the dam come to her young, so as to administer a teat to each? Perhaps she opens different places for that purpose, adjusting them again when the business is over; but she could not possibly be contained herself in the ball with her young, which, moreover, would be daily increasing in bulk. This wonderful procreant cradle, an elegant instance of the efforts of instinct, was found in a wheat-field, suspended in the head of a thistle. In winter, the little animal burrows deep into the ground, and makes a warm bed of grass.
TOWN TRANSIT—THE AIR LINE.
We have had propositions of various kinds to facilitate passenger traffic in our streets—railways on the street-level—railways below the streets—and railways over the house-tops. We have, moreover, the electric telegraph, supposed to dispense with both letters and persons in the way of communicating intelligence. But, strange to say, even the telegraph people themselves, in the dispatch of their own business, found that their public scheme of word-transit would not answer their private purpose. So they revived on a small scale the proposition of the engineer Vallance, for a tube to carry passengers between London and Brighton by means of air pressure, but substituting the natural pressure of air behind by an exhaust in front, instead of direct pressure by mechanism behind. “Better lead than drive,” is an old proverb, and the air and the donkey are alike in this respect, for the air sets up a great resistance to being forced through a tube, but is very amenable to suction.
Coleridge, in the “Ancient Mariner,” asks,
Why drives on that ship so fast,
Without or wave or wind?
And the answer given is
The air is cut away before,
And closes from behind.
With all due submission to the poet, there was no marvel in this case; it was wind—and nothing but wind—caused by the air rushing to supply the vacuum.
The electric people laid down, from one office to another, a lead pipe some two inches in diameter, with an air-pump attached at the delivery end. The pipe passed downwards under the street, up again, and the open end curled over the office desk. A short cartridge-looking case with an opening at the side, to contain a roll of paper, being put into the pipe, and the pump set to work to exhaust in front of it, created sufficient vacuum to cause a rush of air and wind behind, and propel the cartridge like a bullet through a gun-barrel till it fell out on the desk where it was wanted.
To do this on a larger scale simply needed a larger pump or exhaust. But people did not contemplate a tube large enough for passengers, and so Mr. Clegg devised a method of driving a piston in a long pipe with a side slit to connect the piston with a train of carriages, closing it with a leathern valve and a coating of waxen salve. This was put in practice on a steep curving line of railway called the Dalkey, about a mile in length, joining the Dublin and Kingstown. A single carriage worked in this way brought passengers on to the line and took them to the top of a breezy hill by this kind of air-rope, which did not pay by itself, but served as an attraction to make the main line pay. The late Mr. Brunel was encouraged by this to make the South Devon line full of steeps and curves, and applied the system, but it failed at a great loss to the shareholders. It was again tried on the Croydon line, and again failed. The leakage at the long side-valve was fatal. Had the poet stood by the side of it, he would have found that the cutting the air away before did indeed cause a “rush,” not merely behind, but sideways. It would have pulled in a truss of straw, had there been room, or a dog’s leg, or a small child, or any moveable lying at hand, not too large or too heavy. It would have carried off every note in the Bank of England—both “stiff” and “flimsy”—and tried hard at the “blunt.” But the pumps had to work so hard to keep down the leak that it would not pay, and so, one fine morning, the manager caused the whole of the pipes to be pulled up and the pumps to be pulled down, and there was an end of it.
It has been revived again by Mr. Rammell, under the name of the Pneumatic Dispatch. He has got together a company with men in it who have known something of business—the Marquis of Chandos and Captain Huish, so long on the North-Western Line, and a sample has been laid down at Battersea. But in this case the vehicles are put inside the tube, which is thirty inches in diameter, and so form the piston.
The tubes are of cast iron, and are laid with ascents and descents of one in twenty-two and one in twenty-five, and with very sharp curves. The exhaust is produced by a fan of large diameter. When nearly at the end the carriages are turned by the rails into a separate tube with atmospheric air in it, which is compressed by the momentum, and forms a buffer. Just at the time the carriages stop, they touch a trigger, which throws open the door at the end of the tube, and then the carriages run out into the open air.
Without at present entering into the cost of power, there is no doubt that the plan is effective, and effective under very unfavourable circumstances of trial, the friction being far greater than is needed, and the fit of the vehicle in the tube being far from so accurate as it might be. Moreover the test in a small tube is much more severe than in a large one.
The pressure obtained was about 40 lbs. to the square foot, and the area is about five square feet; the speed was about fifteen miles per hour.
With this arrangement transit over the house tops becomes practicable. A tube of wrought iron plate to carry a carriage eight feet square, or sixty-four square feet of section, might be constructed, weighing about 12 cwt. per yard, run, at a cost of about 12,000l. per mile, and this tube might be glazed with small pieces of plate glass, so as to give ample light. A carriage carrying 50 passengers would weigh about 3 cwt. per foot run, or a total of 4½ tons. Thus 200