lying stone tell a wonderful story. The deductions of "Sherlock Holmes" are as nothing when compared with the more wonderful ones of geologists. The parallel grooves or scratches on the stones below prove that a glacier once passed here and dropped this boulder. Similar scratches on other rocks in Central Park and elsewhere, and the so-called Finger Lakes of New York are evidences of the glacial period. Long Island seems to be a moraine. STUDY OF COAL. Coal. The recent coal strike has demonstrated more than ever before the importance of this mineral. We see the word "mine" and "miner" in mineral. All pupils know what an air shaft or an elevator shaft is. You may compare the shaft of a mine with an elevator shaft going from the sidewalk to the cellar. The methods now employed in the subway for rapid transit will explain mining operations in regard to blasting and holding up the roof above. The varieties of coal and their fossils serve as decipherable pages of the earth's history. MINERALS. EXPERIMENTS. Minerals. Do not forget to speak of salt, chalk, graphite, slate and asbestos. Pupils always see these. Make experiments with acid on shell or coral or marble. Burn marble for hours. Let it cool. Now place it in a basin and pour water on it. The marble has been changed to quicklime and the cold water becomes heated. Attempt to burn a piece of asbestos paper with a match. Speak of artificial minerals and metals such as glass, bricks, brass and bronze. Buy a few cents' worth of blue stone (sulphate of copper) from the drug store. Wet a piece of tin. Rub bluestone on it. The tin has become coated with copper. Bricks are not made with straw now, as we might infer from the reading of the Bible. Laborers in the brickyards along the Hudson have told me this. Coal dust is mixed with the clay also. What is the difference between a mineral and a metal? Why is mercury a metal? Interest might be aroused by the writing of supposed speeches of minerals or metals. I will reproduce some pupils' compositions as examples for imitation: COMPOSITIONS. A STORY OF CHALK. An old fairy tale was told to us, from which we learned that chalk is related to marble, limestones, shells, coral and plaster. The teacher tried an experiment on marble and on a shell with acid (hydro-chloric); then it began to bubble. The reason it began to bubble was because it contained lime. "Many, many years ago I was a small, tiny shell of a sea animal and had many brothers; we became hard and years later we became a large chalk cliff. You can see me if you go to Dover, England. "I am used for making small statues, and teachers use me to write on blackboards."-Class 6B2, JOHN MONACO. A COAL'S STORY. "If I could speak I would tell you a wonderful history about my life. At first I was a tree, when one night I fell and never rose again. Then other trees came down on top of me, and after more than one thousand years I became a black lump of coal. "I was now not in a forest, but in a mine in Pennsylvania, when one day I saw men with pickaxes in their hands and lamps on their hats separating my brothers and me from one another. I was then put in a cart and brought into the wide world. That was the first time I again saw a ray of sunlight. I was then brought to this house, where I now am soon to end my life. After I die my remains will be ashes and dust."-Class 6B2, ANNIE MELCHIONNE. EXPERIMENTS IN PHYSICS FOR THE CLASSROOM LEON W. GOLDRICH, Instructor, De Witt Clinton High School, Manhattan The course of study for New York Public Schools limits the presentation of the subject of "Physics" to the Seventh Year-second-half, and during this one-half year, the teacher is required to impart some knowledge of the following: (1) Matter; (2) Force; (3) Gravity; (4) Simple Machines; (5) Heat; (6) Sound, and (7) Light. It will certainly be admitted that within a period of one hour per week for about eighteen weeks, little more can be done than to present to the children the most elementary fundamental principles of the above subdivisions of physics. The aim of the teacher of this grade should, therefore, be to select such simple practical experiments as will readily appeal to the child's interest, calculated to establish the fundamental laws of physics in such a manner as will awaken in the child a love for the subject and an earnest desire to seek for himself the many other laws which the teacher has no time to illustrate. The purpose of this article is not to present a scientific or even pedagogical discussion of the intrinsic value of physics as a branch of knowledge, nor of the relative value of physics to the other subjects of the curriculum. The writer intends to eliminate all academic discussion and restrict himself entirely to practical classroom work, and to present by lessons, experiments which may be performed either by the teacher or pupils in the classroom. Before presenting the lessons, it may not be amiss to offer just a few practical suggestions: I. 1. Whenever possible, permit the pupil to perform the experiments. 2. Ask the pupils to keep a sepa rate note book for physics, and to make careful notes of all experiments, recording (a) the apparatus used and diagrams of same, (b) the observations made, (c) the inferences drawn. 3. In each lesson appeal to the personal experiences and observations of the child, permitting him to add as many illustrations of the law established as possible. 4. By skillful questioning lead the child to the proper inferences. 5. Do not be impatient. Do not talk too much. Do not tell the child the phenomena that he ought to observe, and the conclusions that he ought to reach. Let the child discover for himself and frame his own conclusion. The teacher may then state the conclusion in scientific language. 6. Encourage the child to make his own apparatus at home and discover as many other laws of physics as his physical and mental laboratories will permit. The following lessons and the mode of presentation are merely suggestive: LESSONS. These lessons have been subdivided as follows: Lesson I. and II. on Matter. Lesson III. and IV. on Force. Lesson V. and VI. on Gravity. Lesson VII. and VIII. on Simple Machines. Lesson IX., X. and XI on Heat. Lesson XII., XIII. and XIV. on Sound. Lesson XV., XVI. and XVII. on Light. MATTER. LESSON I. General Properties of Matter. A. Extension, B.-Impenetrability, C.-Divisibility, D.-Inertia. A-Teacher (holding various objects in his hand): What dimensions has this pencil? What dimensions has this book? What dimensions has this chalk? What dimensions has the smallest particle of matter? Can you think of any existing object which does not possess the dimensions of length, breath and thickness? What conclusion do you reach about all matter? Conclusion: All matter possesses the property of occupying space. This property of matter is called Extension. B. Purpose: To teach IMPENETRA BILITY. Apparatus: Fill a large bowl with water. Turn a tumbler mouth downward into the water. Observation: Does the water rise into the tumbler? What is there in the glass? What prevents the water from filling the glass? Apparatus: Fill a glass with water, then add a few pebbles. Observation: What do you notice? Can you tell why the water overflows? What conclusion do you reach from these experiments? Conclusion: Two bodies cannot occupy the same space at the same time. This property of matter is called Impenetrability. Immediately after reaching this conclusion, the teacher drives a nail into a piece of wood, or adds powdered sugar to a glass filled with water, and asks the pupils to explain the apparent contradictions to the general inference drawn. C. Object: To teach DIVISIBILITY of matter. Experiment: Take a single grain of cochineal and drop it into a tumbler of water. Observation: What do you notice? Stir the water and what do you observe? What has colored the water? How did one grain of cochineal reach every molecule of water? Experiment: Break a piece of glass. Can the smaller pieces be broken, and can the still smaller pieces be broken? Tear a piece of paper. Can the smaller pieces be divided into still smaller pieces? State your conclusion. Conclusion: All matter can be divided. This property of matter is called Divisibility. D. Object: To teach INERTIA of matter. Place a piece of thin cardboard on the forefinger of the left hand. On this card and over the finger place a small coin (Fig. 1). Then give a sudden blow to the card with the forefinger of the other hand. Where is the coin? Where is the card? What has put the card in motion? What has caused the coin to remain stationary? INERTIA Fig.1 Can any boy who is running swiftly come to a sudden stop? Why not? When standing in a car in which direction is the body thrown when the car suddenly starts to move? In which direction is the body thrown when the car suddenly stops? Place a heavy weight on the floor and ask two or three boys to pull it, then while the weight is in motion, withdraw all the boys except one and ask him to continue pulling. Why was it necessary to employ so much force to start the weight in motion, and so much less force to continue it in motion? appeal to the individual experiences of the child can be made to illustrate this property of matter. Conclusion: Matter at rest has a tendency to remain at rest, and when in motion has a tendency to remain in motion. This property of matter is called inertia. LESSON II. General Properties of Matter E, Indestructibility; F, Porosity; G, Compressibility; H, Elasticity. Experiment: Take a tumbler and fill it with water, then add a little powdered sugar, then a little more sugar, and more. Next take a tumbler and fill it with shot, then add some dry salt, then more salt, and more. Observation: Does the water overflow? Does the sugar occupy the same space as the water? Does the salt occupy the same space as the. shot? Where does the salt go? Can you explain where the sugar finds its way in the water? Stretch a rubber band. Does the rubber band occupy more space? Have you added matter to the band? Then what have you enlarged? Drive a nail into a piece of wood. Does the nail occupy the same space as the wood? Then what have you decreased in size in order to make room for the nail? What is your conclusion? Conclusion: All matter possesses PARALLEL FORCES. spaces between its molecules. These spaces are called pores, and this property of matter is called porosity. G. and H. Object: To teach the compressibility and elasticity of matter. Take a test tube, and an air-tight fitting piston. Press the piston-rod down slowly and then release it. Take a rubber ball, press it and then release it. What is there in the tube? When the rod is pressed down, does the rod occupy the same space as the air? Does the air remain in the tube? Does the air occupy as much space in the tube as it did before? When the rod is released, what do you notice? Why is the rod thrown back? What happens when you squeeze the ball? What, when you release the pressure? Mention some substances which are easily compressed. Mention some which are difficult to compress. Mention some objects which show a great tendency to regain their original form after being compressed. Mention some objects which do not show much of this tendency. Conclusion: All matter possesses All matter possesses the property of being compressed and of springing back after yielding to pressure. These properties are called respectively compressibility and elasticity. FORCE. LESSON III. Parallel Forces. Object: To determine the effect of parallel forces. Apparatus: Three similar spring balances, a thin steel rod, about 12 inches long; a two-pound weight. Directions: Suspend two of these balances in a parallel position from some convenient support, and in the hooks of these balances, place the steel rod (Fig. 2); (the weight of this rod should be so small that it will not affect the following computations). Suspend the weight on the rod, midway between the balances. Then make a note of the indicated weight on each balance. Move the weight so that the distance between the weight and one balance is just onehalf of the distance between the weight and the other balance. Again record readings on each balance. Change the position of the weight, note its distance from each balance and again make a record of the readings on each balance. Make several changes and tabulate the results. Observation: When the weight is in the middle what is the reading on each balance? What is the sum of the two readings? When the weight is nearer to one balance, is there any change in the reading on the separate balances? Is there any change in the sum of the readings? Which balance indicates more weight? If the weight is twice as far from balance B (Fig. 2), as it is from balance A, |