488 



KNOWLEDGE 



[April 7, 1882. 



more iiimlcm Hyittont. For present illuHtration, I wlect thi> 

 Utt<<r on tho simplest in rpspont to ventilation. Thi* 

 niftlind, a.s nrdiiiiirily worked, consistH cs-sentially in first 

 driving roads tlir(iii);li the roul from the pits to the out<-r 

 iMJiindnry of the nrea to he worki'<l, tlien cutting ii cross- 

 road that shall conncM-t tln-se, therel.y exposing a " long 

 wall ' of i-oal, whii'h is cut away towards the pits, the roof 

 remaining iH-hind U-ing allowed to fall in. 



Let Us iM'gin to do this hy driving, first of all, t"o main 

 roads, one from eaih pit It is e\ident that as we proceed 

 in such liurrowiiig, wi- .shall jiresently find ourselves in a 

 ciil </<} *<ii- so far away from the outer air that suflooation 

 is threatened. This will I.e e(|ually the case with hotli 

 roads. L«'t us now drive a cross-cut from the end of each 

 main road, and thus estalilish a comnninication from the 

 downco-st shaft through its road, then through the drift to 

 the upcast road and pit. I5ut in order that the air shall 

 take this roundalmut course, we must close the direct drift 

 that we pn-viously made lietween the two shafts, or it will 

 proceed liy that shcirter and easier course. Now, we shall 

 iiave air throughout both our main roads, and we may flrive 

 on further until we are again stopped by approximate sufTo- 

 cation. When thi.s occurs, we make another cross cut, but 

 in order that it may act, we must stop the first one. So we 

 go on until we reach the working, and then the long wall 

 itstdf becomes the cro.ss communication, and through this 

 working gallery the air sweeps freely and eflfectually. 



In the aljove I have only considered the simplest 

 possible elements of the problem. The practical coal-pit in 

 full working has a multitude of int<Tvcning passages and 

 ".splits,' where the main current from the downcast is 

 divided, in order to proceed through the various streets 

 and lanes of the sultterranean town as may be required, 

 and these divided current.s are finalh' reunited ere they 

 reach the upcast shaft wliich casts them all out into the 

 upper air. In a colliery worked on the pillar and stall 

 system — i.''., by taking out the coal so as to leave a series 

 of square chambers with pillars of coal in the middle to 

 support the roof —the windings of the air between the 

 multitude of passages is curiously complex, and its ab.soluto 

 oljedience to the commands of the mining engineer proves 

 how completely the most difficult problems of ventilation 

 may be solved when ignorance and prejudice are not per- 

 mitted to liar the progress of the practical applications of 

 simple scientific principles. 



itere the necessity of closing all false outlets is strikingly 

 demonstrated by the niedianisni and working of the "stop- 

 pings" or ]iartitions that close all unrequired openings. 

 The air in many pits has to travel several miles in order to 

 get from the downcast to the upcast shaft, though they 

 may be but a do/en yards apart (Formerly the same 

 shaft served both for up and down cast, by making a 

 wooden division (a /mi/tiri') down the middle. This is 

 now |irohibited, on account of serious accidents that ha\e 

 been cau.se<l by the fracture of the hrdllu-f.) But it would 

 not do to carry the coal from the workings to the pit by 

 such sinuous courses. NVhat, then, is done '( If any direct 

 road were h-ft open, the air would clioose it, but this is 

 prevented by an arrangement similar to that of canal locks 

 and g'.ites. \'al\e-doors or stoppings are arrangeil in pairs, 

 and when the hurrier arrives with his rorvr, or pit carriage, 

 one door is opened, the other remaining shut ; then the 

 corrr is hurried into the space between the doors, and the 

 entry -door is closed ; now the e.\it-door is opened, and thus 

 no continuous op<'ning is ever permitted. Oidy one such 

 opening would derange the ventilation of the whole pit, or 

 of that portion fed by the split thus allowed to escape. It 

 would, in fact, correspojid to the action of our open fire- 

 places in rendering efTei-tive ventilation impossible. 



Thr- following, from the report of the Lords' Committee 

 on Accidents in (Joal Mine.s, 1849, illustrates the magnitude 

 of the ventilation arrangements then at work. In the 

 Hetton Colliery there were two downcast shafts and one 

 upcast, the former aUiut 12 ft and the latt<-r lift 

 diameter. There were three furnaces at the \K>ttnin of 

 the upcast, each al>out 'J ft wide and about 4 ft length of 

 gnit<'-bars. The depth of the upcast and one downcast 

 1)00 ft, and of the other downcast l,Or)C ft The quantity 

 of air introduced by the action of these furnaces was 

 1GS,.")G0 cubic feet per minute, at a cost of about eight tons 

 of coal per day. The rate of motion of the air was 

 1,007 ft per minute (above 12 miles per hour^. This 

 whole current was divided by .splitting into 16 currents of 

 about 11,000 cubic feet each per minute, having, on an 

 average, a cour.se of 4| miles each. This distance was 

 however, verj- irregular — the greatest length of a course 

 being 9-f'jj miles ; total length 70 miles. 



All these magnitudes are greatly increased in coal mines 

 of the present time. As much as 250,000 cubic feet of air 

 per minute are now passed through the shafts of one mine. 



The ventilation of our houses may be conducted on the 

 same principles, and with corresponding efficiency, as I will 

 endeavour to show in my next. 



FOUND LINKS. 



Bv Dr. Andrew Wil.sok, F.R.S.E., F.L.S. 



BACKWARDS in time, and in the course of the geo- 

 logical :eons, we find the Cretaceous or Chalk rocks. 

 To the naturalist these deposits have yielded a rich and 

 suggestive harvest of bird-fossils, which, in their approxi- 

 mation to the reptiles, certainly serve as " found links " in 

 more ways than one. In the Chalk rocks of North America 

 we disco\er the remains of " toothed birds," whose teeth 

 in every respect agree with the structures of that name, 

 and are not mere bony projections, as in the old swimmer 

 of the Loudon clay. The curious Ilespproriiig (Fig. 1) and its 

 neighbours the Iclilln/oriiis and Ajmtornis, thanks to the 

 exertions of Professor Marsh, appear before us as veritable 

 links, connecting the birds and reptiles in respect of 

 their teeth, as well as in other features of tlieir economy. 

 Hesperornis stood at least five feet high, and in respect of its 

 bony framework exhibits a close alliance with the grebes of 

 our own day. But strange to saj%He.speromis (Fig. I) wants 

 one marked peculiarity of other birds (save the ostrich- 

 group), namely, the prominent " keel " or bony ridge on 

 the breast-bone, to which the wing-muscles of birds are 

 attached. The wings were certuinly of rudimentary 

 character, but this is a feature we see exemplified in the 

 auks and penguins of our own day ; and it is probable that 

 the tail of this great diver of the chalk seas was unusually 

 mobile, and adapted possibly to serve as a rudder. The 

 reptile characters crop out, however, most clearly 

 in the teeth of this bird. There were no teeth 

 in the front of the upper jaw, and presumably this 

 region was covered with a horny beak. The teeth 

 themselves arc curved structures ; but they are set in a 

 common groove, and not lodged each in a socket, as is 

 commonly tlu' case in higher animals. In living reptiles 

 themsehes, it may be added, the teeth, save in crocodiles, 

 are not implanted in sockets. Thus, in serpents and 

 lizards the teeth arc simply united by bony union to the 

 liones which bear them ; but certain extinct lizards had 

 socket-fastened teeth, and the giant fossil ivptiles (Ic/il/ii/o- 

 saurxs, &c.) of the Lias, Oolite, and Chalk, possessed teeth 



