B[2l.l 



KNOWLEDGE 



[November, 1902. 



front 200 yarils wiflo and 8 feet deep."* In Ixith the 

 cases last quoted the catastrophe was clearly traceable to 

 unscientific turf-cuttinj^. To the same cause is to be 

 attributed tlic t'lital bo^'-tlow of 2Hth December, ]89(i, near 

 Killaruey, whereby Lord Keumare's quarry steward, his 

 wife, and six children, lost their lives, and much arable 

 land was destroyed. The writer can speak from his own 

 knowlcdi,'e of this botj-flow, havintr visited the ground and 

 prep;ufd, in conjunction witli Prof. Sollas, a reportf to 

 the Hoyal Dublin Society on the catastrophe. This was a 

 lar^e bog, 750 feet above sea-level, lying on a watershed, 

 and draining in three directions. The rupture took pla(« 

 along the face of a turf-cutting, and a vast flood poured 

 forth, overwhclniiug two roads and the cottage in which 

 the unfortunate Donclly family were asleep, and rushed 

 down the valley with diminishing violence till it reached 

 the Lake of Killarncy, fourteen miles away, in which some 

 of Donelly's furniture was afterwards found floating. 

 The flood continued in diminishing quantity for five days, 

 not regularly, but intermittently, as fresh portions of the 

 bog gave way, with loud noises, and slid into the torrent, 

 the lighter upper crust being borne along in floes on the 

 surface of the inky flood. Before the outburst, the surface 

 of the bog had been convex. When the flow subsided, a 

 valley extended from the point of collapse, over the greater 

 portion of the bog, 7 furlongs long by 5 furlongs wide, 

 with a maximum depth of 28 feet. As the former height 

 of this part of the bog above the margin of the depression 

 was some 7 feet, it follows that the total maximum sub- 

 sidence amounted to 3.5 feet. Here, and along the centre 

 of the new valley, the bog was completely evacuated, the 

 white bottom gravel showing among the stranded floes of 

 surface crust. A well-marked lip marked the margin of 

 the disturbed area. Inside this, the crust was broken by 

 a series of parallel crevasses, caused by the slipping in 

 of bog, and filled with water and bog that had risen from 

 below. These crevasses were narrow at first, becoming 

 wider further in, till near the centre line of the flow the 

 area of heathy surface was small compared with that of 

 semi-liquid peat. 



Calculation of the volume enclosed between the surface 

 of the bog before and after the catastrophe showed that 

 six million cubic yards of material had been discharged, 

 the greater portion of it within the first few hours of the 

 outburst. This matter consisted of water charged with 

 bog-mud, and carrying along with it great lumps of the 

 more solid crust of the bog, innumerable stools of Scotch 

 Fir from the lower layers of the bog, with trunks of trees 

 and every other movable or breakable thing that the flood 

 encountered. As the discharge lessened, these were left 

 stranded, and the sight of the valley filled with black 

 slime, out of which stumps and roots protruded like wildly 

 waving arms, and in which, no man knew where, the naked 

 corpses of the Donelly family lay entombed, was melancholy 

 in the extreme. The high- water mark of the flood was 

 rendered conspicuous by the fact that there was deposited 

 the lightest portion of the material, forming an abrupt lip 

 two feet in thickness, which, in our report, we likened to 

 out])oured oatmeal porridge. 



It will be noted that all our examples of bog-flows have 

 been drawn from Ireland. Ireland is, indeed, not only as 

 regards Europe, but as regards the whole world, essentially 

 the country both of bogs and of bog-flows. A recent 

 estimate shows that in spite of continued reclamation, 

 1861 square miles, or one-seventeenth of the whole surface 

 of the country, is under low-level peat-bogs. As regards 



• "Census of Ireland, 1851," Part V., Vol. I., p. 189. 1853. 

 t Sci. JProc. E.D.S., Vol. VIII., N.S., Part 5. 1897. 



bog-flows, Klinge,* one of the most recent investigators 

 of the subject, after a diligent hunt through European 

 literature, produces records of but two occurrences of the 

 kind outside Ireland. To these. Prof. Sollas and the writer 

 have added but two others ; these four are located, one in 

 England (Solway Moss), one in Germany (Treuenfeld, 

 01deii})urg), and two in the Falkland Islands, off Cape 

 Horn. In Ireland bog-flows are of comparatively frequent 

 occurrence. Seventeen are listed in the report on the 

 Kerry flow, already referred to, and many have passed 

 unrecorded. 



DR. 



AITKEN ON SUNSHINE AND CLOUDY 

 CONDENSATION. 



By Dr. J. Gr. McPheeson, f.e.s.e. 

 Although no man has wrought so hard as Dr. Aitken to 

 establish the principle that clouds are mainly due to the 

 existence of dust-particles which attract moisture on 

 certain conditions, yet even twenty years ago be said that 

 it was probable that sunshine might cause the formation 

 of nuclei, and allow cloudy condensation to take ])lace 

 where there was no dust. 



Eobert von Helmhotz and Professor Richarz, in their very 

 beautiful experiments made with the steam jet. endeavoured 

 to show that cloudy condensation was due to the molecular 

 shock produced by the chemical processes going on in the 

 neighbourhood of the jet. This theory Dr. Aitken has 

 ingeniously exploded in his communication to the Royal 

 Society of" Edinburgh. He says : " Supposing we even 

 admit that a molecular shock of the kind could determine 

 condensation in a supersaturated vapour, it must be 

 remembered that the degree of supersaturation in a steam 

 jet in the open air where there is dust is extremely slight 

 — the particles of water are so close that any strain easily 

 relieves itself. Further, it must be remembered that the 

 vapour in the jet is nearly in equilibrium with the drops 

 of the size jJi'esent in the jet." 



There must, therefore, be some other means of ac- 

 counting for cloudy condensation, in cases where there is 

 no dust. Under certain conditions the sun gives rise to 

 a great increase in the number of nuclei. Accordingly, Dr. 

 Aitken has cai'efully tested a few of the ordinary con- 

 stituents and impurities in our atmosphere to see if sun- 

 shine acted on them in such a way as to make them 

 probable formers of cloud-particles. 



He tested various gases, with more or less success ; and 

 he has communicated his results to the Society. He found 

 that ordinary air, after being deprived of its dust-particles, 

 and exposed to sunshine, does not show any cloudy con- 

 densation on expansion, but when certain gases are in the 

 air a very different result is obtained. 



He first used ammonia, putting one drop into six cubic 

 inches of water in a flask and sunning this for one 

 minute ; the result was a considerable quantity of con- 

 densation even with such a weak solution. When the 

 flask was exposed for five minutes the condensation by the 

 action of the sunshine was made more dense. Though 

 double the quantity of nitric acid was put into six cubic 

 inches of water, the condensation was not so dense. 



Hydrogen peroxide was tested by Dr. Aitken in the 

 same way, and it was found to be a powerful generator of 

 nuclei. Curious is it that sulphurous acid is puzzling to 

 the experimentalist for cloud formation. It gives rise to 

 condensation in the dark. On some days it was impossible 

 to get the coudeusatiou to cease entirely. But sunshine 

 very conclusively increased the condensation. 



Sulphuretted hydrogen, which one always associates 



• Ueber Moorausbruche. So^ J^aAriweAer, Bd. XIV., p. 42(J. 1S92. 



