106 Progress in Science. [January, 
or painting external work, especially for iron work, either exposed to the 
atmosphere or submerged in water. There appears to be no difference in the 
quantity of ammonia obtained, but it is stated to be produced in a better, 
purer, and more marketable form. 
Mont Cenis Tunnel.—We have on several former occasions referred to the 
operations in connection with this chef d’euvre amongst engineering works, 
and its course of progress has thus been duly noted. On the present occasion, 
when we have to record the final completion of this gigantic undertaking, 
it may not be uninteresting at the same time to note a few of the leading par- 
ticulars regarding it. On the last day of August, 1857, Victor Emmanuel fired 
the first blast on the Italian side of the tunnel. On the 25th of December, 1870, 
the headings from either end met under Mont Fréjus; and the official inaugu- 
ration of the tunnel took place on Saturday, the 16th of September last, when 
Italian ministers passed through it from Bardonnéche to receive French con- 
gratulations at Modane. The length of the tunnel is 13,364 yards, or rather 
more than 74 miles, and its sectional area is 71} yards, so that about 960,000 
cubit yards of rock had to be excavated and carried to spoil with an average 
lead of 1°875 miles. The weight of the mass of excavation could not have 
been less than 2 millions of tons, representing a work of 32 millions of ton- 
miles in the carriage to spoil. The ground cut through by the tunnel may be 
divided into six zones. 1. The anthracite zone that is first followed in 
leaving Modane, after traversing 420 feet of loose earth, and which is the 
most ‘elevated in the order of superposition of the beds. It represents an 
oblique thickness of 6456 ft. 6 in., corresponding to a real thickness of 3732 ft. 
6 in. 2. The quartzite zone, 1251 ft. 3 in. thick, following the axis of the 
tunnel, and of an absolute thickness of 725 ft. 6 in., the thinnest and best 
defined of all. 3. The gypso-calcareous zone, of an oblique thickness of 2815 ft. 
and an actual depth of 1627 ft. 3 in. 4. The upper calcareous zone, which 
has an oblique thickness of gto4 ft. 10 in., and a normal thickness of 5263 ft. 
Ir in. 5. The middle zone of calcareous schist which the tunnel traverses for 
8563 ft., and the thickness of which is 4950 ft.6in. 6. The lower zone of cal- 
careous schist, which extends to the Bardonnéche opening of the tunnel. Its 
oblique thickness is 11,482 ft. 11 in., corresponding to a depth of 6638 ft. 8 in. 
The total cost of the tunnel amounted to 65 millions of francs, of which Italy 
will pay something less than 20 millions of francs, and France will have to 
pay 25,500,000 francs. 
Ballooning.—During the late siege of Paris, no less than fifty-four balloons 
left that city between the 2oth of September, 1870, and the 28th of January, 
1871, charged with letters and despatches ; the letters thus transported being 
about 2,500,000 in number, and weighing altogether about 10 tons. Besides 
this freight about a hundred persons were conveyed from Paris by these postal 
balloons. The principal dimensions of these balloons were as follows:— 
Diameter, 51 ft. 8 in.; superficies, 8390 square feet; and contents, 72,240 
cubic feet. The balloons were of a spherical form, and were made of highly 
glazed calico varnished, each being composed of forty gores. The gores were 
cut to shape with perfect regularity, and were strongly sewn together with a 
coarse double waxed thread. This being done, the exterior received two coats 
of varnish, and then as soon as the balloon was dry it was ready for inflation, 
ordinary coal gas beingemployed for the latter purpose. In the lower aperture of 
the balloon was fitted a woodenring, 2 ft. 7} in. diameter, which was united to 
the sheet-iron pipe, 5 ft. long, which placed the balloon in communication with 
the gas pipes. Above, the balloon was fitted with a valve, consisting of a ring 
of oak, 2ft. 74 in. in diameter, provided with a couple of semicircular valves, 
kept close by india-rubber bands, and arranged so that they could be opened by 
means of a cord which passed down to the car through the interior of the 
balloon. The balloon was enveloped and conneéted to the suspension ring by 
strong tarred hempen cords, while the suspension ring, which was 3 ft. 34 in. 
in diameter, by 3:2 in. high and 2 in. thick, was provided with gabillots, to which 
were attached the eight cords of the car. The latter was made of wicker work 
and Indian reeds, and was 3 ft. 7} in. deep, by 4 ft. 7 in. long, and 3 ft. 74 in. 
