NA TURE 



{Feb. 5 , 1885 



EARTHQUAKES AND FIRE-DAMP 

 On the Observation of Earth-shakes or Tremors in Order 



to Foretell the Issue of Sudden Outbursts of Firedamp. 



By M. Walton Brown. Excerpt Minutes of Proceedings 



of the North of England Institute of Mining and 



Mechanical Engineers, vol. xxiii. 1884. 

 A Theory of Mine Ventilation. By M. Walton Brown. 



(Printed by Lambert and Co., Limited, 50, Grey Street, 



Newcastle-on-Tyne, 1884.) 



THE first of Mr. Brown's two papers contains a pro- 

 posal to institute the systematic observation of 

 earth-tremors for purposes which he describes as 

 follows : — 



" Whatever may be the cause of the issue of sudden 

 outbursts of firedamp the quantity of gas produced is 

 extremely variable and irregular. Many theories have 

 been from time to time advanced with the object of 

 defining the laws which govern these sudden outbursts of 

 gas from coal and adjacent strata. 



" It would appear that there is some connection between 

 sudden outbursts of gas and the motions to which the 

 crust of the earth is subject : in other words, that slight 

 motions of the earth's crust may be followed by more or 

 less violent outbursts of gas. Thus, if there were a large 

 body of gas pent up in a subterranean reservoir, and some 

 movement of the earth's crust took place forming fissures 

 of varying depth and width, affording channels for the 

 escape of this gas, upon such a fissure being reached in 

 the workings of the mine, a blower would be the result, 

 the volume and duration of which would depend upon 

 the volume of the reservoir, pressure of the gas, and width 

 of the fissure. If this theory is the true solution of the 

 problem, it follows that the systematic and regular obser- 

 vation of earth movements would eventually prove a 

 reliable means to some extent of foretelling when out- 

 bursts of gas should be anticipated." 



If gas existed in subterranean reservoirs such as those 

 imagined by Mr. Brown, then, undoubtedly, when the 

 workings of a mine reached a fissure communicating with 

 such a reservoir all that Mr. Brown anticipates would 

 happen. Supposing it possible, however, that a fissure 

 could be formed by an earth-tremor at the depths at 

 which firedamp exists in a sufficient state of tension to 

 give rise to an outburst when tapped, it does not by any 

 means follow that the observation of earth movements 

 could assist us in foretelling when such outbursts would 

 be likely to happen. For the position of any given fissure, 

 relatively to that of the workings, must obviously be an 

 unknown quantity, so that, for anything we could know to 

 the contrary, the fissure might either be broached on the 

 day of its formation or not for many years afterwards. 



This paper is illustrated by two plates : one, a seismo- 

 graphic map of Western Europe, showing the distribution 

 of earthquakes, copied from the map prepared by the 

 Messrs. Mallet ; the other a diagram showing, by curves, 

 the relative fiequency of earthquakes and fatal explosions 

 of firedamp, and the mean height of the barometer 

 monthly from January of one year to April of the fol- 

 lowing year. The explanation of the second plate 

 appears to be incomplete. As regards the barometric 



unc, we consider this a good opportunity of remarking j 

 that all attempts to correlate mean barometrical observa- I 



tions extending over longer periods than a few hours 

 with explosions in mines appears to us to be labour lost, 

 and similarly we are satisfied that the bald statement so 

 often met with, that the barometer was rising or falling at 

 the moment any particular explosion happened, is devoid 

 of value, and leads simply to confusion. This subject 

 was most carefully investigated by Mr. R. H. Scott, 

 F.R.S., and the writer some years ago, and the results 

 were published in various papers at the time {Proc. Roy. 

 Soc, 1872; Quart. Jour,,. Met. Soe., 1873 and 1874). 

 The diagrams which accompany these papers show very 

 distinctly that the barometric curve ought to be known 

 accurately for several days before the occurrence of an 

 explosion if it is desired to form a true opinion as to the 

 probable influence of atmospheric agencies in the case. 



In his second paper Mr. Brown does good service by 

 calling the attention of the English reader to the manner 

 in which the problem of ventilating mines has been 

 simplified by the recent researches of M. Murgue, the 

 able director of the Besseges Collieries in France. M. 

 Murgue's articles were contributed to the Bulletin de la 

 Socle te' de V Industrie Minirale, second series, vols, ii., iv., 

 and ix. ; and his views are also very clearly set forth in 

 the second volume of M. Haton de la Goupillieres's excel- 

 lent and concise " Cours d'Exploitation des Mines," just 

 published. 



It is evident from the nature of the case that the details 

 of no two mines can be exactly alike as regards the 

 resistances which they oppose to the circulation of venti- 

 lating currents through them. The diameter and depths 

 of the shafts, the lengths, areas, bends, ascents, and 

 descents, and comparative roughness of the sides, of the 

 air-ways, the temperature, tension of water vapour, and 

 the velocity of the air-currents, must all vary with every 

 varying circumstance. Accordingly, any attempt to com- 

 pare the total resistance of one mine with that of another 

 by finding the value of each element in the calculation 

 and summing up the results could produce nothing but 

 complication and disappointment. 



M. Murgue has solved the problem by referring the 

 sum total of all the resistances to one single and very 

 simple resistance, namely, that of an orifice in a thin 

 plate, which he calls the equivalent orifice. He describes 

 it as the area in square metres of the orifice through 

 -.chieh the same manometrical depression will cause the 

 same volume of air to pass in the same lime as in the 

 mine. This area is found as follows : — Let a be the area 

 required, q the quantity of air, v its velocity in passing 

 through the orifice, and C65 as the value ofvena contractu. 

 Then — 



q = C65 a v. 



Taking w the specific gravity of the air (estimated by 

 M. Murgue at i'2 kilo, per cubic metre), and A the mano- 

 metrical depression (expressed in kilograms per square 

 metre, or, what is the same thing, in millimetres of water), 

 we have : 



h = w '—, or v = \l \, r 'i 

 ig v * w 



whence 



q = 0-65 a \J 2 ° ■- 



Then by introducing the numerical values of w as given 

 above, and of g as 9/S088 metres, we get — 



