♦ KNOWLEDGE ♦ 



[November 1, 1886. 



and the timber beams. It was completely undermined to a 

 creat distance beyond its base all ai-ound, although the drift 

 of the gravel was checked by woodwork. It suggested the 

 old story of the sword of Damocles ; a more deadly weapon 

 than a sword was hanging perpetually over the heads of the 

 men as they worked below ; a failure of the chains or the 

 beams, or of the ground abDve, and the whole of this sus- 

 pended tower must come crushing down, hopelessly buryingall. 

 At last the gi-avel was fully pierced and so'id rock was 

 reached ; then a stout kerb was laid, and a double wall, an 

 inner cylinder of bi-ickwork corresponding to the finished 

 diameter of the pit, and another outside of this, leaving a 

 space hetn'een all round. This space was puddled with 

 clay, " coffered" as Jones called it, in order to keep back^he 

 water, which was especially abundant in the gi-avel. As the 

 double wall advanced upwards, the space behind it was well 

 and firmly filled and rammed. At hxst the suspending kerb 

 was reached, and when firmly connected with the double 

 tower below, the su?pendirig apparatus was removed. 



The coffering to keep out the water is variously devised. 

 Sometimes "tubbing" is substituted for the above-described. 

 This I understand is more frequently used now than 

 formerly. Cuvelage is the French name. A detailed 

 technical description of ths various kinds of tubbing would 

 be out of place here. It will be sufiicient to state that both 

 wood and iron are used ; that " plank tubbing," effecting a 

 result similar to cooper's work, is used ; also solid wood 

 tubbing, which, broadlv speaking, may be described as a 

 lining of kerbs well wedged and caulked at all their joints 

 to make them watertight. Then there is iron tubbing, 

 formed of cast-iron cylinders, which are let down in short 

 lengths and line the pit. Other iron tubbing is formed of 

 cast-iron segments carefully built in. It is always expen- 

 sive, the cost amounting in deep and large pits to as much 

 as about 50^. or GOl. per yard. When substituted for brick- 

 work, it has to support the lining structure above, and 

 must be strengthened accordingly as the depth increases. 

 If coalpits were permanent structures, such iron tubbing 

 would be quite inapplicable, as in spite of brick linings 

 and other devices the iron is gnidualh' corroded by 

 the water, and by the gases from the ventilating furnaces. 

 If, however, it lasts until all the coal within its reach is 

 worked out, this is sufficient. 



As two pits mast, in this country, be available for the 

 ventilation of every colliery, it is convenient in opening 

 new ground to sink the pair simultaneously. One of the ad- 

 vantages of this is the facility aflbrded for ventilation during 

 the sinking, as the pits ai-e usually placed near to each other. 

 Man is so constituted that he cannot simply bore a hole in 

 the earth to any depth he pleases and remain therein. He 

 must make arrangements for causing a current of air to 

 rise, and another to simultaneouslj' descend, or he will be 

 suffocated by the exhalations from his own lungs and the 

 earth around. In sinking a pair of pits near to each other 

 this ventilation is easily obtained by descending until the 

 air begins to foul, then driving a horizontal communication 

 and establishing an upcast of air in one pit and downcast in 

 the other. The methods of doing this and of producing, 

 directing, and controlling subterranean air currents generally 

 will be treated hereafter. 



We understaud the Amateur Photographic Exhibition held by the 

 London Stereoscopic Company in the spring has resulted in a loss 

 to them. Tliis was fully anticipated by the directors when they 

 inau.i^urated it ; and that the Company, in the face of this know- 

 ledge, have given the amateur world a second exhibition is, we 

 think, most enterprising, and will undoubtedly be appreciated by 

 amateurs as it deserves. We have no hesitation in saying to those 

 amateurs wlio may be amongst our readers that, in common fairness, 

 they should reciprocate and make their purchases from the Company. 

 We have seen and can vouch for the quality of the articles supplied_ 



THE RECENT TOTAL SOLAR ECLIPSE. 



tAR the TOO.st interesting results obtained 

 during the recent eclipse are (1) Ta echini's 

 discovery that the spectroscopic method of 

 observing the sun's coloured prominences 

 shows only the brighter parts of the pro 

 minences as they actually exist and as 

 they are seen during totality. He ob- 

 served the eclipsed sun through a telescope 

 6 inches in diameter, and noted (as during the eclipse of 

 1882) the existence of whitish extensions around and above 

 the ruddy flames. Making spectroscopic study round the 

 edge of the sun's disc after the eclipse, he found that the 

 ruddy part — so to speak — the core of these prominences, 

 was all that could he seen of them by the s|)ectroscopic 

 method. This discovery seems only explicable by the theory 

 that the ruddy, jet-like portion of the prominence owes its 

 light, and therefore its heat, to the velocity of outrush with 

 which ejected matter passes through the hydrogen and 

 helium already outside the sun, and not to the outrush of 

 those gases themselves in an intensely heated condition. 

 For, outrusting gases brought from a region of great 

 pressure to a region of very small pressure would expand 

 rapidly and be qiiickly cooled, so that the outlines of the 

 hexted and luminous portion would be sharply defined, 

 and would be surrounded by a region not only cooler than 

 the ejected matter, but even cooler than the surround- 

 ing atmosphere. On the other hand, ejected matter 

 would travel outwards with diminishing velocity owing 

 to the retarding action of solar gravity, while such portions 

 as returned after reaching a certain height would not only 

 be scattered around somewhat widely, but would reach the 

 sun's surface with less velocity than they had had at leaving 

 it, because of the etfects of frictional resistance. Hence, 

 above and around the region of rapid outrush, intense heat, 

 and brilliant ligiit, there would be a region where the 

 hydrogen and helium in the sun's atmosphere would be 

 heated by the rush of matter through it, and would there- 

 fore be luminous, but would lie less heated than the region 

 of outrush. This exactly corresponds with what Tacchini 

 has discovered. 



We should expect, as a further consequence, that the 

 corona would sho^\- a gradual diminution of heit with in- 

 creasing distance from the sun's edge, and therefore a gradual 

 change of spectrum, those spectral lines brought otit in the 

 laboratory with high temperatures being .shorter in the 

 coronal spectrum than those visible when lower tempera- 

 tures are employed. This was observed first in the eclipse 

 of 1882. But the observations by Messrs. Turner and 

 Perry, by which, on the present occasion, the results of 1882 

 were confirmed, must be regarded as of considerable import- 

 ance, though not altogether new. An attempt has been 

 made to reconcile the observation with the old and exploded 

 theory that the corona is a solar atmosphere ; and strangely 

 enough the attempt has been made in the very .same quarter 

 where the idea was longest and mast obstinately maintained 

 that the corona is not a solar appendage at all. Whatever 

 else we may surmise about the corona, we cannot any longer 

 admit the possibility that it is of the nature of a solar 

 atmosphere properly so-avlled. Ga.seous matter is there in 

 plenty, but it can no more form a solar atmosphere than can 

 the gaseous matter present in the comas and tails of sun- 

 circling comets. 



U nfortunately, one of the most important results of the 

 recent eclipse observations has been the complete and final 

 disproof of the .solar character of the corona jMf. Huggins 

 has succeeded in showing in photographs of the uneclipsed 



