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side of the other box by two bits of wood, F, G, screwed across it but not into it, so that the rod may be slipped forward and backward. Over the mirror of the upright rod is pasted a piece of paper one inch square with a hole in its centre a quarter of an inch in diameter. A beam of light from a heliostat or a lamp is allowed to enter the room. In case a lamp is used, it must be covered all but the opening through which the light passes, and a Lens must be set in the
beam so as to make the rays parallel. The box supporting the upright rod is so placed that the beam falls squarely on the mirror at the end of the rod. The other box is placed on a table, and the horizontal rod is slid out till just thirty inches of it are beyond the box. The box is now disposed so that the beam is reflected from the upright rod to the mirror on the horizontal rod, and thence to the wall, or a screen at S, where it appears as a bright spot. If the up length of the horizontal rod. With the length given above—that is, where the vibrating rods are equal it will be like that in Fig. 2. Unless the rods have been very exactly adjusted, the figure will change, becoming in turn each of those represented in the illustration. Other curves are shown in Figs. 3 and 4, and many others still will be obtained by sliding the rod D in and out.
VIOLIN, Experiments with a. These can be tried equally well on a banjo, or guitar, but a violin bow is necessary for some of them.
1. Loosen all the strings but one—preferably one of the middle strings. Pluck or bow it first exactly in the middle and then close to one end, listening carefully. There is a difference in the sound, which has more " twang " when the string is plucked at the ends. This is because the note given by the string is composed of several faint ones, called "overtones," beside the loud one which is most plainly heard, and more overtones are present when the string is plucked at the end.
2. Press the finger firmly down
exactly on the middle of the string, and sound it again. The note heard will be an octave higher than the original note. Touch the finger lightly to the same spot, and sound the note as before. The result will be the same, but by looking closely it will be seen that both halves of the string are vibrating. By pressing the string at a third its length from the bottom and drawing a bow across the smaller part, the fifth above the note given by the whole string is obtained. By touching the same spot lightly and bowing as before, the whole string can be made to vibrate, the longer part vibrating in halves. The whole string thus vibrates in three parts. The points between the vibrating parts, which are almost still, are called "nodes." If it cannot be seen that the string is vibrating in
parts, bend a little narrow strip of paper and hang it over the string where the node ought to be. When the string is made to vibrate the paper will be agitated only a little, whereas if it be moved along a little way it will shake violently, or be thrown off the string. By touching different points of the string a skilled violin player can make it vibrate in four, five or more sections. Notes thus produced are called "harmonics."
This experiment will succeed better if a Sonometer is used, which is easily made as follows: Take a piece of violin string, or piano wire, a little longer than the table you wish to use. Tie it to a nail at one end of the table and pass it over a pulley screwed horizontally into the other end. To the end of the string tie a tin pail filled with sand. nails or scraps of iron. It may, instead, be fastened to a second nail, as in the diagram, but the other way is best, as the pull on the string can then be easily altered. The string should now be flat on the table, or nearly so. Cut wedge-shaped sticks of wood and place them under the string, as shown in the picture at A, B and D. By letting the wedges at the ends remain and moving the third, the same results will follow as if the string were touched with the finger. Two ways of vibrating are shown in the diagram, the nodes being at C. The weight of the pail can be varied by taking out or putting in nails or sand, thus stretching the string to the desired degree.
3. Sound a string and then touch it lightly in the middle. It will give the octave faintly.
4. Loosen all the strings of a violin but two, and tune those to the same note, pluck one, and then stop it; the other will continue to sound. Tune one slightly higher or lower than the other, and try the same experiment. The second string will still sound, but not as loud or as long as before. This is called "sympathetic vibration." The notes which are most sympathetic, or are set in motion most easily by a vibrating string, are the same note, its octave, the fifth above the octave, the second octave, and the third and fifth above that. This is shown best by experiments on the Piano.
5. Tunc the two lower strings as nearly as possible to the same note, and loosen the others. Place the ear behind the drum, if the instrument be a banjo, or close to the openings in the body, if it be a violin or guitar. Pluck the two strings together, and the resulting sound will be heard, first louder and then softer, in waves or pulsations. These are called beats. If they are not heard, raise or low
er the pitch of one of the strings a little. The beats will be slower the nearer in tune the two strings are, and faster the farther they are apart; but if the notes are not very near, the beats will be so fast that they cannot be distinguished. They can be heard still better with
VITESSE. A game played by two persons, each with a full pack of Cards. Each player sits with his pack face downward before him, and at a signal both begin to turn over their cards one by one, face outward, and throw them on the table. They do not take turns, but each plays as fast as he can, repeating as he does so the names of the thirteen cards from Ace to King, over and over again, one for each card he turns. Whenever the card turned is the same as the one called out, he must lay it by itself, and begin again at the Ace in calling out. The player who first lays aside thirteen cards in this way wins. But if a card is once passed that should have been thrown out. the player must go on as if it had been any other card. The game of Vitesse thus requires quickness of hand and eye, and at the same time close attention, and a practised player will always win over a beginner, though it looks so simple.
The word Vitesse is French, and means Quickness.
VOLTAIC PILE. A kind of ELECTRic Battery, named after its inventor, Alexander Volta. A simple one may be made as follows: Take a glass tube about an inch in diameter—an argand lamp chimney from which the lower part has been removed may be used. Paste two sheets of ordinary gold paper back to back and cut out disks just large enough to slip into the tube. The disks can be cut several at a time by first folding the paper. Cut an equal number of disks in like manner from silver paper, and then
WALKING TRIPS. In making a walking trip as few things as possible should be carried, as every pound of weight adds to the fatigue. In this article only necessities are considered.
Outfit. The shoes should fit the feet easily, and the soles should be neither so heavy that their weight is uncomfortable, nor so light that the feet feel through them the roughness of the ground. Low shoes should not be worn, as they admit dust and dirt. For climbing rocky hills or mountains heels filled with iron nails are best, as they hold to the rocks. Steel should not be used, as it is hard and slippery. The inside of the sole should be perfectly smooth. A roughness or lump which would not be noticed in an ordinary walk may become painful after a tramp of twenty or thirty miles. The best plan is to wear movable leather in-soles. As soon as the least lump is perceived the shoe should be taken off, the sole removed, and part of its under surface pared off with a sharp knife, just under the uncomfortable spot. If this is done faithfully, the soles will be perfectly fitted to the feet at the end of a day's walk, and the trouble of doing it will be amply repaid by the increased comfort. This simple method of adapting the sole to the foot
was devised by Russell A. Bigelow, a New York lawyer. Some people put sweet oil or salve on the feet when they begin to chafe, and they should be washed frequently.
The other articles of dress may be according to the fancy of the wearer, so long as they are easyfitting and comfortable. For warm weather, gauze underclothing and a loose flannel shirt are best, with a light jacket to wear when not walking. For colder weather the shirt may be tighter at the wrists and neck and the underclothing thicker. In all seasons knee-breeches and a soft hat are best. One can buy a knapsack, which may be strapped on the back, or, if his bundle is small, it may be carried in the hand. It is generally better to carry a small weight in the hand than in a knapsack. Other articles that may be carried are slippers, to rest the feet at night (some think that these should be taken, even if nothing else is); a change of underclothing; needle and thread; buttons; adhesive plaster; fish-line and hooks; extra handkerchiefs; pen, ink and paper; a ball of twine and matches. If the trip is to last more than a few days, so that a change of underclothing is positively necessary, it may be packed in a valise and sent by express to some town on the road. One valise