124 Progress in Science. [January, 
instance, to make only a small harbour, but subsequently gave directions for 
the enlargement of the scheme. In 1856, the design, then in course of con- 
struction, consisted of a harbour of 150 acres, with a depth of water of 
3 fathoms and upwards, sheltered to the west and east by two breakwaters. 
The western breakwater, about 4700 feet in length, had been constructed, but 
the eastern breakwater was abandoned; and the harbour was consequently 
exposed to winds blowing from any quarter between N.N.E. and E.S.E. The 
western breakwater was exposed to the whole force of the Atlantic, and the 
effect of the fury of the storms was increased at Alderney by the rapidity of 
the tides near the island, occasioned by a peculiar confluence of currents in 
the bay of St. Malo. The breakwater was constructed on the “‘ pierres 
perdues”? system—a mound of rubble-stone being deposited in the line of 
the proposed work from hopper barges towed out by steam-tugs. As soon as 
the mound was sufficiently consolidated, it was surmounted by the super- 
structure, consisting of a sea wall and of a harbour wall 14 feet and 12 feet 
thick respectively, flooded at first at the level of low water, and built without 
mortar, the intermediate spaces being filled up with rubble, the batter of the 
sea wall being g inches and of the harbour wall 4 inches to1foot. To protec 
the lower or quay level, a promenade wall, 14 feet high, was built on the sea- 
side, consisting of two masonry walls set in mortar, with filling between. In 
1860, when the superstructure had been carried out 2700 feet from the shore, 
the design was somewhat modified. The breakwater was narrowed by 
reducing the width of the quay to 20 feet, the batter on the sea face was 
altered to 4 inches in a foot, solid masonry was substituted for the concreted 
hearting, and the foundations of the harbour wall were commenced at the 
same level as the sea wall. The head was built in 1864. The foundations 
were laid 24 feet below low water level, across the whole width of the break- 
water. The first nine courses, each 3 feet thick, consisted of concrete blocks 
faced with granite headers; the upper portion was built of masonry in cement. 
The most exposed face stones were joggled and dowelled together, and several 
of the corner quoins were further secured by iron bars and diagonal straps. 
Two red leading lights on the shore mark the entrance to the harbour at night. 
The cost of the works of construction and maintenance to 1872 amounted to 
£1,274,200, of which £57,200 was expended in repairs. 
Water Supply.—With a view to improving the water supply of Paris, the 
Montsouris Reservoir is now in course of construction to receive the waters of 
the Vanne. It occupies an area of 54,000 square metres, or 13} English acres, 
and will contain 300,000 cubic metres, or 66,000,000 gallons of water, being 
the amount of three days of the normal flow of the canal which supplies it. 
The entire work is constructed of stone and cement, the exterior walls being 
strengthened by oblique arches having a thickness of 3 metres. The bottom 
is level except at the approaches to the wall, where is a series of sumpts of 
little depth, separated by partitions in order to form a number of arches which 
support the interior gallery. In front of each of the recesses thus formed are 
pillars, carried up to support the vaults of the arches which form the top of 
the building. The river Vanne is expected to afford daily a supply of about 
100,000 cubic metres, or 22,000,000 gallons of excellent water. Hitherto the 
daily supply of water to Paris per head, as a mean, has been but 24 gallons; 
with the addition of the Vanne water, this will be raised to about 34 gallons. 
Sewage.—The great development of the industries of the town of Rheims, 
and its consequent increase of population, having led to the necessity of pro- 
viding facilities for the disposal of the sewage, a commission was appointed to 
investigate the subject, and it was decided, in 1870, to establish on a large 
scale a system of chemical purification, and a dire@ application of the sewage 
to agricultural purposes. Two processes have been tried—purification direc 
by chemical means, and irrigation. The Suvern agent, composed of chloride 
of magnesia, of lime, and of tar, was tried without effect, and the application 
of sulphate of alumina was equally unsuccessful. The latter process did, 
however, produce a certain effe@, but an imperfect one, and that at an enormous 
cost. The most successful trial was that made with a mixture proposed by 
