.474 Reports and Proceedings cancer tit ng the fultcrrcmeom 



'fifty miles to carriages pnflTmg from one county to the other \ and that the fituation at or 

 •near Gravefend is peculiarly eligible from its natural facilities, as the greateft part of k\\c 

 ground to be pafTed tlirough is chalk. Thefe obfervations are followed by the propofil 

 and eftimate vvhiih have already been given at the page of our Journal lad quoted. Mr. 

 Dodd obferve€ that 12I. per running yard nuift be confidered as a handfome allowance, 

 •fince it is a fact, tiiat fome of the mplT; confiderable tunnels in this kingdom on a fcale of 

 nineteen fettby feventecn, which is larger than the tunnel at prefent recommended, have 

 been executed at that price. 



On the iSthof Jt^ly I7c>8, a meeting was held in the Town Hall of Gravefend, the 

 Earl of Darnley in tlie chair ; when it was refolved, That there being no reafcn to doubt 

 the pradlicabilify of fo deGrable a tneafure, the co-operation of government, the aflent of 

 the neighbouring lar.d Qwners, or the willingnefs of the public to fubfcribe to its accom- 

 plifliment, the opinion of the meeting was, that transferable fhares of lool. each would 

 afford the bed meaas" of efiefl iiig it ; and that a I'libfcription fliould be opened at the office 

 of Meflrs. Evans and Son, at Gravefend, for its fupport and encouragement. 



In the report and efliniate which the engineer prefented to this meeting, he flates, that 

 from the a£lual furvey he finds no reafon to add to the former eftimate, but rather to abate 

 fome\^hat more than 30C0I. on account of the excellent chiilk which lie finds will be af- 

 forded at the mofl eligible place for the CAcavation. The deviation from an horizontal 

 line of the tunnel, which pafles at about tliirty feet below the bed of the river, will be 

 four inches in the yard. Several military and commercial advantages of the undertaking 

 ^re likewife clearly ftated, and an eftimate given of the coft of a twelve feet tunnel, ad- 

 mitting carriages to pafs only one way at a time, in cafe the fixteen feet turmel (liould be 

 thought too expenfive. In the fubfequent obfervations the author enlarges dill more upon 

 the fame interefting topics, and makes a comparifon between the communication by tun- 

 nels and the great modern improvement of iron bridges, which lad ereiSlioii he Ihcws to 

 be much lefs durable, and more liable to fpeedy deftrudion by an enemy, than the tunnel. 

 He remarks, that the dedruitive eladic fluids, which are known to be extricated in mines, 

 ■cannot affeft the prefent work when once finiflied, becaufe of the clear communication 

 with the external air at both ends ; and he gives fome practical remarks on the difcovery of 

 inflammable air or fire-damp, which, on account of the intercding nature of the fubjefl, I 

 lliall here tranfcribe. 



" On entering any excavation under ground, where this fire-damp is fufpccled to He, 

 the candle ought to be held in the left hand (the fmaller the candle the more to be de- 

 pended upon), and the flame thereof to be fliaded by the right-hand fingers being placed 

 liorizontal, and on a level with the top of the flame of the candle. If the air be good, and 

 ■ pcrfeflly free from any inflammable air or hydrogen, a fmall brown top or pinnacle is 

 feen on the top of the flame, the fame as is fcen in the chamber of a houfe; but on ap- 

 proaching the real fire-damp airother top or fpire is feen of a blue colour, above the brown 

 jud defcribed as arifing therefrom ; and on advancing a dep or two forward the damp is 

 commonly more denfe, and confequently the appearances over the candle aflume a more 

 feiious afpe£l by the brov,-n fpire or fmall top beginning to difappear; another dep per- 

 haps reduces it altogether, on which the danger commences ; and the fpire or top fits down 

 altogether blue on the dame. At this lad dagc it Is not fafe to proceed further without 



great 



