140 " Transactions. 
attempt to force smoke by an air-current in the rear producing generally a 
dense fog, in which 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 
