416 
NARURE 

[ Sept. 21, 1871 

After giving these figures, it may be of interest to pre- 
sent the reader with the account given by an eye-witness, 
M. Génési, of the meeting of the workmen last winter in 
the depths of the earth, more than 5,000 feet beneath the 
summit of Mont Fiéjus. ‘On the 9th of November, 
1871,’ says M. Génési, “I was on my regular round of 
inspection as usual, when I fancied | heard through the 
rocks the nose of the exp'osion of the minrs on the Bar- 
donnechia side. I sent a dispatch to discover if the 
hours agreed. They did, and then there could be no 
longer any doubt we were nearing the goal. Each follow- 
ing day the explosions were to be heard more and more 
distinctly. At the beginning of December we heard quite 
clearly the blows of the perforators against the rocks. 
Then we vaguely heard the sound of voices. But were 
we going to meet at the same level and in the same axis ? 
For three days and three nights engineers, foremen, and 
heads of gangs never left the tunnel. ‘he engineers 
Borelly and Boni directed the works on the Bardonnechia 
side, M. Copello on that of Fourneaux. We could not 
eat or sleep ; every one was ina stateof fever. At length, 
on the morning of the 26th De-ember, the rock fell in 
near the roof, The breach was made, and we could see 
each other and shake hards, The same evening the hoie 
was clear—the last obstacle—and the mountain was 
pierced, our work was done. What a rejoicing we had! 
In spite of the war, the cheers of all scientiic Europe 
came to find us in the entrails of our mounta‘n when the 
happy termination of our enterprise became known, The 
two axes met almost exactly ; there was barely half a yard 
error, The level on our side was only 60 centimetres 
(less than three-quarters of a yard) too high. But 
after thirteen years of continual work, who could even 
hope for so perfect a result ? We placed at the point of 
junction an inscription on a marble tablet, commemorative 
of the happy event.” 
How was the happy event brought about? For the 
variation of less than a yard in more than 13,000 is 
surely one of the triumphs of modern engineering skill. 
We cannot do better than borrow the description of the 
method pursued given by Mr. Kossuth :—“ The observa- 
tories placed at the two entrances to the tunnel were used 
for the necessary observations, and each observatory con- 
tained an instrument constructed for the purpose. [his 
instrument was placed on a pedestal of masonry, the top 
of which was covered with a horizontal slab of marble, 
having engraved upon its surface two intersecting lines 
marking a point, which was exactly in the vertical plane 
containing the axis of the tunnel. The instrument was 
formed of two supports fixed on a tripod, having a delicate 
screw adjustment. The telescope was similar to that ofa 
theodolite, provided with cross webs and strongly illumi- 
nated by the light from a lantern, concentrated by a lens, 
and projected upon the cross webs. In using this in- 
strument in che king the axis of the gallery at the northern 
entrance, for example, after having proved precisely that 
the vertical flame, corresponding with the point of inter- 
section of the lines upon the slab, also passed through the 
centre of the instrument, a visual line was then conveyed 
to the station at Lachalle (on the mountain), and on the 
instrument being lowered the required number of points 
could be fixed in the axis of the tunnel. In executing 
such an operation it was necessary that the tunnel should 
be free from smoke or vapour. The point of collimation 
was aplummet suspended from the roof of the tunnel by 
means of an iron rectangular frame, in one side of 
which a number of notches were cut, and the plummet 
was shifted from notch to notch, in accordance with 
the signals of the operator at the observatory, These 
signals were given to the man whose bus ness it was to 
adjust the plummet by means of a telegraph or a horn 
The former was found invaluable throughout ail these 
operations. At the Bardonnecchia entrance the instru- 
ment employed in setting out the axis of the tunnel was 


similar to the one already described, with the exception 
that it was mounted on alittle carriage, resting on vertical 
columns that were erected at distances 500 metres apart 
in the axis of the tunnel. By the help of the carriage 
the theodolite was first placed on the centre line approxi- 
mately. It was then brought exactly into line by a fine 
adjustment screw, which moved the eye-piece without 
shifting the carriage. In order to understand more clearly 
the method of operating the instrument, the mode of pro- 
ceeding may be described. In setting out a prolongation 
of the centre line of the tunnel, the instrument was placed 
upon the last column but one ; alight was stationed upon 
the Jast column, and exacily in its centre, and 500 metres 
ahead a trestle frame was placed across the tunnel. Upon 
the horizontal bar of this trestle several notches were cut, 
again-t which a light was placed and fixed with proper 
adjusting screws. The observer standing at the instru- 
ment caused the light to move upon the trestle frame 
until it was brought into an exactline with the instrument 
and the first light, and then the centre of the light was 
projected with a plummet. In this way the exact centre 
was found. By a repetition of similar operations the 
vertical plane containing the axis of the tunnel was laid 
out by aseries of plummet lines. During the intervals 
that elapsed between consecutive operations with the in- 
struments, the plummets were found to be sufficient for 
maintaining the direction in making the excavation. To 
maintain the proper gradients in the tunnel it was neces- 
sary at intervals to esiablish fixed levels, deducing them 
by direct levelling from standard bench marks placed at 
short distances from the entrances. The fixed level marks 
in the inside of the tunne] are made upon stone pillars 
placed at intervals of 25 metres, and to these were re- 
ferred the various points in setting out the gradients.” 
There will be two lines of rail in the tunnel. The vault 
itself will be six metres high and eight metres wide. The 
tunnel will be walled in along its whole length, and the 
lime rock will be nowhere exposed. The thickness of the 
internal masonry forming the tube is trom half a yard to 
a yard and more, according to circumstances. On the 
French side the masonry cost on the average 1,300 francs 
the square meire. On the Italian side only 1,000 francs. 
The tunnel is wonderfully dry in comparison with many 
smaller works, There is only one subterranean spring of 
any importance in it. A water course, or rather aqueduct, 
has been constructed beneath the permanent way, in 
order to carry off any water which might drain into the 
tunnel, 
Much has been said about the heat in the tunnel. All 
accounts agree that it is not excessive, and a recent 
French visitor to the tunnel gives the following figures :— 
At the entrance, 54° Fahrenheit ; at the telegraph station 
inside, 76° Fahrenheit; the average temperature being 
about 65° Fahrenheit. 


NOTES 
THe first session of the Newcastle-on-Tyne College of Phy- 
sical Science will be opened by inaugural addresses from Pro- 
fessors Herschel, Aldis, Page, and Marreco, from the 9th to the 
12th of October. The examination for the four exhibitions will 
be held on the 13th and 14th. On the roth the Inaugural 
Ceremony will take place, when the Dean of Durham will de- 
liver an address ; after which the successful candidates for the 
exhibitions will be named, Furvher particulars are given in our 
advertising columns. 
WE announced some time ago that the Council of the Working 
Men's College, in Great Ormond Street, was prop sing a larger 
infusion of Science in the programme of the College course ; and 
we are now very glad to be able to state that during the next 
term, which will commence on October 2, courses of lectures 
