354 Mr. W. Galloway on the Influence [Mar. 2, 



Are you quite sure that the molecular structure of the platinum wire 

 is constant while it behaves as you say it does ? 



I beg you will permit your letter and this to appear in the Proceedings. 

 It will make my note more useful if you will. 



Believe me 



Very faithfully yours, 



J. Norman Lockyer. 



III. " On the Influence of Coal-dust in Colliery Explosions/'' 

 By W. Galloway. Communicated by Professor Fran kl and, 

 F.R.S. Received February 4, 1876. 



In coal-mines in which the temperature of the workings is considerably 

 higher than the mean annual temperature at the surface, there is usually 

 a layer of rubbish on the floor of the roadways and air- ways, which con- 

 sists, in some places, almost entirely of dry coal-dust, and in others of 

 coal-dust mixed with small pieces of coal and stone. 



If it could be shown, therefore, that a mixture of air and coal-dust is 

 inflammable at ordinary pressure and temperature, there would be no 

 difficulty in accounting for the extent and violence of many explosions 

 which have occurred in mines in which no large accumulations of fire- 

 damp were known to exist ; for it is only necessary to suppose that a 

 sudden gust of wind (originated, for example, by the explosion of a small 

 accumulation of firedamp) had swept through the adjoining galleries, 

 raising a cloud of dust into the air, and then all the other phenomena 

 would follow in regular order. The flame of the originally inflammable 

 mixture would pass directly into the newly formed one, expanding its 

 volume; the disturbance would be propagated over an ever -widening 

 area, until that area might possibly become coextensive with the work- 

 ings themselves ; and the consequences would be the same as if the whole 

 space had been filled with an inflammable mixture before the disturbance 

 began. 



The accounts of colliery explosions published in this country hardly 

 ever allude to the existence of coal-dust ; and when they do so, in one or 

 two cases, it is for the purpose of suggesting that the gases disengaged 

 from it by the heat of the firedamp-flame would no doubt be ignited, and 

 tend to increase the force of the explosion*. This seems all the more 



* Since the above was written, my attention has been called to the following obser- 

 vations by Faraday and Lyell (Phil. Mag. 1845) : — " In considering the extent of the 

 fire for the moment of explosion, it is not to be supposed that firedamp is 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 in the 

 air present to support its combustion ; and we found the dust adhering to the face of 

 the pillars, props, and walls in the direction of and on the side towards the explosion, 



