140 Transactions. 



attempt to force smoke by an air-current in the rear producing generally a 

 dense fog, in wMcli candles are of little use. 



A very curious fact connected with the bratticing in the Lyttelton 

 tunnel may be here mentioned. The brattice is formed of inch boards laid 

 on joists running across the width of the tunnel, and housed at each end 

 into the solid rock. Both joists and boards rapidly became covered with 

 fungus, and required to be replaced from time to time with new material. 

 Although, after the first year, portions of the brattice repeatedly fell from 

 decay, these falls invariably happened on Sunday, when the men were absent 

 from the work, no fall having taken place whilst the men were at work 

 until quite recently, when the decay of the timber had rendered neces- 

 sary an extensive renewal of the brattice. The explanation of this 

 curious fact is probably the difference in temperature on week days and 

 Sundays, the furnace fire at the foot of the upcast shaft being allowed to 

 go out on Saturday night, and not being lighted again for twenty-four 

 hours ; the hot smoke which occupied the flue during the working days 

 being replaced on Sunday by a comparatively cool atmosphere. 



I may here mention that a tunnel is now being driven in France, on the 

 new line of railway between Lyons and Roanne, under Mont Sauvage, 

 which divides the valleys of the Rhone and the Loire. This tunnel will be 

 two miles in length, and will be driven from five shafts, of which the deepest 

 will be upwards of 600 feet in depth. From the geological character of the 

 district, it is anticipated that the rock to be bored through will be of the 

 hardest description ; and it is stated in scientific journals that in one of the 

 shafts the difficulties met with are such that a progress of two inches in 

 twenty -four hours is all that can- be accomplished. 



It will be interesting to watch the progress of this work, especially in 

 reference to the question of how far boring machinery can be introduced 

 with advantage in tunnelling through rocks of equal hardness with those 

 met with in the Lyttelton tunnel. 



Some curiosity has been expressed as to the correctness of the alignment 

 of the two ends of the Lyttelton tunnel, and the method employed for 

 checking any error that might be committed in the direction of the work. 



The system employed is very simple. A permanent mark is fixed in the 

 centre line of the tunnel, on a tower built on the dividing range, nearly 

 midway between the two ends. A transit instrument being placed on the 

 meridian of the tunnel, in a position to command a view into the tunnel as 

 well as of the tower on the hill, it can be seen at once whether the flame of 

 a candle placed on the centre line of the work, inside the tunnel, is in a 

 vertical plane with the mark on the tower. But it is also desirable, in case 

 of error, to have the means not only of correcting, but of calculating the 



