really knew very little, though each member thought he knew enough to prepare a pretty fair meal for people who were not particular. So they all tried their hands at getting up that dinner, and a sadder culinary failure was never made. Everything was smoked, burned, underdone, or in some other way made uneatable, and they finally partook of a most unsatisfactory meal of dry crackers and smoked herring, which made them so very thirsty that but for the firmness of their young captain they would have drained the small cask then and there.

The cooking of succeeding meals was equally unsatisfactory, and by nightfall of the second day after the departure of their friends our Rangers had not only expended most of their provisions and drunk up all their water, but were thoroughly alarmed at their situation. The whole of that day had been spent on the highest point of the island, gazing with strained eyes over the surrounding waters in the hope of sighting some approaching sail. With the coming of darkness they sadly returned to camp, and flinging themselves gloomily down on their blankets, sought forgetfulness of their unhappy situation in troubled sleep.

Some hours later Will Rogers was awakened by little Cal Moody, who said, in a terrified whisper: "Oh, Will, there are pirates on the island, and they are swearing dreadfully, and I know we're all going to be murdered. I've been listening and watching them for a long time. See their lights down there?"

Sure enough, Will could see lights, like moving lanterns, down on the beach and out on the water, where they seemed to be passing to and fro between the land and a vessel that was dimly visible in the little harbor. He could also hear loud rough voices, and, as Cal had said, some of them were swearing.

[to be continued.]

THE BUILDING OF MODERN WONDERS.

AN ELECTRIC TROLLEY-CAR.

BY HERBERT LAWS WEBB.

One day, not very long ago, when electric cars were something of a novelty, a city official was talking about them to one of the electrical engineers in charge of a certain electric railway.

"It seems to me," said he, "that those trolley-poles on top of the cars ought to be very much stronger than they are."

"Why so?" asked the electrical man. "We very seldom have any accident with them. They almost never break."

"Don't they!" queried the other, with some astonishment. "Well, they don't look to me half strong enough to push those heavy cars along."

I suppose very few readers of the Round Table have such very foggy ideas about electric cars as that man had. But still it is something of a mystery to many people how the slender wire stretched along the street takes the place of the hundreds of tugging horses or of the rattling, whirring cable that glides ceaselessly through the long iron trough under the pavement.

Many years ago one of those famous scientific men who were always making experiments to discover new things about electricity, so as to enable practical men in these days to invent machines to do useful work, discovered that when he moved a wire about in front of a magnet an electric current appeared in the wire. This was a great discovery, because it brought to light the wonderful sympathy between magnetism and electricity. It made no difference whether the wire or the magnet were moved; as long as they were close enough together any movement of either caused a current to appear in the wire.

Then another famous discoverer found that by winding a wire round a bar of iron and sending a current of electricity through the wire he turned the bar of iron into a magnet. As long as the current was passing through the wire the iron bar acted just like a permanent steel magnet; it would attract pieces of iron and hold up nails, but the moment the current was stopped the bar lost its magnetism, the nails or pieces of iron dropped off, and it became just an ordinary bar of iron again. This invention is called the electro-magnet, and the electro-magnet is used in some form or other in every electrical industry.

The electric dynamo owes its being to those two discoveries. It consists of coils of copper wire wound on a shaft, and that shaft is revolved close to a powerful magnet. The influence of the magnet causes electric currents to be produced in the coils of copper wire, and these currents are delivered by the coils into suitable conductors or wires by means of which the currents are led to the place where they have to do their work. One very interesting thing about the modern dynamo machine is that it is what electrical men call "self-exciting." That does not mean that it gets into a state of excitement about itself. It means that the dynamo provides its own magnetism. At first dynamos were made with great big steel magnets, but those were very expensive and unsatisfactory. Then a clever inventor hit upon the plan of using electro-magnets, and sending part of the current of the dynamo through their coils to give them magnetism. This is the action of the self-exciting dynamo. When the collection of coils wound on the revolving shaft first begins to turn, very little current is produced, because there is very little magnetism in the iron magnets. Part of this current goes through the magnet coils and increases the magnetism; this strengthens the current in the coils, and this process goes on until, after a few minutes, the magnets are fully magnetized and the coils are giving their full strength of current.

Diagram showing the electric circuit through each car, and illustrating the method of sending more than one car along the same wire.

Some time after this was discovered, it became known that if the two wires from a dynamo were joined to a second dynamo instead of to an electric lamp, this second dynamo would revolve, and could be used to drive a machine, such as a sewing-machine or a printing-press.

At first this electric motor, as it was called, was used only for turning wheels that were stationary, but it was soon seen that there was good work for it to do in turning wheels that should travel along over the ground. Then began the electric railway.

Having got your electric motor it would seem a comparatively easy job to mount it on a car, to fix up a moving connection with an electric wire, and to make the motor turn the car-wheels. It looks easy enough to-day in places where hundreds of horseless cars are running about in all directions as if by magic. In the beginning it was not such an easy job, and those who led the way in the building and running of electric cars had many difficulties to contend with and many obstacles to overcome before they made the electric street-car the practical everyday affair that it is now.

Just look first at your electric motor. It is, like all electrical instruments and machines, a pretty delicate affair, very likely to suffer serious injury from hard usage or exposure to bad weather.

To place such a machine underneath a jolting car close to the surface of the street, and make it work properly at all times and in all weathers, is no small feat. One great difficulty was to keep the wire coils of the motor properly insulated. If two neighboring coils get connected with each other the motor goes wrong, and as water is a powerful conductor of electricity such accidents often happened at first through parts of the motor getting wet from splashings from the street. Now motors are made water-proof, and the cars go along merrily, even though there may be an inch or two