The chemical causes the clay to coagulate and settle to the bottom of the reservoir while waiting its turn to pass into the city-bound watermains.

WHERE THE WATER IS "GASSED"

At the outlet of the Kensico Reservoir there is a chlorination plant. Here the Water Department practices the German art of "gassing" on the germ tribe. A very small quantity of this gas will kill many millions of germs. Nowhere else in the world, except on. the battlefront, is "gassing" practiced as much as in the battle against the disease germ armies that seek to invade New York via its water supply.

After leaving Kensico Reservoir, the Catskill Aqueduct flows another 17 miles to Hill View Reservoir, used for equalizing day and night consumption of water. This brings the water to the metropolis, where the great 18-mile tunnel through solid rock under the city begins. This tunnel is the longest of its size in the world.

Starting at Hill View Reservoir it is 15 feet in diameter through Harlem and under Harlem River to 135th street. It is within three inches of being as large in diameter as the Hudson Terminal tunnels under North River. It crosses the Harlem between High Bridge and the Polo Grounds and extends through Central Park and Madison Square to a point between Williamsburg and Manhattan bridges, where it dives under East River. On the Manhattan bank of the river there is a shaft in which the Woolworth Building could be buried, so far as depth is concerned.

HEEDLESS OF HUMAN MOLES BLASTING

THEIR WAY BENEATH THE CITY

After passing under the river the tunnel rises to the surface in Flatbush, where it connects with the 5-foot-6-inch Brooklyn main. Hence its water runs on to the Narrows, where a three-foot ball-andsocket pipe-line, with joints calked with 300 pounds of lead, was laid in a trench cut in the floor of the inlet. This line carries the water to Staten Island and into Silver Lake Reservoir, 119 miles from the intake at Ashokan.

Here we find how much an uncon

sidered thing in every-day experience may count in a big project. Take a U-tube and put water into it. The water rises to the same level in both sides. But, although Ashokan and Silver Lake are the two terminals of the figurative Catskill Utube, their waters by no means reach the same level. The surface of Silver Lake is 362 feet lower than that of Ashokan Reservoir, because of the friction in the big waterway. When it is remembered that a column of water 362 feet high exerts a pressure of more than a thousand tons per square foot, one can appreciate the amount of friction the water encounters in its journey to the city.

Although, on an average, five tons of dynamite were exploded daily during the long period in which the city tunnel was being built, New York might never have known that rock-defying human moles were boring their way through the big town, from the Yonkers line to Flatbush, except for the shafts sunk from the surface at convenient spots.

URBAN TRANSPORTATION

As a completed project, the Catskill Aqueduct stands as one of the wonders of the engineering world. With a length of 119 miles, with a capacity that exceeds the combined flow of all the aqueducts that imperial Rome ever built, with 35 miles of tunnel sunk deep in the primeval rock, the great subterranean stream that brings the life-giving, health-protecting, industry-quickening waters of the mountains to the people at the gateway to the seas represents the indomitable spirit of a municipality that is as virile as it is big, ready to shoulder any burden its unceasing growth imposes upon it.

In no other phase of its complex life has New York felt so acutely the problems that its size and peculiar geographic situation involve as in the matter of urban transportation. With its own population supplemented by the army of commuters living in Jersey, on Long Island, and up the Hudson, twice as many people are transported in a single day within the confines of Greater Gotham as are moved by all the steam railroads of the United States.

Go to Grand Central Station during the rush hours of the morning and after

noon, and you are easily convinced that beyond the Bronx live a million people whose bread-winners work below Harlem River. Go to the Pennsylvania Station at the same time, and you see the wage-earners of tens of thousands of Long Island and Jersey homes coming or going. And at the Hudson Terminal one is ready to conclude that half of Jersey's homes have wage-earners and salaried folk who work in Manhattan and live in Rahway, Orange, Montclair, or somewhere down Jersey way.

A new skyscraper lifts its head toward the blue and straightway 15,000 people find working quarters. Let us load these workers on subway trains and see what it means. A ten-car subway train can carry a thousand people to or from work. It takes fifteen such trains to handle the new skyscraper's tenants. And it takes twenty-six minutes to put fifteen such trains through the necks of the traffic bottle-as at 42d street.

In no other city in the world do as many people live out of walking distance. to their work as in New York. Manhattan Island is 13 miles long and only a mile or so wide, and downtown Manhattan is the habitat of the skyscraper and not of the home, except on the East Side. The result is an unbelievable amount of travel. Subway, elevated, and surface cars carry two billion people a year. Every day 30 tons of nickels flow into the coffers of the rapid transit and surface lines. Every year 200 car loads of "jitneys" are harvested from the ridebuying public.

THE NEW YORKER A GREAT RIDER

If New York had only to meet its annual increase in population, that in itself would be a sizable task; for taking care every year of the comings and goings of a new population equal to that of Wvoming were no mean undertaking. But that is only the beginning of the big city's transportation troubles. The people ride more frequently with every extension of facilities.

When New York had only its surface lines to depend on, Mr. Average New Yorker took 147 rides a year. Then came the elevated and he began taking 215 rides a year. When the first subway

went into commission, he jumped the annual number of his rides to 298. Now he is using the cars more than ever-is this Mr. Average New Yorker-with some 348 rides a year to his credit. How many rides he will take when all the new subways and elevated lines are completed can only be surmised, but the extensions under way will enable the overhead and underground systems to handle three billion passengers annually without aid from the surface lines.

Crowding her debt limit to the utmost to meet other conditions imposed by her extraordinary growth, New York was financially "up against it" when traffic demands called loudly for new facilities. She was not willing to have new subways built and owned by private enterprise to compete with those already in operation and owned by her, though leased to an operating company; and yet she was not able to finance the extensions without outside help. Meantime, subways that were built to handle 400,000 people a day were approaching the time when they would be called upon to move 1,200,000 every twenty-four hours.

FURTHER EXTENSION OF SUBWAY AND ELEVATED LINES

So the city made a deal with the two rapid-transit companies to "go fifty-fifty" with them in building all subway extensions and to allow the companies to extend the elevated lines.

The result is that instead of one line up Manhattan, on the East Side to 42d street and on the West Side above that street, there will be, when the present project is completed, a line all the way up the East Side and another up the West Side, with branches into the boroughs of Queens, Bronx, and Brooklyn.

And yet, with all the effort that has been made to anticipate the city's traffic needs, every New Yorker feels that there are other needs ahead. Already there is agitation for a through line from downtown to uptown that will make even "rapid transit" a slow phrase. It is believed that the time is not more than a decade distant when it will be imperative to establish an entirely new sort of service-a "high-speed service." This may be given by a line built under one of the

avenues east of Fifth from Bronx to Battery, upon which trains will run which will make only three or four stops between the Harlem River and the financial district.

THE BRIDGES OF MANHATTAN

The "river ring" around Manhattan Island has long forced expansion along abnormal lines, resulting in a shoe-string borough instead of a compact one. The center of the business district is at one end of the borough and not in its heart. But, at last, the city is going to grow like other cities, rivers or no rivers. The Harlem presented no serious obstruction to the plan. Narrow and in a deep valley, it was readily bridged. But East River and North River were different propositions.

It costs millions upon millions to build a big bridge like the Brooklyn, the Williamsburg, the Queensboro, or the Manhattan, but one by one, in the order named, these great structures, towering high enough above the river to avoid interference with navigation, have been thrown across, in order to permit the metropolis to occupy its natural territory on the west end of Long Island.

These bridges have cost the city nearly one hundred million dollars. They have an aggregate length of nearly six miles and are crossed by eight hundred thousand people every day. They could carry that many persons every hour if they were used by the maximum number of elevated, subway, and surface cars which they can accommodate and if each car were loaded to capacity.

SIXTEEN TUBES UNDER THE RIVER TO

RELIEVE THE BRIDGES

Although Manhattan Bridge is the world's greatest suspension bridge, and although its neighbor bridges in conjunction with it constitute the greatest aggregation of water-spanning structures in existence, they are wholly unequal to the task of caring for the tide of humanity that ebbs and flows during rush hours between Manhattan and Long Island.

Eight tunnel tubes have been built to share the burden; but in spite of these reinforcements the bridges still carry an increasing number of passengers every year. Eight other tubes are now eating

their way through the silt of the river's bottom, and when they are in commission there probably will arise a necessity for as many more.

Bridged over and tunneled under, East River has heard the verdict of the indomitable metropolis, that it can no longer force the city to grow in shoe-string shape.

Not less serious than the blockade imposed by East River against the eastward expansion of the city is the lack of north and south streets in Manhattan. With the spread of the motor-car, the city finds. the comparatively few-and-far-between avenues that run north and south inadequate. The men who laid out the city made the east and west thoroughfares close together and those north and south far apart, producing oblong blocks instead of squares. Yet so long have the north and south thoroughfares become that a vast amount of travel must be concentrated in a few avenues.

THE AVENUE PROBLEM

Many suggestions have been made for overcoming this congestion. One was to raze a way through Manhattan, driving a new avenue into the great breach. Another was to double-deck one of the avenues, using the second level for light vehicular traffic. Still another proposal is a subway for heavy trucks. It is the hope of the city that the bridge and tunnel conquest of East River will make the day a little more remote when the solution of the problem of providing new facilities. for north and south vehicular traffic will become imperative.

The problem of getting across North River is almost as acute as has been that of overcoming the obstacles interposed by East River. Prior to the recent order of the Railway Administration, only one of the many trunk lines that approach New York from the West and South entered the city. All the others discharged their passengers in Jersey-sidestations, where water and rail meet.

Up to the time that the present Secretary of the Treasury and Railway Administrator, William G. McAdoo, showed. how to cut the Gordian knot of an unbridgeable river by going under it instead of over it, the ferry boat was the