372 



♦ KNO^A^LEDGE ♦ 



|Dec. 21, 1883. 



possiVjle mode of generation of solar systems which he has 

 advanced in his " Fuel of the Sun." But these wild fancies 

 of a mind really most practical in terrestrial matters, are 

 not our present (or likely to be our future) game. What 

 follows, apart from references to such matters, is well 

 worth studying, and especially useful reading for those 

 Oanta'is or Oxonians who seem to have advocated the doc- 

 trine of monstrous internal lunai- or terrestrial cavities: — 



" ' The Curiosities of Science ' would form a subject for 

 quite as thick a book as Disraeli's ' Curiosities of Litera- 

 ture.' Whoever may write it should devote a full chapter 

 to the hypotheses of the moon's senUity, Jupiter's juvenility, 

 the eaith'a middle age, the cooling down of the sun and 

 stars, and the general dying out of the universe." [Another 

 might be devoted to theories of perpetual motion, on what- 

 ever scale imagined.] 



"A full discussion of this subject would far outrun the 

 limits of a note, but I may remark, in passing, that I have 

 stated in ' The Fuel of the Sun ' my reasons for concluding 

 that our sua and solar sy.steni, and all the other suns, 

 systems, and nebuhe within the reach of human observa- 

 tions, have during all time within the limits of human 

 conception been on the average just as hot and as bright 

 as at present, though subject to a fluctuation both up and 

 down ; and that Jupiter, Saturn, Uranus, and Xeptune 

 were always minor .suns, and must always continue to be 

 such." [Perpetual motion on a large scale is very properly 

 put, " in passing," as a striking illustration of the idea 

 broached in the preceding paragraph]. 



" A branch of the dismal hypothesis now in fashion is 

 the supposition that the moon was formerly a verdant 

 world with land and sea, rivers and lakes, atmosphere and 

 clouds ; and that by internal shrinking, which its crust has 

 not followed, there are caverns as big as its former oceans, 

 and so deep that all their waters and all the ancient lunar 

 atmosphere are swallowed into them : that our earth will 

 ultimately grow old, will die, and become a-s cavernous 

 inside, and as arid and airless outside, as the moon is now. 



" That such a dream should occupy the waking hours of 

 men living on this planet, and knowing something of the 

 properties of the materials of its surface, Ls curious indeed. 

 Had they been educated in a colliery instead of Cambridge 

 or Oxford, they could not possibly have been deluded by 

 any such monstrous physical fable. 



" They would have known that when a cavity of notable 

 horizontal area is formed anywhere in the crust of this 

 earth, whether 20 yards, .50 yards, 100, 200, or .')00, or 

 1,000 yards or more below the surface, the mere weight of 

 the superincumbent rock squeezes itself down until the roof 

 of the cavity touches the floor ; and that the permanency of 

 any such a cavity (or its existence even for a year or two) 

 is a physical impossibility. 



" So inevitable is this that in the old mode of coal 

 working by ' pillar and stall ' a deplorable waste of coal 

 occurred. ' The pillars of coal that are left to support the 

 roof form frequently as much as three-fourths, and never 

 less than one-third, of the whole seam ' (Tomlinson). A 

 portion of these are finally removed, but in order to protect 

 the miners artificial wooden pillars or ' juds ' are supplied 

 to support the roof. When these are removed, the roof 

 falls in by the bending down of the hundreds of yards of 

 rock above, and shivering of the immediate surface of the 

 root 



" If those who believe the moon to be the abode of 

 caverned oceans and atmosphere, and who imagine that our 

 earth will follow its example, would make a pedestrian trip 

 through the Black Country between Birmingham and 

 Wolverhampton, under which the great ten-yard coal seam 

 formerly existed, the spectacle of leaning chimney shafts. 



split cottages, and toppling houses would show them what 

 would happen if the interior shrinkage of the earth pro- 

 duced but very remote approaches to their imaginary 

 caverns. 



"The most remarkable of these effects is that of the 

 yielding — I say ' flowing ' — of the rock not immediately 

 over the removed coal. The area of the superficial sinkage 

 basin is considerably larger than that of the hollow filled 

 up, but, of course, proportionately less deep. From this 

 it follows that houses not actually undermined are some- 

 times wrecked or damaged. ' Sunnyside,' near Caergwrle, 

 P^lintshire, a house occupied by a friend of mine, was 

 split down through the middle while his family were 

 in occupation. It was well built and of good size. 

 Had it been a London suburban villa of the ordinary 

 Jericho order of architecture the consequences would 

 have been serious. As it was, he deliberately moved to 

 another house, and Sunnyside was left until the subsidence 

 was completed, when the chasms in the wall were filled up 

 by the proprietors of the colliery, whose workings had only 

 approached but had not reached it This is merely one 

 example, hundreds might be quoted. 



" In modern ' long wall ' working the coal is removed by 

 working away from a long face of coal at the boundary 

 farthest from the pit, then approaching the pit in a long 

 line, supporting the part where the men are immediately 

 at work. As soon as the distance from the original wall 

 exceeds a certain extent the roof collapses, and thus the 

 collapse follows the workers. 



" If such puny excavations cannot exist, how monstrous 

 is the assumption that caverns capable of swallowing the 

 Atlantic Ocean could remain for even half an hour ! 



"Natural caverns rarely attain the span of Brunelleschi's 

 dome, or that of the Albert Hall, and never reach that of 

 the Midland Railway station at St Pancras, unless sup- 

 ported by stalactites and stalagmite.s. A multitude of 

 proofs of the limits of their possible area is afibrded by 

 their collapse, cases of which (like Daddy Hole Plain, 

 Torquay) may be traced in almost every great Limestone 

 district. At earth depths corresponding to maximum ocean 

 depth?, not only great caverns but even minute filtration 

 pores are impossible, as proved by the experiments of 

 Spring, described in my notes on ' Regelation and Welding' 

 (August, 1882), and on 'Transfusion by Pressure' 

 (February, 1883). 



" As the origin of natural caverns is not generally under- 

 stood, I may supplement the above note with a short 

 explanation. 



" Generally speaking, they occur in limestone rocks. 

 There are a few exceptions, such as that on the Island of 

 Thermia (Greece) in argillaceous schist, and those on Etna 

 formed by the hardening of lava during the escape of pent- 

 up vapour, but such exceptions are very rare ; while, on 

 the other hand, there are very few ranges of compact lime- 

 stone where caverns are not more or less abundant. 



" Take a little clear lime-water in a wine-glass, and blow 

 through it by means of a glass tube, a quill, or tobacco-pipe. 

 It becomes turbid by the conversion of the soluble caustic 

 lime into insoluble carbonate. ^Nlost of the limestone rocks 

 have been formed by chemical action nearly resembling this 

 precipitation. 



" Now continue the blowing, and the further supply of 

 carbonic acid will ultimately dissolve the carbonate of lime 

 it first [irecipitated. This is the action that excavates the 

 limestone caverns. 



"Rain-water picks up a little carbonic acid on its way 

 through the air, then more and more as it flows over vege- 

 table matter. Thus charged it dissolves, slowly it is true, 

 but surely, the most compact limestone. I have walked 



