Sept. 21, 1871] 
NATURE 
415 

also a signal for clear weather. These will be displayed 
by day and by night by a very simple and suitable con- 
trivance now being perfected by General Myer. In New 
York already arrangements have been made for displaying 
the signals to shipping in the harbour from a lofty struc- 
ture on the roof of the Equitable Life Insurance Company’s 
office, the best station that could be chosen. The display 
of these storm signals proper will place the American 
Signal Bureau at once in a position to render inestimable 
service to shipping and all commercial interests. 
These signals will at first be neglected by ruder and 
more unskilful seamen and shippers ; but, as in the case 
of the famous Fitzroy signals on the English coast, every 
week will add new demonstrations of the value and wiility 
of this system—one of the most splendid gifts bequeathed 
by modern science to the human race. 
The signalling of storms and desolating cyclones to the 
unsuspecting seainan will, itis believed, mark a new era 
in our lake and coast navigation, and be the means of 
annually saving many lives and millions of dollars’ worth 
of our floating property. 
The comparison of these signals with the weather fol- 
lowing the signals will be then a matter of special atten- 
tion. Every discrepancy can then be carefully noted and 
probed, and every day the meteorologists in charge of the 
“probabilities” will find the means of rectifying any 
errors they may have fallen into, and daily increasing the 
accuracy and perfecting the plan of their forecasts. 
The storm signals will be displayed at any hour of the 
day or night when the instrumental indications give notice 
of bad weather ; and experience has already shown that 
generally at least twenty-four hours’ forewarning can be 
given from the central office in Washington of all im- 
portant weather phenomena. With the telegraph to pre- 
monish, forecasts for two or three days in advance are 
hazardous and unnecessary. For almost all practical 
purposes of life a day’s notice of atmospheric disturbances 
is quite sufficient, and more reliable than longer premo- 
nitions. It will be a grand triumph for American science 
when the electric telegraph is so utilised that it will 
bring all citizens of the United States into electric com- 
munication with each other, and the most fearful storm, as 
well as the sunshine and shower, shall be every day a 
subject of forewarning or congratulation throughout the 
land, and even on the lakes and oceans that wash the 
American coasts. 
OPENING OF THE MONT CENIS TUNNEL 
app te project of constructing a tunnel under the Alps 
—one of the favourite designs of that ardent pa- 
triot and eminent statesman, the late Count Cavour—has 
now been accomplished, thanks to the skill of the Italian 
engineers. The scientific requirements and methods 
- adopted are well stated in a recent article in the Daz/y 
WVews, to which we are indebted for the following inter- 
esting particulars :— 
The tunnel was commenced on the 15th of August, 1857. 
The two points at which it was determined to begin the 
boring were two wretched little Alpine villages, Bar- 
donnecchia and Fourneaux, the former on the Italian, the 
latter on the French side of Mont Fréjus, the tunnel being 
nearly pierced under the above-named mountain, and not, 
as common report would have it, beneath Mont Cenis. 
These two villages were of the smallest size and most 
miserable character, and offered no accommodation what- 
ever to the many hundred workmen employed on either 
side the mountain. Bardonnecchia, on the Piedmontese 
side, is a village which, in 1857, when the works com- 
menced, contained about 1,000 souls. The houses 
in it were really little better than huts, being 
mostly occupied by shepherds, who were absent with 
their flocks on the mountains during the summer 

months. At Fourneaux things were even worse, there 
being an ordinary population of only 400 inhabitants, 
The first problem to be solved, says Mr. Fras. Kossuth, 
one of the Royal Commissioners of Italian Railways, in 
his able report on the Mont Cenis Tunnel, was threefold. 
(1) To fix across the mountain several points which would 
all be contained in the vertical plane drawn through the 
axis of the tunnel. (2) To obtain the exact length between 
the openings. (3) To know the precise difference of level 
between the two extremities of the tunnel, so as to obtain 
the proper gradients. In order to execute this programme, 
a series of observations was established on all the fa- 
vourable points, and an elaborate trigonometrical survey 
of the district was commenced. By the end of the season 
little could be done in the way of surveying ; in the winter 
of the year 1858 all the surveys relating to the alignment 
and to the length of the tunnel were completed, and all 
was ready to compile the longitudinal se-tion along the 
axis of the tunnel. The whole system consisted of twenty- 
eight triangles, and eighty-six was the number of mea- 
sured angles. All of these were repeated never less than 
ten times, the greater part twenty, and the most important 
as many as sixty times. To give the reader an idea of 
the extraordinary care and accuracy with which the sur- 
veying operations were carried out, it may be mentioned 
that Signor Mondino repeated his experiments for obtain- 
ing the level of the tunnel, or rather of the signals over 
the mountain in 1857 and 1858, and the difference in the 
two surveys (over more than 13,000 yards), was only 
3°93 inches. Even this was reduced afterwards by Signor 
Termine to 1°57inch. The preliminary measurements 
gave a distance of 13,861°5 yards between the two tempo- 
rary openings We say temporary openings, because, 
although the tunnel is itself constructed in a perfectly 
straight line from Fourneaux to Bardonnecchia, passen- 
gers will not pass through the original straight tunnel, but 
will be conveyed through a branch one which joins the 
main line a short distance from Fourneaux. The nature 
of the ground was such as to necessitate the definite 
and permanent tunnel being taken through the moun- 
tain In a curve; but even the unprofessional reader 
will see that a_ straight line was _ indispensable, 
in order to secure not only accuracy of direction, 
but also a through draught of air through the whole 
length of the tunnel. A most important considera- 
tion this latter, as one of the main objections brought 
against the scheme was the supposed difficulty there 
would be in keeping the tunnel thoroughly well ventilated. 
It was also much easier to transmit the necessary motive 
power along a straight line than onacurve. The tunnel, 
although its axis was straight, was not constructed on a 
dead level. The gradients were: From the Bardon- 
necchia (Italian) end, 4,408°50 feet above the level of the 
sea, I in 2,000 (0002 per metre) for a distance of 20,997°33 
feet. From the Fourneaux entrance (French side), 3 945 
feet above the sea, the rising gradient was I in 43 4782 
(023 per metre) for 20,587 feet. 
~ The absolute figures are as follows : 
Total length of thetunnel, 13, 364°86 yards, 
Elevation above the sea-level of the Bardonnecchia 
entrance 3 B ; ‘ . 4,381 '25 
Rise of gradient of I in 2,000 for 20,048 feet . 10°024 
Summit level from Bardonnecchia 4,391°274 
Elevation above sea-level at Fourneaux entrance 3,946'50 
Rise of gradient of 1 in 45,045 for 200,045 10 feet. 44500 
Summit level from Fourneaux 4,391 50 
This shows a very slight difference from the calculations 
of the summit level as reckoned at Bardonnecchia, and 
gives a mean level for the highest point of 4,391°386 feet. 
The greatest height of the mass of the Alps over the 
tunnel is 5,307 feet. 
