160 
POPULAR SCIENCE REVIEW. 
generating power, but the perforating machinery was to be 
driven by the action of compressed air, the modus ojperandi of 
which had to be determined and put to the test of actual work 
and experiment on a grand scale before the real labour of the 
excavation began. 
Besides driving the perforating tools, the same air had to 
ventilate the tunnel, and keep it in a fit state for respiration ; 
for it will be seen that a tunnel without shafts, more than 
7^ miles long, could not be ventilated by the ordinary method 
usually employed for such purposes. 
Passengers traversing Mont Cenis pass through the little 
Alpine town of Modane, where there are numerous works con- 
nected with the tunnel ; and also the hamlet of Fourneau, 
where again are seen extensive establishments of an appear- 
ance and character little dreamt of by travellers in a wild and 
romantic pass like this. The mass of pipes and tubes for air 
and water look quite bewildering, looming like the apparatus 
of some Titanic distillery. It seems incredible to the passing 
stranger that this pile of pipes, tubes, tanks, and reservoirs, 
are employed for the purpose of boring into the bowels of an 
Alpine mountain of hard and solid rock without the aid of 
steam, and little help from manual labour. 
A novel machine for perforating hard rock was not easily 
brought to perfection ; it required a long and elaborate series 
of practical working experiments, and numerous modifications 
in detail, before being considered fit for the real work it had to 
do. It required to be of sufficient power to do the work 
with ease and precision, of such size and weight as to be easily 
managed by one or two men, and so strong and simple in 
form and construction as to avoid the necessity of frequent 
stoppage and repair; for the work such a machine was 
required to do should be continuous night and day as far as 
possible. 
It appears from the report of the engineers, that the time 
the machines were actually at work, during the year 1861, at 
Bardonneche, was only two hundred and nine clear days, with 
an actual advance of the whole front of the excavation of 
559 feet, which only gives a daily progress of about 2 feet 
8 inches. At the same place, during 1862, there appears to 
have been three hundred and twenty-five full working days, 
with an actual advance of the tunnel of 1,216 feet, which gives 
for the daily working progress of the complete tunnel about 
4 feet 5 inches. At the northern end of the tunnel of Modane, 
for the same year, 1862, the advance is stated to have been at 
the rate of nearly 40 inches per diem. 
Since 1,216 feet were actually advanced in three hundred and 
twenty-five days at Bardonneche, this will give for the entire 
year, if in full operation at the same rate, an advance of 
