decreases the quantity of crustacea and sand-eels must exercise great influence on herring-shoals; but these are even more acted upon by their great destroyers. The latter may be ranged under the heads of fish, birds, marine animals, and man. Of these, by far the greatest destroyers are fish and marine animals, as porpoises and other cetacea. It is estimated that the total annual take of herrings by British fishermen is 900,000,000; a prodigious number; but great as this is, it sinks into comparative insignificance when compared with the destruction effected by other agencies. Cod alone destroy ten times as great a number as are captured by all our fishermen. It is a very common thing to find a cod-fish with six or seven large herrings in his stomach. When it is further considered that the conger and dog-fish do as much mischief as the cod and ling, that the gulls and gannets slay their millions, and that porpoises and grampuses destroy additional countless multitudes, it will be evident that fishing operations, extensive as they are, do not destroy five per cent. of the total number of full herrings that are destroyed every year by other causes. These facts, which cannot be controverted, prepare us for the conclusions arrived at by the commissioners with reference to the legislative enactments relating to the herring fishery.

They recommend that all prohibitory or restrictive laws bearing on the herring fishery be repealed, and that the fishermen be allowed to follow their business in any manner they may think proper. In conclusion they add: "If legislation could regulate the appetites of cod, conger, and porpoise, it might be useful to pass laws regarding them; but to prevent fishermen catching one or two per cent. of herring in any way they please, seems, in the opinion of the Commissioners, a wasteful employment of the force of law."

We present to the readers of the Annual of Scientific Discovery for 1864, the portrait of Major-General Q. A. GILLMORE, U. S. A., best known in science for his investigations and researches respecting "limes, mortars, and cements," and for the brilliant military engineering displayed by him in the reduction of Forts Pulaski, Sumter, and Wagner.

THE

ANNUAL OF SCIENTIFIC DISCOVERY.

MECHANICS AND USEFUL ARTS.

THE SEWERS OF PARIS.

THE present system of sewerage in Paris, decreed by the Emperor Napoleon III. in 1852, consists of six main galleries, called collectors, fifteen secondary ones opening into the former, and themselves fed by a vast number of smaller ones intersecting the city in every direction. Three of the collectors are located upon the right bank of the Seine, and three upon the left bank. The united length of the former is 8.600 metres; of the latter, 9.200 metres.

The ratio of the section to be given to the various sewers has been fixed, as experience required, at from two to three square metres of wet surface for every 100 hectares. On this principle, twelve different sizes have been chosen, the smallest having a section of 2.15 metres in height by 1.15 in breadth, and the largest one of 4.40 metres in height by 5.60 in breadth. The former is of an ovoid shape, and offers ample space for a man and a wheelbarrow. The largest sewer or collector has a circular segment for its section; its breadth is divided into three parts, the two lateral ones being foot pavements, and the middle one a gutter or drain 1.20 metres broad. On each foot pavement, a series of iron forks support a water pipe, varying in diameter from 1.10 metres to 0.80. In some of the galleries there is but one water-pipe. To cleanse the drain a small cart, running on iron rails laid along the bottom, is pushed forward by two men; the front of this cart is provided with a drop-plank, acting like a sort of sluice, which, when down, exactly closes the section of the gutter, and pushes all the mud before it as the cart advances. By the sewers above described, all the foul waters of the right bank are easily brought to the Place de la Concorde, where a general collector receives them and carries them off to Asnieres. But what was to be done with the sewerage of the left bank, which, according to the system adopted, was also to be poured into the

general collector. After much reflection, it was decided that the waters of the left bank should be carried over by a siphon passing under the bed of the Seine; and this singular engineering feat has actually been accomplished. An enormous pipe of wrought iron having an interior diameter of one metre, and about 200 metres in length, is sunk, a little above the Pont de la Concorde, two metres below the low-water mark, and thus the desired communication is established. As to the general collector, it is the most stupendous work of the kind in existence. It is 5 metres in height by 5.61 in breadth, with a length of about five kilometres and a half, in nearly a right line, except a turn under the Place de la Madeleine. The foot pavements are 1.90 metres on each side, the central drain is 3.60 metres in breadth, with a depth of 1.35; so large, in fact, that a well sized boat is kept afloat on it for the purpose of cleansing. This boat is also provided with a drop-plank in front; this is let down to a distance of 15 centimetres from the bottom, while the boat advances, whereby such a head of water is obtained in front as to drive all the sedimentary matter-nay, even stones-to a distance of 100 metres. There the boat finds it again as it advances, and drives it further and further, till the orifice of the emissary is reached. Four boats perform this work, and it takes sixteen days to cleanse the whole length. Ventilation is provided for by air-traps at certain distances, and the gallery is lighted with oil lamps. The execution of this immense system of sewers has cost fifty millions of francs. M. Dezobry, comparing this gallery with the far famed Cloaca Maxima of Rome, shows that it is infinitely superior to it in size, not to mention the improvements in construction, of which the Romans had no idea. The Cloaca Maxima is two metres in height, and only 4.48 broad, and is supposed never to have exceeded a length of 900 metres. The dimensions we have given abundantly show how vastly superior the modern French construction is to the ancient Roman one.

THE NEW SEWERS OF LONDON.

It is well known to our readers (See Annual Sci. Dis., 1859-60) that for the last few years, there has been in the course of construction in London, a system of sewage, of such magnitude as to form one of the marvels of modern engineering, and of such cost, as but few cities could afford to pay for. The object of the scheme is to do away with the present plan, whereby all the enormous drainage of London is discharged into the Thames;- a plan which has latterly converted the river itself into one vast sewer, to the great annoyance and sanitary detriment of the vast population contiguous to its waters. "At the very first glance," says the London Times:-"This arrangement seems bad enough, though it is infinitely worse when we come to examine how it was arranged to work. On both sides of the river the banks are very little above high-water mark, while the average level of the ground immediately behind them is much below it; half Lambeth and Rotherhithe being six feet below high-water level. Of course, when this is the level of the ground, the sewers are much lower still, and their outlets so completely tide-locked that it is only at dead low-water that they can empty themselves at all. Thus, for nearly eighteen hours out of the twenty-four, the sewage on both sides of London is to an immense extent, pent up, giving off its miasma into every street and house. As

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we have said, it could only escape at dead low water, when the returning tide immediately churned it up the river, keeping all its abominable 'flotsam and jetsam' above bridge till the tide ebbed out, finding 200,000 or 300,000 gallons of filth to be operated upon in a similar manner on its return. This was the arrangement twelve years ago, and is almost entirely so still; but, even bad as this was, it was capable of being made worse, and worse accordingly it was made. In 1849, most of the houses in London had cesspools attached to them, and a very large proportion were without any drains at all. The alarming nature of this evil showed itself slowly but surely in the Bills of Mortality, and the then Commissioners of Sewers, who were feebly battling with the evils of the drainage system, set to work to mitigate the cesspool danger by drainage, making the Thames, as usual, the general receptacle. From that time to the present some 700 or 800 miles of new drains have been made, and all cesspools made to drain at once into the river. By this 'improved' drainage some 200,000 additional gallons of sewage were daily added to the Thames at low water, containing no less than 300 tons of organic matter,' which in this case is the scientific term of filth. The result, as a matter of course, has been that in the summer months the stench from the river has occasionally been intolerable. In 1857, great quantities of lime and chloride of lime were put in daily; in 1858, the same expedient had to be resorted to again; and in 1859, the dose had to be increased into 110 tons of lime and 12 tons of chloride of lime, costing 1,500l. per week. Even in a pecuniary point of view, however, this was not the only evil of the system. The Thames in hot weather runs short of water; and when there is no rain, the collections of refuse in the sewers have to be flushed into the river by artificial means. This flushing alone during summer costs 20.000l. a year to get the poison into the Thames, where 20.000l. more is generally required to keep it from breeding a plague." To obviate these difficulties, an immense new sewage system was devised, and for the last few years has been in the course of construction, whereby London will be effectually drained, and the Thames purified. As may easily be imagined, it is impossible, in an article like the present, to give more than an outline of this great plan, which may best be briefly described as consisting of three gigantic main tunnels or sewers on each side of the river. These completely divide underground London, from west to east, and cutting all existing sewers at right angles intercept their flow to the Thames, and carry every gallon of London sewage under certain conditions into the river at a point far below the city limits and not far distant from the sea. "These main drains are called the High, Middle, and Low Level sewers, according to the height of the localities which each respectively drains. The High Level, on the north side, is about eight miles in length, and runs from Hampstead to Bow, being at its rise only four feet six inches in diameter, and thence increasing in circumference, as the waters of the sewers it intercepts require a wider course, to five feet, six feet, seven feet, ten feet six inches, eleven feet six inches, and at its termination to twelve feet six inches in diameter. drain is now entirely finished, and in full work. Its minimum fall is twelve feet in the mile; its maximum at the beginning nearly fifty feet a mile. It is laid at a depth of from twenty to twenty-six feet be

This

low the ground, and drains an area of fourteen square miles. The Middle Level, as being lower in the valley on the slope of which London is built, is laid at a greater depth, varying from thirty to thirty-six feet, and even more below the surface. This is nearly complete, and extends from Kensal Green to Bow. The Low Level will extend from Cremorne to Abby Mills, on the marshes, near Stratford. At Bow, the Low Level waters will be raised, by powerful engines, at a pumping station, to the junction of the High and Middle Level ducts, thence descending by their own gravity through three tunnels to the main reservoir and final outfall. These three tunnels are each nine feet six inches in diameter, and nearly four miles long. Great engineering difficulties existed in the construction of these main arteries, as, from the height at which they all meet, it was necessary to take them above the level of the marshes leading to Barking. For a mile and a half the embankment which encloses the three tunnels is carried on brick arches, the piers going eighteen feet below the surface, and being based on solid concrete. In the marshes at Barking, a reservoir for the reception of the sewage of the north side has been formed. This reservoir is a mile and a half long by one hundred feet wide, and twenty-one feet deep. It is made of this great length in proportion to width to allow of its being roofed with brick arches, which are again covered with earth to a considerable thickness, so that not the slightest smell or escape of miasma can take place. This is capable of containing more than three times the amount of sewage which can enter it while the pipes are shut, and thus, when all is complete, the works will not only be large enough to take off all London's sewage now, but its sewage when London is double its present size.

"While the sewage is in the reservoir we have spoken of, it will be completely deodorized by an admixture of lime. When the tide is at its height the sluices which pass from the bottom of the reservoir far out into the bed of the river will be opened, and the whole allowed to flow away. It takes two hours thus to empty the reservoir, by which time the tide will be flowing down strongly, and will carry its very last gallon a distance of thirteen miles below Barking, which, being itself thirteen miles below London, will place the contents of the sewers, every twelve hours, twenty-six or more miles distant from the metropolis. Thus, instead of letting loose the rankest of this great city's abominations in the very midst of London, and leaving it to stagnate, or, still worse, to be agitated backwards and forwards in a small body of water, it will all be carried away a distance of thirteen miles, then deodorized, then suffered to escape into a body of water more than a hundred times greater than that into which it now crawls, and thus disinfected and diluted, so as to be without either taste or smell, swept still further down the stream, till every trace of it is lost.

"On the south side, the three great sewer arteries are constructed on similar plans, the High Level, from Dulwich to Deptford; the Middle, from Clapham to Deptford; and the Low Level, from Putney to Deptford. At this point is a pumping station, which raises the water from the low to the high level, whence it flows away through a ten feet tunnel to Crossness Point. One part of this tunnel, passing under Woolwich, is a mile and a half in length, without a single break, and driven at a depth of eighty feet from the surface. At the outfall will