384 Miscellaneous — Colliery Exj)losiom. 



an outcrop, to find form of furrow ; an operation to which Mr. 

 risher's equations are at once applicable. The rest of his remarks 

 appear to have been written in great haste, and are singularly- 

 inaccurate. Does he mean to say that when he has again inter- 

 changed a and j3, his equation proved on p. 142 even looks like 

 Mr. Fisher's equation (2) ? Again, how can he suppose that 

 (p. 142, 1. 10) Mr. Fisher assumes the trail to lie in one plane, when 

 it has been expressly stated to lie in a " surface which may be 

 formed out of a folded plane." His figure, on p. 142, represents an 

 altogether different set of angles to Mr. Fisher's. It can, however, 

 be used to prove equation (2) if the following description be sub- 

 stituted for that given in the text. 



Let AB, CD be horizontal lines in the inclined plane. 



AF, BE lines perpendicular to the inclined plane. 



CDEF a. horizontal plane. 



CE a line of strike, supposed horizontal. 



ThenECD = a; BDE = 0; BGD = <f) 



BD DEcosB 

 And tan <p = -^, = —j^ — = cos /3 tan a. 



Christ's College, Cambridge. A. F. GRIFFITH. 



Colliery Explosions. — A Parliamentary paper which was issued 

 yesterday throws very important, and in one point unexpected, light 

 on the causes of colliery explosions. After the Seaham accident last 

 Sept. Sir William Harcourt requested Prof. F. Abel, the chemist to 

 the War Department, to report on some samples of dust which had 

 been collected in the workings where the explosion took place. Prof. 

 Abel has now reported the results of his experiments, which entirely 

 confirm those which Mr. W. Galloway has described to the Eoyal 

 Society. Mr. Galloway showed that though a mixture of air and 

 coal dust was not explosive, it became so when a very small, and 

 apart from the coal dust, an innocuous, quantity of fire-damp was 

 mixed in the air. Prof. Abel's experiments show that not coal dust 

 only, but any dust, even calcined magnesia, will act in the same 

 wa3^ The proportion of fire-damp which is needful to bring dust 

 of any kind into operation as an exploding agent is below the 

 smallest amount which can be detected in the air of a mine, even 

 by the most experienced observer, by the means at present in use. 

 Coal dust shows a tendency to become inflamed and to propagate 

 flame when it comes in contact with a large volume of flame, such 

 as is made by the firing of a shot, and may thus convey the fire 

 from a safe part of a mine to an unsafe part. These discoveries, 

 which finally confirm a long existing opinion, impose a new duty 

 on colliery owners and inspectors. They offer an explanation of 

 many mysterious colliery accidents, and suggest the means of 

 preventing them in the future. There are two sources of explosion, 

 and we have been only guarding against one of them. Henceforth, 

 it is not only fire-damp, but what we may call fire-dust, that must 

 be looked after, and a great decrease of explosions will probably 

 result. — Daily News, June 21, 1881. 



