March 20, 1890] 



NATURE 



475 



Geneva, in Switzerland. The water of the lake in the harbour, 

 which is surrounded by houses on three sides, was then examined 

 by a distinguished micro-biologist, M. Fol, who discovered it 

 to be full of micro-organisms ; the water supplied to the town 

 for drinking-purposes was taken from the River Rhone im- 

 mediately as it flowed out of the harbour. The inquiry was 

 pursued further, and it was found that just outside the harbour, 

 on the surface of the water, there were still a number of micro- 

 organisms, though less than in the harbour ; but a few feet 

 below the surface, say 3 or 4 feet, they had greatly diminished 

 in number, indeed to such an extent that there were very few 

 present. The obvious remedy was at once carried out. A 

 wooden aqueduct was constructed, opening into the lake about 

 150 yards outside the harbour, and some 3 or 4 feet under the 

 surface. As stated by Dr. Dunant, a Geneva physician who has 

 given a very interesting account of this epidemic,^ eighteen days 

 after the source of the water-supply had thus been altered, a 

 marked decline took place in the epidemic, and it was clearly 

 being mastered. A similar epidemic due to a like cause occurred 

 about the same time at Zurich. 



There is one point connected with the properties of dust of 

 organic origin which I think cannot fail to be of interest on the 

 present occasion. I mean its inflammability, and its liability to 

 explode when mixed with air. By explosion is meant that the 

 propagation of flame by a very finely-divided material, such as 

 coal-dust, mixed in due proportion with air, may proceed with 

 a rapidity approaching the transmission of explosion by a gaseous 

 mixture. 



An interesting lecture was delivered on this subject at the 

 Royal Institution, in April 1882, by Sir Frederick Abel, en- 

 titled " Some of the Dangerous Properties of Dust." The 

 lecturer refers to instances of explosions in flour-mills, due in all 

 probability to a spark from the grinding mill-stones, occurring in 

 consequence of a deficient supply of grain to the stones. 



Messrs. Franklin and Macadam, who investigated the subject, 

 found that accidents of this nature were of frequent occurrence. 

 In May 1878 a flour-mill explosion, quite unparalleled for its 

 destructive effects, occurred at Minneapolis, Minnesota. Eighteen 

 lives were lost, and six distinct corn-mills were destroyed. 

 Persons who were near the scene of the calamity heard a 

 succession of sharp hissing sounds, doubtless caused by the 

 very rapid spread of flame through the dust-laden air of the 

 passages inside the mill. The nearest mill to that first fired was 

 25 feet distance, and exploded as soon as the flames burst 

 through the first mill. The explosion of the third mill, 25 feet 

 from the second, followed almost immediately ; and the other 

 three mills, about 150 feet distance in another direction, were at 

 once fired. The fire was attributed to a spark from friction of 

 the mill-stones. 



Coal-dust in coal-mines is a cause of accident from explosions, 

 which has been closely investigated in this country, in Germany, 

 and other mining districts. Sir Frederick Abel has given this 

 subject especial attention, and brings it prominently forward in 

 his valuable and exhaustive paper on "Accidents in Mines," read 

 to the Institution of Civil Engineers in 1888. Some mines are, 

 of course, more dusty than others, and coal-dusts are not all 

 equally inflammable. That which is deposited upon the sides, 

 top timbers, and ledges in a dry, dusty mine-way is much finer 

 ami more inflammable than the coarser dust which covers the 

 floors. The lecture I have referred to alludes to the case of a 

 considerable quantity of coal-dust accidentally thrown over some 

 screens at a pit mouth bursting into flame as the dust cloud came 

 into contact with a neighbouring fire, and burning a man very 

 severely. There appears good ground for believing that fire may 

 travel to a considerable extent through the workings of a mine 

 from the ignition of coal-dust, as will be seen in the following 

 account, extracted from Messrs. W. W. and J. B. Atkinson's 

 book on "Explosions in Mines": — "An appalling accident 

 happened at the Seaham Colliery, in the county of Durham, on 

 September 8, 1880, at 2.20 a.m., causing the death of 24 men. 

 An explosion occurred in the mine, and a loud report was heard 

 at the surface, accompanied with a cloud of dust from the shaft, 

 but no fire was seen. Owing to damage to the shaft it was more 

 than twelve hours before a descent could be effected, and then a 

 scene of destruction was witnessed by the explorers. Doors and 

 air-crossings destroyed ; tubs broken to pieces, and hurled one 

 over the other ; timber blown out, attended with heavy falls 

 from the roof ; and the bodies of men and horses in many cases 



' '■ Epidemic de fievre typhoide a Geneve en 1884," par P. L. Dunant, 

 Rnme Mcdicale de la Suisse Romande, 1887. 



terribly mutilated. The explosion was found to have extended 

 over roads of an aggregate length of about 7500 yards, the 

 greatest distance between the extreme points reached being 

 about 3800 yards." 



When discussing the cause of this terrible accident, Messrs. 

 Atkinson remark that it was apparently impossible to account 

 for the eff'ects of the explosion on the assumption that it was due 

 to fire-damp, as the presence of fire-damp was most unlikely to 

 occur at any part at which the explosion could have happened ; 

 and therefore attention must be turned to coal-dust. There 

 was coal-dust on all the roads traversed by the explosion, and 

 there was coal-dust at the supposed point of origin. These facts 

 are of striking significance. After the explosion, all parts of the 

 mine in which its effects could be traced were covered on the 

 bottom and on flat surfaces with a coating of fine dust, which, 

 when examined under the microscope, appeared to have been 

 acted on by great heat. This fine dust covered the surface for a 

 depth of from \ to ^ an inch and under. Dust of this kind was 

 entirely absent on those roads over which the explosion had not 

 extended. With reference to the original ignition, a shot had 

 been fired apparently simultaneously with the explosion. The 

 road at the place was of stone, and would probably be coated 

 with the finest coal-dust ; and, moreover, just above the spot 

 where the fatal shot was fired were large baulks of timber, on 

 which dust was plentifully stored. The shock caused by the 

 explosion would throw the dust into the air, and the flame set 

 fire to it. Thus initiated, the flame would extend through all 

 the roads on which. there was an uninterrupted supply of coal- 

 dust to support it. 



The second part of this address relates to inorganic or 

 mineral dust. When on the Peak of Tenerife in 1878, engaged 

 in a pursuit mostly of a physiological kind, I had occasion to 

 use a very delicate chemical balance. My object was to deter- 

 mine the amount of aqueous vapour given out of the lungs while in 

 the shallow crater at the summit of the Peak, 12,200 feet above 

 the sea. The heat was intense, as the sun shed its nearly vertical 

 rays at midday on the fine white volcanic sand spread over the 

 floor of the crater. At various places rocks projected, covered 

 here and there with crystals of sulphur, and so hot that the hand 

 could scarcely bear coming in contact with them. Anticipating 

 some difficulty in the use of the balance frorli the action of the 

 wind, I had brought up with me a hamper and a blanket. After 

 placing the hamper sideways, with the lid off, I proceeded, 

 though not without some little trouble, to dispose the balance 

 satisfactorily inside the basket ; then, having thrown the blanket 

 over the hamper, I stretched out at full length on the burning 

 sand, nestling under the blanket, much as a photographer 

 would cover himself and camera with a dark cloth. On trying 

 to use the balance, it refused to act ; its beam would not oscil- 

 late. A careful examination showed the instrument to be 

 apparently in perfect order, when it occurred to me to wipe the 

 knife-edges at the points of suspension of the beam and pans. 

 The balance then worked quite well, though but for a few 

 minutes only, again most provokingly declining to oscillate j. 

 indeed, it was only by constant wiping of the knife-edges that I 

 succeeded with my experiment. The cause of my trouble was 

 clearly the presence of very fine mineral dust in the air, of which 

 my senses were utterly unconscious. Hence it is that extremely 

 fine particles of mineral dust may exist in the atmosphere, while 

 escaping detection by our senses, and such an occurrence is 

 probably more frequent than generally thought. 



Prof. Piazzi Smyth, while on the Peak of Tenerife, witnessed 

 strata of dust rising to a height of nearly a mile, reaching out to 

 the horizon in every direction, and so dense as to hide frequently 

 the neighbouring hills. The Report of the KrakatjTo Commis- 

 sion of the Royal Society contains the following interesting 

 account, p. 421 (Mr. Douglas Archibald's contribution to the 

 Report): — "In 1881, Prof. S. P. Langley ascended Mount 

 Whitney, in Southern California, with an expedition from the 

 Alleghany Observatory ; at an altitude of 15,000 feet his view 

 extended over one of the most barren regions in the world. 

 Immediately at the foot of the moimtain is the Inyo Desert, and 

 in the east a range of mountains parallel to the Sierra Nevada, 

 but only about 10,000 feet in height. From the valley the 

 atmosphere had appeared beautifully clear, but, as stated in 

 Prof. Langley's own words, "from this aerial height we looked 

 down upon what seemed a kind of level dust ocean, invisible 

 from below, but whose depth was six or seven thousand feet, as 

 the upper portion only of the opposite mountain range rose 

 clearly out of it. The colour of the light reflected to us from 



