions of the Federated Institution of Mining 

 Engineers (Vol. VI., p. 180) ; there we find descriptions of a 

 , fan, capable of propelling more than one hundred thousand 

 cubic feet per minute, or sufficient air to change the 

 entire atmosphere of Westminster Hall thirty times an 

 hour. 



It can well be imagined that the question of dealing 

 satisfactorily with this small artificial storm is one of 

 great importance to the mine manager, and has received 

 considerable attention ; indeed, the problem of diluting the 

 atmosphere of a coal mine may be regarded at the present 

 time as resolving itself into a question of the economic and 

 effective employment of the vast volumes of air that are 

 caused to sweep through the mine. It is generally admitted 

 that the best use of this vast volume of air is made by 

 '■ splitting " it, that is, causing it as it enters the mine to 

 split up, by placing at appropriate spots directing screens, 

 each having an aperture that can be adjusted to any desired 

 size ; the great main current thus becomes divided into 

 several smaller currents of a magnitude thai can be varied 

 so as to provide each section or district, into which the 

 mine is for the purpose divided, with sufficient fresh air 

 thoroughly to ventilate it. In this way the men in each 

 set get fresh air, and in case of explosion the disaster is 

 generally limited to one section only, instead of jeopard- 

 izing the whole mine. Then, large and straight galleries 

 with smooth walls cause less waste of air current than 

 small crooked galleries with rough walls. 



The air currents are, of course, expensive to maintain, 

 and as it would be wasteful to have them too strong and 

 hazardous to have them too weak, it becomes a matter of 

 considerable importance that their strength should be 

 properly gauged. This is done by taking the temperature 

 with a thermometer, their pressure by means of a water- 

 gauge, their velocity by means of an anemometer, and 

 testing them for the presence of marsh gas after traversing 

 the workings. There is, however, some diversity of opinion 

 as to the proper manner and the best means of taking the 

 velocity and pressure, and this, therefore, is another point 

 in the ventilation question that remams to be decided, but 

 It is satisfactory to find that difterences of opinion as regards 

 the diluting problem are restricted now to what may be 

 regarded as refinements and not of vital importance. 

 Therefore we may regard the present position of this 

 point of our subject as satisfactory. 



Referring now to the second problem, namely, how to 

 light the mine without running the risk of igniting the gas, 

 it may be pointed out that gas does not always come ofl' 

 regularly, but occasionally may be given off in excessively 

 large quantities, and so for a time render the atmosphere 

 of a mine or district of a mine dangerous ; this is quite 

 sufficient to demonstrate the need of considering the 

 second problem. 



This problem, like the first, was scientifically attacked 



by Sir Humphry Davy, and although George Stephenson, 

 who subsequently invented the locomotive, was simul- 

 taneously and independently studying the same problem, 

 and brought out an early form of his safety lamp, called 

 the " Geordie," yet to Davy is due the invaluable dis- 

 covery that the explosion would not pass wire gauze. This 

 was in the year 1815, and since that time a vast amount 

 has been done by a host of experimenters and discoverers 

 towards the elucidation of this problem— indeed, so much 

 thought and ingenuity have been expended on the con- 

 struction of the safety lamp with such fruitful results, 

 that any adequate treatment of it would require a separate 

 article ; for in spite of the multitude of such devices 

 already introduced, new ones are constantly appearing, but 

 the old principle of having gauze at the air inlets and 

 outlets is adhered to. In the illustration below, the old 

 Davy lamp and the recent Ashworth-Hepplewhite-Gray 

 lamp are shown side by side. The former, it will be seen, 

 consisted of an oil vessel A, upon which was screwed a 

 ring B, supporting a cylinder of gauze F, which surrounded 



Sir Humphry Da^•v's Lamp. 



The Ashwortli-Hepplewhite-Grray 

 Lamp. 



the flame, and had an extra gauze cap at G.; the supporting 

 rods I kept the gauze in place, and the top plate protected 

 the lamp from falling objects, and the miner's hand from 



