December 27, 1894.] 



NATURE 



2 1 1 



IV. The curves again disappear at about the same time ; but 

 to judge from the time of greatest steadiness before the disturb- 

 ance commenced at Nicolaiew, it appears to have reached 

 Strassburg first. The last small increase at l4S7h. and I4'95h. 

 is, on the contrary, earlier at Nicolaiew than at Strassburg, 

 but this might be an independent disturbance. After the 

 strongest motion, the light-point resumes its steadiness much 

 sooner at Strassburg than at Nicolaiew. 



It is evident that the case is, on the whole, not favourable to 

 an hypothesis which first occurred to me, that all four disturb- 

 ances migbt have been caused by four successive waves emanat- 

 ing from a single centre and a single shock, and circulating 

 round the earth. The fact that II. and IV. are more consider- 

 able than I. and III. does not appear of much importance, for 

 it is proved by many examples that the intensity of a disturb- 

 ance is not alone dependent from the distance from the centre ; 

 but, if the hypothesis were right, disturbances III. and IV. 

 ought probably to be much smaller. Besides, the velocity of 

 about 100 km. per minute would be a very small value com- 

 pared to those determined on other occasions. 



I reject this hypothesis, but I do not think it improbable 

 that I. and II., III. and IV. may be connected in the way just 

 mentioned, and that both disturbances came from the same 

 part of the world. It is the principal object of this com- 

 munication to induce persons interested in the subject to study 

 carefully the records of all self-registering instruments. If the 

 disturbance originated at the bottom of the sea, something 

 about it might be found in the ship journals, the tidal records 

 might show a trace, or perhaps the magnetical records at distant 

 places. I have many proofs that the .'-ize of a disturbance, 

 traced by the horizontal pendulum, is not always a measure 

 for the importance of the catastrophe which produced it ; but 

 in the present case many instances indicate an extraordinary 

 phenomenon, of which an account is likely to appear sooner or 

 later, in case it should have taken place at some remote corner 

 of the earth. 



Merseburg, May i8, 



P.S. — Some time after having written the above, I received 

 the third volume of the Seismolo;^ical Journal of Japan (1894), 

 in which there is an interesting paper by F. Omori on the erup- 

 tion of Azuma-san in 1893. From this paper it appears that 

 the volcano was in an active state since May 19, when an ex- 

 plosion took place, which was followed by two other one* on 

 June 4, 4.10 a.m., and on June 7, of which the former is said 

 to have been the strongest. It was accompanied by an earth- 

 quake, which was felt at the meteorological station of Fuku- 

 shima. Supposing the above time to be Standard Time (9h. 

 east of Greenwich), the explosion took place at 7h. lom. p.m. 

 G. M.T. on June 3, and thus it is seen that it coincides with a 

 part of our great disturbance. I do not, however, believe that 

 this is more than a casual coincidence, for the two other erup- 

 tions produced no disturbances. It is also a well-known fact 

 that volcanic eruptions, even when accompanied by earthquakes, 

 are generally not felt to any great distance, unless they bear a 

 very violent character, like the eruption of Krakatoa ; but from 

 Mr. Omori's description it appears that the eruption of Azuma- 

 :n was nothing very extraordinary. I therefore believe that 

 we must wait to find another explanation for our disturbance. 

 E. VON Rebeur-Paschwitz. 



EXPLOSIONS IN MINES. 



T N a lecture on some modern developments in explosives, 

 given at the Society of Arts on December 17, Prof. Vivian 

 B. Lewes threw out a suggestion as to the cause of explosions 

 in dusty mines free from fire-damp, which explains the 

 anomalies which have presented themselves in several recent 

 explosions. 



It was pointed out that until quite recently explosions in 

 mines were always attributed to the accidental ignition of mix- 

 tures of air and methane, to which the name of " fire-damp " 

 is given, and undoubtedly this cause is the prime factor in this 

 class of disaster, and the introduction of such precautions as 

 safety-lamps at once brought about a considerable reduction in 

 the nuniber of explosions taking place. Many disasters, how- 

 ever, still continue<l to occur under apparently mysterious cir- 

 cumstances, the conditions being such that any large propor- 

 tion of methane in the air of the mine appeared practically 



impossible, but investigations of such explosions showed that 

 coal-dust in a dry and finely powdered condition had generally 

 been present in the mine at the time of the explosion, and the 

 coked residue of this dust was found afterwards on the surface 

 exposed to the explosive wave, and years of experimental in- 

 vestigation by scientific men of the greatest ability proved the 

 fact that air containing so small a proportion of methane as to 

 be itself perfectly non-explosive, becomes a good explosive 

 again when holding dry and finely divided coal-dust in suspen- 

 sion, and within the last few years explosions having taken 

 place in mines, which have always been celebrated for their 

 freedom from any trace of methane. Further experiments 

 have been made by Mr. H. Hall and Mr. W. Galloway, who 

 have shown that the violent ignition of dust-laden air is pos- 

 sible by a blown-out shot, even if free from any trace of marsh 

 gas, and there is evidence to show that the explosion is de- 

 veloped in throbs or waves. 



It is therefore found that the explosions in mines may be 

 brought about, first, by the ignition of a mixture of methane 

 anil air, in which the former rises above a certain percentage ; 

 secondly, by mixtures of air, coal-dust, and methane, in which 

 the amount of the latter may be excessively small ; lastly, by 

 mixtures of coal-dust and air. With regard to these explosions 

 caused by coal-dust and air alone, the Royal Commission on 

 Explosions from Coal-Dust in Mines, in their second report, 

 published this year, say : — 



" On a general review of the evidence on this point, we have 

 no hesitation in expressing our opinion that a blown-out shot 

 may, under certain conditions, set up a most dangerous explo- 

 sion in a mine, even where fire-damp is not present at all, or 

 only in infinitesimal quantities ; and while we are prepared to 

 admit that the danger of a coal-dust explosion varies greatly 

 according to the composition of the dust, we are unable to say 

 that any mine is safe in this respect, or that its owners can 

 properly be absolved from taking reasonable precautions 

 against a possible explosion from this cause. But even if we 

 had been able to come to a diiTerent conclusion, and to agree 

 with the minority of the witnesses examined, who think that 

 coal-dust alone cannot originate an explosion, we should still 

 have to call attention to the serious danger which results from 

 the action of coal-dust in carrying on and extending an 

 explosion which may originally have been set up by the 

 ignition of fire-damp." 



One of the most interesting and instructive explosions which 

 have taken place recently was that which occurred a little more 

 than a year ago at the Camerton Collieries, Somersetshire, in 

 which as far as investigation could go, no trace of combustible 

 gas could be found in the mine at any peiiod prior to the ex- 

 plosion or subsequent to it, and in which everything pointed to 

 the explosion being entirely due to the presence of dry coal-dust 

 in the air. 



Of absorbing interest, also, are the experiments made by Mr. 

 Hall at the latter end of 1S92 and the early part ol 1S93, and 

 reported upon by him to the Secretary of State on January 23, 

 1893, in which he shows by conclusive experiments that dry 

 coal-dust under conditions frequently present in coal mines and 

 in the entire absence of fire-damp, may be inflamed by a blow- 

 out gunpowder shot, and cause a disastrous colliery explosion. 



The evidence which can be collected from the investigation 

 in the Camerton disaster, and from Mr. Hall's experiments, 

 point to a cause for such explosions, which has apparently 

 been overlooked, and which Prof. Lewes thought worthy of the 

 gravest attention. Both at the Camerton Colliery and in Mr. 

 Hall's experiments, powder w.as the blasting agent used, and 

 such powder as is employed for this purpose, gives amongst the 

 products of combustion nearly half the volume of permanent 

 gases in the condition of carbon monoxide, methane, and 

 hydrogen. 



In the Camerton explosion, it seems probable that about 

 l,j lbs. of such powder were used in the shot which caused the 

 disaster, and this quantity of powder would i;ive, roughly, a little 

 over three feet of inflammable gas, which when mixed with pure 

 air would give over 10 cubic feet of an explosive or, at any rate, 

 rapidly burning mixture, and experiments which have been 

 made upon the effect of fire-damp and dust combined in causing 

 colliery explosions show conclusively that even when the fire- 

 damp is present in such minute quantities as to form a mixture 

 very tar removed from the point of explosion, it still makes the 

 mixiure of coal-dust and air highly explosive ; and from experi- 

 ments which Prof. Lewes has made, it is clear that traces of 



NO. 13 I 3, VOL. 51] 



