The switchboards themselves are made of hard, black rubber, and are honeycombed with innumerable holes, each of which is connected with a subscriber. Below the switchboard is a broad shelf in which are set the miniature lamps and from which project the bra.s.s plugs in rows. The flexible cords containing the connecting wires are weighted and hang below, so that when a plug is pulled out of a socket and dropped it slides back automatically to its proper place, ready for use.

Many subscribers nowadays have their own private exchanges and several lines running to central. Perhaps No. 4341 Eighteenth Street, for instance, has 4342 and 4344 as well. This is indicated on the switchboard by a line of red or white drawn under the three switch-holes, so that central, finding one line busy, may be able to make connection with one of the other two, the line underneath showing at a glance which numbers belong to that particular subscriber.

If a subscriber is away temporarily, a plug of one colour is inserted in his socket, or if he is behind in his payments to the company a plug of another colour is put in, and if the service to his house is discontinued still another plug notifies the operator of the fact, and it remains there until that number is a.s.signed to a new subscriber.

The operators sit before the switchboard in high swivel chairs in a long row, with their backs to the centre of the room.

From the rear it looks as if they were weaving some intricate fabric that unravels as fast as it is woven. Their hands move almost faster than the eye can follow, and the patterns made by the criss-crossed cords of the connecting plugs are constantly changing, varying from minute to minute as the colours in a kaleido-scope form new designs with every turn of the handle.

Into the exchange pour all the throbbing messages of a great city.

Business propositions, political deals, scientific talks, and words of comfort to the troubled, cross and recross each other over the black switchboard. The wonder is that each message reaches the ear it was meant for, and that all complications, no matter how knotty, are immediately unravelled.

In the cities the telephone is a necessity. Business engagements are made and contracts consummated; brokers keep in touch with their a.s.sociates on the floors of the exchanges; the patrolmen of the police force keep their chief informed of their movements and the state of the districts under their care; alarms of fire are telephoned to the fire-engine houses, and calls for ambulances bring the swift wagons on their errands of mercy; even wreckers telephone to their divers on the bottom of the bay, and undulating electrical messages travel to the tops of towering sky-sc.r.a.pers.

[Ill.u.s.tration: A FEW TELEPHONE TRUNK WIRES This shows a small section of a complicated telephone switchboard.]

In Europe it is possible to hear the latest opera by paying a small fee and putting a receiver to your ear, and so also may lazy people and invalids hear the latest news without getting out of bed.

The farmers of the West and in eastern States, too, have learned to use the barbed wire that fences off their fields as a means of communicating with one another and with distant parts of their own property.

Mr. Pupin has invented an apparatus by which he hopes to greatly extend the distance over which men may talk, and it has even been suggested that Uncle Sam and John Bull may in the future swap stories over a transatlantic telephone line.

The marvels accomplished suggest the possible marvels to come.

Automatic exchanges, whereby the central telephone operator is done away with, is one of the things that inventors are now at work on.

The one thing that prevents an unlimited use of the telephone is the expensive wires and the still more expensive work of putting them underground or stringing them overhead. So the capping of the climax of the wonders of the telephone would be wireless telephony, each instrument being so attuned that the undulations would respond only to the corresponding instrument. This is one of the problems that inventors are even now working upon, and it may be that wireless telephones will be in actual operation not many years after this appears in print.

A MACHINE THAT THINKS

A Typesetting Machine That Makes Mathematical Calculations

For many years it was thought impossible to find a short cut from author's ma.n.u.script to printing press--that is, to subst.i.tute a machine for the skilled hands that set the type from which a book or magazine is printed. Inventors have worked at this problem, and a number have solved it in various ways. To one who has seen the slow work of hand typesetting as the compositor builds up a long column of metal piece by piece, letter by letter, picking up each character from its allotted s.p.a.ce in the case and placing it in its proper order and position, and then realises that much of the printed matter he sees is so produced, the wonder is how the enormous amount of it is ever accomplished.

In a page of this size there are more than a thousand separate pieces of type, which, if set by hand, would have to be taken one by one and placed in the compositor's "stick"; then when the line is nearly set it would have to be s.p.a.ced out, or "justified," to fill out the line exactly. Then when the compositor's "stick" is full, or two and a half inches have been set, the type has to be taken out and placed in a long channel, or "galley." Each of these three operations requires considerable time and close application, and with each change there is the possibility of error. It is a long, expensive process.

A perfect typesetting machine should take the place of the hand compositor, setting the type letter by letter automatically in proper order at a maximum speed and with a minimum chance of error.

These three steps of hand composition, slow, expensive, open to many chances of mistake, have been covered at one stride at five times the speed, at one-third the cost, and much more accurately by a machine invented by Mr. Tolbert Lanston.

The operator of the Lanston machine sits at a keyboard, much like a typewriter in appearance, containing every character in common use (225 in all), and at a speed limited only by his dexterity he plays on the keys exactly as a typewriter works his machine. This is the sum total of human effort expended. The machine does all the rest of the work; makes the calculations and delivers the product in clean, shining new type, each piece perfect, each in its place, each line of exactly the right length, and each s.p.a.ce between the words mathematically equal--absolutely "justified." It is practically hand composition with the human possibility of error, of weariness, of inattention, of ignorance, eliminated, and all accomplished with a celerity that is astonishing.

[Ill.u.s.tration: THE LANSTON TYPE-SETTER KEYBOARD As each key is pressed a corresponding perforation is made in the roll of paper shown at the top of the machine. Each perforation stands for a character or a s.p.a.ce.]

This machine is a type-casting machine as well as a typesetter. It casts the type (individual characters) it sets, perfect in face and body, capable of being used in hand composition or put to press directly from the machine and printed from.

As each piece of type is separate, alterations are easily made. The type for correction, which the machine itself casts for the purpose--a lot of a's, b's, etc.--is simply subst.i.tuted for the words misspelled or incorrectly used, as in hand composition.

The Lanston machine is composed of two parts, the keyboard and the casting-setting machine. The keyboard part may be placed wherever convenient, away from noise or anything that is likely to distract or interrupt the operator, and the perforated roll of paper produced by it (which governs the setting machine) may be taken away as fast as it is finished. In the setting-casting machine is located the brains. The five-inch roll of paper, perforated by the keyboard machine (a hole for every letter), gives the signal by means of compressed air to the mechanism that puts the matrix (or type mould) in position and casts the type letter by letter, each character following the proper sequence as marked by the perforations of the paper ribbon. By means of an indicator scale on the keyboard the operator can tell how many s.p.a.ces there are between the words of the line and the remaining s.p.a.ce to be filled out to make the line the proper width. This information is marked by perforations on the paper ribbon by the pressure of two keys, and when the ribbon is transferred to the casting machine these s.p.a.ce perforations so govern the casting that the line of type delivered at the "galley" complete shall be of exactly the proper length, and the s.p.a.ces between the words be equal to the infinitesimal fraction of an inch.

The casting machine is an ingenious mechanism of many complicated parts.

In a word, the melted metal (a composition of zinc and lead) is forced into a mold of the letter to be cast. Two hundred and twenty-five of these moulds are collected in a steel frame about three inches square, and cool water is kept circulating about them, so that almost immediately after the molten metal is injected into the lines and dots of the letter cut in the mould it hardens and drops into its slot, a perfect piece of type.

All this is accomplished at a rate of four or five thousand "ems" per hour of the size of type used on this page. The letter M is the unit of measurement when the amount of any piece of composition is to be estimated, and is written "em."

If this page were set by hand (taking a compositor of more than average speed as a basis for figuring), at least one hour of steady work would be required, but this page set by the Lanston machine (the operator being of the same grade as the hand compositor) would require hardly more than fifteen minutes from the time the ma.n.u.script was put into the operator's hands to the delivery complete of the newly cast type in galleys ready to be made up into pages, if the process were carried on continuously.

This marvellous machine is capable of setting almost any size of type, from the minute "agate" to and including "pica," a letter more than one-eighth of an inch high, and a line of almost any desired width, the change from one size to any other requiring but a few minutes. The Lanston machine sets up tables of figures, poetry, and all those difficult pieces of composition that so try the patience of the hand compositor.

It is called the monotype because it casts and sets up the type piece by piece.

Another machine, invented by Mergenthaler, practically sets up the moulds, by a sort of typewriter arrangement, for a line at a time, and then a casting is taken of a whole line at once. This machine is used much in newspaper offices, where the cleverness of the compositor has to be depended upon and there is little or no time for corrections. Several other machines set the regular type that is made in type foundries, the type being placed in long channels, all of the same sort, in the same grooves, and slipped or set in its proper place by the machine operated by a man at the keyboard. These machines require a separate mechanism that distributes each type in its proper place after use, or else a separate compositor must be employed to do this by hand. The machines that set foundry type, moreover, require a great stock of it, just as many hundred pounds of expensive type are needed for hand composition.

[Ill.u.s.tration: WHERE THE "BRAINS" ARE LOCATED The perforations in the paper ribbon (shown in the upper left-hand part of the picture) govern the action of the machine so that the proper characters are cast in the proper order, and also the s.p.a.ces between the words.]

Though a machine has been invented that will put an author's words into type, no mechanism has yet been invented that will do away with type altogether. It is one of the problems still to be solved.

HOW HEAT PRODUCES COLD

ARTIFICIAL ICE-MAKING

One midsummers day a fleet of United States war-ships were lying at anchor in Guantanamo Bay, on the southern coast of Cuba. The sky was cloudless, and the tropic sun shone so fiercely on the decks that the bare-footed Jackies had to cross the unshaded spots on the jump to save their feet.

An hour before the quavering mess-call sounded for the midday meal, when the sun was shining almost perpendicularly, a boat's crew from one of the cruisers were sent over to the supply-ship for a load of beef. Not a breath was stirring, the smooth surface of the bay reflected the brazen sun like a mirror, and it seemed to the oarsmen that the salt water would scald them if they should touch it. Only a few hundred yards separated the two vessels, yet the heat seemed almost beyond endurance, and the shade cast by the tall steel sides of the supply-steamer, when the boat reached it, was as comforting as a cool drink to a thirsty man. The oars were shipped, and one man was left to fend off the boat while the others clambered up the swaying rope-ladder, crossed the scorching decks on the run, and went below. In two minutes they were in the hold of the refrigerator-ship, gathering the frost from the frigid cooling-pipes and s...o...b..lling each other, while the boat-keeper outside of the three-eighth-inch steel plating was fanning himself with his hat, almost dizzy from the quivering heat-waves that danced before his eyes.

The great sides of beef, hung in rows, were frozen as hard as rock. Even after the strip of water had been crossed on the return journey and the meat exposed to the full, un.o.bstructed glare of the sun the cruiser's messcooks had to saw off their portions, and the remainder continued hard as long as it lasted. But the satisfaction of the men who ate that fresh American beef cannot be told.

Cream from a famous dairy is sent to particular patrons in Paris, France, and it is known that in one instance, at least, a bottle of cream, having failed to reach the person to whom it was consigned, made the return transatlantic voyage and was received in New York three weeks after its first departure, perfectly sweet and good. Throughout the entire journey it was kept at freezing temperature by artificial means. These are but two striking examples of wonders that are performed every day.

[Ill.u.s.tration: THE TYPE MOULDS Moulds for 225 different characters are contained in this frame.]

Cold, of course, is but the absence of heat, and so refrigerating machinery is designed to extract the heat from whatever substance it is desired to cool. The refrigerating agent used to extract the heat from the cold chamber must in turn have the heat extracted from it, and so the process must be continuous.

Water, when it boils and turns into steam or vapour, is heated by or extracts heat from the fire, but water vapourises at a high temperature and so cannot be used to produce cold. Other fluids are much more volatile and evaporate much more easily. Alcohol when spilt on the hand dries almost instantly and leaves a feeling of cold--the warmth of the hand boils the alcohol and turns it into vapour, and in doing so extracts the heat from the skin, making it cold; now, if the evaporated alcohol could be caught and compressed into its liquid form again you would have a refrigerating machine.

Alcohol is expensive and inflammable, and many other volatile substances have been discarded for the one or the other reason. Of all the fluids that have been tried, ammonia has been found to work most satisfactorily; it evaporates at a low temperature, is non-inflammable, and is comparatively cheap.

The hold of the supply-ship mentioned at the head of this chapter was a vast refrigerator, but no ice was used except that produced mechanically by the power in the ship. To produce the cold in the hold of the ship it was necessary to extract the heat in it; to accomplish this, coils ran round the s.p.a.ce filled with cold brine, which, as it grew warm, drew the heat from the air. The brine in turn circulated through a tank containing pipes filled with ammonia vapour which extracted the heat from it; the brine then was ready to circulate through the coils in the hold again and extract more heat. The heat-extracting or cooling power of the ammonia is exerted continually by the process described below.

Ammonia requires heat to expand and turn into vapour, and this heat it extracts from the substance surrounding it. In this marine refrigerating machine the ammonia got the heat from the brine in the tank, then it was drawn by a pump from the pipes in the tank, compressed by a power compressor, and forced into a second coil. The second coil is called a condenser because the vapour was there condensed into a fluid again.

Over the pipes of the condenser cool water dripped constantly and carried off the heat in the ammonia vapour inside the coils and so condensed it into a fluid again--just as cold condenses steam into water. The compressor-pump then forced the fluid, ammonia through a small pipe from the condenser coils to the cooling coils in the tank of brine. The pipes of the cooling coils are much larger than those of the condenser, and as the fluid ammonia is forced in a fine spray into these large pipes and the pressure is relieved it expands or boils into the larger volume of vapour and in so doing extracts heat from the brine.

The pump draws the heated vapour out, the compressor makes it dense, and the coils over which the cool water flows condenses it into fluid again, and so the circuit continues--through cooler, pump, compressor, and condenser, back into the cooling-tank.

In the meantime, the cold brine is being pumped through the pipes in the hold of the ship, where it extracts the heat from the air and the rows of sides of beef and then returns to the cooling-tank. In the refrigerating plant, then, of the supply-ship, there were two heat-extracting circuits, one of ammonia and the other of brine. Brine is used because it freezes at a very low temperature and continues to flow when unsalted water would be frozen solid. The ammonia is not used direct in the pipes in a big s.p.a.ce like the hold of a ship, because so much of it would be required, and then there is always danger of the exposed pipes being broken and the dangerous fumes released.