"Y

OU press the button, we do the rest." While a few people are so busy or so indolent that they are content with pressing the button and letting someone else do the rest, the average beginner sooner or later wants to do the rest himself. In fact, the successful, persistent amateur is always the one that does the rest, for the various mechanical and chemical processes of making a picture are in most cases of greater interest than the pressing of the button.

But what is "the rest?" It may be defined as the making of the negative, and then the finishing of the photographic print. In photography, a negative is a thin film of gelatine having transparent portions, opaque parts, and some areas midway between, or tones. It is called a negative because the colors -or, rather, the shades-are reversed; that is, white and light-blue objects appear black or nearly opaque, while deep shadows or black portions are represented by transparent areas.

Pressing the Button

Pressing the button, or "making the exposure," is the act of admitting light to the dark box, called the camera, which light affects chemically the substances of which the film of the dry plate is composed. It is not only possible but practicable to make a picture by admitting light through a pin-hole; but one of the chief drawbacks to this method is the great length of time required. A lens substituted for the pin-hole makes it possible to shorten the exposure materially by collecting and condensing the rays of light and arranging them on the dry plate.

Although the lens is the most important part of the photographic outfit, few have opportunity to study its complex principles; and although a thorough knowledge of optics is not necessary to the making of satisfactory pictures, yet a few principles should be understood.

For

The diagram on the blackboard shows the direction of the rays of light passing from the image into the camera. instance, light from A passes through aperature (or lens) at O, and thence to the plate at B; similarly, light from C passes to D.

This diagram shows why the image is inverted on the ground glass; and a similar diagram would show why objects at the right-hand side of the picture appear at the left when one looks at the ground glass. From this is seen, also, why the field of the camera dry plate is limited in extent, and the reason for placing the camera at considerable distance when high buildings are being photographed. A ray of light from a point above 4, such as Y, in passing into the camera does not strike within the boundary lines of the plate. The remedy for this is to go back far enough to have the image from C to Y so reduced in size as to be entirely within the limiting edges of the ground glass; or, raise the lens a little cutting off the picture just above C. Sometimes one method is preferable, sometimes the other.

Focus

A ray of light from any point, such as E, passes through the lens, and is sharply defined at some point F, the distance from 0 to F depending upon the shape and character of the lens. If the ground glass B D is at a greater or a

less distance than this from the lens, the image thrown upon it will not be sharp. The correct position is found by trial; and it is a very simple matter if all points of the image are in the same plane, as in A C.

Suppose the landscape has important points in many different planes repre- . sented by lines passing through L, M, R, and S. Evidently all will not be perfectly defined on the ground glass when in any one position, because their focal distances are found to be at L', M', R', and S'.

What is to be done in this case? By stopping down the lens-that is, by decreasing the size of the opening through which light passes-the points on the ground glass will be sharper. It is customary to focus on the most important object, or, if there are several objects of special importance, find the extreme positions of the ground glass, and then place it midway between them. These differences in distance are greater or less according to the kind of lens used. With a wide-angle or short-focus lens, the variation is slight; but this lens is slower than the long-focus, the perspective is not

so good, and it is liable to cause distortion at the edges of the plate. Its chief value is for interiors and cramped places. If but one lens can be purchased, it is better to select a long-focus.

Exposure

Assuming that the camera is in position, focused, and the plate-holder slide drawn, the next move is the exposure of the plate; and many an amateur has asked, "How long?"

The time of exposure depends upon so many factors that experience only will enable one to get good results, although many attempts have been made to produce tables, etc. Plates vary in rapidity or sensitiveness; but a medium speed is best for most work, because it is fast enough to require but a short exposure, and it has more "latitude" than a very fast plate.

For marine views, snow scenes, and pictures made in the middle of the day in summer, a very short exposure should be made-usually under one second. Interiors, pictures in the shade, and pictures of dark objects, require much longer time. In photographing machinery, which is usually black, a soft interior light and a slow plate is best, the exposure requiring three to five minutes. If there is danger of undesirable reflections from polished parts, a few dabs of putty on these parts will overcome the difficulty; the putty can be removed with benzine or gasoline.

all skilled artisans must in time realizethat men are not machines, cannot com

instances of the loss of livelihood through the onward progress of mechanical invention-men of expert skill acquired perhaps through long years of training, now cast aside as useless tools, supplanted through the more efficient devices of automatic machinery and other triumphs of modern invention. Such has been the life-story of Louis Julien, a Frenchman, now an inmate of the Northampton County Poorhouse, near Nazareth, Pennsylvania. Like his father and grandfather before him, he was a clockmaker, and for many years earned a comfortable living at his trade in Belgium, and later in the United States. In time, however, he realized what perhaps

LOUIS JULIEN AND HIS WONDERFUL AUTOMATIC CLOCK.

cease to do any and all sorts of work of which machines are capable.

This lesson is a hard one, and it was none too easy on Louis. Seven years ago he was forced to go to the almshouse. Here he has made himself generally useful at odd jobs of repairing.

During his spare moments in the past five years, he has constructed an eightday clock which is a marvel of mechanical ingenuity. It has second, minute, and hour hands, and a dial showing the days of the week and month, and the signs of the zodiac. In a separate apartment are shown the rising and setting of the sun and moon. In addition to the hours, the quarters, half-hours, and three-quarter hours are struck. And in the darkness of the night, or if a blind person wishes to consult the clock, the time may be ascertained by pulling a cord, whereupon the hour will be struck at once, followed by whatever quarter-hour it may then happen to be. But perhaps the most interesting feature of the clock is the work done by a great number of automatons. At Christmas time the advent of the Christ is shown, the manger, and the oxen and asses in their stalls. The Wise Men come from the East; and an angel appears to warn the parents of the plot of Herod. Joseph places Mary and the Babe on an ass, and they flee into Egypt. Herod and his soldiers arrive only to find their intended victim gone.

The clock is run by weights, and in its mechanism the "parts" of three timepieces are used.-GEORGE F. KUNKEL.

Kites in Wireless Teleg

raphy

PROF. ALEXANDER

ALEXANDER

GRAHAM

BELL has attracted much attention in recent years through his experiments with tetrahedral kites, which have marvelous lifting power in proportion to their weight and dimensions. An important test of the application of these kites to wireless telegraphy was made on March 27th at Arlington, Virginia.

It is known that one of the greatest difficulties in sending messages across the ocean and over mountain ranges is concerned with the raising of the antennæ to a sufficient height to pick up the transmitted Hertzian waves. It is thought that with the help of kites of the tetrahedral pattern sent up from steamers along the ocean track, the difficulty may be overcome.

For the purpose of the test, Professor Bell loaned one of his largest kites, having 230 cells. This was sent up 2,000 feet; and from antennæ 400 feet long, messages were caught and transmitted down over a steel wire. Messages were received from the government wireless station at the Washington Navy Yard, from the De Forest station at Galilee, New Jersey, and from a steamer 100 miles out from New York and over 350 miles from the scene of the test.

Shaft

FORE-AND-AFT SECTION OF SLIDER.

Sliding Motor-Boat

FRENCH designers have recently put

into service a peculiar model of motorboat designed to slide over the water instead of cutting through it. As will be seen from the accompanying section, this result is achieved by the peculiar shape of the under part of the vessel, which slopes backward slowly from the bow to a maximum depth at about the center of the craft, somewhat like the smooth under surface of a saucer.

In general appearance this new motorboat is not unlike a submarine. It is built of steel plates, and has been found to pitch and roll but little under swells and heavy seas. It is 39 feet long, 9 feet 10 inches beam, and 5 feet draft, displacing about six tons. With 4 cylinder engines of 66 horse-power at 400 revolutions per minute, it has made a speed of about 13 knots. A speed of 32 knots, it is believed, can be made by a boat of this type with less beam and draft and more powerful machinery.

TORPEDO-LAUNCH "DRAGONFLY" AT FULL SPEED.

New Torpedo-Launch THE 40-foot torpedo-launch Dragonfly,

recently constructed in England, is the first of an interesting new type of war craft designed to operate at a speed of 18 knots an hour. It is built to carry a 14-inch Whitehead torpedo, which is lowered over the side by means of a specially designed side drop gear. The body is first directed bow-on in the direction of the object which it is desired shall be destroyed, and then launched.

This torpedo-boat is propelled by a 120-horse-power gasoline engine, and is of 8,500 pounds' displacement, with a draught of 2 feet 7 inches, and a beam of 6 feet 2 inches. The boat is built of galvanized mild steel and is provided with a water-tight bulkhead so that it will not sink even if it sustains a damage to the stem, while it also has a very broad stern, which is said to overcome any difficulty as to stability when launching the torpedo over the side.

The accompanying illustration shows. the arrangement of the torpedo on the craft. The turtle-back deck arranged in the bow extends as far to the rear as the after end of the engine, and is a portable piece carried over the engine to protect it from the weather. The steering wheel and reversing lever are located on the port side, and detachable spray guards are so placed as to prevent the splash from the bow waves being carried into the launch. The fuel tank holds 100 gallons-enough, it is claimed, to operate the launch for a period of ten hours.

The engine is 4-cylinder, operating at a speed of 900 revolutions per minute. The cylinders have 8-inch bores and a stroke of 8 inches.

The engine weighs about 2,500 pounds, or at the rate of 23.25 pounds per brake horse-power. It is maintained that there is very little vibration even at a speed of 900 revolutions per minute, as the engine is of very light construction and is very carefully and exactly balanced as to its moving parts. This is most essential-in fact absolutely necessary-on account of the very light construction of the hull, in order to insure very high speeds and effectiveness in service. The engine is started by means of compressed air contained in a reservoir placed in the stern of the launch. A small Brotherhood compressor is provided, for supplying the necessary air pressure, driven by a Thornycroft single-cylinder oil engine of 6 horse-power capacity.