fflMWMMMMlii THE MARCH •g- From the collection of the z n m o PreTinger Jjibrary San Francisco, California 2006 Photo by Warren Boyer, Westport, Conn . It is a great thing to have a hobby. These boys have formed a field club and are off on a collecting trip. THE MARCH OF SCIENCE MY OWN SCIENCE PROBLEMS GEORGE W. HUNTER, Ph. D. Lecturer in Methods of Education in Science Claremont Colleges, California Formerly head of the Department of Biology, De Witt Clinton High School, New York AND WALTER G. WHITMAN, A. M. Department of Physical Science, State Teachers College Salem, Massachusetts Foundei and Editor of General Science Quarterly now Science Education AMERICAN BOOK COMPANY NEW YORK CINCINNATI CHICAGO BOSTON ATLANTA COPYRIGHT, 1935, BY AMERICAN BOOK COMPANY All rights reserved MY OWN SCIENCE PROBLEMS. H. & W. W. P. 6 MADE IN U.S.A. FOREWORD TO THE TEACHER Education in a Changing World. Great changes in educational methods and objectives have recently taken place. The growth of the junior high school is an experi- ment in education brought about through a desire on the part of educators to integrate the work of the elementary school with that of the high school. The growing empha- sis on secondary education has forced these changes in organization. Along with this has come a new psychology of learning which emphasizes individual learning rather than group teaching. As a result of these changes in ideals and objectives, the curriculum has come into the limelight. Much recent work has been done in curriculum making, and while some has been scientifically made some is of little value. There is much evidence that the newer curricula in science are being made with objectives that are attainable. Changes in the world of today have been brought about by means of science, and some seventh grade pupils of today know more about some of the applications of science than their fathers do. There is need for interpretation of these changes in terms of the child's activities, especially in terms of his leisure-time activities. The modern science curriculum recognizes this. If we consider what has just been said, it would seem that the underlying philosophy of the course should be based on the relationship of the environment to the child ; first as an individual, and later as a growing citizen in the environment of school, community, and nation. Into such a course the materials of science should be integrated with the curricular materials of geography, history, civics, vi FOREWORD TO THE TEACHER and especially health education. At the earlier levels the ultimate outcomes from the child should be the organ- ization of the integrated knowledges in such a way as will make for some first-hand experiences with the factors of his environment and an understanding of the part played by such factors in his life activities — a desire to know more about and to help in the improvement of his environment ; while at the highest grade level of the junior high school understanding of control and usage of the factors of the environment might well be the ultimate aim. This integration, especially of positive health materials, has been made in the pages which follow. To properly present learning elements in an integrated science curriculum at different grade levels, it is obvious that the mental age, and especially the point of view of the pupil, must be carefully considered. A terraced plan of attack must be used in which the capacities, interests, and science backgrounds of the seventh grade child must be considered as a distinct level in the development of the concepts treated in the course. Children grow much in capacity between the seventh and ninth grade levels. At the seventh grade level the teacher must use simple language. The science vocabulary should be restricted to the use of relatively simple terms. The experiments and demonstrations should be easy to understand and to perform. The teaching techniques should all be adjusted to the levels of the immature youngster of this group. At the eighth grade level, after a year of exposure to the junior high school activities, our boy or girl comes back to school in the fall with a perspective much enlarged and with a social viewpoint quite different from that held in the previous year. The instruction at this level and the quality of work will therefore be not only at a higher terrace of difficulty but should be given from quite a different social point of view. FOREWORD TO THE TEACHER vii Classroom psychology and teaching procedures have shown that while the pupil in seventh grade is an individ- ualist, the same pupil at the eighth or ninth grade level has a quite different outlook on school life. He has be- come a school citizen with the responsibilities of citizen- ship as a part of his mental outlook. It would seem very logical therefore to make our seventh grade science center on the individual and his personal reactions to his envi- ronment by integrating his science interests, leisure-time activities, and health education material with the science concepts fundamental to an exploratory knowledge of his environment. On the other hand, as the ideals of citizen- ship and co-operation are developed at the eighth grade level, it would seem logical to make science concepts lead to a better understanding of such problems as are con- cerned with the purity of water supplies, the protection of food supplies, the control and prevention of disease in the community, and such other science topics which show the need for co-operative effort for environmental improve- ment on the part of school children. As the outlook of the child broadens in the third year of the junior high school, a third cycle of science activities will develop at a still higher terrace of difficulty. At this age level the child might well transfer his science interests to the wider field of the nation and the world. The underlying theme for junior high school science should be first, at the lowest level, simple knowledges about the interesting and useful science in the immediate environment of the individual. In the second year under- standing is more the goal, while in the last year interpre- tation and application of science are the desired outcomes. The philosophy of presentation should result in the ulti- mate generalization that man of all the animals is the only one who can control and artificially change his environment. As such he has dominion over the earth. viii FOREWORD TO THE TEACHER Emphasis in science teaching is coming, more and more, to be placed on method, on problem solving, and on the use of science facts in the solution of such simple problems as are within the pupils' comprehension. Although generali- zations and fundamental concepts are teachers' goals, they are not so evident to the pupils. Therefore science courses must lead the child to see and later to understand the reasons for many simple demonstrations and experiments to the end that these understandings will lead to the goal of forming correct generalizations. Mature generaliza- tions are not the immediate goal ; it is the forming of these generalizations through science experiences gained through the usage of science materials that makes for the best teaching of science. Moreover, these generalizations should be so mastered that they may be used by the student in explaining new science experiences with which he is continually coming in contact. Thus his knowledge is made usable and applicable. Science teaching will never function with the mere learning of generalizations; they must be used and applied intelligently in other science situations. Our coming social group is bound to have more leisure time, as the economic conditions in the future will doubtless make for a substantially shorter working day and more and more time for avocations. The place of science in the junior high school points primarily to adjustment of the pupil to his environment so that he may best use these leisure hours. Science can do much for him in awakening interests and making hobbies worth while. Hobbies are important, both for young people and for older ones : collecting, fishing, hiking, keeping pets, gardening, anything that makes for intelligent interpre- tation and use of the environment. This series of texts has been prepared keeping in mind not only the recommendations of the most scientific FOREWORD TO THE TEACHER ix workers in the junior high school curriculum, but also such experimental work as is available. Interest studies, controlled classroom experiments, research studies in the use of science material, the pooled experiences of teachers, the work of the Science Committee of the National Edu- cation Association, and the outstanding recommendations of the Thirty-first Yearbook have all been used in an attempt to make this series educationally as well as scientifically sound. Certain unique features in the series stand out. In the first place the texts are written from the pupil view- point and great care has been taken to present the material so that it may fit the age level of the pupil. Concepts grow and what may be meaningful to the ninth grade pupil could not be understood clearly by the pupil in the seventh grade, therefore a cyclic plan of treatment is used which is believed to be psychologically sound. Young people are interested in the science of the world around them, not in blocks of a given part of science. As Cox so well says : " A child of the junior high school age lives in a world of things, forces, phenomena, and people. He does not live in a plant and animal world in the seventh year, and in a health world his eighth year, and a physical science world his ninth year." l Emphasis throughout the series is placed on thinking rather than on the reproduction of facts. Factual mate- rial is necessary. In this series of texts the factual material is used in a purposeful way to the end that simple science problems may be solved. These problems are fitted to the age level of the pupil so that even in the seventh grade he may become habituated in the methods used by the scientist. A conscious effort has been made to give the pupils reasons why the method of the scientist is useful 1 Cox, P. W. L., The Junior High School Curriculum, Scribner, 1929. By permission of the publishers. x FOREWORD TO THE TEACHER in daily life to the end that a transfer of training may take place. The psychology of the unit with its social aspect is a force which makes for pupil interest and learning. The Morrison techniques, with modifications which have been found desirable, are used throughout the series. Empha- sis has been placed upon learning devices, and a conscious attempt is made to show the pupil reasons for doing because of the desirable outcomes in transfer of training. Cuts and diagrams are presented as learning devices. The Chinese saying, " A picture is worth 10,000 words," showed a deep pedagogical insight. In this text many pictures are used and thought questions are so worded that the child will use the text as well as the picture in trying to answer the questions in the legends. While the value of the child's recognition of the big ideas and generalizations in science is seen, the greater impor- tance of properly arriving at these generalizations has been stressed in this series. Numerous devices are used to this end : The Review Summary outline, with its suggestions to the pupil for the proper method of pre- paring for the recitation; the practice in problem solv- ing by means of the presentation of the textual material in problematic form ; the various types of self-testing exercises and the many thought questions at the ends of the units are examples of such aids. In the so-called " Story Tests" more factual material than appears in the text is often given, to the end that teacher and pupil discussion will be stimulated and reading encouraged. In addition constant use is made of the motivation which comes through desirable activities such as those obtained by science clubs and excursions. Leisure-time activities are also used as a means of stressing interest in learning science. ACKNOWLEDGMENTS It would be impossible to write a series of science text- books for the Junior High School without mentioning the many pioneers in curriculum making such as Barber, Briggs, Carpenter, Charters, Cureton, Cox, Curtis, Frank, Harap, Pieper, Powers, and many others, including the committee who were responsible for the curriculum find- ings in the Twenty-sixth and the Thirty-first Yearbooks of the National Society for the Study of Education. The establishment of courses in science at this age level is still in the experimental stage. But successful courses must be based on the findings of interest studies as well as suc- cessful practice of teachers who are practical and pragmatic in their philosophy of teaching. The writers of this text have frankly belonged to this latter school, and the pages which follow are the results of practical work in the classroom, together with the accept- ance of such findings in experimental teaching as best illustrate these objectives. It would be impossible to name all the teachers who have given help and inspiration to the writers, but the mention of the following must be made because of the personal contacts involved : Dr. Edna Bailey and Dr. Anita Layton of the University of California ; Dr. Otis T. Caldwell of Columbia University ; Professor W. L. Eikenberry, State Teachers College, Tren- ton, New Jersey ; Miss Winifred Perry, Roosevelt Junior High School, San Diego, California ; Dr. Frank M. Wheat, Head Department of Biology, George Washington High School, New York City ; and Professor Herbert E. Walter, Department of Zoology, Brown University, Providence, Rhode Island. From each of the above, the writers have had help and inspiration. xi xii ACKNOWLEDGMENTS The following have read the manuscripts either com- pletely or in part and have given valuable constructive criticisms : Edith H. Bourne, the Fannie H. Smith Train- ing School, Bridgeport, Connecticut ; Francis R. Hunter, Assistant in Biology, Princeton University; George W. Hunter, III, Assistant Professor of Biology, Wesleyan Uni- versity ; Roy A. Knapp, Principal Antelope Valley Joint Union High School, Lancaster, California; and Frank M. Wheat, Chairman of Department of Biology, George Washington High School. In addition Dr. Wheat has added much to the teaching effectiveness of these books by his excellent diagrams and skillful cartoons. Wright Pierce has also added much to the attractiveness of the text with his illuminating photographs. Professor Francis B. Sumner has kindly allowed the use of photographs from an original experiment. Miss Florence E. Wall, F.A.I.C., has given valuable suggestions on the hygiene of the skin. Dean Collins P. Bliss of the School of Engineering of New York University has offered much technical advice in certain parts of the text. To all of the above is given the sincere thanks of the authors. TABLE OF CONTENTS PAGE UNIT I. GETTING ACQUAINTED WITH THINGS. 1 PROBLEM I. How Do WE GET ACQUAINTED WITH THINGS? ... 3 II. WHAT Is OUR ENVIRONMENT AND How Do WE USE IT? . 11 UNIT II. LIFE DEPENDS ON ADAPTATIONS . 25 I. WHAT ARE ADAPTATIONS AND WHAT Do THEY Do? . . 26 II. How ARE WE FITTED TO LIVE IN OUR ENVIRONMENT? . 33 UNIT III. LIVING IN AN OCEAN OF AIR . 43 I. WHAT MAKES THE AIR USEFUL TO MAN? .... 45 II. OF WHAT IMPORTANCE Is ATMOSPHERIC PRESSURE? . . 52 III. How Do WE USE AIR? 59 IV. How Do WE BREATHE? 67 UNIT IV. WATER AND ITS EVERY-DAY USES . 79 I. WHAT Is WATER? .82 II. WHAT USES Do WE MAKE OF WATER? .... 88 UNIT V. HOW WE USE HEAT . . .103 I. How Is HEAT PRODUCED? . . . . . . . 105 II. WHAT ARE SOME OF THE CHARACTERISTICS OF HEAT? . 109 III. How DOES CLOTHING AFFECT THE HEAT OF THE BODY? . 117 UNIT VI. HOW WE USE LIGHT . . 127 I. How Do I USE LIGHT? 129 II. WHAT ARE SOME OF THE PROPERTIES OF LIGHT? . . 134 III. How ARE PHOTOGRAPHS MADE? 142 IV. How DOES THE EYE RESEMBLE THE CAMERA? . . . 149 V. WHAT Is COLOR? .154 UNIT VII. HOW WE MAY PRODUCE ELECTRICITY AND MAGNETISM .... 165 I. WHAT CAN MAGNETS Do? 167 II. WHAT ARE SOME WAYS OF PRODUCING ELECTRICITY? . 173 xiii xiv TABLE OF CONTENTS UNIT VIII. GETTING ACQUAINTED WITH THE STARS 187 PROBLEM I. How FAR AWAY ARE THE STARS? 189 II. WHY Do THE STARS APPEAR TO MOVE? .... 196 III. How TO GET ACQUAINTED WITH THE CONSTELLATIONS . 200 UNIT IX. ROCKS AND SOIL . . . 213 I. How WERE THE ROCKS FORMED? 216 II. WHAT Is THE STORY OF THE FOSSILS? . . ... 220 III. How Is SOIL MADE? 228 IV. WHAT SOILS ARE BEST FOR AGRICULTURE? .... 236 UNIT X. LIVING THINGS IN THEIR ENVIRONMENT . 249 I. WHAT Is BEING ALIVE? 252 II. How Do GREEN PLANTS SOLVE THEIR LIFE PROBLEMS? . 257 III. How Do ANIMALS PERFORM THE BUSINESS OF LIFE? . 266 IV. WHAT LIVING THINGS ARE FOUND IN MY YARD OR GARDEN ? 270 V. LIFE IN STREAM AND POND 281 VI. LIFE IN FOREST AND ON THE MOUNTAINS .... 288 VII. LIFE ON THE SEASHORE 294 UNIT XL THE FOODS WE EAT . . 307 I. WHAT ARE FOODS AND WHERE Do THEY COME FROM? . 309 II. How Do WE USE FOODS? 313 III. SHOULD EVERYBODY EAT THE SAME KINDS AND AMOUNTS OF FOOD? 326 IV. WHY Do FOODS SPOIL? 333 V. How MAY WE KEEP FOODS FROM SPOILING? . . . 339 UNIT XII. THE HUMAN MACHINE AND HOW TO CARE FOR IT 351 I. How DOES THE HUMAN MACHINE OIFFER FROM AN AUTO- MOBILE? 354 II. How Is THE HUMAN MACHINE PROTECTED? . . 359 III. How DOES THE BODY MOVE? 368 IV. How DOES THE HUMAN MACHINE MAKE USE OF FOOD? . 375 V. How Do WE CONTROL THE HUMAN MACHINE? . . . 384 VI. ALCOHOL, NARCOTICS, AND THE HUMAN MACHINE . . 392 VII. WHAT Is THE IMPORTANCE OF SAFETY EDUCATION AND FIRST AID? 399 GLOSSARY 417 INDEX 425 SURVEY QUESTIONS How do we get acquainted with things around us ? Do you know what is meant by a scientific habit of mind ? What does open-mindedness mean? Do you know of anyone who is superstitious or who has beliefs not founded on facts ? Why are our sense impressions not always reliable ? Do you know the meaning of the word environment? What is the difference between a physical and a chemical change? Armstrong Roberts UNIT I GETTING ACQUAINTED WITH THINGS PREVIEW Have you ever climbed a high hill and looked off over the countryside ? What a lot of things you could see — trees and open fields, brooks and lakes, hills and valleys — with perhaps homes scattered here and there through the landscape. If you looked more carefully, you could see many other smaller things : the leaves on the trees, birds flying, insects buzzing through the air, stones on the ground. You could count hundreds of different things that you could see from that one hill. But how were you able to know that all these different things existed. You could see them, touch them, perceive that some things had a pleasing odor and that some tasted good or bad. It was different from seeing a picture. You could tell these different things existed and were real because of your ability to see, touch, smell, or taste them — in other words, you became acquainted with them through your senses. A good many years ago before science was used very much in people's thinking, it was the custom for some philosopher to write a book, and then his pupils and all who believed with him would follow exactly what was said in the book without using their senses for themselves. It is said that John Hunter, a famous Scottish physician and surgeon, was once present at a meeting of scientists when they were discussing the structure of birds. The dif- ferent men present quoted from various books the sayings H. & W. SCI. I — 2 1 GETTING ACQUAINTED WITH THINGS of the old philosophers, Aristotle,1 Galen,2 and Hippoc- rates,3 concerning the structure of the bird. One philoso- pher said one thing and another something else. They did not seem to be in agreement. Natu- rally this set up a great discussion in the group, for some believed what one philosopher said and others took sides with another statement. But John Hunter got a bird, killed it, and cut it open and showed the position of the various organs to the group. Naturally they had nothing to say because John Hunter had used the method of the scientist; he had used his senses in ob- taining evidence ; something real that could be seen and touched, not just read about. Have you ever tried to discover all the different forces and things that go to make up your surroundings ? There is first of all the air, which seems to be necessary for all living things. Then there is water and fire and sunlight, all essential to our existence. The soil or the earth's surface with its living inhabitants might be considered as another part or factor of our surroundings. Scientists also consider such forces as electricity and radio activity, Aristotle (ar'fe-t6t'l) . A Greek philosopher who lived 384-322 B. c. 2 Galen (ga'len). A physician of ancient Greece. 3 Hippocrates (hl-p6k'rd-tez) . A Greek physician born about 400 B.C. Culver Service John Hunter. After reading this unit de- cide if he showed the method of the scientist in his actions. HOW DO WE GET ACQUAINTED WITH THINGS? 3 forces which act upon living things. All of these forces and things we collectively call our environment, and each one by itself is a factor of the environment. This unit is intended, first of all, to show us the way that we get acquainted with our surroundings and how we may use the method of the scientist in learning something about this wonderful world that surrounds us, what our surroundings are composed of; and, finally, how we as living creatures use this environment in which we are placed. PROBLEM I. HOW DO WE GET ACQUAINTED WITH THINGS? Indians Were Keen Observers. Those of you who have read The Last of the Mohicans remember Uncas, Wright Pierce The next time you are in the forest look on one side of the tree trunk for a green mosslike growth. This is not moss, but algae or lichens, low forms of plant life. GETTING ACQUAINTED WITH THINGS the Indian brave, who was able to find his way through the trackless forest because he observed and remembered all the things in the forest that might serve as guide posts. The green growth on the trunks of the trees, a mark on a rock or tree trunk, a broken twig, or unusual sound, each had its message to the keen- sensed Indian. We think this was very wonderful, but a boy or girl who uses his senses carefully and makes ob- servations that are accu- rate will soon find that these signs, which might be unnoticed by the poor observer, have a real story to tell. More Than Observa- tion Necessary. But observation alone will not take us far. The Indian saw accurately but he also said to him- self that this green growth on a tree means "north side," and that broken twig means "some one has passed this way." So it is with any one who Turn book so that top of cut a is at bottom. Slowly turn book while watching the stairs. Result? Are the two horizontal lines in b parallel? Do the two horizontal lines in c appear the same length? Measure them. Is the line cut diagonally by the two oblong blocks a straight line ? Which of the three figures in d appears tallest ? Measure. HOW DO WE GET ACQUAINTED WITH THINGS? 5 studies science. His observations may be good, but, unless he relates his observations to something that he wants to know, he will not get very far with his study. Sense Impressions Are Not Always Reliable. If you look carefully at the picture on page 4, you are quite sure that the man in the picture is taller than the little girl shown in the foreground. But if you draw lines touching the tops of the heads of the three figures and the bottoms of the feet of the three, you will be surprised at what you find. Try it and see for yourself. This shows us that sense impressions, even when carefully made, cannot always be relied upon. We Need to Know Where We Are Going. Uncas, in his -wanderings through the forest, made his observations with some object in mind. If he was stalking deer, it was signs of deer that he looked for. If going through a hostile country, it was signs of enemy that he sought. So it is with any one who studies science — or indeed any school subject. He must know where he is going and what he is after. Our observations must be directed toward one goal and we must know just what this goal is. In science we call it a problem and we say we are trying to solve a problem. This interesting old world in which we live has so many interesting problems for us to solve - secrets which can only be discovered when the observa- tions we make are directed to a goal in which we are interested. Remember this in your science work and it will always seem worth while. Life Is a Continual Solving of Problems. But, you say, this isn't true. We are not solving problems when we are at play. Think a moment — tag, or swimming, or football. In tag, you must dodge ; but does quick dodging just happen — or do we learn to dodge skillfully ? Did we ever have to learn to swim? Ask the football player about the successful plays that win the game. GETTING ACQUAINTED WITH THINGS Wide World Tennis tactics require problem solving. The couple at the net have been suc- cessful in solving theirs. You will find that most things in life that are worth while involve thinking, and thinking ought to mean problem solving. The Scientist Has a Way of Looking at His Problem. One of the most characteristic things about a scientist is that he is open-minded. He never makes his mind up until the evidence is all in. Some people say, "I make up my mind and keep it made up." Such people are not open-minded. They are not willing to accept new evi- dence that might oppose what they think. The scientist, on the other hand, is always lobking for new evidence. He is always open-minded. He may have a theory, but he will give it up if his experiments give him answers which do not agree with it. Charles Darwin is said to have experimented with certain animals in hopes that they would do something that would prove a theory he then held, but when they didn't, he would say in an ad- miring way, "The perverse little beggars, they will do it their way." HOW DO WE GET ACQUAINTED WITH THINGS? 7 How Do We Form Habits ? A habit is said to be an act or attitude which is learned through practice. Habits are of many kinds. Some are concerned with our way of looking at life. We may be habitually happy or grouchy, kind or cross, scatter-brained or able to concentrate, depending on the habits we form when young. A good many rules have been made to aid us in habit formation. Here are some worth remembering : 1. Know what habits you want to form and then act on every opportunity. 2. Make a strong start. No half-hearted effort was ever successful in forming new habits. 3. Allow no exceptions. Habits are only established by keeping right at it. One misstep means we start all over again. 4. In place of bad habits establish good ones. Habits always have opposites. 5. Use every effort of will. Never say, "I can't," and you will one day wake up to the fact that you have estab- lished your new habit. Straight thinking is really a habit of mind. If we can only get the habit of making our decisions on evidence which is real and not on hearsay, we would be saved much trouble in later life. The Scientist's Method of Thinking in Everyday Life. You can see from what has just been said that the scientist looks at things fairly and squarely, and that he always tries to find out the truth by means of the evidence ob- tained from asking questions of nature. He is not satisfied with anything but the truth. How much it would mean to each one of us in daily life if we could take the scientist's method of thinking and refuse to be satisfied with propa- ganda or newspaper stories which tell half truths. We would be less likely to believe many of the superstitions which many people have faith in. What evidence have you that bad luck is associated with number 13? What How many of these beliefs do you hold? Can you find any reason for holding these beliefs? Do you believe that the ground hog can foretell the weather? Or that you will have good luck if yoti see the new moon over your left shoulder with money in your pocket ? If you do you are not scientific in your attitudes. HOW DO WE GET ACQUAINTED WITH THINGS? 9 evidence have you that breaking a mirror carries bad luck with it, or that a black cat crossing your path means bad luck, or that walking under a ladder will be harmful ? A moment's thought will show you that there is no evidence for the truth of these superstitions. Every boy or girl who studies science should determine that he will carry over into his daily life this way of looking at science problems. You may be sure it will mean much to your peace of mind now as well as make you a more intelligent and thoughtful citizen. Use of Workbooks. Every pupil should keep a note- book in which are recorded observations and facts noticed and learned demonstrations, statements made by the teacher, and notes from supplementary readings. Outline drawings of the apparatus used in some of the experi- ments, and of the machines, animals, or plants, which he wishes to remember, should be in this book which we will call a workbook. When the work of each unit is organized for review, an outline form of the unit should be recorded, as well as brief but clear reports of special projects, ex- periments, labeled diagrams, and figures which are neces- sary for a clear understanding of the various problems of the unit. Finally, the workbook may contain a collection of clippings, pictures, and photographs, related to the vari- ous topics. Your workbook will be something that you can keep after your course is finished. It will not only be a memento of a worth-while bit of individual work, but it also will serve as a reference book to be used if you go on with the subject of science. How to Use the Self-Testing Exercise. In the pages that follow we shall find at the end of each problem a self- testing exercise ; the object of this exercise is to help you master the problem which it closes. To make the best use of this exercise, you should place the numbers of the blank spaces in columns on a sheet of paper. Then read- 10 GETTING ACQUAINTED WITH THINGS ing the self-testing exercise carefully, try to see how many of the blanks you can fill in. After you have done all you can, go to your teacher and see how many words you have missed. Then go back to your text and your notes in your workbook and study again the part you missed. After a short time try the test again and see if you now can fill in all the blanks. Do not give up until you can fill in every blank correctly without looking at your text. If you can do this after an interval of say half an hour after you looked at the book, you should have mastered the facts contained in the problem. How to Use the Story Test. Next try the story test. This may contain some misstatements and is supposed to help you get some of the big ideas or generalizations contained in the problem. Use this test as you did the self-testing exercise, checking up with your teacher to see where you are wrong. Then go back to the text and see what it is that you did not understand. These tests should help you greatly if you use them in the manner just suggested. SELF-TESTING EXERCISE Select from the following list those words which best fill the blank spaces in the sentences below, and arrange them in proper numerical order. A word may be used more than once. problem impressions method characteristic problems determination play concentrate open work observer goal closed learn experiment success thought study judgment weighing scientific signs will solving propaganda attacks constantly evidence sane reliable unnoticed sense Perhaps the Indian could not repeat many science principles, but he learned to become a keen (1) His watchful eye noted many (2) which had a meaning to him, but which might pass (3) by you or me. One must (4) to recognize illusions OUR ENVIRONMENT AND HOW WE USE IT 11 because not all sense (5) are (6) Throughout life one (7) has (8) to solve, not only in his (9) but also in his (10) In science one learns a (11) of solving (12) The scientist (13) problems with an (14) mind. It needs strong (15) power and (16) to change a habit. The habit of (17) (18) before forming a con- clusion is (19) of the (20) method. STORY TEST GEORGE WRITES ON THE METHOD OF THE SCIENTIST Read carefully and critically. List all the errors and suggest corrections. I want to be a scientist when I grow up so I have decided to form the habit of thinking like a scientist. First of all, a scientist always makes his mind up as to whether a thing is so or not and never changes it. That is the way to successfully solve problems. You must try to see the end or reason for doing certain things. It is not wise to have an open mind and listen to everybody's views. It is much better to have a mind of your own and not allow your ideas to be changed by anyone. The scientist may find out the truth by means of evidence, but the easiest way to be sure to have the right evidence is to ask someone rather than to depend upon your own experiments or experience. If the Indians had only made some practical use of their ability to observe accurately, we might credit them with using reason. The scientist always tries experiments and asks questions of nature to see if he is right in his problem. I would never study books in science for you cannot learn anything from books. I would always make experi- ments, and if they came out the way I thought they ought to come out, then I would believe them. In other words, a scientist always believes his senses. PROBLEM II. WHAT IS OUR ENVIRONMENT AND HOW DO WE USE IT? What Are the Factors of Our Environment ? Just what do living things need in order to live ? Growing boys and girls use air in breathing, drink water, eat food, are com- fortable at a certain temperature, need light, and also need something to live on, the earth. With our present GETTING ACQUAINTED WITH THINGS Photo by U. S. Forest Service Orient and Occident Photo What factors of the environment are alike in these pictures? Which are different? N. Y. Times and St. Louis Post Dispatch knowledge it would be difficult to prove that plants and animals use in one way or another all of these forces and things which surround them, but such is the case. The bird in the air, the fish in the water, the tree in the ground - all living things — use some part of the air, water, a favorable temperature, light, and some kind of supporting substance, as the soil, in order to live. Hence we call these the factors or parts of the environment. Living things depend upon the factors of the environ- ment. We could easily prove that these factors of the environment were necessary for life by simple experiments. A fish will die out of water, and no animal or plant will live long without this important substance. If the plant or animal were placed in a jar from which it could exhaust the air, we would find that it woujd die as soon as the air supply was cut off. Light is essential to most living things, for all green plants and most animals prefer light. Some require much heat ; others, like the polar bear, pre- fer a cold climate. Some plants can exist in temperature which would mean death to others. And all living things find some support necessary for their bodies, usually either water or soil. We know that living things need and use factors of their environment, but how they use these factors is much more difficult to understand. OUR ENVIRONMENT AND HOW WE USE IT 13 The Nature of Matter. The person who considers only plants or animals in relation to their environment might be satisfied to stop with the factors mentioned above. But the scientist wants to know more about the environment. He is not content to know what things do ; he wants to know how they are made. He will tell you that all these factors of the environment as well as the living things found in these are made up of something he calls matter. Matter, according to the scientist of yesterday, was anything that had weight or filled space. But the scientist in our changing world is not content to stop with this definition. He says experiments show him that matter behaves as if it were made up of tiny particles separated by spaces. He can take a hollow iron ball filled with water, which looks quite solid to the human eye, and by subjecting it to great pressure, can squeeze water right through it. This, he says, could not be done unless the iron were built of particles which are not con- tinuous but are separated from each other by spaces. The scientist calls these particles molecules. But he does not stop there. He says that the molecules can be broken a molecule of voter Read the paragraph on " The Nature of Matter " carefully. The electrons are repre- sented by dots and the protons by small circles. Can you explain this diagram ? 14 GETTING ACQUAINTED WITH THINGS down into still smaller particles called atoms and those into still tinier bits of matter which he calls electrons and protons. We see a good deal in the papers and magazines about these tiny electrons, which the physicist says are a form of electrical energy, but nobody has ever seen one. Our present idea of the nature of matter is only a theory, but so sure is the scientist of his experiments that the modern world has come to accept this theory as a basis on which we build all our knowledge of matter. Elements and Compounds. In order to understand a little about what goes on in the world we must know something about how changes in matter are brought about. To do this we can make a little excursion into the field of chemistry. The chemist says that all matter is compounded of simple substances called elements. The entire universe is made up of these substances, of which there are about 90, and he says that these elements can combine to form compounds which are so numerous that everything, living or dead, is made up of these sub- stances. Some elements we know : oxygen, for example, is the gas we need if we are to breathe. You have per- haps seen the experiment made in which a red powder, red oxide of mercury, is heated in a test tube. As the substance gets hot, we see the red substance change to glistening drops of mercury such as you see in the bulb of a thermometer. If you insert a glowing match into the test tube, it bursts into flame, showing the presence there of a gas which supports the flame. This is oxygen, a gas which helps things to burn. This experiment shows that we can break down a compound into its original elements, which in this case are the elements oxygen and mercury. Energy. A lighted match gives out heat and light. Exploding gasoline can move an automobile. A thrown stone may break a window. When matter is in a con- dition of motion it can exert a force it does not have when OUR ENVIRONMENT AND HOW WE USE IT 15 it is at rest. When wood burns it produces factors of our environment that did not exist before. These new factors, such as light, heat, chemical action, electricity, and mechanical action, are forms of energy. Matter without energy would make a very different world from ours. Energy is just as useful as matter and the two always are to be found together and they are present in everything in the universe as far as we can tell. What Is a Chemical Change ? When we burn a strip of magnesium metal, we get a bright flame, and there is left a white brittle compound called magnesium oxide. Here we have combined oxygen from the air with the magnesium and have an example of a chemical change called oxidation. When magnesium is burned, oxygen combines with it and a single new product results. The change is chemical. The chemist expresses this change as follows : 2 atoms of Magnesium 2Mg. 2 atoms of Oxygen 02 2 molecules of Magnesium oxide 2MgO When iron rusts, we have a similar chemical change taking place : oxygen of the air unites with the iron, forming iron oxide. Such changes are continually taking place in nature. We shall see later that life itself depends upon this process of oxidation. Physical Changes. When your knife gets dull and you have to sharpen it, you do not change the composition Which of these changes are chemical and which physical? How many similar changes can you list for your workbook ? 16 GETTING ACQUAINTED WITH THINGS of the blade. Some of the molecules are scraped off by mechanical means, but they are still iron molecules. Such a change is physical. Physical changes are illus- trated by writing on paper, boiling water, bending a wire, grinding corn, and plowing soil. The composition of the molecules is not changed by a physical change, but is changed by a chemical change. We Use the Factors of the Environment. What do these facts about chemistry and physics have to do with us? What is the meaning of chemical and physical changes in the world about us? All we need to know now is that such changes are continually going on and as a result of such chemical and physical changes we are able to use our environment. Take, for example, the burning of coal. Energy or power to do work is locked up in the coal. It is unused until the coal is burned, then heat is released and this heat may make water boil, turn the wheels of a locomotive, draw cars and passengers, and cook our food. How does this energy get out? It gets out simply because the elements, hydrogen and carbon, in the coal unite chemically with the oxygen of the air, forming new substances and releasing the heat which may be transformed by machines into work. Chemical changes of this sort are constantly going on in nature ; rocks are crumbling and breaking down into soil ; the soil itself is uniting with oxygen and breaking into still finer pieces ; foods in the bodies of plants and animals are being combined with oxygen or oxidized to release energy. Life Is a Series of Physical and Chemical Changes. And physical changes are going on as well. Wind and water break down and wear away solid rocks, and water turns wheels to transform their energy into power, perhaps in the form of electricity. Ice is formed from water. We may see it in the form of a glacier moving slowly down a OUR ENVIRONMENT AND HOW WE USE IT 17 mountain side or it may fall from the clouds as snow or hail. In our own bodies hundreds of chemical and physical changes are taking place every minute as the human machine changes its position in walking, running, swim- ming, driving, and even sitting or resting. Our mus- cles are always at work, — contracting, relaxing, — thus showing physical changes. And inside the body com- plicated chemical changes are taking place : food is being digested ; we breathe and the oxygen of the air unites with the digested foods as we do work. Work done by the muscles involves still more chemical changes. All life as seen from the standpoint of the chemist and physicist is a series of chemical and physical changes. And in the com- plex environment of today more and new physical and chemical changes are found as man makes use of new and different helps in his everyday life. Man's Environment Much More Complex Than It Used to Be. If we were to compare the life of Uncas, the Compare the living conditions of the Indian with those in a modern city, what ways do they differ ? In what ways are they alike ? H. & w. sci. 1 — 3 In 18 GETTING ACQUAINTED WITH THINGS Indian, with the life of the average boy or girl of today, we would find a vast difference in the environment. The Indian lived simply on natural foods ; if he had a fire, it was rarely used for anything but cooking ; his shelter was primitive and his methods of transportation and communication even more so. Contrast his life with that of the boy or girl who reads these lines — paved streets ; rail, motor, and air transportation ; the telegraph, telephone, and radio; the elaborate homes and great apartment houses of the cities ; the systems of water supply, lighting, and heating that are now a part of our lives would seem very strange to the Indian who occupied this land not so many years ago. Man has greatly changed his original environment and made this world a pretty complicated place in which to live. This book will help us to understand better how to enjoy and control our environment. SELF-TESTING EXERCISE Select from the following list the words that best fill the blank spaces in the sentences below and arrange the words in proper numerical order. A word may be used more than once. chemical continuous particles electrons compound physical elements factors molecules largest oxide magnesium atoms electricity protons oxygen masses smallest * pressure separated united microscope rust inanimate composition environment electron weight Water, air, and light are three of a group of things which are called (1) of the (2) Matter which appears (3) is really made up of minute (4) called (5) which are (6) by spaces. These (7) are made up of atoms, and according to the latest theories, all matter is composed of still smaller electrically charged bodies called (8) and (9) When the element magnesium is burnt, it combines with the element (10) and produces the (11) magnesium (12) . Chemical changes OUR ENVIRONMENT AND HOW WE USE IT 19 always involve a change in the (13) of the molecules ; all other changes are (14) Boiling water is a (15) change, and burning a match illustrates a (16) change. STORY TEST MARY TELLS How WE USE THE ENVIRONMENT Read carefully and critically. List all the errors and suggest corrections. The environment is everything around us. It may be natural or artificial. The factors of the artificial environment are air, light, water, temperature, and something to rest on, or grow from, such as rocks, soil, or the ocean. I have a little garden where I put seeds into the dry earth and the warm sunshine makes the plants develop and grow. It certainly is like magic. Air, water, food, and soil are factors of our environment, but heat, light, and gravity, while we make use of them on occasion, are not really factors of the environment because they are not substances. They are mere creations of the imagination. Fish can live with- out light. We do not need to burn coal to get heat, we can move south where we shall not need it, and gravity is harmful as well as beneficial. It is gravity that makes the disastrous land-slides and causes us to fall down. THE REVIEW SUMMARY You have now come to the point where you want to find out how much you really understand of the unit you have just studied. To do this best you should be prepared to get up before the other members of your class and, with a brief outline of the unit in your hand, explain to the class any or all of the problems, as your teacher may wish. Perhaps you will be asked to make a recitation on only a single brief topic, or you may be asked to discuss an entire problem. In any event, you will want to prepare an outline from which to recite so that you will not miss any important parts of the unit. In this first unit a suggested outline will be given ; but in the later units you must make your own outline. If you wish to change them, you may do so. These outlines should be based upon what you have read, learned, and done, and upon the big 20 GETTING ACQUAINTED WITH THINGS ideas or generalizations that are found in each unit. In this first unit, for example, those placed below are examples. Perhaps you will want to add or subtract from this list. 1. The scientist observes carefully and uses his observations to form conclusions. 2. The scientist is open-minded. He will base his conclusions only on evidence. 3. The scientist's way of thinking becomes habitual if practiced in daily life. 4. People who are influenced by superstitions are not using the method of the scientist. 5. The environment is everything that surrounds us. 6. Living and lifeless things are made up of matter. 7. Matter is not continuous but is made up of very small particles. 8. All we know about matter has been learned through the method of the scientist. Your outline should be based on all the facts that you have learned plus the generalizations formed as the result of applying these facts in your daily thinking. If you follow this method, it will help you in preparing your outline because you will thus focus on the most important things in the unit. A suggested out- line follows. Perhaps you can improve upon it. How we get acquainted with things : By sense impressions These not always reliable The method of the scientist is : Problem solving Open-mindedness necessary Habits : How formed , Habits necessary for scientist What is environment What are its factors What is matter : Theories of composition molecule atom electron — proton Chemical and physical changes : in matter in living things Man has changed his environment by applying scientific facts, OUR ENVIRONMENT AND HOW WE USE IT 21 TEST ON FUNDAMENTAL CONCEPTS Make two vertical columns in your workbook. Head one CORRECT, the other INCORRECT. Under the first place the numbers of all statements you believe to be correct. Under the second place the numbers of all state- ments you believe to be incorrect. Your grade = right answers X 2. I. We get first-hand knowledge of our environment through : (1) our minds; (2) our senses; (3) our sense organs; (4) the nerves which cause movement of muscles ; (5) talking with our friends. II. The factors of the environment are : (6) water ; (7) clouds ; (8) the things inside of a house; (9) air; (10) degrees of heat. III. The method of the scientist: (11) uses the experiment; (12) means having a decided point of view and holding to it ; (13) uses the senses ; (14) is essentially problem solving ; (15) uses the facts in order to draw conclusions from them. IV. Green plants use from their environment: (16) water; (17) dissolved minerals; (18) sunlight; (19) insects; (20) milk. V. The following things are made of matter: (21) water; (22) a feather ; (23) a thought ; (24) a person's brain ; (25) light. VI. There is energy used when: (26) we chew our food; (27) a balloon rises ; (28) a falling balloon hits the ground ; (29) water freezes ; (30) lightning strikes a tree. VII. Animals use the following from their environment : (31) plants; (32) nitrogen of the air; (33) water; (34) oxygen from the air; (35) sound. VIII. The following are chemical changes : (36) cooking meat ; (37) soldering two pieces of tin together ; (38) freezing ice cream ; (39) sharpening a knife on a stone ; (40) digesting food. IX. An example of a physical change is : (41) throwing a stone ; (42) lighting a fire ; (43) putting out a fire ; (44) dissolving salt in water ; (45) writing these words. X. The use of the scientific method helps (46) to dispel superstitions ; (47) to tell which horse will win every time ; (48) one to think straight ; (49) to make discoveries ; (50) to apply facts in useful inventions. THOUGHT QUESTIONS 1. What are two things which everything contains and neither of which would be of any use without the other ? 2. Can you usually tell by observation whether a change in body is a physical or chemical change? Explain. 22 GETTING ACQUAINTED WITH THINGS 3. Which of the following actions are chemical changes and which are physical changes? Why? a. Melting of lead d. Boiling of water 6. Burning of wood e. Rusting of iron c. Making a pencil mark on paper /. Souring of milk 4. How can you train yourself in observation? REPORTS ON OUTSIDE THINGS I HAVE READ, DONE, OR SEEN 1. Report upon an article related to some topic discussed in this unit. The article may be from a current number of a science magazine or from some popular science book you have read. 2. My home environment (in one of the following localities : a farm, a city, a mining town). 3. Compare the environments of the American Indian and the early cliff dwellers. 4. What superstitions do your friends have that actually influence their behavior in any degree? 5. How some important elements are obtained from compounds. SCIENCE RECREATION 1. Chemical and Physical Changes. Making a smoked sun glass with which one may safely look at the sun to view sun spots (through a telescope) or at an eclipse. When a candle is lighted, notice the melting of the wax — some wax runs down the sides and hardens. Bring the glass down over the flame. Keep it moving so that the glass will not break. Try to get an even deposit of black carbon over the surface of the glass. The molecules of the wax of the candle contain hydrogen and carbon. When the flame is cooled, the hydrogen burns, but all the carbon does not burn. This unburned carbon is deposited over the surface of the glass. List the kinds of changes — melting wax, solidifying wax, burning wax, separation of carbon, deposit of carbon on the glass. 2. Are You Superstitious? Make a list of superstitions that have to do with the number 13, broken mirrors, salt, black cats, ladders, posts, moon, umbrellas, warts, etc. Tell how you could subject some one of these superstitions to a scientific test to see if they have any foundation of truth. 3. How Is Your Second Sight? Place 10 pairs of objects on a table. They may be of the following nature : a pair of scissors OUR ENVIRONMENT AND HOW WE USE IT M cutting cloth, a knife cutting an apple, thread in a needle, pencil on a pad of paper, pen in an ink bottle, stamp and an envelope, cup and saucer, cracker and cheese, soap and water, baseball and player's glove. If you have a party of 12, invite six at a time into the room to look the things over on the table. After two minutes (perhaps one minute) send them back. Give each a pencil and paper — warn them not to talk — and have them write out a list of the pairs of objects seen. Have each check their answers when you read the correct list. Have a simple prize for the winner. To make the game more difficult, separate the paired articles on the table so that no two things to be paired will be together, but ask them to make their list of pairs of things which commonly are used together. SCIENCE CLUB ACTIVITIES 1. A field trip to discover as many kinds of environment as possible. 2. To make a list of superstitions of your locality and find out how many members of the science classes are influenced by any of them. 3. Visit a factory or a hospital to see some of the recent results of science in these places. 4. PHYSICAL VERSUS CHEMICAL Divide the club into two teams. One team will bring to the meeting a list of important common physical changes. The other team will bring in a list of important common chemical changes. Have the two teams present in turn a change and argue why it is important. Give a point for each important change and see which team runs up the largest score. Choose some dis- interested party to act as umpire to decide questionable points. REFERENCE READING Darrow, F. L., Boys' Own Book of Science. Macmillan, 1923. Darrow, F. L., The Story of Chemistry. Bobbs-Merrill, 1930. Harrow, Benjamin, Romance of the Atom. Boni and Liveright, 1927. Heyl, P. R., New Frontiers of Physics. Appleton, 1930. Hunter, G. W., and Whitford, R. C., Readings in Science. Mac- millan, 1931. Yates, R. F., Boys' Playbook of Chemistry. Century, 1923. SURVEY QUESTIONS Do you know what the term adap- tation means ? Do you know why these plants are able to live in the desert? Do you know how a bird is able to fly? Can you mention any ways in which your own body is fitted to live ? How does your way of solving a problem differ from that of a fish ? Of a bird? Would you say it is true that man is the only animal that can success- fully change his environment ? • Wright Pierce UNIT II LIFE DEPENDS ON ADAPTATIONS PREVIEW Every boy or girl who reads these lines has at one time or another kept a pet. Perhaps it was a dog or cat or a bird. Some of us enjoy watching goldfish or the brightly colored tropical fish that are so much seen in the home aquariums today. Some boys keep turtles and find them very interesting pets. We might take a census of animal pets kept by pupils taking science and add many new animals to the list. Some of us prefer gardening or the keeping of plants at home. Hyacinths, jonquils, or other bulbs make a fine showing in the spring, while geraniums are always pretty and easy to grow. We may even have collections of strange spiny-covered cactus plants or a "burl" from a giant redwood. But no matter whether you had plants or animals to care for, you must have noticed that each particular living thing seemed to be fitted to live under certain conditions and only under those conditions. Our desert plants grow best in sand and when it is hot and dry like the deserts from which they originally came. Our goldfish would certainly be very unhappy if they were taken out of the water and it would not be long before they were dead. Our pet canary would be equally unhappy if we tried to keep it in a screened tub of water. Even our pet dog or cat would resent a change of living from the conditions to which it was used. Wherever we go, we are constantly seeing examples of the fitness of living things to succeed in the places where 25 26 LIFE DEPENDS ON ADAPTATIONS Wright fierce This gentleman has a hobby. How many of his pets can you find ? they are found. Biologists call these fitnesses adaptations. They are still uncertain just how these adaptations are handed down to new generations of plants and animals or just how it is that some plants and animals can adjust themselves to new conditions of life. We may learn more about this when we come ,to our study of biology. For the present all we are concerned with is to learn a little about adaptations in living things and to try to understand how we, as living things, are fitted or adapted to live in our surroundings. PROBLEM I. WHAT ARE ADAPTATIONS AND WHAT DO THEY DO? What Are Adaptations ? Probably every boy and girl who reads these lines has seen a porcupine, if not alive, WHAT ARE ADAPTATIONS? then in a museum. At first sight you might wonder how in the world he uses his spiny covering. But if you had been out hunting and had your dog come in whining with his nose full of quills, you would not have to ask this question. Evidently the spiny covering gives protection to the otherwise defenseless animal. Or perhaps you have wondered how it was that some plants could stand severe drying while others wilted at once if they became dry. When you examined the leaves of the first plants, you probably found them either covered with tiny hairs or having thickened waterproof surfaces, which prevented rapid evaporation of water, while the plants that wilted quickly might have large, thin leaves with much surface from which to evaporate water. You may have wondered what the elephant did with its long trunk until you saw it use it for getting food or water. When we find in plants and animals structures which are fitted for some definite, useful purpose, we call that structure an adaptation and say it helps to fit or adapt the living thing to do some particular work. But plants and animals do not stop there. Often we find, in order to adjust themselves better to their surroundings, they do certain things. Some plants may twist or twine around objects, thus rising above other plants and so place their leaves in the light where they can make food. Animals hide in the American Museum of Natural History When the porcupine becomes angry or fright- ened the quills stand out so that no enemy can touch him without getting hurt. 28 LIFE DEPENDS ON ADAPTATIONS grass like the grasshopper, or burrow in the ground like the gopher, or withdraw into a protective shell like the snail or turtle, and in hundreds of ways perform actions that result in getting protection from their enemies or food for themselves. In shallow water at the seashore you may have caught little hermit crabs which protect their defenseless bodies by thrusting them into the cast- off shell of a sea snail, and retreating into it in time of danger. Such adjustive actions we also call adaptive, for they result in some good to the animal or plant. Some animals are even adapting themselves like man to the changed conditions of modern life. The English sparrow, which used to subsist in our cities very largely on the partially digested seeds in horse and other manure, began to disappear in the cities when automobiles took the place of horses. Now we occasionally see the sparrows perched on the radiators of cars picking out insects which have been caught in these radiators as the cars went through the country highways. Adaptations, then, may be structures which help the animal or plant to live, or acts performed by the animal or plant which result in better living conditions. The Problems of Living Things. If you will think for a moment, you will see that living things, both plants and animals, have two big problems in life. The first is the care of themselves, the Second the reproduction of young. The business of living means adjusting them- selves to their surroundings so that they may get food, grow strong, and be able to protect themselves from their enemies. No matter what the living thing, be it a fish, a bird, a snail, a tree, or a weed, the problems of living are the same in the end. Some Ways in Which a Bird Is Fitted for Its Life Work. Let us take, for example, a robin. You say such a bird is well fitted for its life. It has its legs provided with flexi- WHAT ARE ADAPTATIONS? ble toes which lock around the branch on which it perches. Study the wing of a chicken and you will see that the feathers with the wing form a light but effi- cient structure which offers resistance to the air when pushed against it. The feathers are so con- structed that the tiny barbs which grow out from the quill to form the vane of the feather are all locked together by tiny hooks, thus making a strong, wind-resisting surface. Beebe1 esti- mates that a single feather may have as many as 990,000 of wngM pierce these tiny hooks. You A magnified view of a feather- Can y°u **A " the place where the barbs are hooked together ? will also find that strong muscles are attached to the wing and fastened to the breastbone so that the wings can be moved rapidly. The bones of the robin are very light and it has a large heart and large lungs ; all these things together help to make it an efficient flying machine. But we have just begun to mention the ways in which our robin is fitted to do his work. Think of the food he eats, then look at the beak and claws and see how effi- ciently they are built for the work they have to do. Think of the nest of the robin, of the fact that its eggs are hatched there and protected by the mother bird, that the little 1 William Beebe, living naturalist, explorer, and writer. 30 LIFE DEPENDS ON ADAPTATIONS ones are fed by the mother until they are able "to go on their own," and we see that in very many ways the robin is fitted or adapted to meet these big problems of living. How a Green Plant Meets the Problems of Living. It is not so easy for us to understand how a green plant meets its problems of life, for at first they seem so differ- ent from those of an animal. But are they very different? An ani- mal has to have food in order to live ; so does a green plant, only a green plant makes its food out of substances from the air and soil and the water it takes in. We must remember that both plants and animals have to breathe. They therefore need oxygen from the air. They both need a certain amount of heat and light, some more, some less. They must be protected* and they must produce offspring if they are to be successful. The cactus is an example of a plant that has been successful in spite of unfavorable conditions. What special fitnesses or adap- tations do we find which help it solve its problems of life ? In the first place, instead of green leaves, we find spines. Leaves would wilt in the hot desert air, because they have large surfaces which allow water to evaporate from the plant. The cactus conserves its water by having a soft pithy stem which holds water and by having this Wright Pierce What kind of food does this bird eat ? WHAT ARE ADAPTATIONS? 31 stem covered with a hard and corky covering which keeps the water in. By doing away with leaves entirely, the green stem instead of the leaves takes on the work of food manufacture. The plant is protected by its spines. No animal will eat it and it produces its young either by seeds or by means of buds from the parent plant. The cactus has solved its problems of life by means of its adaptations. Success for Plants and Animals Comes through Adap- tations. You all know how difficult it is to get rid of weeds in a garden. It seems as if they come up over night and that as soon as you pull one up, another takes its place. Weeds are successful plants, but why? If you examine a full-grown weed carefully, you will soon see why. Usually they produce very many seeds, and they have excellent means of scattering them. Look at the tumble weed as it rolls along, dropping seeds as it goes. Look at the dandelion or thistle with its seeds sailing through the air — or the stick- tight or cocklebur, with its fruits get- ting a ride by stick- ing to animals. Then weeds produce many more seeds than other plants. Sometimes a single plant forms hun- dreds of thousands of seeds. The seeds sprout under con- wngm pierce ditions Unfavorable This cactus has been cut so as to show the watery for ntViPr rJnnta pulp which is held inside the hard skin. What plants takes the place of the leaves in this plant? Why With which they are there no leaves? LIFE DEPENDS ON ADAPTATIONS compete and they grow very quickly. They usually have deep, tough roots which help them to crowd out other plants by steal- ing their water sup- ply. Choose some weed and note all the adaptations you can find. You will soon see why it is so suc- cessful in life. We can also show that animal success is due to adaptations. Take any animal you know and name over the ways it is fitted for the life it leads. Hoofs, claws, furry or hairy coats, feathers or shells, wings, fins, flip- pers or legs, different types of teeth, all these and many more you might name as adaptive structures. Wright Pierce What devices can you find for scattering seeds in this thistle ? SELF-TESTING EXERCISE » Select from the following list those words which best fill the blank spaces in the sentences below and arrange the words in proper numerical order. A word may be used more than once. life adjustment animals rearing acts nature death leaves structures protection plants fitted survive fear stems make care similar food species break roots elephant spines Adaptations are found everywhere in (1) and by means of them (2) and (3) are (4) to meet their problems of LIVING IN OUR ENVIRONMENT 33 living. These consist of getting (5) , (6) from enemies, (7) to surroundings and the (8) and (9) of their young. Both plants and animals have the same (10) prob- lems and have to meet them in (11) ways, although green plants have to (12) their food as well as use it. Adaptations may be (13) such as the proboscis of an (14) or the (15) in a cactus, or they may be (16) which help the plant or animal to (17) in its struggle for life. STORY TEST JOHN WRITES ABOUT ADAPTATIONS Read carefully and critically. List all the errors and suggest cor- rections. Our teacher has asked me to tell you about the adaptations I found in my pet turtle. In the first place my turtle can live either on land or in water and has adaptations that fit him for both kinds of life. His claws, for example, are useful in swimming and the heavy shell helps him to sink when he goes under water. I think my turtle breathes under water, for he lets up a little stream of bubbles when he is under the surface and can stay under for a long time. But he always comes to the surface after a while, and I notice at night he stays on land and seems to sleep there. He has horny jaws which seem to be fitted for chewing his food. I have watched him eat an earthworm. He grabs it with his jaws, he tears it in two with his claws and then swallows the piece whole. My turtle can swim, although his toes are not webbed. I guess from this he is a water turtle. PROBLEM II. HOW ARE WE FITTED TO LIVE IN OUR ENVIRONMENT? Man Is a Bundle of Adaptations. It is a common say- ing that man is a bundle of adaptations. Did you ever try to prove it true or false? Think of your own life and the wonderful ways in which your body is fitted for the work you do. You walk and run and jump and swim without giving much thought to the mech- anism of the human machine. But if you examine any part of the body at all carefully, you will be amazed to find the numerous adaptations that exist in it. Take, H. & W. SCI. 1 — 4 34 LIFE DEPENDS ON ADAPTATIONS for example, such a simple act as walking. Simple, but is it ? So many parts of the body act together — muscles, bones, nerves, heart, lungs, sense organs, and the master of them all, the brain — that what seems a simple act is found to be very complicated. You cannot with the little knowledge you have at this time explain such an act. But take something you can see and try to find adaptations there. Have you ever thought how wonder- fully your hand is adapted to the work of holding ob- jects, such as a pen or pencil? You know in a general way that it is a complicated mechanism, but do you know how it is built ? For example, we have a bony framework, in which the individual bones are held loosely together in order to allow movement. But these bones are also bound together tightly enough so that they cannot get out of place. Not only are they held together, but each is separated from its next neighbor by a pad of soft elastic cartilage which gives a certain amount of play to the whole hand skeleton. Then each bone has attached to it scores of small, elastic bundles of muscles, some thirty- one in number, which will expand and contract. These muscles work in pairs, one relaxing as its partner con- tracts, and since they are attached to the bones, they give movement to them. But think of the numbers of muscles, guu What kinds of food would you think these birds eat ? Can you describe the kind of feet each of the above birds would have ? LIVING IN OUR ENVIRONMENT 35 some large, some small, that go into this work of moving the hand and wrist. The muscles are attached to bones by means of cords called tendons. You can feel these cords in your wrist and you may have found that movement of the fingers is controlled by them. Study of the figure will show that these tendons are attached to muscles of the forearm so that movement of the hand is controlled by them. But we have again only begun to find the adaptations in the hand. All of the muscles must act together and must be directed by means of our nervous system. They must be supplied with blood contain- ing food and oxygen (see page 376) if they are to do work. The skin must study this carefuiiy be sensitive so we may know when we and then explain how touch anything. If we see the thing we touch, the eye plays a part. And now that we have mentioned all of these structures, we do not begin to understand how each part acts in grasping the pencil, let alone how we make the complicated and delicate actions which occur when we write our names. The human body is full of adaptations, most of which are far more wonderful than those just described. To understand them thoroughly we must study physiology, a subject to be taken up in the senior high school. But we can see that the human body is a very complicated machine and that our job in life is to learn to run it effi- ciently. Adaptations May Be Acts as Well as Structures. But animals often have ways of doing things which are adap- tations. Certain tropical ants, for example, cut leaves from trees, carry the pieces to their nests, and there use you can move your fingers. Dr. Francis B. Sumner The photographs above show the results of experiments made by Dr. Francis B. Sumner of the University of California. He first photographed flounders in aquariums in which the flounders rested on different natural backgrounds of sand, mud, and stones. The fish always changed their color markings to blend with their background, as we see in figures 1 and 2. What advantage would this be to the fish ? He then changed the fish into aquariums having artificial back- grounds like figures 3 and 4. What happened ? Can you account for these changes ? 36 LIVING IN OUR ENVIRONMENT 37 them on which to grow tiny fungi ; colorless plants that cannot make their own food. The fungi, not the leaves, are used as food by the ants. The habit some animals have of feigning death is one method of protection. Many birds which look like their surroundings will keep absolutely quiet on the approach of an enemy, thus escaping notice. Some animals can even change their colors or the markings on their bodies to blend with their surroundings. Man himself shows many examples of such adaptive acts. Have you ever thought that if babies did not instinctively suck soon after they are born, they could not live ? Our lives depend on this one adap- tive act. Can you think of any others ? Man, the Only Animal That Can Adapt His Environment to Suit Himself. We can find many examples of adapta- tion to the environment in plants and animals, but man alone seems able to change his environment to suit him- self. We know that desert plants will not live long in the water and water-loving plants will soon die if placed in a hot, dry place. Sheep having long wool when transferred to a hot country like Cuba soon die, because the long wool unfits them for life in the hot, moist climate. But if man has to change his place of living from a cool to a hot climate, he dresses differently. In other words, he adapts himself to the new conditions. Some animals and plants can do this to a degree if the changes are gradually made ; thus they may become slowly accustomed to changes in environment. But man is constantly changing his envi- ronment for the better. Look at what science has done to make living conditions more comfortable. We move from cold climates to warm ones by means of automobiles, railroads, steamships, or airplanes. We have fruits and vegetables at all times during the year because of refrigera- tion and cold storage. We are able to eat foods which were grown thousands of miles away because of rapid 38 LIFE DEPENDS ON ADAPTATIONS transportation and refrigeration. We have learned to control disease so well that we have increased the number of years man can live. In other words, man is a thinking animal and as such has learned to control and improve his environment. How We Make Adaptations. Have you learned to swim? You soon will if you have not already done so. You may remember how hard it was at first to keep your head above water and not to be frightened. You found that as you learned the different motions, you gradually improved, and then all at once you were able to swim. You will never lose this adaptation so long as you live. You have mastered this problem. When any one has completely mastered anything, like learning to swim, skate, read, or write, he has made an adaptation. So in this book we have given you a number of helps so that when you finish a unit of work, you may be sure that you have complete mastery of the subject. You have, for example, at the end of each problem, self -testing exercises which will help you find out if you have mastered the information in the pages just preceding. If you cannot fill in the blanks correctly, you should study those facts in the problem that you do not remember and then try the test again. Keep at it until you have mastered the prob- lem. Then there are other tests which help you apply the information you have gained. You may know all the facts in the unit, but if you cannot apply these facts in the solving of simple problems, then you will not get very far in the mastery of the subject. Let us try to use these helps to gain the mastery which means success. SELF-TESTING EXERCISE Select from the following list those words which best fill the blank spaces in the sentences below and arrange the words in proper numer- ical order. A word may be used more than once. LIVING IN OUR ENVIRONMENT 39 change improve nervous framework adaptations blood structure muscles doing friend adapted successful cartilage adapt endocrine efficiently movement muscle food drink enemy tendons adaptation unsuccessful The human body has numerous complicated (1) which enable us to live (2) The hand is an example of an organ (3) for grasping or writing. It has a (4) of bones, loosely jointed with pads of elastic (5) between. Thirty-one (6) help to give (7) to these bones. Each (8) is attached to one or more bones by tough cords called (9) The whole apparatus is controlled by the (10) system. Adaptations are not always (11) , they may be (12) ways of (13) things, such as getting (14) or escaping from an (15) Man is the only living thing that can successfully (16) the environ- ment to himself. He can (17) it or (18) it, making an (19) in that way. STORY TEST WALTER WRITES ABOUT ADAPTATIONS IN MAN Read carefully and critically. List all the errors and suggest cor- rections. Animals and plants seem to be able to get along by means of adaptations. These are usually structures which make it possible for the plant or animal to live successfully where it happens to be. But man, who is able to travel and to change his place of living, does not have any such structures. He is the master of his sur- roundings and can change them to suit himself. If, for example, he is cold, he can put on more clothes or go where it is warmer. Of course a man has arms and legs, but they are in no way like the front and hind legs of a cat or dog. Since man can adjust himself so well to new conditions, he does not need adaptations. THE REVIEW SUMMARY In preparing a summary of what you have learned in this unit, you will want to place emphasis on the big ideas which have come out of the applications of the facts you have learned and the demon- 40 LIFE DEPENDS ON ADAPTATIONS strations you have seen. These big ideas we call generalizations. For this unit they are as follows : 1. Adaptations are fitnesses for living in a given environment. 2. There are adaptive acts as well as adaptive structures. 3. Life depends upon adaptations. 4. Man shows many adaptations. 5. Man is the only living thing that can adapt the environment to himself. Before making your review summary, test your knowledge of the facts of the unit by checking over the text so as to be sure you know the facts underlying the generalizations. Then, using the generalizations, the material in the text and everything you have read, seen, or done yourself, make a summary outline for your notebook. This outline you may use when you make a recitation. TEST ON FUNDAMENTAL CONCEPTS Make two vertical columns in your workbook. Head one CORRECT and the other INCORRECT. Under the first place the numbers of all state- ments you believe to be correct. Under the second place all the numbers of all statements you believe to be incorrect. Your grade = right answer X4. I. Adaptations: (1) make it possible for plants or animals to exist under certain conditions favorable to the adaptation ; (2) make it possible for a plant or animal to live under any condi- tion; (3) are adjustments; (4) are never found in the young but appear late in life ; (5) are always structures. II. Adaptations make it possible: (6) to obtain food; (7) to protect the offspring successfully ; (8) to obtain money and fame ; (9) to escape from one's enemies; (10) to adjust oneself to his surroundings. III. Some adaptations for life in the water are: (11) claws; (12) gills; (13) fins; (14) slimy body; (15) heavy bones. IV. Some adaptations for life in a hot, dry climate are : (16) elec- tric fans; (17) spines instead of leaves; (18) in animals, thick hair to keep off the heat ; (19) in plants, a thin body covering which easily allows the escape of heat; (20) sweating, which gets heat out of the body. V. Man can control or change his environment: (21) by means of clothes; (22) because he can solve problems and thus adapt the environment to his needs ; (23) through scientific discoveries ; (24) because he has a nervous system ; (25) because he is a " bundle of adaptations." LIVING IN OUR ENVIRONMENT 41 THOUGHT QUESTIONS 1. The trees near a smelter are found to be dying, although the condition of water supply, soil, light, etc., seem unchanged. Is this due to a lack of adaptation on the part of the tree? 2. Your pet goldfish is found dead in the aquarium which has just been cleaned and from which you removed all of the green plants ? Is this due to a poor adaptation on the part of the fish ? 3. A frog is green with dark spots on the upper surface and white underneath. Are these colors adaptations? If so, how? REPORTS ON OUTSIDE THINGS I HAVE READ, DONE, OR SEEN 1. Report upon an article related to some topic discussed in this unit. The article may be from a current number of a science magazine or from some popular science book you have read. 2. Adaptations of a boy or a girl for work in the classroom. 3. Compare the adaptations of the elephant and the giraffe. 4. Discuss adaptations in " Teeth of Animals." 5. How plant seeds are adapted for scattering. SCIENCE RECREATION 1. Make a list of all the adaptations found in a pet dog or cat. 2. Make a list of strange or uncommon adaptations in plants. 3. Prove that success in the life of some plant or animal depends upon adaptations. SCIENCE CLUB ACTIVITIES 1. Visit a museum to study adaptations. 2. Make a field trip to list adaptations in plants and animals. 3. Divide up an area between members of the club and see which member can give the longest list of adaptations for his area. REFERENCE READING Borradaile, L. A., The Animal and Its Environment. Oxford, 1923. Du Puy, W. A., Our Animal Friends and Foes. Winston, 1925. Metcalf, C. L., and Flint, W. P., Insects, Man's Chief Competitors. Williams and Wilkins, 1932. Guyer, M. F., Animal Biology. Harper, 1931. Chapter IV. Jordan, D. S., and Kellogg, V. L., Evolution and Animal Life. Apple- ton, 1907. Chapter XVI. ... SURVEY QUESTIONS How do you know that air is all around you? Why is air needed for fire ? Can air be weighed ? Can you prove that an " empty " glass is really full ? How dots air on a tall mountain differ from air at sea level ? Do you understand how the barom- eter is used ? How does the atmosphere hold things together? How do we breathe? Do you know how much air you need every day? How much is " one atmosphere " ? © Wright Pierce UNIT III LIVING IN AN OCEAN OF AIR PREVIEW It is commonly said that " we live in an ocean of air." But you never see air as you do water and there is certainly no appearance of an ocean when you are in a room con- taining air, or even when you go for a hike in the open. What do we mean by this statement ? We know that air exists, for we feel it when the wind blows ; it holds up our kites, sails our boats, cools us when we are warm, and when it is heated, warms us when we are cold. In tires it holds up our automobiles. It works our compressed-air devices ; turns wind-mills, stops trains by air brakes, and allows people to live and work under water in the caisson and diving bell, Sometimes in storms it blows down houses and wrecks ships. And, although we may not know just how we use it, air is necessary for life because living things breathe it. Have not Piccard and other high altitude explorers taken oxygen of the air with them into the stratosphere, and has not Beebe taken it into the ocean depths in order to exist there? It has taken a good many people a long, long time to find out much about air. While the Greek philosophers knew something about it and even invented some devices that made use of the fact that air had weight, it was not until the time of Galileo1 (1564-1642) that it was proved that air had weight. Galileo did this by first weighing a hollow copper ball and then forcing air into it until the air was compressed in the ball. He weighed it a second Galileo (gal'I-le'o). 43 44 LIVING IN AN OCEAN OF AIR © National Geographic Society The start of the stratosphere flight above Rapid City, South Dakota. Do you know the use of any of the instruments contained in the gondola under the balloon ? time and found it weighed more. He concluded this greater weight must be due to the extra air in the ball. Our knowledge about what the air is dates back a little more than a century, when Priestley, an Englishman, separated oxygen out of the air, thus showing it to be a mixture of gases. Then the Frenchman, Lavoisier,1 dis- covered that oxygen causes things to burn and an English- man named Cavendish shortly after found that carbon dioxide was a gas formed when things burned. Priestley discovered the gas that made up almost four-fifths of the atmosphere and Lavoisier named it nitrogen. Recently small quantities of other gases have been found to be a part of the air mixture. As discoveries in pure science are followed by applica- tions of science useful to man, so the discovery that air pressure could be measured by an instrument called the 1 Lavoisier (la'vwa'zya'). WHAT MAKES THE AIR USEFUL TO MAN? 45 barometer started a long line of applications in the use of this instrument. The heights of mountains can be meas- ured and weather changes can be foretold. The air pilot's altimeter is a type of barometer with a scale marked off in distances above sea level. The various things that scien- tists have found out about the air have been used in thou- sands of ways to make life more efficient and comfortable. air* PROBLEM I. WHAT MAKES THE AIR USEFUL TO MAN? Demonstration 1. Does Air Occupy Space? Cut the bottom from a narrow-necked pint bottle.1 Stretch the open end of a rubber balloon over the mouth of the bottle. Close the clamp over the neck of the bal- loon near the neck of the bottle. Thrust the large open end of the bottle down into a quart jar half full of water. a. Does water enter the bottle? b. Does the level of water change in the jar? c. Explain. Open the clamp on the rubber balloon. Notice three things that happen as a result. d. Record these three changes. e. If you find any evidence to prove that air occupies space, ex- plain what it is. Air Is All about Us. Air makes an envelope for the earth that extends high above us. Those of us who have climbed a 10,000-foot mountain know how hard it is to breathe as we near the summit. We say that the air has become thin. As a matter of fact if one could rise above sea level at will, he would eventually pass out of the atmosphere into space where 1 Process explained on page 77. 46 LIVING IN AN OCEAN OF AIR f 9ou.-nd.Tng balloons t tnati has ,»~ ac f clouds ^ highest airplane A A^iS^k there is no air. Air is found in water, as can easily be shown by bringing a glass flask of water nearly " to a boil." Bubbles of air will be seen to form on the inside of the flask. Air is also found in the soil, as can be seen by packing a tumbler about half full of soil and then adding water. Notice what hap- pens when the water soaks into the soil. We can easily show that air fills the space in a vessel we call "empty." The simplest experiment is to push an inverted glass into a vessel of water and see if anything keeps the water from filling the glass. A more interesting way of showing the same principle is used in the demonstration on page 45. How our atmosphere tapers off. It is 30 Xhe Atmosphere Ex- times as dense at sea level as it is 15 ^ rm miles above. » erts Pressure. The atmosphere is the entire body of air which surrounds the earth; the term "air" is commonly used when we refer to any small part of the atmosphere. Since the atmosphere gets thinner and thinner as one rises in it, a cubic foot of space at the earth's surface must have more air in it than a cubic foot of space several miles above the surface. While some people say that the air reaches a distance of 200 miles or more above the earth, about half of it is below the tops of mountains 3^ miles high. But wherever we are, the Sea level WHAT MAKES THE AIR USEFUL TO MAN? 47 atmosphere is always pressing upon us and upon every- thing it touches. Air Is a Mixture. In the latter part of the eighteenth century several men of science, working in their labora- tories, proved that air consists of several gases, the most important of which are oxygen, nitrogen, carbon dioxide, and water vapor. Among other substances in the air are the gases, argon, neon, and helium. Besides this, there is a variable quantity of dust, consisting of pollen, soot, soil, and many other tiny particles of matter. Oxygen forms about one fifth and nitrogen nearly four fifths of the air near the earth. What Causes Rust. You have all seen examples of rusting : the brown flakes and yellow dust on unpainted iron fences, unused rails, your knife on a fishing trip, on a tin can left for a time in a damp place. Since unprotected iron surfaces are so easily acted upon by the oxygen in moist air, exposed surfaces of iron are covered with material which keeps the air from them. A "tin" can is iron with a thin wash of tin on the surface. But you know that a tin can will rust. This is because there are microscopic openings in the tin covering through which air reaches the iron. A "tin" roof again is tin- coated iron. To protect it, various paints may be applied. Steel bridges costing millions of dollars are preserved for many years by painting at proper in- tervals. When iron is dipped into molten zinc and withdrawn, a coat of zinc clings to the iron, making What is Called gal- iron. This What is rust and what causes rusting? How could the screen have been protected from rust? protects the iron even better than the coat of tin. 48 LIVING IN AN OCEAN OF AIR I f Oxygen — a Harmful and Useful Agent. There are few useful things in this world which cannot at the same time be harmful or objection- able. The air is no exception to this general statement. Man makes iron fences, iron bridges, iron mosquito netting, and sheet iron for cans, dishes, covering for boats and roofs of dwellings. Sooner or later the oxygen of the air may combine with the iron, making a worthless mass of iron oxide, without even strength enough to hold itself up. What Substance in the Air Aids Burning? If one were to place three lighted candles on the table and at the same instant cover them with three jars of different sizes, would the candles all burn for the same length of time? You know what will happen : the candle in the largest jar burns the longest. The largest jar has the most air, and there is something in the air that helps things to burn. Demonstration 2. What Gas Helps Things to Burn? Fill two wide-mouth bottles, one with oxygen and the other with nitrogen.1 Place them mouth up, but cover with a small glass plate. 1. Plunge a flaming wooden splint into the nitrogen. Result? Plunge a glowing coal on the end of the splint in the nitrogen. Result? 1 Prepare nitrogen by the following method : Put bundle of wet steel wool in wide-mouth bottle, put mouth down in jar of water. Next day remove wool while under water. Close mouth of bottle, remove from water, and set right side up. The gas in the bottle will be practically all nitrogen. Wright Pierce Why are iron pipes sometimes unreliable carriers of water ? WHAT MAKES THE AIR, USEFUL TO MAN? 49 2. Plunge the glowing end of a splint into oxygen. Remove instantly and cover the jar. Result? Twist a wire around a small bundle of steel wool. Heat the steel wool in a flame and immediately plunge it into the oxygen. Result ? The results are so striking that there is no doubt what it is that helps things to burn. The two gases, nitrogen and oxygen, appear to have opposite properties. Nitro- gen quenches a fire just as water would, but oxygen causes it to burn with greater force. Air supports a flame because of the oxygen in it. But things do not burn as fiercely in air as in pure oxygen because of the large amount of nitrogen in the air. What Is Oxidation ? When a substance combines with oxygen, the process is called oxidation. When this com- bination of a substance with oxygen results in a flame, the process is called combustion. Iron combines with oxygen when it rusts, but there is no flame ; therefore this process is oxidation but not combustion. What Is a Flame ? Flame is defined as a burning gas. It is easy to understand this in the case of burning manu- factured or natural gas. When oil burns, it must first be changed to a gas by heat before there can be any flame. Have you ever noticed when a candle burns that the wax melts and is taken by the wick up to the flame ? There it is changed to a gas which burns, and in doing so, pro- duces the candle flame. If you hold one end of a glass tube in the center of a candle flame so as to conduct gas through it, the gas will burn with a flame at the other end. Demonstration 3. What Substances Result When a Candle Burns ? 1. Bring a dry pint jar down on a burning candle. When the candle goes out, remove the jar and quickly close with a glass plate or cardboard. What appears to be on the inside surface? H. & W. SCI. I — 5 LIVING IN AN OCEAN OP AIR 2. Pour 50 cc. (about 2 oz.) of limewater into the jar. Close and shake. There is only one common gas, carbon dioxide, that causes limewater to become milky.1 If we find a change from clear to a milky liquid, what does it prove? What substances does this demonstration suggest are produced when oxygen of the air combines with the candle? It may seem strange to you to find that water comes from the burning of a candle. But if you know that oxygen in the air is a gas that supports the burning of the candle, then it is easily understood. The candle con- tains hydrogen and carbon. Both of these elements will burn. The hydro- gen unites with oxygen and forms I water (H20). The carbon unites with oxygen to form carbon dioxide (CC^). These two compounds also result from the burning of other substances con- Where will water appear taining hydrogen and carbon, such as in the jar after the candle & J bums for a short time? gasoline, oil, coal, and wood. They HOW do we know it comes are therefore, always present in the from the candle ? , . ' , . smoke coming from chimneys. The Air Is Useful in Many Ways. The air of the at- mosphere was just as useful to Columbus as was the water of the ocean, for while the ocean buoyed up his 1 To show that it is carbon dioxide that turns limewater milky, generate the gas by adding hydrochloric acid to marble chips in a test tube and conduct the gas through a delivery tube, making it bubble through lime- water in another test tube. WHAT MAKES THE AIR USEFUL TO MAN? 51 vessels, it was moving currents of air, or winds, that carried him to a new and unknown land. Today the air buoys up airships, and propellers push- ing against the air can make the airships move without the aid of a wind. It is not merely in mechanical ways that air is im- portant. There are many vital chemical processes dependent upon it. Breathing animals take oxygen from the air. If the water were all driven out of plants, by far the greater part of the material left would be carbon taken out of the air by the plant. Since plants are essential for ani- what causes this boat to move ? mal life, we can truly say the air is no less important, for without air there would be no plants ; nor would there be animals. SELF-TESTING EXERCISE Select from the following list those words which best fill the blank spaces in the sentences below and arrange the words in proper numer- ical order. A word may be used more than once. oxidation oxygen out air heat rust extinguish combustion nitrogen fire dioxide oxide 52 LIVING IN AN OCEAN OF AIR carbon acids kindled cold water weak chemical put vapor light action carbon melt germs hydrogen dark It is fortunate for us that (1) constantly surrounds us. If there were no (2) in water, fish would die. The part of the air that helps things to burn is (3) and (4) which makes up four fifths of the (5) will (6) a flame. Moist air causes iron to (7) in a process called (8) Combustion is (9) in which both (10) . and (11) are produced. Two impor- tant compounds produced when a candle burns are (12) and (13) (14) Limewater is used to test for the presence of (15) (16) STORY TEST RUTH TELLS WHY AIR Is USEFUL TO MAN Read carefully and critically. List all the errors and suggest cor- rections. Air is the medium which extends far out into space from the earth, and if man ever reaches the moon, it will be by sailing through the air which connects the two bodies. Two bodies of matter cannot occupy the same space at the same time. It is for this reason that there is no air in soil or in water. Air is a mixture. Oxygen and hydrogen make up about 97 per cent of the air. If there were no carbon dioxide in the air, fires once started could not be extinguished. A burning candle adds oxygen and water to the air. Iron can be burned in oxygen. The com- bustion oi iron is called rusting, and the burning of coal is rapid oxidation. Paint is used on iron bridges because air hardens the paint and makes a tough coating, which increases the strength of the bridge. Limestone is used as a test for carbon dioxide. Air supplies man with helium for airships, and carbon dioxide for charging soda water. The most important use of air is for air- planes and airships. PROBLEM H. OF WHAT IMPORTANCE IS ATMOSPHERIC PRESSURE? Why Air Can Exert Pressure. Have you ever noticed how dust and other light objects, as loose papers, will rush ATMOSPHERIC PRESSURE 53 into the space immediately behind a swiftly moving train ? It is the pressure of the atmosphere that causes air to Galloway Why does this rapidly moving train pick up dust and papers directly behind the observation car? move into a place from which any object has been re- moved, and moving air can move other bodies with it. If we remove the air from a closed space, the air will try to get back in, and failing, will perhaps push the walls together. When the air is pumped out of an ordinary rubber tube which has one end closed, the tube is pressed until it is flat, just as if a heavy weight had been laid upon it. A ten-pound block of stone resting on the table presses down upon the table because the force called gravity is pulling on the stone. Any body of matter which has weight will in a similar way exert force upon anything that is under it. This leads us to ask, "Does air have weight ?" Many years ago Galileo, who was the first man in the world to make extensive use of experiments to answer his questions, was the first to weigh air. While he used a copper globe as a container, you could do it in your own GALILEO GALILEI, 1564 1642. A S a boy, Galileo, as he liked to be called, showed great promise. -^- He was a keen observer and a straight thinker, as his com- panions soon learned. We all know the story of how in the Cathe- dral of Pisa he noticed that as the great lamp which hung from the arched roof swung back and forth it always took the same length of time for its journey. This gave him the discovery of the laws of the pendulum. Later he worked out the law of falling bodies by letting two balls of unequal weight fall from the top of the leaning tower of Pisa. They reached the bottom at the same time, thus disproving the belief of Aristotle held for over 2000 years, that heavier bodies fall faster than lighter ones. He also made the first thermometer and learned many new facts about light, heat, and air pressure. But we remember him best for his improvement of the telescope and his discoveries in astronomy. He was the first to see that there were moons revolving around Jupiter, to discover the rings of Saturn, and to observe the rotation of the sun. The movement of sun spots across the sun's disk proved to him that the sun revolved. Galileo weighed air and started his pupil Torricelli upon many experiments involving air pressure and vacuums. It was while engaged in this work that Torricelli produced the first mercury barometer. Galileo was one of the first men to make use of the scientific method and to apply the test of the experiment in order to learn new facts and to prove the unchangeable relation between cause and effect. ATMOSPHERIC PRESSURE 55 home with a football or a basket ball. Suspend a yard- stick at its middle point. Hang a fully inflated football from one arm about twelve inches from the center. The rubber tube should extend and be closed with a clamp. Balance the ball exactly with weights on the other arm. Open the clamp to allow the excess of air to escape. The ball will rise, showing that it is lighter and has lost weight. If it has lost air and weight, what is your conclusion about whether air has weight or not ? Atmospheric Pressure. Since air has weight, it must exert force upon the objects upon which it rests like all other matter. Torricelli (tor're-chel'le), a pupil of that great Italian scientist, Gali- leo, proved that air exerts pressure by means of the following experi- ment. He took a glass tube about three feet long, closed at one end, and filled it with mercury. Then hold-* ing his thumb over the end, he in- verted it in a cup of mercury. The column of mercury dropped until the height was about thirty inches above the mercury in the cup. This showed that the pressure of air on the mercury in the cup was sufficient to balance a thirty-inch column of mercury. Torricelli called the in- strument he used for measuring air pressure a barometer. Later, when why does the column of the barometer Was Carried to the top mercury remain at a height . . . , , , T i /« of 30 inches ? of a mountain three thousand feet high, the mercury column dropped about three inches. Can you explain why? 56 LIVING IN AN OCEAN OF AIR If you had seven bricks piled one upon the other, how will the pressure under the third brick from the top com- pare with the pressure under the bottom brick? Just lib. lib. lib. lib 1 1 >b. lib. lib lib. lib. lib. Observe that the matter in the pillows at the bottom of the pile is crowded into a smaller space, thus making it denser. In this respect which is more like the conditions in the atmosphere, the bricks or the pillows ? as seven bricks exert more pressure than three bricks be- cause they have more weight, for that same reason air at the level of the ocean will exert more pressure than air on top of a mountain. We would then expect the pressure at a seaport like New York to be greater than at a moun- tain city like Denver. The pressure at seaport towns is 14.7 pounds per square inch, or enough to hold a column of mercury 29.92 inches. It is common practice to regard 30 inches for the barometer or 15 pounds per square inch as standard atmospheric pressure at sea level. How the Atmos- Imile phere Holds Things Together. If you lay one square of glass upon a second glass, you can easily pick the first one off from the second. But if you wet the two pieces of glass and place them together, the Does the air press down with as much force at Watei> takeS the PlaCG the top of this mountain as it does at the bottom ? of the air between the 4 mile/ ATMOSPHERIC PRESSURE 57 pieces of glass and fills the entire space. When there is no air between the pieces of glass, there is no air pressure tending to sepa- rate them, and it is with great dif- ficulty that you can pull apart the two pieces. This is because the air on the outside is E atmospheric pressure •glass- , v • i i Explain this diagram. Can you mention any other W 1 1 n a devices that make use of this same principle ? pressing them to- a force of about fifteen pounds to the square inch. After you fill a bottle with water, put a small piece of wet paper on top and invert it, what happens? Why? Application of this principle is made in the disks used for coat hangers, supports for shelves in display windows, and the ash tray that clings to the wind shield of the automobile. A very famous experiment was tried in Magdeburg (mag'de-boorK), Germany, in 1650. Two metal hemi- Eiplain this renowned experiment with the Magdeburg hemispheres. 58 LIVING IN AN OCEAN OF AIR spheres, about two feet in diameter, were placed together, making a hollow ball, and the air was pumped out of them. The atmosphere held these two hemispheres to- gether so tightly that eight horses on each side were unable to pull the hemispheres apart. Importance of Atmospheric Pressure. The common uses of atmospheric pressure are varied and numerous. From the act of breathing to the measurement of the height of mountains there are thousands of ways in which man makes use of atmospheric pressure. It assists in the pumping of water. The barometer tells how high air- craft rise, and assists in foretelling weather. Variations in atmospheric pressure make our winds and storms and cause droughts and floods. The success of farmers' crops or of curing foodstuffs in the open may depend upon atmos- pheric pressure. In the development of life from the beginning, animals and plants on the earth have been accustomed to a certain atmospheric pressure, as can be seen when deep-sea fish are rapidly brought to the surface. Such fish sometimes actually explode when they are drawn suddenly to the surface of the water, where atmospheric pressure is much less than that to which they are accus- tomed. People who go to the tops of very high mountains fail to get enough oxygen, and the decrease in air pressure causes bleeding from blood vessels which break under the lessened pressure. SELF-TESTING EXERCISE Select from the following list of words those which best fill the blank spaces in the sentences below and arrange the words in proper numerical order. A word may be used more than once. weight Aristotle water space support vacuum push speed height pounds pressure Torricelli sea atmospheric weather mercury ounces square height mountain cubic force vacant Galileo HOW DO WE USE AIR? 59 Air can exert pressure because of its (1) At (2) level the pressure is 14.7 (3) per (4) inch. (5) was the first to measure the (6) of the atmosphere. He did this by finding how tall a column of (7) the atmosphere would (8) Atmospheric (9) decreases as we go up from the surface of the earth. The barometer, by measuring (10) (11) , is useful in (12) forecasting, in measuring the (13) of (14) and to tell the (15) of an airplane. STORY TEST ARTHUR TELLS ABOUT THE PRESSURE OF THE ATMOSPHERE Read carefully and critically. List all the errors and suggest cor- rections. Classmates : I have been reading about the pressure of the atmosphere. Pressure is the force exerted by any body on one unit area. We speak of anything as being "light as air" because air has no weight. However, when I hold my open hand out horizontally, the air or atmosphere is pressing down on my hand with a force of more than 100 pounds. Galileo made the first barometer with a long glass tube and mercury. He found that the air pressure was about 15 pounds on every square foot of area at sea level. As one goes higher into the air, the pressure increases roughly in proportion to the elevation. A barometer can be used to measure the height of a mountain, but an altimeter is used to tell how high an airplane is above sea level. A barometer could be used to tell the altitude of an airplane, but the altimeter could not be used to measure the height of a mountain. When a glass of water is inverted so that the water runs out, the glass has nothing in it and is said to be "empty." A space that contains no matter is a vacuum. When you drink soda water through a straw, you pull the liquid up by suction. The air is denser in Death Valley, which is below sea level, than at sea level, but less dense than on a high mountain. When an automobile moves, it must push the air away to make a space to move into. The air pressure on the front of a moving auto is balanced by an equal air pressure on the rear surfaces. PROBLEM III. HOW DO WE USE AIR? How Is the Air Used? Most boys and girls would not think very long over this question, but what answers would they give. For breathing, most would say, but not 60 LIVING IN AN OCEAN OF AIR many could tell how the air was used. It might be easier to answer the statement that air helps us fly our kites, sail our boats, hold up toy balloons, and turn toy wind- mills. Practical boys will at once think of air in bicycle What holds a kite up ? How do you get a kite up in the air ? Why does the boy run with his kite? and auto tires, while a girl might think of a cool breeze produced by means of an electric fan. Perhaps someone knows how the air helps fill a fountain pen or a medicine dropper or at least how it helps you to drink soda water through a straw. Let us look into some of these uses of the air and see if we can explain them scientifically. What Is a Vacuum? Air not only fills what we call "empty" bottles, but it fills our houses and all outdoor space. The Greeks had a saying, "Nature abhors a vacuum," which was handed down from generation to generation. They knew, as we know, that it is difficult to keep air out of any space. If air is pumped out of a jar so that there is nothing in it, we say a vacuum is HOW DO WE USE AIR? 61 formed. Actually we do not produce a complete vacuum, for there is always a little air left. It is practically im- possible to remove all matter from a space, hence we call any space from which nearly all the air has been removed a vacuum. Demonstration 4. Making a Vacuum by Condensing Steam in a Glass Flask. Stretch the neck of a rubber balloon over the neck of a flask which is filled with steam. As the steam condenses, a partial vacuum is formed. Explain the action. A Useful Vacuum Maker. The demonstration shows how the atmos- phere presses towards a vacuum. There are simpler ways of making a vacuum than by condensing steam. The rubber bulb is a common and useful device for making a vacuum. After a vacuum has been made, it is a simple matter to get the atmosphere to work for you. Take the medicine dropper. Place the open end under water ; squeeze the bulb. Did anything come out? Release the bulb. The elasticity of the rubber makes it spring back to its original size. The air that was squeezed out has left some room in the tube so that the atmospheric pressure on the water outside the tube can push water up into the tube. A fountain pen has a rubber bulb which is squeezed by a lever to make the vacuum, after which atmospheric pres- sure lifts the ink into the reservoir of your pen. The Atomizer. Another use of the rubber bulb in producing movement of a liquid is in the atomizer used for perfume or for spraying your throat. This bulb has a valve so that it can send a series of puffs of air through. As each puff of air is forced across the open end of the 62 LIVING IN AN OCEAN OF AIR tube B some of the liquid comes out of B; as the pressure is decreased inside the tube, atmospheric pressure on the surface of the liquid inside the container pushes it up through C. When this liquid meets the current of air from the bulb, it is caught and separated into a spray of finely divided particles which are carried along with the How does the liquid rise from C to B? What causes the fine spray above A? What is the use of the valve y ? current of air. Many spray-guns for spraying liquids to kill garden insects and house moths work on this same principle, but use a cylinder and piston instead of the rubber bulb to produce the current of air. The Air Pump. The hand air pump used to fill bicycle and auto tires has a piston with a leather facing so arranged that when the cylinder is full of air and the piston is pushed in, the air inside is compressed and pushes the leather against the cylinder wall so tightly that none can escape there. The outlet pipe is coupled to the tire stem. There is a valve in the tire stem which allows air to go into the tire but prevents it from coming out. When the air in the cylinder is under greater pressure than the air in the tire, it will pass from the cylinder of the pump into the tire. A basket-ball or a football pump must have a valve because there is no valve in the tube of the ball. HOW DO WE USE AIR? 63 Why Air in a Tire Will Support a Load. What can be more useless than a flat tire ? And how different the tire becomes after it is pumped up. Let us see what holds the tire out after more air is forced into it. You laboratory pump bicycle pump Explain the movement in the valves A and B during the upstroke and the down- stroke of the piston. What serves as an inlet valve in the bicycle pump ? remember that all matter consists of molecules in motion. Study diagram 1. Here the dots represent molecules of air, which are constantly moving. They bump into each other and against the wall of the inner tube. As each molecule hits the tube it gives a push. As a stream of the mole- cules are pumped into the tube, they are squeezed in close to- gether and in conse- Explain what happens in a flat quence more and more the tire stay up? why does 64 LIVING IN AN OCEAN OF AIR of them hit against the tube (see diagram 2), thus increas- ing pressure against it. Thus air pressure causes the tube to bulge out and we say "the tire is up." The tire stays up as long as it holds these gas molecules, and it goes down when the number of the molecules decreases so that there are too few to strike enough blows to maintain the pressure. A Household Use of the Vacuum. Recall the demon- stration in which steam drove the air from a flask. When the steam condensed, the pressure in the flask was less than that of the atmosphere. In canning fruit and vegetables, the heat used produces three important re- sults. It cooks the food, it kills the bacteria that might cause it to spoil, and it produces steam that drives all the air out. If the cover is put on before the water present cools, after the cooling and condensing of the steam a vacuum is formed. Out- side atmospheric pressure, being so much greater than the pressure inside, presses the cover on so tightly that no germs (bacteria) can get in to harm the food. How to Empty a Liquid from a Vessel with a Small Opening. Many people make no use of their science outside the classroom because it is difficult for them to apply scientific facts and prin- ciples to new situations. Did you ever try to suck water out of a bottle that is full of water having a glass tube passing into it through a tightly fitting stopper ? Try it if you think you can do it. .cork Try sucking water from each of these bot- tles. Which gives the better result ? HOW DO WE USE AIR? 65 You can make a vacuum in the tube, but there is no force to push the water up. If you loosen the stopper, air can get in and with its force of fifteen pounds to the square inch lifts the water out as air replaces it in the bottle. Have you seen anyone pour oil, sirUD Or Other Rea<* the paragraph and explain the diagram. liquids out of a gallon tin can having a flat top? They usually tip the can so that the opening is at the lowest part of the top surface. Study the diagram. Do you see that air must enter and push upward through the liquid in order to displace it ? The flow is jerky and irregular, often spattering. When the can is lifted up, the liquid runs over the top of the can. How can one prevent the bubbling of air up through the liquid and so make a more even flow ? This is done very simply. Hold the can with the outlet at the highest level in pouring. The liquid will then flow out and the air will pass in above the liquid. Some people prefer to punch a hole through the top at the corner op- posite the outlet and then the liquid passes out without interference just as it does from the evaporated milk can when two holes have been made in the top. If you do not understand why this helps to make an even flow, ask to have it explained. Man's Use of the Air. The most important use of the air is for breathing. We may go without food for weeks, without water for days, but we cannot go without air for much more than a minute. Try to see how long you can hold your breath. It is said that divers for pearls have been known to remain under water for two or three H. & W. SCI. 1 — 6 66 LIVING IN AN OCEAN OF AIR minutes without breathing, but this is the limit of human endurance. Incidentally the air all around us presses upon every square inch of our surface with a force of nearly fifteen pounds to the square inch. This great force is necessary to hold us together because the fluids within us are pressing outward with an equal force. Can you imagine what would happen to a person who was suddenly thrust into a vacuum ? Would he die in a short time because of lack of air for breathing or would some- thing startling happen quickly? Discuss this with your classmates and your teacher. SELF-TESTING EXERCISE Select from the following list those words which best fill the blank spaces in the sentences below and arrange the words in proper numerical order. A word may be used more than once. fan coals piston air atmosphere bulb reduce sail mass greater into winds less pushed breathing cools pressure pump walls vacuum refrigerator row more valve volume heats tube increase weight space Air in motion is useful in many ways. The electric (1) cools us on hot days. A fan in the automobile (2) the radiator. Natural air movements as (3) may move (4) boats and kites. Artificial conditions to make the (5) work for us are found in devices which are capable of making a (6) For example, squeezing the (7) of a medicine dropper and then releasing it produces a (8) If this space containing the (9) is open to a liquid, the pressure inside the tube over the liquid is (10) than the pressure of the (11) on the liquid outside the tube; as a result the liquid is (12) (13) the tube. Another common device to (14) the pressure and so make a (15) is the cylinder having a (16) which can be moved back and forth in it. The bicycle or tire (17) is an example of this. Air molecules always are pushing against each other and against the (18) of whatever is holding them, so the more air we pump into a tire, the (19) the load it can hold up. The most important use of air is for (20) HOW DO WE BREATHE? 67 STORY TEST RALPH EXPLAINS How HE USES AIR Read carefully and critically. List all the errors and suggest cor- rections. I began the day with a sneeze. I used air for that. I did not use air during the night: I never do. I opened the -faucet to get water for washing, the atmospheric pressure made the water run out. I pressed the tube to get tooth paste upon my tooth brush, air pressure made the paste come out. I squeezed the bulb of a sprayer to use an antiseptic for my sore throat, pressure of the air lifted the liquid out of the bottle. Coffee was made for the older folks for breakfast ; in the coffee percolater pressure of the air made the liquid spurt out over the coffee. After breakfast I had target practice with an air rifle and with vacuum-tipped arrows, both of which make use of atmospheric pressure. I tried to fly my kite but the atmospheric pressure was too great and I had to give that up. It was a sunshiny day with absolutely no wind ; the water was calm — just the time to have a safe trip in my sail boat. I took a friend across the lake but had to tack coming back. We pumped up an inner tube to take in with us while bathing. We made use of the air in the tube, but atmospheric pressure was not needed as we forced the air into the tube by means of a piston pump. We went home in an automobile. I noticed a fan under the hood and I think it drew air into the cylinders so the gasoline could burn. James and I had a race today. We had gallon jugs just alike, both filled with water. We were to see who could empty the water out first. I tipped mine upside down and held it still. James tipped his as I did but gave it a whirling motion at first to make the water whirl. I won. I started writing this by electric light, but the lights went out and I am finishing by candle light, but the wind blows the flame out every little while. If it were not for the difficulty of lighting, the candles could be sealed in a glass bulb just as the wires of the electric lamp are. They would not blow out so easily then. PROBLEM IV. HOW DO WE BREATHE? A Day's Air Supply. Did you ever stop to think how much air you take into the body in 24 hours? At the smallest estimate it is over 60 barrels. This seems a lot of air, for most of us could get inside of a single barrel. 68 LIVING IN AN OCEAN OF AIR It is possible for you to find out roughly the amount of air you use by the following home experiment : Count the number of times you breathe per minute. It will likely be some- where from 12 to 16. The average breath is 30 cubic inches. Con- sidering your own size, about how many cubic inches of air do you think you take in at a single breath ? Find the amount for one day by multiplying the number of breaths per minute by the volume of each breath and then by the number of minutes in an hour and by 24, the number of hours in a day. A barrel holds about 31^ gallons and there are 231 cubic inches in a gallon. You take much more air when you are exercising, since you breathe more rapidly and take deeper breaths. Then, on the other hand, you breathe much slower when you are asleep. 4 You must remember, of course, that your estimate will be only approximately correct because of these differences. Why We Breathe. We must think of the human body as any engine. Just as an automobile engine releases energy by burning fuel, so the human body likewise burns or oxidizes fuel to release the energy for daily work. But our work is done not in any one part of the body, but in the little units or cells which go to make it up. Evidently Why can this small boy use so many barrels of air? HOW DO WE BREATHE? 69 then, if work is done in the cells, oxygen must get to all parts of the body in order to release energy there. To get oxygen there, it is first necessary to get it in- side the body. Here is where the process of breathing comes in. How Do We Breathe? Study carefully the diagram below. You will notice that the air passage leads from the mouth down into the chest, where it divides into two branches and finally breaks up into small branches which end in a mass of tiny air sacs in the lungs. The lungs are really spongy masses of air sacs and connecting tubes. The walls of these little clusters of sacs are lined with blood vessels, and when air passes into them from the outside when we take a breath, oxygen gets through these thin walls of the blood vessels into the blood. While this is happening, another gas, carbon dioxide, passes out from the blood into the air in the little sacs. Thus we see an exchange of gases takes place in the lungs. But this does not get the air into the cells ; that is accounted for by the circulation of b,lood, which, as we shall see later, carries the oxygen to all parts of the body by means of the red corpuscles and unloads it where it will be used in the cells. The breathing apparatus of man. Read the text and explain how and where oxygen might get into the blood. 70 LIVING IN AN OCEAN OF AIR air enter-s Demonstration 5. To Show How We Breathe. a. Take a bell jar, insert in the upper end a Y-shaped glass tube, and fasten over the lower ends of the Y two small rubber balloons. Over the lower open end of the jar tie a piece of sheet rubber. Pull on the rubber so that the cavity inside of the jar is made larger. What happens to the rubber balloons? b. Allow the rubber to go back to its former position and press it upward into the jar. What happens to the Walloons fill \vlth, >i~rS Y> space s mcrea-sect. balloons ? c. Cover the open tube in the cork with your finger and pull down the rubber as before. What happens? Explanation. Try to explain from the movements you have observed why the rubber balloons fill with air when the sheet rubber is pulled down. In the experiment let us suppose the rubber balloons represent the lungs, and the Y-tube corresponds to the air passages connecting the lungs with the mouth. We move our ribs outward when we take air into the lungs. This action is not shown in our experiment. At the same time we pull down a thin wall of muscle (called the dia- phragm), which in the experiment is represented by the rubber sheet. This makes the chest cavity bigger and pressure of the air in the lungs becomes less than that of the atmosphere outside. The lungs fill with air, because it is pushed in by the greater pressure outside. The higher we raise the ribs, the more the diaphragm stretches and the larger the space in the chest cavity. So deep breathing brings in more air than ordinary shallow breath- ing does. When the ribs go back into place, the diaphragm is curved upward into the chest cavity, which is thus made smaller. The air in the lungs is now under greater than HOW DO WE BREATHE? 71 atmospheric pressure : in other words, the air is com- pressed and forced out of the lungs. The process by which the lungs are enlarged and air is taken into the lungs is called inspiration; and the process by which the lungs are compressed into smaller space, forcing out the air, is called expiration. SELF-TESTING EXERCISE Select from the following list those words which best fill the blank spaces in the sentences below and arrange the words in proper numerical order. A word may be used more than once. exhaled air compressed pulled inhaled oxygen upward more decreases hydrogen cells greater increases water tissues less liquid curved blood pressure dioxide organs lungs lowering atmospheric carbon atmosphere pushed Oxygen from the (1) enters the (2) in the (3) and is then sent to the (4) in every part of the body. Here it gives up (5) , takes on (6) (7) __, and is returned to the (8) to be (9) (10) air has more carbon dioxide and less (11) than normal air. Muscular action expanding the ribs and (12) the diaphragm (13) the chest cavity, making the air pressure in the lungs (14) The greater (15) (16) outside forces air into the lungs. When we exhale, the air in the lungs is (17) , and having (18) pressure than that of the outside (19) , it is (20) out. STORY TEST FRANK EXPLAINS BREATHING Read carefully and critically. List all the errors and suggest cor- rections. The human lungs are the largest organs in the body. Together they hold 31^ gallons. When we make the space in the lungs larger by lowering the diaphragm and expanding the ribs, air from outside is pushed in under greater than atmospheric pressure. Pressure on the air in the lungs is never more than 14.7 pounds 72 LIVING IN AN OCEAN OF AIR per square inch at sea level and decreases as one goes to the top of a high mountain. One breathes much easier on top of a very high mountain because the atmospheric pressure is less. In the lungs the blood takes oxygen and water vapor from the air. None of the nitrogen taken into the lungs is used by the body. The air sacs are those small cavities in which the air is never changed. One generally takes deeper breaths when awake than when asleep. The lungs become empty after making an expiration so that there is no air at all in the pleural cavity. This is why we gasp for breath after running a hard race. THE REVIEW SUMMARY In preparing a summary of what you have learned in this unit, you will want to place emphasis on the big ideas which have come out of the applications of the facts you have learned and the demonstrations you have seen. These big ideas we call generaliza- tions. For this unit they are as follows : 1. The gaseous envelope of the earth, called the atmosphere, extends upward for many miles, rapidly becoming less dense at high altitudes. 2. The air contains elements essential both to plants and animals. 3. Air can be removed from a closed vessel. 4. Atmospheric pressure is of great value to man. 5. The breathing and hence the life of many living things depend upon both the composition and the pressure of the air. Before making your review summary, test your knowledge of the facts of the unit by checking over the text so as to be sure you know the facts underlying the generalizations. Then, using the generalizations, the material in the text, and everything you have read, seen, or done yourself, make a summary outline for your notebook. This outline you may use when you make a recitation. TESTS ON FUNDAMENTAL CONCEPTS Make two vertical columns in your workbook. Head one CORRECT and the other INCORRECT. Under the first place the numbers of all state- ments you believe to be correct. Under the second place all the numbers of the statements you believe to be incorrect. Your grade = right answers X 2, HOW DO WE BREATHE? 73 I. Air: (1) fills " empty " glasses; (2) is dissolved in water of falling raindrops ; (3) is a factor in winds ; (4) is present in most soils ; (5) brings us light and heat from the sun. II. The air is useful because it supplies us with : (6) oxygen ; (7) carbon; (8) hydrogen; (9) argon; (10) water for clouds. III. Exhaled breath contains some: (11) oxygen; (12) nitro- gen; (13) carbon dioxide ; (14) water vapor ; (15) sulphur dioxide. IV. Oxygen from the air is used in : (16) rusting iron ; (17) tar- nishing silver ; (18) fires; (19) electric lamps; (20) making a gas flame. V. The following assists one in taking air into the lungs : (21) muscular action in chest wall; (22) the larynx; (23) the upward curving of the diaphragm ; (24) atmospheric pressure ; (25) the movement of blood through the tissues of the lungs. VI. The pressure of the atmosphere : (26) depends upon the fact that air has weight ; (27) can be measured with a thermometer ; (28) will hold up a column of mercury nearly 34 feet high at sea level ; (29) can be removed from a surface ; (30) is greater at the top of a mountain than at sea level. VII. A vacuum: (31) has only air in it; (32) does not contain any matter ; (33) is useful in making the atmosphere do work ; (34) is used to make balloons rise; (35) can be made by blowing all the air out of a bottle. VIII. Canned molasses and evaporated milk are easily poured out : (36) from a hole in the center of the top of the can ; (37) when two holes at opposite edges of the top are made ; (38) from a single small hole near one edge of top ; (39) from two small holes close together ; (40) when the entire top of can is cut out. IX. Expiration in the process of breathing is : (41) to stop breathing; (42) to die; (43) to exhale air; (44) to inhale air; (45) to force all air from the lungs. X. A vacuum can be made in a vessel by (46) condensing steam in it ; (47) filling with water to get rid of air and then pouring the water out ; (48) pumping air into it ; (49) blowing through a tube into a bottle ; (50) by squeezing an atomizer bulb and then releasing it. THOUGHT QUESTIONS 1. Oxygen, carbon dioxide, water vapor, nitrogen, and dust are constantly being taken from the air and they are constantly being returned to the air. Make a diagram to show the " cycles " of these substances ; that is, show all the ways by which they are removed from the air, 74 LIVING IN AN OCEAN OF AIR 2. John wishes to devise an apparatus to measure the air capacity of his lungs. How can he make it? 3. Gerald has his wind knocked out while playing football. What are his team mates likely to do for him? Is this the most effective remedy? 4. Find out and explain why it is so difficult to remove the glass cover on a jar of canned fruit. REPORTS UPON OUTSIDE THINGS I HAVE READ, DONE, OR SEEN 1. Report upon an article related to some topic discussed in this unit. The article may be from a current number of a science magazine or from some popular science book you have read. 2. Galileo, an experimental scientist. 3. Trips made by man into the stratosphere. 4. Uses that boys and girls make of air. 5. Rare gases of the atmosphere. SCIENCE RECREATION 1. If the tube is inverted, what evidence will indicate that air cupies Fpace? 2. What will happen when the clamp C is flp-__~wi~~ occupies ____ Ctr" opened? Explain why. • »«t JiMffl (MHW\\T\>CZX<^nt'H~» ^fcw_ *. -deflated: balloon 3. MAKE A FOUNTAIN-IN- VACUUM Procure an 8-oz. bottle, a 1-hole stopper to fit it, and a glass tube 12 inches long. Soften the glass tube in the middle in the flame. Draw it out to a fine thread. Break off the fine thread so there is only a small opening leading out of the glass tube. These tubes are called jet tubes. Wet one of the tubes and place it in the stopper, so that a jet end (small opening) will be inside. Never push a glass tube into a stopper when the stopper is in the bottle. Hold the bottle in a towel over the nose of a steaming teakettle for a few minutes. WJien the steam has driver; the ajr out. cork HOW DO WE BREATHE? quickly and tightly. Immediately dip the glass tube into a glass of water. As the steam cools, what condition results in the bottle? Explain why the water rushes in and forms a fountain. A Voter.., flf- ., ^balloon. air- 4. What will happen when A blows through the tube? Explain why. 5. What will happen if one sucks air from the large bottle through A? Explain reasons for two results which you can see. 6. Make a booklet of clippings, " Air and Its Uses." Use pictures and articles. SCIENCE CLUB ACTIVITIES 1. ATMOSPHERIC PRESSURE AND VACUUM DEVICES Ask every club member to bring to the club meeting something which uses vacuum or atmospheric pressure, or both, in its opera- tion. He should be expected to demonstrate or explain to the group just how his device works. 2. GALILEO AND TORRICELLI Reports on the scientific works of these early scientists. 3. FOUNTAINS: A GOOD WAY TO MAKE A FOUNTAIN A. Gravity Pressure The tin can has a tight- fitting stopper with a tube passing through it. This is joined by a rubber tube to the jet tube in the glass 76 LIVING IN AN OCEAN OF AIR bottle. A hole is punched through the can near the bottom to allow air to enter the fountain. Water may run out. The higher the reservoir is placed above F, the greater the force in the fountain. 4. EXPLORING IN THE UPPER ATMOSPHERE Read up on this topic in books and periodicals. Find out what people have explored the atmosphere higher than the highest point of land and how they have done it. What do they expect to achieve by these adventures? What are the dangers? Have different members of the science club report upon different achievements. 5. How TO SHOW THE CRUSHING POWER OF THE ATMOSPHERE Use an empty gallon oil or sirup can which has a small opening that can easily be closed air tight with a cork. Put about one half inch of water in it. Place it over a fire, and boil the water. When the steam has driven out all the air (two minutes of boiling), shut off the gas and put the stopper in air tight. Place the can in the sink and pour cold water upon it. Do you understand the reasons for the re- sult? How many square inches of surf ace has the can ? What is the pressure of the atmosphere on 1 sq. in.? On the total surface? 6. How TO SHOW THE CHANGES THAT TAKE PLACE IN THE CHEST CAVITY WHEN WE BREATHE Have some member of the club make a large chart of the diagram shown on this page and a large model of the me- chanical device shown on the opposite page. Have the club members study the chart carefully and then have the dem- onstrator work the model while asking the follow- ing questions : (1) What happens to the human diaphragm when the ribs are raised ? „ HOW DO WE BREATHE? 77 (2) What happens to the human diaphragm when the ribs are lowered ? (3) What causes air to come into the lungs? (4) What causes air to pass out of the lungs? The chart and appara- tus should be presented to the science department of the school for class use after the meeting. It will be valuable for class dem- onstrations. ..cardbooret -brass -fastener atrctboccrcC strip ...papci 7. How TO MAKE A BATTERY JAR FROM A BOTTLE Cut the top off a large glass bottle or jar — one quart or one gallon — the larger better. Make a deep file scratch where you wish to cut it. Heat a heavy metal — soldering iron or curling tongs — red hot and press upon the scratched glass. After a crack is started, keep applying the red hot metal just a little ahead of the crack and it will follow it around. Another method is to wet a cotton string with kerosene. Wind two or three layers around the bottle and tie. Set fire to the string, holding the bottle hori- zontally and turning slowly. When fire goes out, wet the bottle. This jar will be very useful in many experiments. REFERENCE READING Archibald, D., The Story of the Earth's Atmosphere. Appleton, 1915. Compton's Pictured Encyclopedia. Houston, E. T., The Wonderbook of the Atmosphere. Stokes Co. Meister, M., Water and Air. Scribner's, 1930. Talman, C. F., The Realm of the Air. Bobbs-Merrill, 1931. SURVEY QUESTIONS Why is water so important to man? Is water in nature always pure ? Do you know which is hotter, boiling water or steam ? What is the water cycle in nature ? How does water get to oceans, rivers, clouds? How can water be made safe for drinking purposes ? What is water made of? How is the purest water produced artificially on a large scale? Do you know what makes water rise in the soil ? Dawn Mist Falls. Photo by Hileman UNIT IV WATER AND ITS EVERYDAY USES PREVIEW Did you ever think what the world would be like with- out water? There could be no rainy days, no snow storms, no coasting or skating, no bathing, swimming, or sailing, and no water to drink. Without water there could be no plants, hence no vegetables or fruits, no animals and no food for man. You can readily see that without water on the earth there could be no life, not even man. The nearest thing to a waterless earth is found in the desert, but even in this parched and dry area there may be a few springs or pools of water left after a desert storm. Mile after mile of shifting sand, no plants except an occasional cactus, and a few dried-up bushes ; perhaps a snake, a lizard, or a desert mouse, and once in a while a bird is all the life that we see. But visit this same spot after the spring rains have swept down from the moun- tains, and we find the whole desert floor covered, as if by magic, with little plants having many bright-colored, red, magenta, blue, and violet blossoms. Even the dried-up desert bushes have put on leaves and are in flower. All these changes have come because of the temporary presence of water. Some deserts, such as the Sahara, however, are so unfavorably situated that they do not receive enough water to sustain life at any time of year. Such places are a barren wilderness and sometimes so extensive that it is with great hazard that man attempts to cross them. 79 80 WATER AND ITS EVERYDAY USES The desert in California before the rainy season. Note the dry sandy foreground. Water is one of the most important factors of our environment. While there are some living things like earthworms and some fish that can get on without light, and while there are some animals and plants that can live in a very low or a very high temperature, none of them can get on without water. We even know of some plants that can live without air, but these plants, tiny bacteria, get oxygen from their foods and must have water in order to grow. Living things need water be- cause they are largely composed of this substance. Pure water is one of man's most desired possessions. It comes from the clouds and after a long or short stay with us goes back again. The adventure of a drop of water would make an interesting story. Dropped from the clouds as rain, it might fall into a river and from there pass into a large body of water, where it would stay until THE WATER CYCLE 81 The same spot after the winter rains. Compare the trees in the background in both pictures and you will see the photographs are taken at the same place. How do you account for the difference? the hot sun caused it to evaporate into vapor and pass again into the clouds. Its next trip might take it to a forest, where it would fall into the ground, remain there for a time, be absorbed by the roots of the tree, and pass up through the stem to the leaves, where perhaps it could be used by the green leaves of the tree in the manufacture of food. Or perhaps it might be evaporated through the holes in the leaf as the tree made food in the sunlight. Again in the air it might be condensed as dew and then get into the soil again. Eventually, however, our drop of water would become a part of the vapor of the air, would become condensed, and again come back to the earth as rain, or snow, or hail. This continual round of water is known as the water cycle. H. & w. sci. i — 7 WATER AND ITS EVERYDAY USES PROBLEM I. WHAT IS WATER? Those of you who live where snow falls in winter have had the experience of a cold rain changing first to sleet and then to snow. You have at some time brought ice and snow into the house and seen it change back to water. Per- haps you have placed it in a vessel over the fire and watched it pass off into the air as steam. You What kind of changes are taking place here? have all seen water How do you know ? . ,-, ,, in the three states — solid, liquid, and gas. But in all of these conditions, its molecules are still made up of the same elements. How Scientists Found Out the Composition of Water. Water is so common it seems absurd at first to ask, " What is water?" And yet if any one asked you the question, what would you answer? Is water an element? Is it a compound? Does it contain several things mixed together? The chemist has at his command several methods by which he can solve such a problem as this. As long ago as 1784, Henry Cavendish burned hydrogen in oxygen and produced a liquid. This liquid he found had all the properties of water and in fact was water. Sixteen years later, two chemists, Nicholson and Carlisle, reversed the process of Cavendish. They began with water, and by using electrical energy tore the molecules apart and produced hydrogen and oxygen. This process is reproduced now in thousands of schoolrooms every year. The process is called electrolysis of water and is WHAT IS WATER? 83 carried out as follows : The jar has two coils or plates of platinum (A and B) extending upward into some water which has been made acid by having about a table- spoonful of strong sulphuric acid added to half a pint of water. The test tubes are each filled with this water \*y cell drx cell drx cell dry cell • switch. Electrolysis of water. What does this experiment show about the composition of water ? and placed over the platinum wires. The acid is used to make the water conduct the electric current When the current from four dry cells is sent through the water, small bubbles rise from the platinum wires and collect in the tops of the tubes. One gas forms twice as fast as the other. If this gas is removed and lighted, it burns or pops with a slight explosion. This gas has been proved by experiment to be the element hydrogen. When the other tube of gas is tested with the glowing end of a splint, it causes the splint to burst into flame. The gas is the element oxygen. These two elements have come from the water because the chemist finds that there is the same quantity of sulphuric acid left as he used at the beginning. We may now conclude that pure water is a compound made up of hydrogen (2 parts) and oxygen (1 part). This is expressed in the familiar formula H2O. What Is Pure Water? Water in its purest natural state is rain water. It comes from the clouds, where it is 84 WATER AND ITS EVERYDAY USES made from pure water vapor which was condensed high in the air, therefore having little opportunity to get any impurities into it. We can make any water pure by distilling it, because this process forms water in much the same way that it is made in the clouds. Demonstration 1. To Show How Water May Be Purified. Place a Florence flask on a ring stand, and bend a tube as shown in the illustration. Pass it through a perforated cork which will fit in the mouth of the flask. Fill the flask half full of water colored with red ink and add one teaspoonful of salt and two of sugar. Place a lighted Bunsen burner under the flask and put a test tube at the lower end of the tube. Allow the tube to stand in cold water to keep it cool. Observation. Soon after the water boils, notice what happens. Where do the drops of water appear? Why do they appear more frequently here? What is the color of the water in the test tube? Taste it. Result? What substances put into the flask do you find in the test tube ? This process of obtaining water is called distillation. How does distillation purify water? Distillation. Distillation of water is very important. It involves two distinct processes : vaporization, in which the water is changed to steam, and condensation, in which the steam is changed back to water. Natural waters, which contain some impurities, if put into the storage battery of the automobile would soon ruin the battery. When large quantities of artificial ice are made, unless the water is very pure it is first distilled before freezing. When a large can of dirty water is freezing, the im- purities separate and move to the center of the can where the water is frozen last. WHAT IS WATER? 85 What Is Evaporation ? When ice is left in a hot kitchen uncovered, it absorbs heat and soon changes its state from solid to liquid, and if it is left exposed to the air for a short time, some of it will pass off into the air. Evap- oration is the changing of water to a gas when the change is at the surface of the liquid. Some water evaporates into the air when- ever air and water are in contact. The warmer it is, the faster it evaporates. The Water Cycle in Nature. Air, soil, and living , things play an important part in the ceaseless changes of water on our earth. The at- mosphere receives water in the form of water vapor and gives it back in a variety of ways. Evaporation of water from all surface bodies of water, from wet rocks and soil, and even from snow and ice charge the air with moisture. To this must be added the moisture given off from the burning of fuels, by the breathing of animals, and from trees and other plants. A single tree sometimes gives off almost half a ton of water in a day. This water vapor in the air is an invisible gas. When air that has become saturated with moisture is cooled, some of the water separates out into minute particles. Continued cooling increases the size of the particles. The particles may make dew drops, fog, clouds, and rain, or if the temperature is very low, frost or snow will result. The great bulk of this condensed Read the text and then explain this diagram of the water cycle. 86 WATER AND ITS EVERYDAY USES Galloway Is the sun really drawing water? Explain the picture after reading the text. water will come back to the earth from the atmosphere in the form of snow and rain. This return of the water makes the earth moist ; fills the rivers and ponds ; and supplies animals and plants with the necessary water. Evaporation then starts another cycle and the process is continued. Thus there is on the earth a never-ending cycle of water from solid or liquid to gas and back again from gas to liquid or solid. This is the water cycle in nature. Sometimes there are many tiny particles of moisture in the air. They are too few to form a cloud but sufficient to reflect and show rays of sunlight. This phenomenon is responsible for the saying, "The sun is drawing water." Clouds at a higher level often have "holes" in them and sunshine passes through. If small particles of water or dust are in the air lower down, the beams of light become visible just as they do when shining into a dark attic or barn chamber through a knot hole or other small opening. WHAT IS WATER? 87 SELF-TESTING EXERCISE Select from the following list those words which best fill the blank spaces in the sentences below and arrange the words in proper numerical order. A word may be used more than once. nitrogen evaporation impure mixture composition boiling cheap electrons compound union hydrogen oxygen elements twice oxygen separated rain costly water method pure molecules gas solution purifying distillation distilled stream Water is a (1) formed by the (2) of the elements (3) and (4) When water is separated into its (5) , it is found that there is (6) as much hydrogen as (7) When solids are dissolved in water, the water can be (8) from them if heat is applied. Heat causes some of the (9) of pure water to change to a (10) which leaves the (11) This process of (12) a liquid is called (13) The purest water that we make artificially is (14) water. When hydrogen burns (15) results which is also (16) , but this (17) , of producing (18) would be very (19) When distilled water is not available, the next purest water we can get is (20) water. STORY TEST CATHERINE REPORTS ON "WHAT Is WATER?" Read carefully and critically. List all the errors and suggest cor- rections. It seems almost too commonplace to tell you what water is. How can one ever be in doubt ? A glass of milk is white, ginger ale is amber and has bubbles in it, sulphuric acid is very heavy, and gasoline has an odor. If I can see, lift, and smell a liquid in a glass, I can tell if it is water. Some may say a glass of lye (caustic soda in water) or potassium cyanide solution would look the same as water and could not easily be told by weight or odor. Even if this is true, you could tell the difference after you drank them, so what does it matter? The chemist tells us that water is made of hydro- gen and nitrogen and that the amount of hydrogen is double that of the other compound. When water is boiled, it goes off in two separate gases, one of which will burn. Natural water is always pure water, but the artificial water made by vaporization and condensation is almost always impure. We have read a lot about heavy water recently. That is water that has lead in it. 88 WATER AND ITS EVERYDAY USES PROBLEM II. WHAT USES DO WE MAKE OF WATER? Uses of Water. If you were to make a list of all the ways in which you use water, you would doubtless think of its first uses in the morning for washing your body, clean- ing the teeth, and then drinking at breakfast. Keeping clean is certainly important. If a Roman Emperor wished to become popular with his people, he caused a bathhouse to be built. The Romans took their bathing seriously. They had magnificent bathhouses with hot and cold showers or tubs, and the wealthy Roman lounged away a good part of the day enjoying the various steps of his complicated bath. It was the place where a Roman gentleman sat and gossiped and swapped the day's news, for there were no newspapers. They knew the value of a clean skin, and knew the feeling of exhilaration that came from a cold bath following a warm one. A Roman bath in Bath, England. When the Romans invaded England they built baths like the ones they had in Rome. WHAT USES DO WE MAKE OF WATER? 89 Why Keep Clean? There are two reasons why we should keep ourselves and our clothing clean. First because we wish to be decent and attractive to others, and second because good health demands that we keep our clothing and bodies free from dirt and germs. What Makes Water So Useful? The uses of any kind of matter are determined very largely by its properties. Water is no exception. The form in which water exists, whether solid, liquid, or gas, determines some of its uses. We cannot wash clothes in ice nor can we skate on steam. What do you suppose makes water sometimes liquid, sometimes solid, and at other times a gas ? After a little thought you will say correctly that heat determines the state in which water exists. In general it is true that the warmer the water the more solid the water can dissolve, but at any given temperature there is a limit to the amount that it can hold. When water has dissolved all that it can at a given temperature it is said to be saturated. If a saturated solution is cooled or if it loses water by evaporation some of the dis- solved solid will separate from solution. With gases the temperature effect is just the reverse. The warmer the water the less gas it can hold in solution. Boiling the water will remove all gases which are in solution. Demonstration 2. Water as a Solvent. Arrange six test tubes half full of water in a test-tube rack. Add a gram of each of the following substances, each one in a separate tube: (1) salt; (2) sugar; (3) oil or grease; (4) charcoal or ashes ; (5) soap chips ; (6) baking soda. * Shake to see if each substance will dissolve in the water. Tabulate the results. Practical Application. Why will water clean some dirt spots more readily than it will others? When a small portion of salt or sugar is put into water and stirred, the salt or sugar disappears. Water has dissolved the solid. Neither an iron nail nor a silver 90 WATER AND ITS EVERYDAY USES spoon will dissolve in water. Water has the property of dissolving some substances which are called soluble ; • lilll Wright Pierce Try an experiment like this and see what results you get. those substances which will not dissolve are insoluble. A liquid which will dissolve a substance is called a solvent of that substance. Every part of a breakfast cereal can be salted evenly if the salt is dissolved in the water before the cereal is added to the water. How to Make Oil and Water Mix. You often hear the saying that " water and oil do not mix." You can prove it if you wish and then you can disprove it. Suppose you put half a cup of water into an 8-oz. bottle and add a tablespoonful of kerosene Or fuel oil to it. Close the ^^ and shake it vigorously, shaking. Upon standing, the oil quiekly WHAT USES DO WE MAKE OF WATER? 91 separates. You have proved that water and oil under ordinary conditions do not mix. Now start again, but put a few shavings of soap in the water. Shake to make a soapy solution. Add the oil and shake vigorously as before. This time the oil does not separate from the water. Shaking divides the oil into many exceedingly fine droplets. 'In water alone they quickly combine and separate out from the water, but when coated with soap which is in the water, they keep their finely divided state and remain mixed with the water for a very long time. Thus you have shown that when soap is present to lend its aid, water and oil will mix. This mixture is different from solution and is called an emulsion. A kerosene emulsion is an insect spray used to kill aphids. Milk is an emulsion. It has oil in the form of butter fat dis- tributed in very fine particles. These rise very slowly, and when they form a layer on top of the milk, they are known as cream. Value of Soap in Cleaning. It is largely the grease and oils that hold the dirt particles to the hands and clothing. Water alone has little cleaning value because it cannot remove the oil. But when soap is added to the water it forms an emulsion with it and this loosens the dirt. For this reason soap is a valuable cleaning aid. When one lives where the water is hard, containing minerals like calcium compounds in the water, the soap is destroyed. Such water must be softened sometimes by boiling, some- times by adding washing powder or other chemicals before using soap. Otherwise a great deal of soap will be wasted. Why We Need Water. Do you know that your body is over 65 per cent water, and that some animals such as the jellyfish are 99 per cent water? Have you thought that the plants we eat, stems like celery, roots like radishes, all contain a large per cent of water, and that 92 WATER AND ITS EVERYDAY USES most foods, even though they seem dry, contain quite a good deal of water? Our doctors tell us we should drink from six to eight glasses of water a day, some of which may be taken in the form of milk. We can see a reason for this now that we know that all foods and our own body contain so much water. Water is also used not only to carry foods from one part of the body to another, for foods have to be dissolved in the blood before Do all living things contain water? Mention something that does not. they can be used, but it is used in the growth and repair of the cells of our body. If we examine a young growing shoot of a plant, we will find that the rapidly growing part is much softer and juicier than the older parts. This is because it contains more water. Not only is water used in the body to transfer foods, but it is also necessary to get rid of wastes. Some of the most poisonous body wastes are passed off in the urine and in perspiration. How We May Make Water Safe for Drinking. Many of us have visited friends in the country and remember with pleasure the cold water from the wells or springs near their homes. But a glance at the picture will show WHAT USES DO WE MAKE OF WATER? 93 that such water might be very unsafe. If water is taken from a well, the well should be protected by a cap of cement, as shown in the diagram, and it should be so located that drainage cannot enter it. Well water should be tested frequently for germs by town or state Boards of Health. A well in ordinary sandy soil situated above and at least 100 feet from any cesspool is safe. You may go camp- ing and be in doubt about the safety of your water supply. Boiling it for 20 min- utes will kill prac- Compare the conditions of these two wells. Under what conditions might the water in B be safe ? When unsafe ? tically all harmful germs and will make it safe for drinking. Unfortunately, boiling drives off the free oxygen and gives it a flat and unpleasant taste. The oxygen can be put back into the water by violently shaking it for a short time in a bottle partly full of air. Water Used in Cooking. Water is also used to cook foods in. We make our bread by mixing flour with water to form dough. We make our tea and coffee because of the solvent action of water which extracts the flavor from the tea leaves or the ground coffee so that the liquid has the flavor instead of the original tea and coffee. We can also transfer heat by means of water or steam, as you see when you cook a cereal in a double boiler. Other Uses of Water. We have seen that both plants and animals are made up very largely of water. This 94 WATER AND ITS EVERYDAY USES A miniature yacht race. Do you know how to sail a boat into the wind ? accounts for the fact that our gardens, lawns, and plants kept in the house need constant watering. We know that they wilt when they do not have sufficient water. Moisture evaporates from bodies of water into the air. We have all had the experience of sitting in the draft of an electric fan in order to cool off. Nature adds moisture to the air in a large way when breezes blow over large bodies of water, or when great forests send off into the air large amounts of moisture. Water helps us to keep more comfortable, and communities near large bodies of water have usually a pleasanter climate than those far away from sources of water. Finally, water is used in our recreation. Every boy and girl ought to know how to swim and sail a boat. Rowing, canoeing, and fishing are all recreations that depend upon water. Life in the Ocean. In addition to all the other uses of water, we can add perhaps the most important of all, the fact that water is the home of vast numbers of living things. Think of the amount of the earth's surface WHAT USES DO WE MAKE OF WATER? 95 covered by water — three fourths of it. Think of the thousands of forms of fish life that dwell in our oceans. Go to a museum and see the groups showing underwater life — sponges, corals, sea anemones, jellyfish, sea fans, and sea feathers, hundreds of kinds of worms — flat, round, or jointed. And besides these there are millions of tiny one-celled animals, sometimes so plentiful that although microscopic in size, they give color to the ocean and furnish food for hundreds of kinds of bigger animals. Variety of Life in Ponds. In addition to the larger bodies of water our brooks and ponds swarm with life, both plant and animal. All kinds of life may be found there. Frogs, turtles, salamanders, and snakes are in Wright Pierce Have you ever gone fishing ? There are bass and trout in this lake. What else do you think you could find on the shores or in the water ? 96 WATER AND ITS EVERYDAY USES the water or on the banks, while snails, mussels, clams, slugs, and worms of various kinds may be found on the mud of the bottom. Then there are fresh-water sponges which look like plants ; little green or gray hydras, and thousands of tiny water fleas which form the food of fish and other inhabitants of the pond. It is true that there are many animals which can live in water or in air, but many of these begin their life in water. Mosquitoes, flies, and dragon flies live in water in the earlier stages of their existence, emerging into the air only for their adult life. The mud at the bottom of the pond will disclose numerous insect larvae. The surface film, the water, and the muddy bottom will all reveal interesting forms of life. Over 70 different forms of life have been found in one eighth of a cubic inch of water when examined with a compound microscope. The water is more densely inhabited than the air or the land. American Museum of Natural History This is a glimpse of pond life as seen under a magnifying glass. Can you name any of the things you see in the glass ? WHAT USES DO WE MAKE OF WATER? 97 SELF-TESTING EXERCISE Select from the following list those words which best fill the blank spaces in the sentences below and arrange the words in proper numerical order. A word may be used more than once. salt bluing solution 56 steam acid liquid solid ice boil gas boiling solvent dissolve form heat evaporation fuels mix soap emulsion mixture washing dissolves oils water boiling oil 65 freezing Water is ordinarily a (1) , but in very cold regions it is a (2) called (3) When heated strongly on the stove, water will (4) , but if left in the open air, it changes to a (5) in the process of (6) When salt is stirred in water, it disap- pears because water is an excellent (7) Water will not (8) insoluble substances. The (9) or condition of water is determined by the amount of (10) it contains. Oils which do not readily (11) with water are made to do so by the addition of (12) The result is called an (13) In the process of cleaning, water is aided greatly by the addition of (14) Much of the dirt we try to remove in the process of (15) is held by fats or grease or (16) Soap in (17) forms an (18) with the fat or (19) and so loosens the dirt. People need to drink much water because it helps carry foods and remove waste and because the body itself is (20) per cent water. STORY TEST ALTON RELATES His EXPERIENCES ON SOLUBILITY Read carefully and critically. List all the errors and suggest corrections. I will tell you of my experiment on testing solubility of substances in water which I did at home. I found that water will dissolve salt and " absorbent " cotton. I presume this kind of cotton is called " absorbent " because the water absorbs it and makes a solution of it. Water will not dissolve ashes or soap chips. I found that oil would not dissolve in water alone, but if I put soap in the water with the oil and shook or stirred vigorously, the oil did not separate. This is because it had dissolved in the water. I boiled some water from a deep well until the water disappeared ; a small amount of solid was left. I put coffee grounds into water and boiled it. I poured the liquid off and the grounds were left, therefore there is no solution formed when one " makes coffee." H. & W. SCI. I — 8 98 WATER AND ITS EVERYDAY USES One reason you do not notice the adulteration of sugar with sand is that the particles look alike and they are all completely dis- solved in water. THE REVIEW SUMMARY In preparing a summary of what you have learned in this unit, you will want to place emphasis on the big ideas which have come out of the applications of the facts you have learned and the demonstrations you have seen. These big ideas we call generaliza- tions. For this unit they are as follows : 1. Water in all its three states, solid, liquid, and gas, produces important changes on the earth. 2. Water is a compound that can be separated into its elements. 3. Through a variety of changes in state, water passes through a cycle in nature. Before making your review summary, test your knowledge of the facts of the unit by checking over the text so as to be sure you know the facts underlying the generalizations. Then, using the generalizations, the material in the text, and everything you have read, seen, or done yourself, make a summary outline for your note- book. This outline you may use when you make a recitation. TEST ON FUNDAMENTAL CONCEPTS Make two vertical columns in your workbook. Head one CORRECT and the other INCORRECT. Under the first place the numbers of all state- ments you believe to be correct. Under the second place all the numbers of the statements you believe to be incorrect. Your grade = right answers X 3£. I. The air receives water from : (1) the ocean ; (2) breathing animals ; (3) condensation of moisture ; (4) living plants ; (5) deep- sea fish. II. When common salt is dropped slowly into boiling water: (6) it forms crystals on the bottom of the dish ; (7) a solution results ; (8) an emulsion is formed ; (9) the water becomes a solvent ; (10) the salt is a solvent. III. Water is a compound whose molecules are composed of : (11) two atoms of hydrogen; (12) like atoms; (13) oxygen and WHAT USES DO WE MAKE OF WATER? 99 nitrogen ; (14) two electrons and one proton ; (15) one part oxygen and two parts hydrogen. IV. In the process of making distilled water : (16) two changes of state are required; (17) a source of heat is required; (18) a source of cold is required to remove heat; (19) pure water must be used to start with ; (20) sea water cannot be used. V. A water is safe to drink if it has been: (21) formed by melting glacier ice ; (22) freshly distilled ; (23) filtered through five layers of cloth ; (24) taken from a river ; (25) boiled 20 minutes. VI. Living things in water : (26) may be more numerous than in an equal sized volume of land ; (27) are all microscopic in size ; (28) are all animals, no plants being found there ; (29) often only pass part of their lives there ; (30) all have to come to the surface to breathe as there is no oxygen in the water. THOUGHT QUESTIONS 1. Why will water clean some dirt spots better than others? 2. What is a solvent? Find the names of three solvents and name one important use of each. 3. Does milk hold cream in solution? What makes cream rise ? 4. If hydrogen will burn in the presence of oxygen, why doesn't the hydrogen burn in water when water is composed of one atom of oxygen and two atoms of hydrogen? REPORTS UPON OUTSIDE THINGS I HAVE READ, DONE, OR SEEN 1. Report upon an article related to some topic discussed in this unit. The article may be from a current number of a science magazine or from some popular science book you have read. 2. The waters of the earth. 3. Trips made by man down into the ocean. 4. Uses boys and girls make of water. 5. Water : in and out of the air. SCIENCE RECREATION 1. MAKE HYDROGEN BALLOONS Prepare hydrogen gas from dilute hydrochloric acid by action on zinc scraps. Carry the gas through water to wash it. The hydrogen is discharged from the end of a fire polished glass tube 100 WATER AND ITS EVERYDAY USES or a clay pipe. Dip the end of the glass tube into the soap solution. Remove quickly. When the bubble is an inch or two in diameter, tutfck 4. basket/ shake it off and watch its movement. Do not have any flame near the hydrogen generator. When mixed with air, hydrogen will explode violently upon the application of a flame. 2. MAKE DISTILLED WATER Devise an apparatus using things you have at home and make distilled water for the automobile battery. 3. CRYSTAL MAKING Make crystals by allowing saturated solutions of salts to evaporate slowly. Suspend strings in the liquid for the crystals to cling to. They will also form on the vessel holding the solution. Salts that are good for this are : com- mon table salt, alum, potassium dichro- mate, and copper sulphate. If you start with a hot saturated solution, crystals will start to form as the solu- tion cools. Make a basket form of cotton-insulated wire #20. Suspend this in a hot saturated solution of potassium dichromate. A beautiful crystal orna- ment will be produced by allowing crystals to grow upon this for 24 hours. \\idC- - £ concentrated f salt. ^ I -Solution SCIENCE CLUB ACTIVITIES 1. TOY RIVER BARGES Materials needed: Three half walnut shells; three small cork stoppers ; stick of wood about size of pencil ; paraffin. Preparation: Cut the corks into halves and fasten them with paraffin to the ends of the shells so that there will be a smooth WHAT USES DO WE MAKE OF WATER? 101 vertical surface when the shells float in water. Have the top of the cork come just level with the top of the shells. Liquid solder may be used in place of paraffin. There is a film over the surface of water like stretched rubber. The force of this film on water is great enough to hold the toy river barges together if they are brought end to end. The whole line of them can be drawn along by holding one end of the stick in the water just in front of one and pulling slowly. By pinning a small piece of soap to one end of the stick and holding that in the water just back of the boat, you can apparently repel a single boat. The soap weakens the surface film so that the boat is pulled in the opposite direction by the film on the other side of the boat. By using soap on one end to repel and the oppo- site end to attract, you can make the boats maneuver in a manner which appears mysterious to one who does not know the secret. 2. POND LIFE AQUARIUM Procure several large glass jars. Have the club members divide into several groups and visit different small pools and ponds on a field trip. Bring back both plant and animal specimens. Ar- range several aquariums and watch development in them. 3. PREPARE A SCRAPBOOK ON WATER Classify the uses of water under : solid, liquid, and gaseous form. Each member report upon the uses. A contest may be arranged by dividing into three groups, the ice group, the water group, and the steam group. An important use named wins a point. REFERENCE READING Innes, W. T., The Modern Aquarium. Innes, 1931. Meister, M., Water and Air. Scribners, 1930. Thompson, J. M., Water Wonders Every Child Should Know. Grosset. Whitman, W. G., Household Physics. Wiley, 1932. • SURVEY QUESTIONS Does all fire produce heat and all heat produce fire ? What must be done to set a com- bustible substance on fire ? Why does a fire sometimes go out by itself? What is our greatest natural source of heat? Do you know how heat travels from one place to another? Do you know the scientific differ- ence between heat and cold ? What instrument measures temper- ature and how does this instru- ment work? Galloway UNIT V HOW WE USE HEAT PREVIEW Have you ever thought how important a part heat plays in your life? Ancient peoples, Babylonians, Aztecs, and our American Indians, worshiped the sun because it gave them heat and warmth in winter and provided for their crops in summer. Probably fire has been more wor- shiped than any other element in nature. The use of fire must have been a great discovery to ancient people. No- body knows how man first got it. The first fire may have come from lightning striking a tree, it may have come from a chance focusing of the sun's rays through a rounded quartz pebble, it may have come from an eruption of hot lava from a volcano, it may even have come as the boy The artist has shown some primitive people worshiping fire. What do you know about fire worshipers ? From a mural in the Library of Congress. 103 104 HOW WE USE HEAT Wright Pierce Is this girl scout going to make a fire correctly? Could you do better? If so, how would you go to work ? scouts make it today, from friction by means of rubbing things together, or it may have come from a chance strik- ing of two hard stones so as to make a spark. But with it came comfort. Think of what home would be without any heating apparatus, or without fire to cook with. Think of the fun you have popping corn or making candy, or getting warm around a bonfire. Think of how heat is used in melting substances such as solder, and how it can be used for casting lead toys. These are only a few of the cases in which we use heat. Our uses of heat depend upon our ability to control it. To control it we must learn how it acts. Heat can make things larger, can make gases from liquids and solids, and can change the flavor of foods. Heat can be transported by water or steam from a furnace in the cellar to our rooms, where HOW IS HEAT PRODUCED? 105 it gives us warmth and comfort. It means warm rooms in winter ; it makes possible the cooking of raw foods ; it gives us hot water, hot air, and hot foods. Today fire has come to be used in hundreds of ways that the ancients never dreamed of. PROBLEM I. HOW IS HEAT PRODUCED? If you are a boy or girl scout, you know how to build a fire. First you get some paper or dry leaves, cover with some shavings or thin kindlings, and then place larger sticks at an angle over the other materials so as to make a good circulation of air. When the fire has started, you fan it or blow on it to keep it burning. Evidently a fire must have something that will burn, a good supply of air which contains oxygen, and enough heat to warm the material to what is called its kindling temperature. Demonstration 1. Kindling Temperatures. Break off and discard the heads of two matches, place the sticks on an asbestos mat. Two inches away from them put a piece of sulphur or brimstone the size of a grain of rice. Melt about 20 grams of lead in an iron spoon supported on a stand as shown in the diagram. Do not use more heat than is needed just barely to melt the lead. When the lead melts, pour half of it on the asbestos so that it touches the sulphur, and pour the rest of it so that it covers the end of the sticks. Does either substance take fire? Remelt the lead in the spoon. When it is just melted, turn the gas under it low and stick the end of a match stem into the lead. Does it take fire ? Rub the end of one of the sticks in the sulphur so that some of it clings to the stick, and touch it to the lead. Look closely, for sulphur burns with a pale blue flame. Which has the lower kindling point, the sulphur or the wood ? 106 HOW WE USE HEAT Kindling Temperature. This shows that different sub- stances take fire at different intensities of heat. The intensity or degree of heat is called temperature. In making matches, the match head contains a compound of phosphorus which ignites at a very low temperature, and a compound that gives off oxygen easily, also pow- dered glass or sand, and glue. By rubbing the match head against a rough surface, enough heat is developed to ignite the phosphorus. In the safety match, the head is made of a substance which burns at a low temperature, while red phosphorus mixed with sand or powdered glass is placed on the box to give it a rubbing surface. The head of the match will not ignite unless it is helped by the phosphorus on the box. What Causes Fire ? Many substances like phosphorus, sulphur, and wood when heated to their respective kindling temperatures in the presence of air or oxygen will burn and produce fire. Such materials if burned to give useful heat are called fuels. As we shall see later, gas, coal, oil, and wood are fuels. When fuels burn, heat is produced by oxidation. In order to keep a fire burning, we must have oxygen and keep the temperature at or above the kindling temperature. You can easily show the effect of cooling below the kindling temperature. Copper is a good conductor of heat. Wind a piece of copper wire into a spiral coil ^ of an inch in height, making it large enough to slip easily over the wick of a candle. Light the candle and bring the cold wire down on the wick, the light will go out. But if you light the candle again, then heat the copper coil to red heat and bring it down over the wick, the candle will continue to burn. This shows us that to HOW IS HEAT PRODUCED? 107 Explain how the candle was lighted by the flint and steel method. keep a fire burning we must not cool it too much. Heat is transferred to the cold copper wire. This transfer of heat from one place to another and from one body to another will be discussed in our next problem. The Use of Tinder in Colonial Days. In colonial days they caught sparks in tinder and produced fire in a much more uncertain way than we do with our modern matches. If you wish to make tinder, get some white cloth - old sheeting or worn handkerchief; cut sev- eral pieces about five inches square. Hold each one separately with a wire or tongs and set on fire. As the flame begins to die down, lay the charred cloth upon a smooth flat piece of tin or other metal and quickly cover with another metal. This cools and pre- vents the tinder from burning up. Lay two sheets of tinder upon some tissue paper and strike a rough edge of hard rock, such as flint or granite, against the sharp edge of the rod of steel so that sparks will fall upon the tinder. When a spark has ignited the tinder, gather up the paper and fold up about the sides to make a ball with a small opening, blow gently to increase the burning, and when it smokes strongly, blow harder. If the paper then bursts into flame, you will have had the experience of making fire by a method that was common a little over a hundred years ago. Our forefathers tried to keep a fire but would sometimes go to the neighbors to " borrow" live coals when their fire was all out. They kept tinder on hand so that in case of emergency they could produce fire by the " flint and steel" method, which is the method 108 HOW WE USE HEAT just described. But even the'flint and steel was a big ad- vance over the many centuries-old friction method with the bow and drill. Your great-grandparents doubtless thought of the wonderful way they had of making fire compared to the people of early times, just as you now think of the match as a wonderful device when compared to the flint and steel of former days. Friction with a match makes fire in a fraction of a second, but friction with the bow and drill under the best of conditions re- quired minutes to make fire. SELF-TESTING EXERCISE Select from the following list those words which best fit the blank spaces in the sentences below. Arrange the words in proper numerical order. A word may be used more than once. kindling go fire same temperature temperatures stops burns helps burn out better different combustible match incombustible below lower higher friction same chemical action fuel physical air (oxygen) stoves goes Fanning the kindlings placed on the glowing coals in a fireplace makes the fire (1) (2) Fanning a candle flame makes the fire (3) (4) In the first case there is much heat ; fanning brings in more (5) and so (6) the burning. In the second case there is little heat; fanning brings in so much air that the (7) is reduced (8) the (9) temperature and so (10) the burning. There can be no burning or com- bustion unless a (11) substance is heated to its (12) (13) and supplied with (14) A common useful article making use of a combination of substances with different kindling temperatures is the (15) In early days of fire making (16) generated the heat. Today we have many devices using friction, but our ability to get fire so easily lies in the use of materials with (17) kindling (18) Sulphur takes (19) at a (20) temperature than wood. WHAT ARE THE CHARACTERISTICS OF HEAT? 109 STORY TEST DOES JANE KNOW How TO PRODUCE HEAT? Read carefully and critically. List all the errors and suggest corrections. This is the way I learned to start a fire when I was a scout: Get a lot of dry leaves and lay them on some sticks of dry wood. If you have paper with you, crumple it and use it with the leaves. Lay large logs loosely over the mass o£ burning leaves. Substances with a low kindling point like phosphorus will take fire at such a low temperature that it is unsafe to hold them with the bare fingers. You can set fire to a thin shaving of pine easier than you can to a dry pine log because the shaving has a lower kindling temperature. A cold metal may extinguish a candle flame because it radiates heat so fast it cools the candle wax below its kindling point. In lighting a match, the first energy used is chemical, then heat and finally light result. There are only three changes of energy involved. PROBLEM II. WHAT ARE SOME OF THE CHARACTERISTICS OF HEAT? When we have a bonfire, we see that fresh air comes in to the fire, while smoke and gases rise from the fire. Such currents of air are called convection currents. cold- -Vater- Demonstration 2. Convection. Fill a battery jar with cold water. Fill a small bottle with hot water colored with red ink ; place in it a perforated cork containing two tubes, as shown in the diagram. Lower the small bottle of hot water to the bottom of the jar of water. What happens? Put in your workbook a dia- gram showing the movement of the water. The movement of the liquid shown in this experiment is called convection. We thus see that convection takes place in liquids, and a bonfire shows that it takes place in gases. Since rising air or water is hot, heat is carried by it. What makes the heated water rise? This rise is caused by the fact that warm water is lighter than cold 110 HOW WE USE HEAT water. Gravity therefore pulls with greater force on a given volume of cold water than it does on the same vol- ume of warm water. Because of this greater pull, the cold liquid is drawn under the lighter one and pushes it up, thus causing a convection current. A similar explana- tion accounts for convection in gases. Demonstration 3. To See if Peat Will Travel Along a Metal Rod. Take a metal rod ; attach it to a stand, as shown in the diagram. Tie threads to each of six tacks. Attach to the rod each of the threads about two inches apart by means of melted wax. Now apply heat to the end of the rod. What happens? /!/ tacks 4 fastenecC Conduction. This dem- -i ^ onstration shows that heat travels from one end of the rod to the other. The flame •\viU2 "\vax. heats the tiny molecules of iron, causing them to vi- brate or move faster. They hit neighboring molecules harder blows and thus cause them to move. In this way, from molecule to molecule, heat travels by conduction. Most metals are very good conductors of heat. Substances like glass, water, and many rocks are fair conductors ; while air, paper, linen, silk, and wool carry heat so poorly that they are called nonconductors. ' Poor conductors of heat are sometimes called heat insulators. Metals are the best and gases the poorest conductors of heat. Radiation. The sun is 93,000,000 miles away from us, and we know there is very little matter in all of this space. Yet heat comes from the sun to us. This method of heat transfer is known as radiation. Experiments show that rough, black, dull substances absorb heat better than WHAT ARE THE CHARACTERISTICS OF HEAT? Ill smooth, light, or shiny substances. Substances which absorb heat give it up easily by radiation. Demonstration 4. Heat Causes Expansion. Gas. A glass flask filled with air having a balloon attached to one end is heated. What happens to the balloon? Let the flask cool. Result? Liquid. Fill a 500 cc. flask full of colored water. Place a stopper carrying a long glass tube so that the colored water rises in the tube. Mark the level of the water carefully on the tube. Now warm the flask by placing in a dish of hot water. What happens ? Remove from the hot water and allow the flask to cool. Result? Solid. Support a copper rod or tube two or three feet long on a block, as shown in the illustration. End A is not movable; TO* -move burner- back Q*ul end B can roll over a wire bent so the end hangs vertically in front of the block. Hang a weight near B to hold the rod firmly upon the wire. Heat the rod by moving the gas flame back and forth along the rod. Watch the position of the wire pointer. Explain result. Let the rod cool. Explain the observed result. 112 HOW WE USE HEAT This demonstration shows very clearly that heat causes expan- sion. Contraction of substances is brought about when heat is withdrawn from them. On a hot day a metal drawbridge after being opened refused to come together again. Why? The draw- bridge tender squirted a stream of cold water upon the bridge and it went back into place. Why? How Temperature Is Measured. We have seen that heat makes things warmer, and the higher the tempera- ture of a body, the more heat it contains. But heat and temperature are not the same thing. Temperature is the intensity of heat and is measured in units called degrees. This measurement makes use of the principle that matter when heated expands, and when cooled contracts. The thermometer is made of a glass tube having a very fine bore. A bulb at one end of the tube is filled with mercury or colored alcohol. Since heat makes the liquid expand, it will rise in the small bore in the tube as it gets warm and thus indicates the degree of heat which is marked on the scale. Thermometer Scales. There are two thermometer scales, the Fahrenheit marked F., used by the weather bureaus and in everyday life, and the Centigrade marked C., used in scientific work and most foreign countries. The freezing point of water is 32° on the Fahrenheit scale and zero on the Centigrade, while the boiling point of water at sea level is 212° on the Fahrenheit scale and 100° on the Centigrade. Heat Causes Changes in the State of Matter. Another thing that heat does is to change the form of different substances. The quantity of heat energy possessed by the molecules of water determines whether water is in the solid, liquid, or gaseous state. The molecules in ice have the least energy. Since heat is taken from warmer objects to change ice to water, ice is used in our refrigerators. Molecules of liquid water have more energy than molecules WHAT ARE THE CHARACTERISTICS OF HEAT? 113 8o1 7o° <5C> 50* 30° do" -10° -17.751 2oo° °f water 1 180° 170' ' 160° 1150° 140° 130* 120° .110° |-l°.0lT7ormal 90° [So' of ice. A tub of water on a cold night gives up heat to the air. Fruits and vegetables do not freeze until the temperature is as low as 28° F. ; and so tubs of water placed in farmers' cellars have many times kept fruits and vegetables from freez- ing. In changing water to steam at 212° F. a large amount of heat is stored in the molecules of steam. This energy may be used in cooking, in heating, and in the production of mechanical energy by means of the steam en- gine. When steam con- denses to a liquid, all this stored heat is given off. That is why a burn by steam is so much worse than a burn by boiling water. Both are the same temperature, but the steam has more heat in it. Freezing and Boiling Temperatures. Water freezes and ice melts at 32° F. It seems strange at first to think of water and ice at the same temperature. But How are clinical thermometers used ? when just enough H. & w. sci. i — 9 room temperature poiTZ.1, of water I lo° 0° If butter melts at 93° F. it will melt at what temperature Centigrade ? 114 HOW WE USE HEAT In how many ways is heat energy used in the kitchen ? heat is added to ice at 32° to melt it, the resulting water also is at 32° F. There is no change in temperature when ice melts or when water freezes. Water boils and steam condenses at sea level at 212° F. During this change of state there is no change in tem- perature. Demonstration 5. Boiling Water. 1. Constant Temperature of Steam and Boiling Water in Open Vessel. Heat water in a flask. Have two thermometers, one placed so that the bulb is in water and the other so that it will be in the steam above the water. After the water is boil- ing, read the thermometers at inter- vals of one minute for five minutes. Tabulate your results. What are your conclusions? 2. Boiling Water at Reduced Pressure. A ring-neck, heavy- walled, round-bottom flask is filled half full of water. Boil the WHAT ARE THE CHARACTERISTICS OF HEAT? 115 water until the air has been driven out. Remove the heat. Close the flask with a stopper holding a thermometer. As the steam condenses, the pressure on the water is reduced. After the bubbling has stopped, condense more steam by placing a cold wet cloth or ice around the upper half of the flask. Does the water boil again? At what temperature did you boil water? After the temperature gets below 90° C. or 190° F. and there is no boiling, place the heat under the flask for a moment. Result? Why Pressure Cookers Are Useful. At sea level water under average atmospheric pressure boils at 212° F. Both water and steam have the same temperature. People who live on . high mountains find that water boils be- fore it reaches 212° F. This is because the pressure of the air is less and the boiling point of water de- pends upon the pres- sure on its surface. On some high moun- tains boiling water is not hot enough to cook vegetables, so they must use some other method or in- close the water in a vessel to prevent the escape of steam. The increased pressure raises the boiling point and makes cooking possible. In the pressure cooker where steam is not allowed to escape, the pressure increases and the temperature rises with the rise in pressure. This ac- counts for the more rapid and thorough cooking of foods Wright Pierce In what ways is a pressure cooker useful? Why would it be useful at high altitudes ? What scientific principle underlies this value? 116 HOW WE USE HEAT cooked in such vessels. Pressure cookers are commonly used in high altitudes, but are also used advantageously at low levels chiefly to save time in cooking, to save fuel, and to make tough cuts of meat more tender. SELF-TESTING EXERCISE Select from the following list those words which best Jill the blank spaces in the sentences below and arrange the words in proper numerical order. A word may be used more than once. matter state heat hot cold temperature under thermometer pushes particle increases contract larger weight decreases change conduction force expand substance more conductors radiation reduction Gravity pulls on one cubic inch of cold water with (1) force than it does on one cubic inch of (2) water. As a result, the (3) water flows in (4) the (5) water and (6) it upward. Heat is transferred from particle to (7) in (&) by a process called (9) Metals are better (10) of heat than clothing. (11) is not always required to carry heat; in the transfer by (12) heat can pass through empty space. When most substances are heated, they become (13) or wo say they (14) The measurement of (15) by means of a (16) takes advantage of the (17) in size of bodies when heated to a higher temperature and of its (18) in size when it is cooled. Many substances like ice and lead, when heated, may (19) their (20) and become liquids. STORY TEST FRED Is AT THE MICROPHONE TODAY TELLING "WHAT HEAT CAN Do" Read carefully and critically. List all the errors and suggest correc- tions. Fellow science students : From my study of heat I have come to the conclusion that heat is a sort of circus trickster. He can get aboard the molecules of air coming from the throat of a trumpeting THE HEAT OF THE BODY 117 elephant and rise to the top of the big tent with no apparent support in a process called conduction. He also can walk a tight wire. You recall how when you hold one end of a metal in the flame, heat comes over and tells you to let go. This method of travel is called radiation. Heat is an austere master; when he gets inside a vessel of water and cracks his whip the molecules of water cower and crowd together making the volume smaller. Heat is a fickle fellow and changes partners often. Believe it or not, he likes ice cream. I was called away from dinner last night when half through my ice cream dessert and when I came back just a pasty liquid was left. Why? Because heat had left the air and gone into the ice cream. They call this a change of state but I call it meddling. There is an instrument called the barometer which is used to tell how hot or cold a body is. I had one under my tongue once. Heat went into it from me and made me feel a lot cooler. PROBLEM III. HOW DOES CLOTHING AFFECT THE HEAT OF THE BODY? What Keeps the Body Warm? We have already learned that the heat of the body is caused by the oxida- tion of food which we eat. The circulation of the blood assists in keeping all parts of the body at about the same temperature. But we know that on a cold day the out- side of the body gets cold. We use clothes, bedclothes, hot-water bottles, or electric pads to keep warm. Evi- dently clothes should be worn not only for their good looks but for their practical value. In hot climates little clothing is needed, while in very cold parts of the world furs and skins act as insulating materials against the cold. In a temperate climate where changes are frequent clothing ought to be adjusted to fit the tem- perature. What Materials Are Used in Clothing? We know that most of our clothing comes from five sources. Outside of leather and rubber, our clothing is made from fibers of wool, cotton, flax, silk, and rayon. Wool and silk are of animal origin ; cotton and linen (from flax) are of HOW WE USE HEAT Two extremes in clothing. Give scientific reasons for the two conditions in clothing shown here. vegetable origin. Rayon is a chemical product made from vegetable matter such as wood pulp and low-grade cotton. Demonstration 6. Fibers and Tests for Fibers. Physical Appearance of Fibers. Examine under the microscope, slides of wool, cotton, flax, silk, and rayon. Wool fibers have little scales projecting from the surface. Cotton fibers look twisted. Flax fibers are never twisted, vary in size, and have small transverse markings. Silk fibers have no markings, are smaller in diameter than flax. Rayon fibers are smooth like silk but much longer. Place in your workbook sketch drawings showing the appearance of the different fibers. Absorption-of-Water Test. Place small equal-sized samples of cloth made of the different fibers in saucers containing equal amounts of water. Which absorbs the most water? Which the least? Chemical Test. Boil each of the five different kinds of cloth in a lye solution (5 per cent sodium hydroxide). Wash carefully in THE HEAT OF THE BODY 119 water before handling. Test the strength of each cloth. Which cloth holds together the best? Burning Test. Using the five kinds of cloth, light each piece separately. Notice the odor and rapidity of burning. Repeat the test, holding strip of moist blue litmus paper in the smoke given off by the cloth. What happens? Do the same with moist red litmus paper. What happens? Sum up all your observations in your workbook. \\ool fibers Cottoia fibers flax fibers silk fibers- What These Ex- periments Show. Wool fiber because of its scales gives gar- ments their rough texture. When such fibers shrink, as they may when passing from hot to cold water or to water containing such a substance as lye, the scales cause the fibers to stick close together. Wool undergarments ab- sorb moisture and allow it to evaporate slowly. This prevents rapid loss of body heat. Cotton underwear leaves an excess of moisture on the skin and the mois- ture may evaporate rapidly, thus chilling the body. The twist in the cotton fibers serves the same purpose as the scales on the wool : it gives spring and elasticity to the material. Cotton fabrics are harder than wool, and there are fewer air spaces in cotton materials than in wool, hence cotton garments permit heat to escape more rapidly from the body. Linen fibers have little elasticity and hence the fabrics manufactured from them do not shape 120 HOW WE USE HEAT themselves to the body. Linen can be washed in hot water without injury, but it is costly and so is not used as much as cotton. Silk both absorbs and loses water rapidly, but it is expensive and hard to wash. Rayon which is made largely from wood pulp is used extensively for underwear. It absorbs water readily and loses it rapidly, and consequently makes good undergarments. Clothing for Winter and Summer. The human body is a self-regulating machine in which the body temperature is normally kept at 98.6° F. Underneath the skin is a fine network of blood vessels from which heat is passed off through perspiration. When we do hard work, the blood becomes heated and circulates more rapidly. The blood vessels of the skin get larger, and give heat off to the sweat glands, which pour out perspiration. This in turn evapo- rates, cooling the skin, and this cools the blood ; thus our temperature is kept constant. Evidently, then, in winter we need underclothes which will not let heat out. Under- clothes which do not hold moisture are best because wet, sticky undergarments cool us by conduction if it is cold, and keep us uncomfortably hot by preventing evapora- tion if it is warm. It does not make very much differ- ence what kind of materials are used, provided the under- clothes are porous. Woolen underclothes are best for winter, because the curly fibers make them porous, and because they absorb moisture and give it up slowly, thus preventing the skin from being cooled too rapidly. We have seen that dark substances absorb heat and light- colored substances reflect heat ; therefore, to wear dark clothes in winter and light clothes in summer is scien- tifically correct as well as more comfortable. If you take two test tubes, place a thermometer in each tube, then wrap a piece of white cloth around one and a piece of dark cloth of the same weave around the other, leave both tubes in the sun side by side for a few minutes, and then read the THE HEAT OF THE BODY 121 .-thermometer temperatures, you will find that the tube surrounded by the dark cloth shows a higher temperature than the other tube. Evidently ab- sorption of radiant en- ergy has been the cause of this difference in temperature. In the winter we wish to put a nonconductor be- tween the body and the outside cold air. For this reason fur coats and other dense materials are used. We sometimes place a newspaper over our chest when going into a cold wind. Can you explain Scientifically In which tabe ^ the thermometer register the reasons for this? higher? why? SELF-TESTING EXERCISE Select from the following list those words which best fill the blank spaces in the sentences below and arrange the words in proper numerical order. A word may be used more than once. reduces 98.6 loss silk scales 76.4 warmth heat wool shrink rayon air rubber nodes light fibers absorbs elasticity dark stretch cold replaced heats smoothness evaporates silky hot wool of In cold regions clothing is very useful to prevent (1)_ (2) from the body. Of the animal fibers (3) and (4) , (5) is the more common while (6) make more beautiful fabrics. In recent years (7) has to a large extent (8) silk because of its low cost. The rough texture of wool is due to HOW WE USE HEAT (9) which when a garment is rubbed, especially in hot water, cling together, causing the garment to (10) Much of the warmth of any garment is due to the (11) held within the meshes of the cloth. The normal temperature of the body is (12) F. Evaporation of water from the surface of the body (13) the temperature. In winter (14) colored clothing is warmer than (15) colored clothing because it (16) more heat. STORY TEST ELISE GIVES Us SOME IMPORTANT FACTS ABOUT CLOTHING Read carefully and critically. List all the errors and suggest corrections. Ever since it was found that fibers could be spun into thread and then woven into cloth, man has had many different kinds of materials from which he can make his clothes. Whether it is the silky rayon made by the silk worm or the linen fibers taken from the seed of plants, it is possible to weave it into many pretty pat- terns. You can tell true rayon from animal silk because it burns with odor of burning feathers and shows nodes along a smooth rod when viewed under a microscope. Cotton can be told from wool because it burns faster and dissolves in alkali. Yesterday I had a temperature of 94.7° F. and Mother kept me in saying I had a fever because the normal temperature is 89.6° F. When we work hard, we increase the body heat and perspiration. Evaporation of the perspiration is a cooling process and so helps to keep the body temperature down to normal. We should choose clothing which checks evaporation in winter and aids it in summer. THE REVIEW SUMMARY In preparing a summary of what you have learned in this unit, you will want to place emphasis on the big ideas which have come out of the applications of the facts you have learned and the demonstrations you have seen. In this unit look carefully for other generalizations than those which follow : 1. Heat is present to some degree in all matter. 2. Our greatest source of natural heat is the sun. 3. Heat is produced from other forms of energy. 4. Heat can be transferred through matter or by radiation. 5. Heat causes many changes in matter. 6. Heat is essential to the human body. THE HEAT OF THE BODY 123 Before making your review summary, test your knowledge of the facts of the unit by checking over the text so as to be sure to know the facts underlying the generalizations. Then, using the generalizations, the material in the text, and everything you have read, seen, or done yourself, make a summary outline for your notebook. This outline you may use when you make a recitation. TEST ON FUNDAMENTAL CONCEPTS Make two vertical columns in your workbook. Head one CORRECT and the other INCORRECT. Under the first place the numbers of all the state- ments you believe to be correct. Under the second place all the numbers you believe to be incorrect. Your grade = right answers X 2. I. Before we can start a fire we must have : (1) heat ; (2) nitro- gen ; (3) oxygen ; (4) an incombustible substance ; (5) inflam- mable material. II. Heat travels from : (6) the sun to the earth by conduction; (7) a flat iron to clothes being ironed by conduction ; (8) hot coals to a kettle above by radiation ; (9) a soldering iron to the solder by convection ; (10) a fireplace to objects in the room by conduction. III. When heat is applied to water, it may change its : (11) tem- perature; (12) state to a solid; (13) size; (14) weight; (15) com- position. IV. The temperature of boiling water is: (16) 32° F. at sea level; (17) less on tall mountains than at sea level; (18) greater in a partial vacuum; (19) never over 212° F. in a pressure cooker ; (20) always the same 98.6° F. V. There is a change in temperature when: (21) water cools; (22) water at 32° F. changes to water at the boiling point; (23) steam at the boiling point condenses ; (24) ice melts ; (25) a hot iron is put into cold water. VI. The principle of heat insulation is used when we use : (26) storm windows; (27) the pressure cooker; (28) hot-water bottle ; (29) asbestos mats on the table ; (30) copper for hot-water pipes. VII. Wool fiber: (31) is a fine, flattened, and twisted fiber; (32) will dissolve in a 5 per cent sodium hydroxide solution ; (33) ab- sorbs water more freely than cotton; (34) conducts heat well; (35) burns faster than linen. VIII. Cotton fiber : (36) gives the odor of burning feathers when burned ; (37) will dissolve in a 5 per cent sodium hydroxide solution ; (38) is a thick, lustrous fiber ; (39) has the same chemical composition as the material from which rayon is made; (40) is a vegetable fiber. 124 HOW WE USE HEAT IX. Silk fiber: (41) is of animal origin; (42) has a more brilliant luster than any other fiber except rayon; (43) has little scales projecting from its surfaces; (44) is composed of cellulose; (45) is stronger than artificial silk when both are wet. X. In washing woolens it is well to use : (46) boiling water ; (47) soap containing free alkali ; (48) little soap but much washing soda; (49) water below boiling point; (50) a small amount of bleaching powder. THOUGHT QUESTIONS 1. Make a list of materials which have a low kindling temper- ature; a high kindling temperature. Which of these would be best to build a fire with? 2. Find ten ways in which heat insulators are used in your home. 3. Why is the outside of a teakettle kept bright and smooth while the bottom is dull, black, and rough? 4. Why does a bicycle tire register greater pressure on a hot day than on a cold day? 5. Why is it when you fill the radiator of your car full to the brim on a cold day that it begins to run over shortly after you start the car? 6. You are going to Duluth for your Christmas vacation. What clothes would you take with you, and why? 7. You are driving from New York City to Florida in March. What clothes would you wear on the trip? Give your reasons. REPORTS ON THINGS I HAVE READ, DONE, OR SEEN 1. Report upon an article related to some topic discussed in this unit. The article may be from a current number of a science magazine or from some popular science book you have read. 2. Everyday activities involving expansion. 3. An account of the work of Bunsen or of Fahrenheit which is related to heat. 4. Uses of heat insulators. 5. How man's activities and habits vary at different latitudes on the earth. SCIENCE RECREATION 1. Pressure of ice. Fill a small bottle with water. Put a cork in tightly. Be sure there is no air space left inside. Put this either in the ice-cube pan and put into the cooling coil of the refrigerator, or place it outdoors on a day when the temperature THE HEAT OF THE BODY 125 is under 25° F., or pack it in a mixture of crushed ice and coarse salt. Examine after two hours. Account for the result. 2. Cast lead weights. Make exactly 1 oz., 2 oz. to use on a letter scale. Cast lead toys. 3. Make a study of heat-conducting materials used in your home and write a report upon them. 4. Make a study of heat-insulating materials used in your home and write a report upon them. SCIENCE CLUB ACTIVITIES 1. THE FORCE OF STEAM Put a cupful of hot water into a half-liter flask. Stretch the open neck of a rubber balloon over the opening of the flask. Fasten the flask to ringstand with a clamp. Boil the water, being very careful not to allow the flame to come near any part of the rubber balloon. Continue the heating until the steam escapes into the room. Have the club members stand several feet away until the climax is over. 2. BOIL WATER IN A PIECE OF PAPER ^ hot Voter Get a piece of stout paper of medium thickness about 5" or 6" square. Fold this to make a conical cup. Have the fold come inside the dish so that outside there is only one thickness of paper be- tween the water inside and the flame outside. Place the cup in a ring on the ringstand. Trim off the paper that is more than -J-" above the top of the iron ring when the cup is filled with water. Put hot water in the cup to start with, and place a low flame under the cup. Heat until you see the water boil. REFERENCE READING Carpenter, F. G., and Carpenter, F., The Clothes We Wear. American Book Company, 1926. Collins, A. F., Experimental Science. Appleton, 1929. Collins, A. F., The Boys' Book of Experiments. Crowell, 1927. Tower, S. F., and Lunt, J. R., The Science of Common Things. Heath, 1922. A study of fire, page 146. Whitman, W. G., Household Physics. Wiley, 1932. Heat, pages 24- 30; Thermometers, pages 55-65; Pressure Cooker, pages 105-114. SURVEY QUESTIONS What makes it possible for you to see some objects in the room ? Do you know why you cannot see the air? If it were not for mirrors, how could you tell how you looked? Do you know where the sky, the moon, and the electric lamp get their light? Why is good light needed in taking pictures ? What causes a rainbow ? Can you define color and tell what causes it ? Why are not all the lenses in eye- glasses alike ? Publishers' Photo Service UNIT VI HOW WE USE LIGHT PREVIEW Have you ever awakened from sleep on a dark night to find yourself in utter darkness? How glad you were to have an electric light close at hand! What a sense of helplessness we get when we are without any light ! We certainly enjoy light, for it gives us so much : our ability to see views and pictures, to read, to see wonderful sun- sets, the colors of birds and flowers, or the gray vastness of the desert. It gives us our food, for we know green plants depend upon it. Sir Isaac Newton, a great English scientist of the seven- teenth century, believed that light consisted of very small particles given off at great speed by all luminous bodies. He thought that when these particles struck the eye, they produced the sensation of light. This theory was accepted by scientists for over a hundred years, and then discarded in favor of a theory suggested by a Dutch physicist, Huygens.1 This theory stated that all luminous bodies caused the ether, which was supposed to fill all space, to vibrate. When these vibrations reach the eye, they give the sensation of light. Recently a new discovery by a German and an Indian professor give other ideas. This is the so-called Quantum theory which is based on the belief that light proceeds in little gusts or packets of energy instead of continuous waves. Still another theory goes back to that of Newton and says that light travels in the 1 Christian Huygens (hl'genz), Dutch astronomer and physicist, 1629- 1695. 127 SIR Bausch & Lonib Optical Co. ISAAC NEWTON, 1642 1727. IVTEWTON must have been a clever boy, for although he did not do *• ^ well in school he was very ingenious. He made a clock which ran by water, a sun dial, and a windmill which actually ground corn. At the university he specialized in mathematics and science and soon showed his genius. He improved methods of calculation in mathematics and applied them in physics; he invented the reflect- ing'telescope; he made navigation safer by making certain the positions of the heavenly bodies; and he proved the pull of gravity was a universal law. Newton's experiments with a glass prism and a beam of sunlight were the beginnings of spectrum analysis, which is now a useful tool of the scientist. The spectroscope, making use of the prism principles, is particularly useful to the astronomer. After over 40 years of service in Cambridge University he died, one of the most honored men of his time. HOW DO I USE LIGHT? form of tiny balls, each of which is spinning very rapidly in space. In this book we will agree with the theory that light is a form of radiant energy and that it passes through space by means of very rapid vibrations. Light travels at the astonishing rate of over 186,000 miles a second. When a candle is lighted, there are changes in the material of which it is made, which produces light energy. This radi- ates through space in all directions. Heat is also radiated from hot bodies, and the disturbances in the aerial of a broadcasting station send out electrical radiations. Evi- dently, then, light, heat, and electricity may travel as forms of radiant energy. It will be the purpose of this unit to learn something about the ways in which light is used in our everyday life. PROBLEM I. HOW DO I USE LIGHT? If you were ever up to see the sunrise, you know that as daylight approaches, objects begin to change from hazy gray outlines and become more and more distinct as light falls on them, till, in the early sunlight, they appear in all the colors of nature. We have just read that light is a form of radiant energy. We know that light is frequently associated with heat, and that plants in the garden get heat energy as well as light energy from the sun. Recent discoveries have shown that we, ourselves, are getting good out of the light that a few years ago we had no idea of. The ultra-violet ray in the sunlight aids us to keep well and prevents certain diseases, while the hardness of our bones and our freedom from certain diseases is due to its effect. We know that light makes it possible to read, to see things in their natural colors, as well as to take pic- tures and make light signals. From times of earliest civilization people used light for signaling. The Greeks and Romans as well as our American Indians all had elaborate light signals, just as we are warned today by our H. & W. SCI. I — 10 130 HOW WE USE LIGHT I lighthouses, airplane beacons, and the more common traffic lights. Heliograph signals, made by reflecting a beam of sunlight on a mirror, have been sent nearly 200 miles. Light-Using De- vices. Let us think over the things we \\ I ~^--, may find at home whose use depends upon light. There is the camera, the opera- glass, the reading glass, and, of course, the mirror and win- By fanning dows. Perhaps there is a magnifying glass, an enlarging mirror, or a bull's-eye flash lamp. Among the toys there might be a kaleidoscope and possibly a stereoscope. If there is a nature lover in the family, you may find bird glasses or field glasses. How an Image Is Made by a Pinhole. If you let a small beam of light enter a dark room in which there is The Indians used smoke signals. the fire puffs of smoke were given off. dusty air, you can see that the light travels in a straight line. If a small hole is made in the window shutter on the first floor of a building and the room is dark, people HOW DO I USE LIGHT? 131 who walk by the window outside will reflect rays of light so that images of them appear on the wall opposite the window. A curious thing about the image is that it is upside down. If we make a pinhole in one end of a small fround glass- How many devices can you name that involve the principle shown here ? box and have a shaded frosted glass in the opposite end, we can see on the frosted glass an inverted image of a bright object that is in front of the pinhole. The diagram will help us to understand this. A is seen by light that comes from A. The light that goes through the pinhole will fall at A'. The light from B will reach the frosted glass at B'. Light from all points between A and B will fall somewhere between A' and B'. The image is inverted because the rays which come from the object cross where they pass through the pinhole. If the hole were not very small and other light was not kept out, there would be such overlapping of light from different parts of the object that no clear image could be seen. This principle of image formation is used in our eyes when- ever we look at any object. There is one difference. There is a lens at the opening of the eye. This allows more light to come in and gives a brighter image. The 132 HOW WE USE LIGHT Galloway How many different kinds of stop lights have you seen ? It would be a good thing to have these signals uniform for all parts of the country. Can you see why ? image in the back of the eye excites the proper nerve end- ings so that the brain can interpret the image and in this way we see objects. Colored Signal Lights. The engineer depends upon colored lights to tell him if there is a clear track ahead. Where other trains use the same track and where switches may lead to branch tracks, a green light is a signal that the track is clear and safe. A red light is the signal for danger. On boats you see green lights on the starboard or right side and red lights on the port or left side. If we travel by train or water, our safety depends greatly upon the watchfulness of the pilot or engineer and his care in heeding signals. Our most common use of signal lights is the traffic signal and automobile tail light. Here again red is the danger sign and green the signal to pass. In HOW DO I USE LIGHT? 133 many places the use of an orange light for pedestrians to pass while auto traffic remains at rest is a very helpful aid to safety. Our use of colored lights and following the messages they bring to us make possible the rapid clearing of traffic jams and greater freedom from accidents. SELF-TESTING EXERCISE Select from the following list those words which best fill the blank spaces in the sentences below and arrange the words in proper numerical order. A word may be used more than once. radiation radiant orange chemical mechanical red electricity image blue lights cross inverted heat green object colored straight light Light is a form of (1) energy just as (2) and (3) are. (4) is used whenever we read or see an object. Since light travels in (5) lines, whenever light from an object passes through a small opening, the rays (6) and produce an (7) image. When (8) signal (9) are used, it is common to use (10) for danger and (11) for safety. STORY TEST FLORENCE WRITES AN ESSAY ON LIGHT Read carefully and critically. List all the errors and suggest cor- rections. There are two kinds of light, black and white. This has been proven by pictures taken of lightning. Some streaks are black and are produced by black lightning. We cannot see objects by black light ; we use the white light. If a candle is behind a block of wood, we cannot see it because light travels in straight lines. If light radiates from a red hot iron, the light goes in all directions and then may go around corners, in curved lines. If light rays from two objects were to meet, they would destroy each other, and where they come together, the two bodies would be invisible. The reason automobiles have red headlights is because it is danger- ous to be in front of a car. The green tail light indicates safety. 134 HOW WE USE LIGHT c£i/fcr;Se PROBLEM II. WHAT ARE SOME OF THE PROPERTIES OF LIGHT? What Happens When Light Meets a Body ? It is inter- esting to play with a beam of light. In a dark room allow a small beam of light to pass across the table from a lantern. Make this beam visi- ble by means of dust, smoke, or ammonium chloride fumes. Hold a piece of window glass at right angles to the beam. You can see the beam al- most as brightly back of the glass as in front. This light that comes through is transmitted light. Tilt the glass and you will see a faint beam sent off from the surface. This is reflected light. A still smaller part of the beam is neither transmitted nor re- flected, but is absorbed and changed to heat. Three things happen when a beam of light /reflected absorbed cccrcCboccra Explain why the frosted glass has a different effect on the light than the window glass does. What happens to most of the light that falls upon a black body? comes to a body that allows light to pass through, but only two things happen when the body does not permit the light to pass through. Can you tell what happens to the light when it meets the latter body ? WHAT ARE SOME OF THE PROPERTIES OF LIGHT? 135 Bodies Vary in Ability to Transmit Light. Have you ever noticed how the " steaming7' of a window at home or on the train changes your vision of objects on the other side? If you wear glasses, perhaps you have noticed that when you come into a warm, damp atmosphere from the cold outdoors the moisture gathered upon your glasses so that you could not see anything distinctly. When you wiped off the moisture or it disappeared after the glasses were warmed you could see clearly again. Clear glass lets light go through without much change in Explain the terms transparent, translucent, and opaque by reference to the diagram. direction. All bodies like glass, cellophane, quartz, air, and water which permit light to pass through so that we can see objects through them clearly are called transpar- ent. Making the surface of glass rough causes a scatter- ing of light that passes through. Frosted glass, con- densed vapor on glass, oiled paper, and very thin paper, gauze, or window shades may allow enough light to pass through to show the presence of objects without their being seen distinctly. These bodies are translucent. Objects that cut off all light are called opaque. A Shadow. If you darken a room and allow a beam of light to enter, you will notice that it travels in a straight 136 HOW WE USE LIGHT line, and that if you put an opaque object in front of the source of light, it will cut off the light and pro- duce a shadow. A shadow is that space from which light is cut off. The dark outline we cast on the pave- ment when we stand near a street lamp we often call a shadow. But remember a shadow is not just a dark sur- face, it is all the dark- ened space back of the object which cuts off the light. Were this not so, we could not enjoy the shade (shadow) of a tree hav- ing dense foliage on a Where is the shadow? Is the word "shadow" bright hot day in the put in the correct place in this cut ? 011™™^*. o Ulillllcl . Reflection of Light. Light, such as a candle flame, a red hot iron, a burning match, or the stars may come to our eyes direct from its source. Bodies which give off light of their own are luminous bodies. Very few of the objects we see in the course of the day are bodies that have light of their own, but we cannot see any object unless light comes from it into our eyes. All nonluminous bodies which we see receive light from some other source and reflect it. That which is reflected into our eyes makes the object visible to us. Do you realize how important reflection of light is ? Without it you could not read, see pictures, nor recognize friends by sight. You could not see the moon nor yourself in a mirror. Sunlight which enters your room may be reflected from one surface to another many times before it is reflected by the particular object you may be looking at. WHAT ARE SOME OF THE PROPERTIES OF LIGHT? 137 Demonstration 1. Law of Reflection. Hold a plane mirror in a narrow beam of light in a dark room. The light is bent or reflected from the mirror. We call the incom- ing ray the incident ray and the outgoing ray the reflected ray. A line at right angles to the sur- face where the ray of light meets it is called a normal. Hold a ruler at right angles to the mirror at the point where the beam strikes the mirror, com- pare the angle between the ruler and the beam coming to the mirror (angle of incidence) and the angle between the ruler and the beam going from the mirror (angle of reflection). Turn the mirror slightly to change the angles. Compare the angles as before. What do you notice with reference to the angle of in- cidence and the angle of reflection? When light is reflected from a plane surface, how does the size of the angle of reflection com- pare with the size of the angle of incidence? How We See in a Mirror. When you look into a mirror, the image appears to be behind it. If you step close to the mirror, the image comes close ; if you step away, the image goes away. If you examine the diagram, you will see that light goes to the eye in the direction it would if the object were really where the image is, but in reality it goes from the object to the mirror, which reflects it to If the image is behind the mirror why can you see it ? the eye. How does the distance ON compare with the distance O'N f How does the angle / compare with the angle R at N ? AiSf At Tf The image we see is an 138 HOW WE USE LIGHT Does this convex mirror give a real or an unreal image ? unreal image because there is no light that really goes to the place where we appear to see the image. When a real image is formed, as in a camera, rays of light actually form the image where the image is seen. Curved Mirrors. You have probably seen a crystal globe. This is a spherical mirror. A small por- tion of the spherical surface would also be called a spherical mirror. It is also a convex mirror. Sometimes a convex mirror is placed on the fender or on an arm projecting to the left of the wind shield of a truck or automobile. The curved surface makes a larger area visible, and an image is seen just as in a plane mirror except that it is smaller. Perhaps you have looked into the convex cylindrical mirrors at some amusement park and have seen yourself tall and thin or short and fat. The inside of a spherical surface is concave. A con- cave mirror will focus rays of light from a distant ob- ject and make a real and enlarged image. Large mirrors of this type are used in the re- How to look stout or thin. Why do some mirrors change your appearance ? fleeting telescopes for viewing the stars. Enlarging mirrors are useful and can readily be obtained. The dentist uses a small enlarging mirror to see your teeth WHAT ARE SOME OF THE PROPERTIES OF LIGHT? 139 when filling them. A point equally distant from all points on the surface of a curved mirror is the center of curvature C. The point where parallel rays are brought image image Where must an object be located with respect to F (focus) and C (center of curvature) of a concave mirror to produce an enlarged real image ? An enlarged unreal image ? together after reflection is the principal focus F. This focal point is about half way from the mirror to the center of curvature. The position of the image depends upon the position of the object. In science the unreal image is usually called a virtual image. A concave mirror is used for auto and locomotive headlights and for search- lights. When a light is placed at a certain point in front of the mirror, it sends out a powerful beam of nearly parallel rays. Diffused Light. When a beam of parallel light rays strikes a smooth surface, it will be reflected in a beam of parallel rays from the surface ; but if it strikes a rough Why does a rough surface diffuse light ? Does the same law of reflection hold in the two cases ? surface, the light will be thrown off in different directions and scattered. Such light is diffused. Light from the sky 140 HOW WE USE LIGHT is diffused, because air is filled with countless millions of tiny irregular dust particles. These particles divert the rays of the sun out of their straight course and give diffused light. Without the atmosphere to diffuse the sun's light, the earth would look very different because contrasts would be much greater than they are now. The whole sky would appear black in the daytime except for the luminous disk of the sun and the points of light made by the stars. In winter our north windows would receive no light at all. It is fortunate for us that the atmos- phere with its particles of dust and moisture diffuses light. Refraction of Light. A famous English philosopher once noticed that if he put a coin in a cup and then stood away from it so that he could just not see it, when he poured water into the cup, the coin came into view. This curious happen- ing is brought about by the fact that light travels more slowly in a dense than in a less dense material. When light enters the water, it slows up and is bent from its course. There is one exception : a ray of light passing into another medium of different density at right angles (90°) to the surface between them is not bent, but continues on in the same straight line. But when any oblique ray of light passes from air into water, it will be bent toward the perpendicular ; and when it goes from water to air, it will be bent away from the perpendicu- lar. The bending of light rays when they pass from one transparent body to another of different density is called Which is the real and which the apparent position of the coin? WHAT ARE SOME OF THE PROPERTIES OF LIGHT? 141 refraction. We appear to see objects in the direction in which the light enters our eyes. Consequently if the rays of light are bent before reaching our eyes, there is an apparent displace- ment of the body. For this reason water in a pond appears to be more shallow than it really is. In other words, the earth at the bottom of the pond looks to be nearer the surface and has often de- ceived adventurous boys and girls who could not swim. Fish in the water may not be in the exact position in which you are looking when you see them. It is refraction that bends the rays of sunlight in a burning glass or lens and that makes letters look larger in a reading glass. § plate glass \l c 2> G, \\ J\ \K Passage of light through plate glass. Why is only one of the rays bent ? SELF-TESTING EXERCISE Select from the following list those words which best fill the blank spaces in the sentences below and arrange the words in proper numerical order. A word may be used more than once. reflection refraction reflected bent send bend left right opaque transparent luminous light dark equals translucent diffused same front back inside outside convex concave plane smooth directions angle image angle, When a beam of light comes to a window at a (1)_ some of the light is (2) back in the direction from which the light comes. An (3) body does not transmit light. Frosted 142 HOW WE USE LIGHT glass is called a (4) body because some light can get through it. (5) bodies give out (6) of their own but most bodies are seen by (7) light. When a smooth body reflects light, the angle of (8) (9) the (10) of incidence. The (11) in a mirror is always the (12) distance (13) of the mirror as the object is in (14) of the mirror. Rough surfaces give a soft (15) light, while (16) surfaces tend to produce a glare if looked at from some (17) (18) mirrors can produce a real image. The slowing up of light after it passes into a more dense medium may cause it to (19) in a process called (20) STORY TEST MORRIS HAS SOME PRACTICAL EXPERIENCES WITH LIGHT Read carefully and critically. List all the errors and suggest corrections. Last night about an hour before sunset I looked across a vacant lot to a greenhouse. At first I thought the place was on fire because there was such a glare of light. I decided however that I was seeing an image of the sun in each of the glass panes. Com- ing at the angle that it did, all the light was reflected and the glass acted like mirrors. After the sun had gone down, thunder clouds quickly shut off the twilight and it became very dark outside. 1 turned on the lights in the room. I turned to the window and looked in the direction of the greenhouse. I saw only objects that were in the room around me. The glass that had been trans- parent in the daylight had become opaque in the night and now acted as a perfect mirror. Out of doors everything was dark because it was in the shadow cast by the earth. A flash of light from my aquarium called my attention to my one gold fish I had put in the water a week before. As I neared the tank, I could see through the top surface and through one side. Imagine my surprise to see two gold fish, and stranger still, every time one moved the other one moved. I then looked straight down through the top surface but could find only one fish. I decided the optical illusion had been caused by the reflection of the fish by the surface of the water. So I had seen the real fish and his image in a mirror. PROBLEM III. HOW ARE PHOTOGRAPHS MADE? Have you ever seen among your family heirlooms a daguerreotype : an old-fashioned picture on a piece of tin set in a gilded frame? This old-type picture was the HOW ARE PHOTOGRAPHS MADE? 143 forerunner of the great photographic industries of today. Think of the persistence of a man working on the idea that sunlight with the aid of a few chemicals could make a per- manent picture. It took Daguerre fourteen years to work out his idea. Some others had devised processes by which a picture could be made if exposed for hours in a dazzling bright light. But that was not practical for photographing people . In 1839, Daguerre had perfected his process so that an exposure of a few minutes was sufficient to take the picture. These were made on a metal base and no duplicates could be printed from it. Today a fraction of a second only is In the first portraits made with a camera the face had to be covered with white powder to reflect as much light as possible. The sub- ject was then exposed to direct sunlight before the open camera for 30 minutes. needed to expose a plate or film and from the negatives any number of pictures can be printed. Such are the strides made by science in a few years. Today photog- raphy has become a leisure time activity for all, and the pages that follow will help you to enjoy this scientific pastime. The Camera. We think of a camera as a light-tight box having a lens at one end and a place at the opposite end for a prepared photographic plate or film. But there is a simpler camera than that because pictures can be taken without a lens. In such a camera there is only a 144 HOW WE USE LIGHT pinhole in the front end of a small box. Brightly lighted objects in front of the pinhole send light through it and an image is formed at the back of the box. If a film coated with chemicals sensitive to light is there to receive the image, the start of a photograph is made. The advantage of having a lens instead of the pinhole is that it pro- duces a sharp image when the opening is large, thus permitting more light to enter. This shortens the time of exposure. With a pinhole camera any opening larger than a small pinhole l will make a blurred image. With a hole small enough to give a good sharp image, it will take from 10 to 20 minutes to make the exposure. The Diaphragm and Shutter. The lens camera has a diaphragm, the ad- justment of which makes possible different sizes of opening through which light may enter. There is a shutter controlled to allow an exposure of a fraction of a second for a "snap shot" exposure or r , Can you tell the use of each of the parts for a time exposure when Of the camera named in the diagram ? 1 See page 162 for directions. Eastman Kodak Co. The camera used by amateur photogra- phers. lens HOW ARE PHOTOGRAPHS MADE? 145 over a second is needed. The shutter and diaphragm are controls for the amount of light which is allowed to pass through the lens to produce the image on the film. Lenses. If you can get two lenses of the same diame- ter but one thicker through the center than the other, you will be able to make an interesting experiment. If you are in a partly darkened room, light a lamp and hold the thick lens five or six feet from the lamp. Move a sheet of white paper back and forth on the side of the lens away from the light. You will soon find a place where a sharp image of the lamp appears on the paper. Now if you place another lamp a foot forward or back of the first and keep the paper still, you will see that objects at different distances give a fairly sharp image. If you repeat this with the thin lens, you will not be able to produce a sharp image of the two lamps when they are very far apart. The thick lens is a short-focus lens, and this is the type used in the box camera. You do not have to change the position of the lens or "focus" the camera because this is a " fixed focus" lens, that is, all objects in front of the lens and more than six feet distant will produce an image which is fairly sharp. Other cameras — the focusing type -use the long focus lens. For photographing near-by objects with such a lens the distance from the film must be adjusted according to the distance scale on the camera, but all objects over 100 feet away will give a sharp image when the lens is set at the 100 mark on the scale. What Makes Some Cameras Expensive? You may have wondered why some people pay $50 to $100 for a special lens for a camera. They are paying for the speed of the lens. Only the central portion of the cheap lens can be used to give a sharp image. If the diaphragm is closed so that light enters through the center only, a longer time must be used for exposing the plate. The expensive lens is ground so carefully that the diaphragm may be H. & W. SCI. I — 11 146 HOW WE USE LIGHT opened much wider and still give a sharp image. This lets more light in and shortens the exposure, and the lens is called "rapid." The cheap lens may give just as good a picture if you can give it sufficient time with the small opening. Making a Negative. Many of you take pictures but give the films to a photographer to develop. If you do this, you lose half the fun. Why not learn to develop the films yourself? Most junior high schools have camera clubs and dark rooms, so you will have no difficulty in doing your own work. The plate or film is coated with gelatin containing silver bromide, a substance sensitive to light. When light from an object in front of the lens is focused on the film, it makes an image upon it which does not become visible until after the film is developed. De- velopment takes place in a dark room which has only a red or ruby light in it. This light does not act upon the film during the short time required to change it into a negative. The film is first treated with a "developer," a chemical solution which causes a deposit of dark particles on the film. No dark deposit is made on those parts of the film not reached by the light. The differences of light and dark at any point is in proportion to the amount of light which acted upon the silver bromide. When development is complete, some silver bromide which was not acted upon by the light and which is still sensitive to it remains on the film. Before the film can be exposed safely to ordinary light, this silver bromide must be re- moved. A chemical salt, hyposulphite of soda, called "hypo," will dissolve the silver bromide and remove it from the film. This is used as a "fixing bath," because it makes the image permanent. After the film has been fixed, washed, and dried, the light and dark areas in it are just the reverse of those in the original picture and for this reason it is called a negative. HOW ARE PHOTOGRAPHS MADE? 147 Which is the positive and which is the negative ? How do the lights and shades in the negative compare with the lights and shades in the positive ? Making a Positive. The print is made by allowing white light to pass through the negative to a paper which is sensitive to light. Since less light will pass through the dark parts than through the light parts of the negative, the print will be just the reverse of the negative, or a positive, which has the same value of light and dark as the original objects photographed. Home printing is easy and is a fascinating pastime. Papers are of two types, those printed by artificial light and those printed by sun- light; the former require more time. Blueprint paper is one form of sun-printing paper ; it is cheap and easy to handle since it can be developed in water without the use of chemicals. Demonstration 2. Making a Print from a Negative. Darken the room until you can barely see objects. Make up a developing bath by dissolving the powders in a tube of developer in water according to directions on the tube. Make a hypo (" fixing ") bath by dissolving a tablespoonful of hypo (hypo- sulphite of soda) in half a pint of water. Arrange three trays or plates as follows : 148 HOW WE USE LIGHT Tray 1. Developer Tray 2. Cold water Tray 3. Hypo You will need two squares of glass and two clothespins. Lay the negative dull side up on one piece of glass. Upon this lay a sheet of sensitized paper, smooth or coated side down upon the negative. Cover with the other piece of glass. Hold the two pieces of glass tightly together with the clothespins. Light a 100-watt lamp and hold the glass film side towards the light and 3 feet from it for 10 to 15 seconds. Extinguish the lamp. Remove the paper. Immerse the paper in the developer. If it comes up too black within 30 seconds, it had too much light; if it does not come up dark enough in 30 seconds, it needs longer exposure. A little experience will help you judge the time of exposure. After the picture has developed to the point you wish it, rinse quickly in water and place in the hypo. Move it around occasionally. After, 15 minutes remove from the hypo and wash an hour in run- ning cold water. Lay face down on a piece of cheesecloth stretched over a frame to dry. With the directions just given you should soon become an expert amateur photographer. Why not organize a camera club if your school does not have one? You will be surprised how much this photography will help you in your science work, besides giving you and your friends a lot of fun. SELF-TESTING EXERCISE Select from the following list those words which best fill the blank spaces in the sentences below and arrange the words in proper numerical order A word may be used more than once. chemical positive fixed camera visible negative focus image diaphragm neutral opening black shutter hypo closed light developer acid dark lens results recorded red sensitive There are chemicals which are (1) to light. When these chemicals are held on the surface of a film or glass plate in a little gelatin and an (2) is thrown upon the film, a latent image is (3) When the film is developed, a picture with (4) and (5) parts reversed from what they were in the original view (6) After development, the film is (7) or made perma- nent in the (8) bath. The resulting film is called a (9) ; from this a (10) print is made. The (11) excludes (12) except when the (13) is open. The size of (14) to control the amount of light is regulated by the (15) HOW DOES THE EYE RESEMBLE THE CAMERA? 149 STORY TEST ALBERT TELLS ABOUT His PINHOLE CAMERA Read carefully and critically. List all the errors and suggest corrections. This box I hold before you is a " pinhole " camera. I made a large hole in the front end of the box. Then I made a small hole in a piece of tinfoil with a needle and fastened this so-called pin- hole over the hole in front of my box. I fastened a film in the back end of the box in a dark room, put the cover on, held my hand over the pinhole, and came out into the light. I placed the camera six feet from a bouquet of flowers which were in the sunlight. All of the rays of light given off by the flowers went through that tiny pinhole. They were bent as they went through and then made an image on the film. After covering the hole and returning to the dark room, I found the film had a picture of the flowers on it. To make this remain on the film, I developed the film in a solution called the developer. I washed the film and dried it in a lighted room because light cannot hurt it after development. After the film was dry, no picture was visible on it, but by printing on sensi- tive paper I could make a beautiful picture of the flowers. I haven't done this yet, but I know just how to do it. Place the paper on the film, coated sides together. Hold film towards the light. Then put paper into a hypo solution to fix it and to make the print permanent. Wash and dry. PROBLEM IV. HOW DOES THE EYE RESEMBLE THE CAMERA? We all know that the camera in its simplest form is a black, light-tight box containing a lens at one end and a place for a sensitive film at the other. Light is allowed to pass through the lens and is brought to a focus on the film. Here the picture is recorded on the film, which may be taken to a dark room and developed and made per- manent. The human eye is like a camera in many ways, but it is much more delicate and complex. If we were to take a section through the human eye at right angles to the front of the face, we would see its likeness to the camera. Near the front of the eye is a transparent lens which throws a picture on a surface called the retina, at 150 HOW WE USE LIGHT the rear. The retina is connected to the brain by the optic nerve. The lens is capable of changing its shape, -lens film... What parts of the camera correspond to the parts of the eye ? thus making it possible to focus the light and so make a real image of near or distant objects on the retina. This change of focus is called accommodation. A colorless fluid fills the space between the lens and the retina. The retina is the most wonderful part of the eye because it transfers the sensations produced by light in the eye to the brain by way of the optic nerve. How the Eye Adapts Itself to Different Intensities of Light. The diaphragm in the camera changes the size of opening through which light may enter. The eye has a similar device, but it is called the iris. The black spot you see as the pupil of the eye is the opening through which light passes to the lens. If you go to the window when there is bright sunlight and look steadily at the sky for a moment, and then bring a mirror before your eye you will see that the size of the pupil or black hole in the colored iris is extremely small. If you turn quickly to a dark part of the room and look in the mirror, you will see the pupil grow larger as the iris adjusts itself to the How does the eye adjust itself to different intensities of light? Which of the two eyes is looking into a bright light ? How do you know ? HOW DOES THE EYE RESEMBLE THE CAMERA? 151 smaller amount of light. This change in the size of the pupil is automatic. The eye cannot stand looking into very strong light, nor into a glare, in spite of this adjustment. The iris cannot contract enough to shut out the intense light without also making it difficult to see objects or printed matter. We should therefore avoid straining the eyes by trying to work or read with a bright or glaring light within our field of vision. Some Eye Defects. In spite of the wonderful mechan- ism that it is, the eye often has slight defects. The most use a Conclave lens to correct. 1135 use a convex lews to Correct. fansigktecCness common one is astigmatism, due to a slight uneven cur- vature of the lens or the cornea. This difficulty is a fre- quent cause of headaches, and should be attended to by an oculist. Another defect is nearsightedness. In this case the eyeball is too long from front to back or the lens too thick, so that the image of distant objects is brought to a focus before reaching the retina. If you have to hold your book close to your eyes, and if you squint when looking at things, you should go to an oculist and have your eyes tested for glasses, as nearsightedness can quickly be cor- rected by this means. 152 HOW WE USE LIGHT What can you say about the light here? Have you any suggestions to offer? Farsightedness is a defect in which the eyeball is too short or the lens too thin and the image of near objects is focused behind the retina. This defect is more difficult to detect and is also the cause of many head- aches. Properly shaped lenses will remedy both nearsightedness and farsightedness by bending the light rays so that they focus properly by means of refraction. Care of the Eyes. Some good rules for care of the eyes are these : 1. Avoid direct glare or reflection from paper, books, or highly polished surfaces. 2. Do not sit facing strong light. 3. Do not sit so that your shadow falls on your work. 4. Do not read or work by a flickering light. 5. Do not read on trains or motor cars. 6. Adjust the intensity of light to your needs. Strong light is needed for fine print. HOW DOES THE EYE RESEMBLE THE CAMERA? 153 7. Do not use the eyes when they ache or when you are fatigued. Remember that your eyes are the most valu- able asset you have. Never abuse them. If tired, a wash of boric acid will help. Do not use any patented drops as they may contain dangerous poisons, and usually you buy only boric acid and salt, which you could mix yourself. Above all, consult a reliable oculist or eye specialist in case your eyes need attention. SELF-TESTING EXERCISE Select from the following list those words which best Jill the blank spaces in the sentences below and arrange them in proper numerical order. A word may be used more than once. front reading image automatically back cornea bend accommodation side iris decreases glasses lens retina increases shaped mirror pupil curvature astigmatism harmful light focus enters beneficial diaphragm inverted farsightedness It is the (1) of the eye that produces an (2) on the (3) The amount of light which (4) the eye is regulated by the (5) which (6) and (7) the size of the (8) It is very (9) to have light directly in (10) of one when (11) Uneven (12) of the (13) or of the (14) may cause (15) In nearsightedness the image is in (16) and in farsightedness the image is in (17) of the retina. (18) to correct these defects may be (19) , so that they bend the rays of light to make them (20) properly. STORY TEST BEULAH'S FATHER Is AN OCULIST Read carefully and critically. List all the errors and suggest corrections. My father is an oculist and fits people with glasses. I have an uncle who is an optometrist; he treats diseases of the eye. So you see I am just the one to talk to you about the human eye. In the first place the eye is rounded or ball-shaped ; this makes it 154 HOW WE USE LIGHT act upon light like a lens. When light from an object passes through the eye, it forms an unreal or virtual image on the cornea. The position where an image is formed depends upon the distance the object is from the eye. However, the eyeball can change its shape and move the back surface of the eye nearer or farther away from the pupil. This is taken care of automatically so that in the normal eye there will always be a clear image formed. This adjustment is called accommodation. Father says most people wear glasses to remedy eye defects but some wear them for " looks." PROBLEM V. WHAT IS COLOR? What Is White Light ? If you pass sunlight through a triangular piece of glass called a prism, the white light is separated into the following colors : red, orange, yellow, green, blue, and violet. The waves of all these colors differ in length. The longest wave affecting sight gives us the color red, the shortest, violet. Color, then, is a property of light which depends upon its wave length. When light is refracted, the blue rays are bent more than the red rays, or the shorter the wave length, the more it is bent. The prism bends the beam of light twice in the same direction, once as it enters the glass and again as it leaves the glass and enters the air. Both times it separates the colors and so produces a band of colors on a screen. This band of colors is called the "solar spec- trum." The rainbow is caused by light being broken up into these colors by bending or refrac- tion in falling rain- drops. When all the different wave lengths from the sun Why does a prism separate sunlight into colors ? . -, , ,-, are mixed together, white light is produced. White substances are those which reflect all wave lengths, hence all colors, while black sub- stances are those which absorb all wave lengths of light. WHAT IS COLOR? 155 Colored Objects. A red body absorbs all the wave lengths except those producing the sensation of red. A •\vkite light. green fight. White peeper- gV-eerj. -peeper Why is such a small part of the light falling upon the green paper reflected? blue body absorbs all the wave lengths except those pro- ducing a sensation of blue. Make a blue spot on white paper and an orange spot a few inches from it and then look at the two colors by means of a glass plate held vertically between them so that one spot is seen by transmitted light and the other by reflected light. A grayish white spot will re- sult. Any two colors which when mixed give a sensa- tion of white or gray are complementary colors. Red glass absorbs all rays except those producing red, hence a blue dress if viewed in a room having red window glass would appear black. This is due to the fact that no blue comes in to be reflected and the dress absorbs the red. Every color except red would appear black when viewed What is the color of the piece of glass? in a red light. What is the color of this leaf? o a 156 HOW WE USE LIGHT Mixing Pigments. Mixing pigments such as paints or dyes is quite a different matter from mixing colored lights or light rays. If you mix blue and yellow paint, \ Why do only yellow rays appear at the right of this diagram ? green will result. A yellow pigment absorbs all the spec- trum colors except yellow and green, while blue pigments absorb all the spectrum colors except blue and green. Green is the only color reflected by both pigments, and is therefore the only color seen when the two are mixed. Color Blindness. In order to drive a locomotive, the engineer must be tested for color blindness. There are about three to four per cent of boys and about one per cent of girls who cannot distinguish certain colors. They are color blind. The most common form of color blind- less is the inability to distinguish between red and green. SELF-TESTING EXERCISE Select from the following list those words which best fill the blank spaces in the sentences below and arrange the words in proper numerical order. A word may be used more than once. wave waves reflects light colors complementary darkness red green blue property refracts neutral normal violet white black length absorbs yellow pigments sensations supplementary length Color is a (1) of (2)_ length. The shortest (4). which is determined by its (3)_ (5) gives the sensation of WHAT IS COLOR? 157 (6) and the longest produces the sensation of (7) All (8) produced in the sun mixed together give (9) Any two colors which when mixed produce white are (10) colors. Blue and yellow (11) when mixed produce (12) If you look at a red book through blue glass, it will appear (13) because the glass transmits only (14) and the book (15) blue. STORY TEST HARRIET REPORTS UPON HER EXPERIMENTS Read carefully and critically. List all the errors and suggest corrections. Having an uncle who is a glass maker, I teased him to make me three prisms ; one of white glass, one red, and the third green. I used these in a dark room into which a beam of sunlight came through a small hole in the shutter. I had a screen of white paper, one of black paper, one of green, and wore a red dress. When I held the white glass in the beam of sunlight to form the solar spectrum, the colors could be seen upon the white screen. When thrown upon my red dress, the whole beam was changed to red. When thrown upon the green screen, I saw only a small green band of color. I then took the red prism and made a spectrum of all colors on the white screen. When thrown on the red dress, the red was absorbed and all the other colors were seen. Then I used the green glass. When the black paper was held in position, there was just a narrow green band of color upon it, but it showed a red band when the beam was directed to the red dress. The green screen showed a green color and the white screen showed all the spectrum colors. THE REVIEW SUMMARY In preparing a summary of what you have learned in this unit, you will want to place emphasis on the big ideas which have come out of the applications of the facts you have learned and the demon- strations you have seen. The generalizations that can be made on this unit are numerous. You may change the list that follows if you so desire, as this is only giving you a partial list of those that you might make for your review summary. 158 HOW WE USE LIGHT 1. Light travels with greater speed than anything else. 2. Light travels in straight lines. 3. Light rays may be bent by reflection or by refraction. 4. Light produces chemical changes of much value to man. Before making your review summary, test your knowledge of the facts of the unit by checking over the text so as to be sure you know the facts underlying the generalizations. Then, using the generalizations, the material in the text, and everything you have read, seen, or done yourself, make a summary outline for your notebook. This outline you may use when you make a recitation. TEST ON FUNDAMENTAL CONCEPTS Make two vertical columns in your workbook. Head one CORRECT and the other INCORRECT. Under the first place the numbers of all state- ments you believe to be correct. Under the second place all the numbers of the statements you believe to be incorrect. Your grade = right answers X 2^. I. Light travels : (1) in straight lines ; (2) through translucent bodies; (3) 1100 feet per second; (4) more slowly through water than through air. II. A real image may be produced: (5) by a plane mirror; (6) by a piece of plate glass; (7) by a pinhole camera; (8) by a concave mirror. III. A beam of light will be bent (refracted) when it goes from : (9) air into glass at a 90° angle to the surface ; (10) air to glass at a 30° angle; (11) water into air at right angles to the surface; (12) water into air at an angle of 60° between the ray and the surface of the water. IV. The ordinary camera lens produces a real image on the film because the lens : (13) reflects the light from the object; (14) re- fracts the light coming into it; (15) sifts or filters out the objec- tionable rays of light which would mar the image; (16) permits light from the object to reach the film. V. When a beam of light from candle flame comes to a piece of plate glass at right angles to the surface, some of the light : (17) is refracted; (18) is reflected; (19) is changed to a gas; (20) is transmitted. VI. The image of an object in a plane mirror is : (21) larger than the object ; (22) unreal ; (23) the same distance back of the mirror that the object is in front of the mirror; (24) inverted. VII. Concave mirrors: (25) may produce real images; (26) are used in some telescopes ; (27) are used in cameras ; (28) are used in automobiles to watch traffic in the rear. WHAT IS COLOR? 159 VIII. You are on one side of a stream of quiet water and see a large oak tree on the other side. The sun shines brightly and lights up the side of a tree towards you : (29) you see a real image of the tree in the water ; (30) there is also a shadow of the tree on the water; (31) as you see the image, the tree appears upside down ; (32) the image is unreal. IX. The eye " focuses " or makes the image on the retina clear by : (33) changing the distance between the retina and lens ; (34) changing the thickness of the lens ; (35) changing the size of the pupil; (36) by a process called "accommodation." X. A blue dress appears blue in daylight because : (37) the material absorbs only blue light from the sunlight ; (38) the material absorbs all the sunlight except blue; (39) its own color added to sunlight gives blue ; (40) it gives out blue color of its own which is stronger than the white of sunlight. THOUGHT QUESTIONS 1. Why are lamp shades made of opal glass? 2. Why are electric light bulbs frosted ? 3. Why are offices in large buildings often inclosed in trans- lucent glass? 4. Make a list of the objects you saw on your way to school that showed regular reflection. 5. How would you point a stick to a given point at the bottom of a dish of water if your stick has to enter the water at an acute angle ? 6. Compare a real and an unreal image and show how you would make each. 7. Why do the re- flectors used for auto- mobile headlights have the shape shown in the illustration ? 8. Why is the image seen in the back of a camera inverted but that seen in the finder up- right? » 9. What happens to a beam of bright sunlight by which you see the white sand on the beach: first without glasses and later through amber sun glasses ? 10. Why is it difficult for you to write your name while looking at your hand, pencil, and paper only in the mirror ? 160 HOW WE USE LIGHT 11. How can you adjust your desk study light to give you efficient lighting ? REPORTS UPON WHAT I HAVE READ, DONE, OR SEEN 1. Report upon an article related to some topic discussed in this unit. The article may be from a current number of a science magazine or from some popular science book you have read. a. The importance of transparent glass. 6. Colors in the sky. c. An automobile headlight. d. The eyes of man and of insects. SCIENCE RECREATION 1. FUN WITH SHADOWS Hang a sheet to cover a doorway. Have the audience in a darkened room. In the other room have one very strong light. ' 1 ctttcCievice 1 i v \ actors- reflector stroi Make pantomime shadow pictures by acting between the light and the screen. Plan a shadow play. 2. AN "ANGLESCOPE" Sometimes you like to watch a person without his suspecting it. You can apparently be looking through a tube in one direction, mirror- but really see what is going on at one side. The diagram will suggest how to place a mirror in a mailing tube having a hole cut in the side. 3. MAKE A PERISCOPE Secure a long mailing tube about 2 inches in diameter and two small mirrors (2 for a nickel .Mirer WHAT IS COLOR? 161 Cover one end halfway across, -IBS. at the 5 and 10). Cut holes near the ends of mailing tube but on opposite sides. Fasten the mirrors back of these openings facing and parallel to each other but at angles of 45° to the long axis of the tube. Then objects in front of the top opening can be seen by looking into the lower opening. 4. A HOME-MADE KALEIDOSCOPE Fasten two strips of mirrors about 2" X 1" or 8" together with the mirror fronts facing each other at an angle of 45°. A tin frame can be bent so it will hold there, leaving a peep hole where the two glasses meet. Cover the wide open space two inches from the end. Support this vertically with the peep hole at the top above a block of wood, leaving a space under it where a disc can be placed so it can be revolved under the two mirrors. By plac- ing colored chips of glass and other objects upon the disc, different patterns and designs may readily be produced. 5. MAKE A SCRAPBOOK ON LIGHT Collect pictures and clippings from newspapers and magazines. Group the clippings according to subject matter. mirrors— v 'revolving ^ SCIENCE CLUB ACTIVITIES 1. TEST FOR COLOR BLINDNESS Buy or borrow a set of Holmgren's woolens for testing color blindness. Test the eyes of each member of the club. 2. MAKING A PICTURE Get some one who knows how to demonstrate the use of a camera with a ground-glass back, also how to print and finish a picture from a negative. 3. BURNING A CANDLE IN A JAR OF WATER Arrange your apparatus as in the diagram on page 162. The plate glass should be 15 to 24 inches by 3 to 4 feet. Double- thickness glass may be substituted. The jar of water is seen by transmitted light, and the candle by reflected light. Have the H. & w. sci. i — 12 162 HOW WE USE LIGHT candle burning and jar empty at the start. Pour water slowly into the jar. Your audience expects the candle to burn until the water reaches the wick, but it continues to burn until they see the water well above the top of the flame. If the jar of water is shown by re- flection, hold the candle where the audience can see it. Have the match ready. Have the cur- tain closed while you " place the candle in the jar of water and light it." You have the proper spot marked on the table where you place the candle. After lighting it, have the curtain drawn aside and the audience sees the candle burning in the jar of water. Test the posi- tions before the audience arrives. 4. MAKE A PINHOLE CAMERA AND TAKE A PHOTOGRAPH WITH IT A small prize may be offered for the best picture made by a member of the club. A pinhole camera may be made in the follow- ing way. Use a box about five inches square and three inches deep. It must have a cover which slides down over the box for a depth of at least one inch. The interior must be painted black and made light-tight. Cut a hole one half inch in diameter in the middle of one side or end of the box. Paste a piece of tinfoil on the inside of the box over the hole. Make a pinhole in the center of this tinfoil. The success of your picture depends on the care with which you make this hole. The best results are obtained when the diameter of the pinhole is in proportion to the square root of the distance from the pinhole to the plate.1 1 Use the following formula : Diameter of pinhole = # ^Distance of plate from pinhole K = .0008 This diameter may be measured by some machinist or science in- WHAT IS COLOR? 163 Paste cardboard strips on the inside of cover to hold the sensitized plate. The picture is made on a glass plate which is held in place by narrow strips of cardboard glued in along the vertical edges of the plate. This plate is to be put into the camera while in a dark room. Of course, the pinhole should be kept covered until you reach the object you wish to photograph and covered again after the picture is taken. The exposure, depending on the light, should be from ten to twenty minutes. REFERENCE READING Comptoris Pictured Encyclopedia. Bragg, Sir William, The Universe of Light. Macmillan, 1933. Dull, C. E., Modern Physics. Holt, 1929. Page 404-498. Houston, E. J., The Wonder Book of Light. W. and R. Chambers, Ltd. Luckiesh, M., Artificial Light. Century, 1920. Meister, M., Energy and Power. Scribner's, 1930. Whitman, W. G., Household Physics. Wiley and Sons, 1932. Prin- ciples of Light, pages 272-290 ; Natural Light, pages 292-308 ; Arti- ficial Light, pages 310-321 ; Illumination, pages 322-342. structor who has a micrometer caliper, with which to measure the needle so you can make the hole just the right diameter. Having obtained a needle of the right diameter, do not force it all at once into the tinfoil, but push it in slowly, first on the one side, and then on the other so as not to tear the foil. When you have made the hole, be sure to smooth off the edges, as a clear picture cannot be made unless you have a clean cut hole. SURVEY QUESTIONS Do you know what magnets are and what they are made of ? What are some uses of magnets ? How does a compass tell direction ? Can a person become charged with electricity? Do you know what electricity is ? Can you produce electricity ? Can you name a good conductor and tell how it is used ? Can you name a good insulator and show how you would use it ? V Edwin Levtck UNIT VII HOW WE MAY PRODUCE ELECTRICITY AND MAGNETISM PREVIEW Long before the birth of Christ, it was known that a certain kind of iron ore which came from Magnesia in Asia Minor had the property of attracting other small bits of iron. To this ore, the name of magnetite was given, from which we get our word " magnet." Early peoples called these stones "lodestones" or leading stones, and thought they had magical powers. Although these magical stones were known to the Greeks 600 years before Christ, the Chinese are credited with having made the first practical use of magnets, for they discovered that a lodestone if it floated on a block of wood in water always pointed in a north-south direction. This discovery paved the way for the development of the mariner's compass in Europe in about the eleventh century. Thus it was that the magical lodestone enabled adventurous sailors and explorers like Columbus to sail away out of sight of land to discover new lands. In 1576 it was discovered that a compass needle properly supported would dip toward the poles of the earth unless one were on tne equa- tor. This caused William Gilbert in 1600 to conclude that the earth acts as a great magnet and attracts com- pass needles more strongly in some places than in others. Later still, in 1831, the arctic explorer, Ross, discovered a magnetic pole 1200 miles south of the north pole of the earth. 165 166 HOW WE PRODUCE ELECTRICITY The influence of the earth's magnetism extends far out into space, and may be one cause of the displays of " north- ern lights" or aurora seen in the sky of the northern and southern hemispheres. You have all heard of "sun spots." While we do not know just what they are, scien- tists find that the activity of sun spots is closely asso- ciated with the magnetic activity on the earth. There are many interest- ing facts which we can piece together in telling the story of how electricity has been harnessed and has become the most powerful of man's servants. The Greeks learned of one property of electricity when they rubbed amber, which they called electron, and found that it would pick up small particles. When Franklin sailed his kite in a thunder- storm and discovered that lightning was a form of electricity, another step was taken. rAnd when Galvani, the Italian scientist, found that the legs of dead frogs twitched when he brought them into a circuit with iron and copper, still another important fact about electricity was discovered. Then came Volta with his discovery that electricity could be generated by chemical means. We might go through a long list of discoveries, each of which gave us more and more knowledge about electricity. Franklin took chances with his kite, but he discovered that electricity could be conducted through the wet kite string. What danger did he expose himself to ? WHAT CAN MAGNETS DO? 167 PROBLEM I. WHAT CAN MAGNETS DO? People have not always depended on lodestones for magnets. It was discovered long ago that magnets could be made out of steel by rub- bing the steel with another Ar How will this change the properties of the knife blade? magnet. You can make a small magnet yourself. If you stroke a needle from the middle to the point several times with one end of a magnet and then, using the other end of the magnet, stroke it from the middle to the opposite end, you will make a magnet of the needle. You can make a magnet of any piece of steel in the same way. Large powerful magnets are made by passing a current of electricity through wires which surround iron or steel cores. What Will a Magnet At- tract ? If we lay steel needles, pins, tacks, gold pins, silver pins, pure nickel, a nickel coin, a copper coin, and a brass key on the table and move a bar magnet slowly over them, will anything hap- pen? What substances are the placed near- all objects n««<€le iron nail What substances will a magnet pick up? picked up ? We see as a re- sult of this experiment that a magnet will not pick up all metals. It has been found that magnets will attract iron, steel, pure nickel, and cobalt, but will not attract any other common substances. Permanent and Temporary Magnets. If you place a powerful bar magnet over a dish of iron nails, you will 168 HOW WE PRODUCE ELECTRICITY find that they cling to each other as well as to the magnet. If you separate the magnet from the nails which are touching it, all the nails will immediately cease clinging to each other. Magnetized nails may cause other objects such as soft iron or tacks to become magnetized for a time, but as soon as they are loosened from the perma- nent magnet, they lose their magnetic properties. Even permanent magnets may lose their power after a while, especially if they are heated. Permanent magnets are made of steel or of some alloys of steel ; tem- porary magnets are made of soft iron. What Happens to a Suspended Mag- net? Take a long bar magnet and suspend it by an untwisted Can a bar magnet be substituted for a compass? gtrmg g() that it swing in a horizontal plane. It will take a position in a north-south line. We may check this with a compass. That end of the magnet pointing north is called the north- seeking or north pole, and the other end is called the south-seeking or south pole of the magnet. Since all magnets have this property, a magnetic needle is used in the mariner's compass. How to Make a Compass. Magnetize a needle by rub- bing it on a bar magnet. Cut off a thin sheet of cork and float the cork in a dish of water. Lay this magnetized needle on the cork. What position does it take? Put a needle that is not magnetized on the cork. Does it act in the same way ? How could you find east and west if you had a compass ? WHAT CAN MAGNETS DO? 169 How to Use a Compass. In the pocket compass the needle is free to move over a disk on which the points of the compass are printed. If the compass is put down flat, the needle of the compass will move to and fro until it finally points to the magnetic north. If now the disk of the compass is shifted so that the N on the disk is just under the needle, all compass directions will be shown approximately correct. Demonstration 1. To Determine the Laws of Magnetic Poles. (a) Do both poles of a magnet attract magnetic substances? Bring the north pole of a bar magnet into a pile of iron tacks. Test the south pole in the same way. Test the center of the bar. Compare results. Do both poles of the magnet attract a magnetic substance? Does the equator of the magnet show strong attraction? (6) Relation of magnetic poles to each other. Suspend a bar magnet vertically, N-pole down. Bring the south pole of a bar magnet near the north pole of the suspended magnet. Bring the north pole of the bar magnet near the north pole ; then near the south pole. What are the results in each case? Make a statement concerning the attraction and repulsion of magnetic poles. Demonstration 2. To Magnetize a Steel Sewing Needle. Drop the magnetized needle (p. 167) into iron filings on a sheet of paper. Move the needle around and pick it up. Where do the filings cling? 170 HOW WE PRODUCE ELECTRICITY Are there many at the ends or in the middle ? Clean off the filings and break the needle into two parts. Place these in the filings. What happens? How the Magnetic Poles Act. These experiments show us that not only do magnets attract certain metals, but that if a magnet is cut in two parts, it will continue to be magnetized. We notice that the greatest attractive force is nearest the ends of the magnet. If we bring the north pole of one magnet near the north pole of a suspended magnet, the north pole of the latter moves away. If we bring the south pole of a fixed magnet to the north pole of a movable one, the south pole is drawn toward the north. This always occurs when two magnets are brought to- gether and gives a law which we may state as follows : Like magnetic poles always repel, and unlike magnetic poles always altract each other. Demonstration 3. To Show the Magnetic Field. Place a bar magnet under a piece of white paper with a strip of board of the same thickness on each side of it. Now shake iron filings evenly over the paper. Tap the paper gently. Notice what happens to the filings. Where are they most numerous? How can you describe their arrangement on the paper? Make a diagram of the magnet and of the lines of filings. How do they compare with the illustration on page 171? A Magnet Influences Space around It. Tacks or iron filings will jump across the air space to a strong magnet. A compass needle will turn when several feet away from a strong magnet. These facts indicate that the influ- ence of the magnet extends in all directions from the mag- net. This force decreases as the distance increases. The space about the magnet in which this magnetic influence exists is called a magnetic field. If a compass is placed in a magnetic field, the needle will take the direction of the lines of magnetic force. These lines are considered as WHAT CAN MAGNETS DO? 171 The magnetic field around a bar magnet. coming out of the north pole, circling around, and enter- ing the south pole of the magnet. The magnetic field is seen clearly in the illustration above. The Earth as a Magnet. If you had a magnet mounted on a horizontal axis and you traveled with it from New York over Canada toward Hudson Bay, you would find that the compass needle pointed a little west of north, and, as you went farther north, it would dip more and more toward the perpendicular. If you were explorers, you would find a place north of Hudson Bay where the compass would point down toward the center of the earth. This is the magnetic pole in our northern hemisphere. A similar magnetic pole exists in the southern hemisphere. These magnetic poles are each a good many hundred miles away from the geographic pole where the earth rotates on its axis. The earth, being a magnet, is surrounded by mag- netic lines of force. It is because of these lines of force that the compass acts as it does. Value of the Compass. We only have to think of the pilot on sailing vessels or steamers shut in by a dense fog, or of aviators flying blind, to realize the great value of the compass in modern life. For many years the great steamships depended largely upon the magnetic compass. 172 HOW WE PRODUCE ELECTRICITY Now they use a gyro-compass which is not magnetic and which is superior to the old type. When Lindbergh made his astonishing solo flight, he was able to put his ship down on the field near Paris because he had worked out his course exactly and had used the magnetic compass in doing this. Can you tell why a dipping compass needle would turn completely over if carried around the earth through the poles ? SELF-TESTING EXERCISE Select from the following list of words those which best fill the spaces in the sentences below and arrange the words in proper numerical order. A word may be used more than once. brass magnetic iron magnetized steel wood silver non-magnetic hard lines soft surfaces center (middle) opposite surrounded field filled earth poles water equator through attract repel force plane passes compass SOME WAYS OF PRODUCING ELECTRICITY 173 Magnets made of (1) keep their strength much longer than those made of (2) iron. A knife blade can be (3) by stroking each half from the (4) with the (5) ends of a strong magnet. Every magnet is (6) by a magnetic (7) which is filled with (8) of magnetic (9) Like magnetic (10) (11) but unlike (12) poles (13) each other. The needle of the magnetic compass takes the direction of the (14) lines of (15) of the (16) Magnetism (17) through (18) which are (19) , such as glass, copper, and wood. A magnet will attract only (20) substances. STORY TEST RALPH GIVES His OBSERVATIONS ON MAGNETS Read carefully and critically. List all the errors and suggest corrections. They make very powerful magnets out of an alloy of steel, nickel, and cobalt. Nickel is not a magnetic substance because when I tried to lift a 5^ piece with a magnet it was not attracted. I saw two of these powerful magnets demonstrated. When the two magnets were laid on the table with unlike poles together and released they pushed apart because like poles repel. One magnet would hold the other in the air above it when guides were placed so that the top magnet could move only vertically and the north pole of one was placed on the south pole of the other. The mag- netic field was so strong that when a compass was placed 8 inches away from the middle of the magnet the needle took a position parallel to the magnet with its poles pointing in the same direction as those of the magnet. When one end of a bar of copper was placed in iron filings and the upper end of the copper touched with the magnet the copper became a temporary magnet and when lifted iron filings clung to it. I saw a magnet held horizontally, lowered into a pan of iron filings and lifted. The largest mass of iron filings was near the middle of the magnet because that is the place where the magnetic force is concentrated. If a magnet is cut in two at its center, the lines of force within the magnet will be cut off and all the magnetism destroyed. PROBLEM II. WHAT ARE SOME WAYS OF PRODUCING ELECTRICITY? You have sometimes made an electric spark when you " scuffed" your feet over the carpet in winter or rubbed the cat's fur the wrong way, or when your hair stood up LUIGI GALVANI, 1737-1798. Galvani was a native of Bologna, Italy. Born of good ' family, he was early destined for the church, but changed to the profession of medicine. Later he became a professor in the University of Bologna, where he became famous for his research work. He had always been interested in the nervous system and wondered why nerves responded to stimulation. A chance twitch- ing of the leg of a frog he was experimenting with gave him the clew for which he was looking. He found that when a moist frog's leg was touched by two unlike metals it would twitch. Until the time of Galvani no one had ever suspected the presence of a current of electricity, although many experiments had been made with static or frictional electricity, and people knew a good deal about magnets. Galvani thought the movement of the frog's leg was due to an electric fluid in this muscle, but a little later Volta, a professor in the near-by University of Padua, proved that Galvani was wrong. He showed that the electric current was due to chemical action taking place between the two unlike metals connected by the moist frog muscle. This made electricity on the same principle as it is made in our galvanic batteries today, and made possible the flash- light, our electric doorbells, and the hundreds of devices we use today that depend upon the electric battery. SOME WAYS OF PRODUCING ELECTRICITY 175 in an astonishing manner when you brushed it. When the air is cold and dry, a hard rubber fountain pen or a rubber comb rubbed briskly with flannel will attract small bits of paper or a pith ball supported by a thread. If the ball or the bits of paper become electrified, as they sometimes will after clinging to the rubber for a moment, they will be repelled and fly away from it. The hard rub- ber was charged with electricity by friction. The objects which touched the charged rod were electrified by contact. Demonstration 4. Properties of Electrified Bodies. You will need these materials : two large rubber balloons, string, silk cloth, fur, glass rod, and a hard rubber rod. Fasten a string across the room near the ceiling. Blow up two large rubber bal- loons until they are tight. Fasten them on strings looped over the ceiling string. Make them at a height level with your head and six inches apart. A. Rub one of the balloons with fur. Is there any action now between the two balloons ? Between the balloon rubbed and your hand held near it? B. Arrange the balloons so that when neither is charged, they hang just touching each other. Rub both the balloons with fur. After you rub one do not let it touch anything until the second one is rubbed. Release the two. What happens? Compare this result with the one when only one was rubbed. C. Separate the two balloons so that you can use one with- out interference from the other. Charge the balloon by rubbing it with fur. Rub the hard rubber rod with fur. Bring rod near the balloon. Rub the glass rod with silk. Bring the glass rod near the balloon. What was the ac- ndt choked & rotor tion between the hard rubber rod and the balloon? Between the glass rod and the balloon? Conclusion and Explanation. At first the bodies were neutral. After being rubbed they were charged with electricity. Does a charged body attract an uncharged or neutral body? Do two of the charged bodies attract each other ? Repel each other ? Do all charged bodies have the same properties ? 176 HOW WE PRODUCE ELECTRICITY Charged Bodies. In this experiment we learned that when a hard rubber rod is rubbed with fur, the rod repels a rubber balloon which had previously been rubbed with fur. But a glass rod rubbed with silk attracted the balloon. Evidently there are two kinds of electric charges. According to our present theory of matter, each neutral atom is composed of a positive nucleus or central portion. The particles which make it positive are called protons. Negative particles of electricity called electrons are believed to revolve around the nucleus. The atom is normally made up of equal numbers of protons and electrons, the former being entirely inside the nucleus . There is a strong attraction between the protons in the nucleus and the electrons, but some of the electrons can be separated from the Where did the electrons shown on the silk outer t of the atom come from? Protons never leave the atom to go into another body. When we rubbed the glass and silk together, some of the electrons were transferred from the glass to the silk. This makes the silk negative. The glass rubbed with silk having lost electrons now has more protons than electrons and so it is positively electri- fied. When hard rubber is rubbed with fur, electrons go from the fur into the hard rubber, making the fur posi- tively electrified and the hard rubber negatively electrified. Whenever electrification is produced by friction between two bodies, the positive charge produced in one equals in amount the negative produced in the other. It was Ben- jamin Franklin who first suggested the names positive and negative for these two kinds of electrification. From these experiments we can make the general statement SOME WAYS OF PRODUCING ELECTRICITY 177 that two bodies with like charges repel each other, while two bodies with unlike charges attract each other and a body with either charge will attract a neutral body. Conductors and Insulators. Soon after 1600, men tried to electrify many substances. They decided that metals could not be electrified. In trying to electrify a metal, they held it in one hand and rubbed it with fur, silk, or flan- nel, and in no case did they get any result. It was not until after 1700 that some one held a stick of dry wood which had a metal on its end and rubbed the metal with fur. The metal re- ceived a charge of electricity which was easily detected. In earlier trials all the electricity produced in the metal by rubbing was given off or conducted from the metal to the hand which in turn conducted it away. This experiment showed that in relation to electricity, bodies are separated into two classes, conductors and nonconductors or insulators. It was this property of some materials to conduct electric- ity that gave Benjamin Franklin the opportunity to get sparks from his kite string during the thunderstorm, and suggested to him that lightning rods would protect build- ings by carrying up streams of electricity from the earth to the cloud above, or from the cloud down to the earth. The charge on the cloud may be so reduced in this way that the possibility of a huge flash to the earth through the building is greatly reduced. H. & W. SCI. I — 13 U. S. Forest Service Lightning results from a discharge of electricity between two oppositely charged bodies. Do electrons play any part in lightning ? 178 HOW WE PRODUCE ELECTRICITY Current Electricity. If we rub wax rapidly with a dry piece of woolen cloth, we can electrify it. The wax is then said to be charged with electricity. A charged body such as this is one in which electricity is at rest. To be sure, the amount in the wax is very, very small, but if we were to connect two oppositely charged bodies, negative and positive, with a good conductor, such as a metal wire, electricity would flow for just an instant from one body to the other. Electricity in motion, as this is, is called current electricity, and this means nothing more than a flow of electrons. This is the kind of electricity which we use in ringing our doorbells, in running our motors, and in lighting our homes. Electric Cells. You may have heard the terms "dry cell" and "wet cell," and doubtless some of you have seen them in your .pitch homes, as these 5anct two kinds of cells are used to ring electric doorbells. The wet cell is made by nearly filling a quart jar with a saturated solution of ammo- nium chloride. In this jar a large carbon plate and a zinc rod are suspended side by side, but not touching each other. When the ends or poles of these elements are joined with a wire electricity results through the release of chemical energy. The zinc rod and the ammonium chloride are gradually destroyed and must be replaced from time to time. mixture In both the wet cell and the dry cell it is the chemical action between the zinc and ammonium chloride that produces the electric current. Why is the dry cell used more than the wet cell ? SOME WAYS OF PRODUCING ELECTRICITY 179 In the dry cell, the zinc used is placed on the outside of the cell, making a container for the other materials, while the carbon is a large rod in the center. Between these are the chemicals, a paste of ammonium chloride being placed next the zinc and a layer of manganese dioxide around the carbon. The carbon pole is called the positive (+) pole, while the zinc is called the negative ( — ) pole. A current of electricity will flow through a wire which connects these poles. Dry cells have come to replace the wet cells in our homes to a large extent because they are more convenient to handle. What Produces the Light in a Flashlight? When an electric cell has been used for a long time, it may fail to produce any more current. In the case of the wet cell, you will very likely find that one of the plates in it has been used up. This suggests that some vigorous chemical action has taken place in the cell between the solution and the plates. This is true. The cell is really a device by which energy resulting from this chemical action in the cell changed into electrical energy. This electrical energy can be changed to heat energy and light energy as it passes through the tiny bulb of the flashlight. SELF-TESTING EXERCISE Select from the following list those words which best fit the blank spaces in the sentences below and arrange them in proper numerical order. A word may be used more than once. attract neutral ammonium conduction silver brass nickel chemical repel negative electrons insulators nucleus silk line conductor attracts friction gold metal repels contact protons charge positive induction wool current copper electricity sodium cotton Every (1) body contains equal amounts of (2) and (3) electricity. (4) between two unlike substances as 180 HOW WE PRODUCE ELECTRICITY sealing wax and wool will produce two unlike charges of (5) The nucleus of every atom of matter contains positive particles called (6) Around this (7) revolve. When glass is rubbed with silk, (8) go from the glass to the silk, making the glass (9) because of the excess of (10) in it and the silk (11) because of the excess of (12) in it. Electrons (13) electrons and protons (14) protons, but protons (15) elec- trons. Current electricity is merely a flow of (16) along a (17) (18) are materials which do not allow electricity to pass readily. In electric cells, electricity results from an expenditure of (19) energy. The common dry cell has two plates, zinc and carbon, and the active chemical (20) chloride. STORY TEST WENDELL EXPERIMENTS AT HOME Read carefully and critically. List all the errors and suggest corrections. I know that friction produces heat, but I have been puzzled to know why it is only in cold weather that I can get enough heat by rubbing the fur on my cat's back to make sparks of fire. Last night I rubbed a comb with flannel and the comb received elec- trons from the flannel. I touched small bits of paper with the comb. They clung to it at first but soon jumped off. Since they were attracted at first I think they must have had a positive charge, and when they jumped off we know they were positive because they were repelled. A positive charge is easily produced by rubbing glass with silk. The protons go into the glass, making it positive. This morning I got a dry cell at the store. I connected it through a button with wire to an electric bell. In connecting to the battery I was careful to have the string or cloth covering of the wire kept in place when I screwed the nuts over the wire on the binding posts because if the bare wire touched them it would make a short circuit and ruin the battery. When I pressed the button the bell did not ring. This shows that the battery was old. I shall take it back to the store and exchange it for a fresh battery. THE REVIEW SUMMARY In this unit we have only begun to find out some of the fact? about electricity, therefore you will not be able to give all the generalizations that you would give later on. See if you can add any to the ones that follow : SOME WAYS OF PRODUCING ELECTRICITY 181 1. There are only a few metals that can be magnetized or that can be attracted by a magnet. 2. Electric charges can be given to bodies of matter. Non- conducting bodies hold these charges for a time. 3. Electricity is believed to consist of negative particles called electrons and positive particles called protons. 4. Electrical energy is produced only at the expense of some other kind of energy. Before making your review summary, test your knowledge of the facts of the unit by checking over the text so as to be sure you know the facts underlying the generalizations. Then, using the generalizations, the material in the text, and everything you have read, seen, or done yourself, make a summary outline for your notebook. This outline you may use when you make a recitation. TEST ON FUNDAMENTAL CONCEPTS Make two vertical columns in your workbook. Head one CORRECT and the other INCORRECT. Under the first place the numbers of all statements you believe to be correct. Under the second place all the numbers of the statements you believe to be incorrect. Your grade = right answers X 5. I. When glass is rubbed with silk : (1) the silk takes a negative charge and the glass a positive charge ; (2) the glass is electrified but not the silk ; (3) the amount of electricity produced is the same in both bodies ; (4) the glass and silk will repel each other. II. Electricity may be produced by : (5) friction between paper and cloth ; (6) putting rods of aluminum and iron into a salt solu- tion and letting the outside ends touch each other ; (7) chemical action in a storage battery ; (8) an electric motor. III. Every magnet has: (9) two poles which attract iron; (10) two unlike poles; (11) a magnetic field; (12) an electric current surrounding it. IV. A dry cell : (13) produces electricity from chemical energy; (14) contains no water ; (15) has two poles, north and south ; (16) produces no current on a closed circuit. V. The needle of a magnetic compass: (17) is a temporary magnet ; (18) points to the earth's geographic north pole ; (19) takes the direction of the earth's lines of magnetic force ; (20) always points in an east to west direction. THOUGHT QUESTIONS 1. What are some objections to the use of the magnetic compass to direct the course of a ship? 182 HOW WE PRODUCE ELECTRICITY 2. How can you take electrons away from a glass rod? How can you add electrons to an insulated piece of metal? 3. Why does a person become charged with electricity when scuffing over a carpet on a day when the air is dry? 4. Why is a spark sometimes produced when one rubs the cat's fur backwards? REPORTS ON OUTSIDE THINGS I HAVE READ, DONE, OR SEEN 1. Report upon an article related to some topic discussed in this unit. The article may be from a current number of a science magazine or from some popular science book you have read. 2. The story of Galvani and Volta. 3. What Benjamin Franklin did for electricity. 4. The use of lightning rods. 5. The passing of the magnetic compass on ships. SCIENCE RECREATION 1. THE OBEDIENT ARROW Procure a dry fish globe. Cut a cover for it from cardboard. Cut an arrow from stiff letter paper. Suspend the arrow, carefully cctrctboarcC balanced, in the middle of the globe by a very fine thread. Fasten to the center of the card- board cover. Tell the arrow to turn to the point on the jar which you rub. Rub the outside of the glass up and down at a place about two inches to the right or left of the place where the arrow points, then rub another Place a few inches away. Rub your hand over the place elec- trified if you wish to take the electricity away and let the arrow go back to its original position. 2. A BALLOON WELCOME Blow up a rubber balloon until it is about eight inches to ten inches in diameter. Tie tightly. Suspend by a string about three feet from the wall and nearly in the path of a person who comes through the door into the room. It should be shoulder high. On a day when the air is very dry (a cold winter day is best) SOME WAYS OF PRODUCING ELECTRICITY 183 rub it briskly all over with a piece of fur or wool. Call some people into the room and if they pass close to the balloon, they will be surprised at the result. 3. MAKE AN ELECTROSCOPE Fasten a piece of silk thread to a celluloid ping-pong ball or to small pieces of cork. Hang this eight inches below a support. Use this to see if objects like sealing wax, fountain pens, and combs when rubbed with fur, wool, or silk are electrified. 4. A TASTE OF ELECTRICITY Get a strip of copper and a strip of zinc about ^ inch wide and two or three inches long. Fasten a copper wire to one end of each. Touch the tongue with the two free ends of the copper wires. Hold the ends of the wires not more than ^ inch apart. Dip the ends of the metal strips (must not touch each other) into a salt solution. Take off the copper wire, and bring the ends of the two strips to the tongue quite near each other. Can you detect a difference in taste when the current flows and when it does not? 5. ELECTRICITY FROM A LEMON Use the zinc and copper strips in Demonstration 4. Cut two slits in a lemon -|- inch apart. Work the knife around in each to cut the tissue. Push the two strips of copper and zinc into the slits but do not let them touch each other either inside or outside the lemon. Test by taste to see if an electric current is produced. Test with a compass. SCIENCE CLUB ACTIVITIES 1. ELECTROSTATIC RACE Make your preliminary tests at home. What can you find that will give you the strongest electric charge — wax, comb, fountain pen, rod of ebonite, hard rubber, or glass? Which gives you the best results — wool, fur, or silk? When satisfied with your results, enter your science club contest which will be held on a named future date. Pieces of paper of graded sizes will be provided, and the contest is to see whose equipment, which he brings from home, can lift the largest piece of paper clear from the table. 2. A MAGNETIC BOAT Build your boat upon any design you may devise. The fol- lowing suggestions may be useful to you : For the magnet use a 184 HOW WE PRODUCE ELECTRICITY darning needle, or a piece of watch spring about 3 inches long. Make a paper boat about 4 inches long. Paraffin the outside and seams if made from magnetic, boat float- . ,-, ,, (-111 pieces rather than folded. After magnetizing the steel, lay it in the boat and cover with a thin layer of melted paraffin. Two such magnets may be used if desired. On the club race day have a tub of water. Anchor 3 or 4 cork floats to mark off the course. Boats must go around the course outside these floats. The same magnet is to be used by each contestant. This should have a wire exten- sion so that the magnet can never be brought nearer than 6 inches to the boat. A stop watch is needed to time each boat, because each boat must be taken around the course by itself. The winner will be the one that makes it in the shortest time. 3. How TO PRODUCE A MAGNET USING ELECTRICITY (A) Connect a cell and push button as shown in diagram. Bring a portion of the wire down over and parallel to the compass needle. Press the button to cause an electric current to flow through the wire. Result ? (B) Diagram B represents a wire brought down over and parallel to the compass needle. Complete the wiring connections so that when the current flows it will make the north pole of the needle turn towards the west, as is rep- resented by the dotted arrow. (C) Wind an insulated copper wire in close layers around a soft iron rod, remove the rod, connect the ends of the H button lie- B SOME WAYS OF PRODUCING ELECTRICITY 185 coil into the electric circuit. Hold one end of the coil near the north pole of the compass needle. Press the button to pass an electric cur- rent. Result ? Hold the other end of the coil near the north end of the compass. Result? Make a similar test with the iron core inside the coil. Compare strength of magnetism. Complete diagram C. Label poles of the electromagnet correctly. REFERENCE READING Lunt, J. R., Everyday Electricity. Macmillan, 1927. Meister, M., Magnetism and Electricity. Scribner's, 1929. Parker, B. M., The Book of Electricity. Houghton, Mifflin, 1928. Wade, H. T., Everyday Electricity. Little, Brown & Co., 1924. SURVEY QUESTIONS Have you ever tried to count the stars? How many can you name? What is the Milky Way? Why is the North Star so called? Are stars all the same color ? What do the differences in color mean ? What is a constellation? What is the astronomer's "yard- stick"? Are all stars the same distance away? UNIT VIII GETTING ACQUAINTED WITH THE STARS PREVIEW We have looked into the sky on a dark clear night and have seen multitudes of twinkling stars, some large and some small. If we look closely, we notice that some of the stars are of a different color, some bright red, deep blue, or white. Boys and girls who are scouts can pick out the North Star and some of the easier constellations. Doubtless boys and girls during the past ages have done the same thing. They have wondered about the stars and how far away they were. The ancients thought the sky was an inverted bowl and that the stars were holes through which light shone. Primitive man worshiped light because he was so much dependent on it. Ancient people studied the stars and used them as guides to help find their way about at night. It is little wonder that the ancients with so much leisure time should find the heavens interesting. Shepherds who watched the flocks by day also watched the stars by night. It is not strange that these imaginative and superstitious people of the olden times saw figures of people and animals in the stars, and created stories about their origin in the sky. Nor is it strange that they made a universe with the earth as a center, and believed that the stars in the heavens revolved around it. They knew that the sun and the moon and the stars helped them to keep time, and they also came, in time, to be more familiar with some stars than with 187 NICHOLAS COPERNICUS, 1473-1543. COPERNICUS, as a Polish boy, studied Latin, Greek, and mathe- ^-^ matics. It was believed at that time by every one that the earth was an immovable body suspended in space, and that the sun, planets, and stars moved around it. The lad studied medicine but was so interested in mathematics and astronomy that when an opportunity arose he became a professor. Later he became a canon, or priest, at the Cathedral of Frauenburg, in Germany. Here he had much leisure and devoted himself to the study of astronomy. Although he had no telescope, he cut slits in the walls of his home and timed the movements of the planets in that way. He came to the conclusion that the sun was the center of our solar system and that the earth and other planets revolved around it. This was a theory then, but we know it to be a fact today. HOW FAR AWAY ARE THE STARS? 189 others. Some of the better informed men became astrol- ogers. These men believed that the stars exercised magic influence over people, and that such people must do the things that the stars ordered them to do. Even today we see ignorant people believing in the predictions of fortune tellers who say that they live under a lucky or an unlucky star. Some of our superstitions of today have been handed down from very ancient times. But the early astrologers knew a great deal about some of the stars. They could tell several planets and gave them names. The name " planet" itself comes from the Greek word meaning to wander, for they saw that these heavenly bodies moved about. The old astronomers could predict with a good deal of accuracy the movement of some stars, although they did not know what caused them to be seen in different positions in the sky. The old idea was that the earth was fixed, and it was not until the 16th century that Copernicus,1 a Polish clergyman, proved that a number of planets were revolving in space around the sun. He believed our own earth was one of these and that the earth rotated on its axis, making it appear as if the stars moved about the earth. In the units that follow, we shall build on the experiences we have had in our geography and try to get a little more knowledge about some of our neighbors in space. PROBLEM I. HOW FAR AWAY ARE THE STARS? When we look up into the sky, we may think that we see myriads of stars, but if we try to count them, we are surprised to find that we rarely see more than 2000 or 3000 at one time. If we were to look through a big tele- scope, such as they have at the Mount Wilson Observatory in California, we could see thousands of stars where we saw only one with the naked eye. This is so because the 1 Copernicus (ko-pur'ni-kws). 190 GETTING ACQUAINTED WITH THE STARS telescope shows us bodies whose light is too dim to be seen with the unaided eye. But if we were to expose a photo- graphic plate behind a telescope lens for several hours under the same space in the sky, we would be amazed to find when the plate is developed that not thousands but hundreds of thousands of stars will appear where we saw only a few with our naked eye. The reason for this is that the chemicals on the plate are sensitive to rays of light too weak to register in the human eye, even when we look through the telescope. The Astronomer's Yardstick. When we look up at the stars, we realize that some are much larger and some much brighter than others, but all look to be very far away. As a matter of fact, some are very much farther away than others. Some appear nearer because they are more brilliant. Astronomers tell us that the nearest fixed star 1 is over 25,000,000,000,000 miles away. Light travels a little over 186,000 miles a second. In a year Solbelman Syndicate This shows a portion of the sky as seen through a large telescope. How many of these stars do you think you could see with the naked eye ? 1 Proxima Centauri. HOW FAR AWAY ARE THE STARS? 191 The light by which we see Aldebaran today left that star 44 years ago, and we apparently see it as the upper star. But in that time the star has moved many miles and it is really at a point 55 billion miles away from the place where we appear to see it. it travels about 6,000,000,000,000 miles, so that it takes a little over 4 years for light from the nearest star to reach us. The distance light travels in one year is called a light year. This is the astronomer's yardstick or a way of measuring distances. When the astronomer tells us that there are probably many hundred thousands of light years separating us from some of the more distant stars, we can see that the distance of the stars from the earth varies greatly. Distances to the Stars Are Enormous. There have been many comparisons devised to make the enormous distances to the stars understood. None of them help very much, but that of Dr. Brashear, at one time a famous lens maker of Pittsburgh, is at least interesting. In the eyepiece of many telescopes a "cross hair" is used. This had to be finer than any thread. Even the fiber of the ordinary spider web is too coarse, but the mother spider spins a very fine and delicate fiber to make the cocoon which protects the young. These fibers were used by Dr. Brashear in his telescope, and he became interested in calculating how far so thin a fiber could reach. A pound of it would circle the earth at the equator and ten pounds would make enough fiber to reach the moon. How much of this fine fiber would be required to go to the nearest star 4£ light years away? By Dr. Brashear's calculation 192 GETTING ACQUAINTED WITH THE STARS By Burton Holmes. From Ewing Galloway Here, in the Court of Honor in front of the science building, light from Arcturus, which had left the star forty years ago, set off the lights of the Century of Progress. The illuminated board which secured the starlight from one of the co-operating observatories is seen in the center of the picture. it would require 500,000 tons to reach the nearest star, and to reach the North Star, it would take over 55,000,000 tons. How Starlight Opened the Century of Progress Exposi- tion. In 1933 the World's Fair in Chicago was opened officially by an electric current set up by light from the star Arcturus. The light from this star, which reached the earth in 1933, left Arcturus 40 years earlier, or about the same time that the previous World's Fair had been held in Chicago. It is interesting to know how this starlight was used. Light from the star was collected by a large telescope and focused on the interior of a photoelectric cell. Photoelectric cells are capable of transforming light energy into electrical energy, and this cell transformed the light from Arcturus into a current of electricity which was amplified and sent by wire from HOW FAR AWAY ARE THE STARS? 193 the observatory to Chicago. Here it operated machinery which turned on the lights and opened the Fair. Each night the great batteries of electric lights at the Century of Progress Exposition were turned on by means of the light from this same star sent from one or more of the observatories which co-operated in this interesting service. If the distance to Arcturus were expressed in miles, it would be about forty times six million million. Can you express this in figures ? Star Magnitudes. Any one who has seen the heavens on a clear night knows that the brightness of the stars varies greatly. The faintest star visible to the unaided eye is called a sixth magnitude star. This furnishes the basis of classifying them. The table which follows gives a rough comparison of magnitudes or brightness. MAGNITUDE TIMES BRIGHTNESS OF SIXTH MAGNITUDE STARS APPROXIMATE NUMBER OF STARS OF THIS MAGNITUDE IN THE WHOLE HEAVENS 6 1 5000 5 2i 1500 4 6 500 3 16 200 2 40 60 1 100 20 The apparent brightness of a star depends upon its temperature, size, and distance. Other things being equal, the nearer the star to us, the brighter it seems. The North Star is about as bright as Betelgeuse, but it appears much dimmer because it is more than twice as far away from us, and yet it appears brighter than some nearer stars which are smaller and cooler. What the Color of Stars Tells Us. The unaided eye can easily notice a difference in color of some of the stars. When an iron rod is heated in the furnace, the first H. & W. SCI. I — 14 194 GETTING ACQUAINTED WITH THE STARS Wright Pierce This picture shows how the spectroscope is used. By means of this instrument the materials burned in the flame at the right are known by the patterns or bands they make in the spectrum of the instrument. indication of its becoming luminous is shown by a dull red color, which, as it is heated longer, may change to orange or yellow. If it is placed in a very hot furnace, it finally becomes " white hot" and gives a brilliant whitish light. Evidently, then, the color of a luminous body differs with its temperature. This experiment gives us some evidence on the temperature of stars. Our sun is believed to have a surface temperature of about 11,000° F., and gives a yellowish light. Some stars have exactly the same color as the sun, and when seen through an instru- ment called the spectroscope, they have the same spectrum as the sun and so are believed to have about the same temperature as the sun. Betelgeuse is a red star and hence is not as hot as our sun, while Sirius, the Dog Star, shines with a bluish-white light which indicates that it is hotter than the sun. Half of the stars are white, while most of the others are yellow. Some bodies that were HOW FAR AWAY ARE THE STARS? 195 stars once now have so little light and heat that they do not even glow. They have become cold bodies like our earth and our moon. The color band and its position as seen in the spectroscope help astronomers to tell whether the star is moving away from us or coming toward us. SELF-TESTING EXERCISE Select from the following list the words that best fill the blank spaces in the sentences below and arrange the words in proper numerical order. A word may be used more than once. million years red color tenth month black photography first century white periscope thousand Heavens light telescope 100 orange dark sixth year yellow stars fourth More stars in the (1) are discerned by (2) than can be seen through a (3) (4) . travels faster than any other known thing. In astronomy the unit of measure for distance is the (5) (6) , which equals six (7) (8) miles. The nearest star is about 4^ (9) (10) away. The faintest star we can see is a (11) magnitude star. A first magnitude star is (12) times as bright as this. The age of a star is told by its (13) Young stars are (14) , while old stars are (15) or (16) STORY TEST URSULA VISITS A GREAT OBSERVATORY Read carefully and critically. List all the errors and suggest corrections. I recently enjoyed a rare privilege. It was open night at the Harvard Astronomical Observatory. Through a 10 in. tele- scope I saw the red Rigel and red Mars. Rigel is ever and ever so much hotter than our sun and the other stars. As I looked at it I could feel the intense heat coming through the telescope, and no wonder, because it is 25,000 times as hot as the sun. I asked if I might see the astronomer's "yard stick" with which they meas- ured the distance to the stars. I wonder why they laughed, but anyway they said that they never let the public see it. On one of the roofs without any telescope we were shown constellations 196 GETTING ACQUAINTED WITH THE STARS made up of stars of varying brightness. We could see stars varying from the 1st to the 10th magnitude. I must have counted at least 30 first magnitude stars, the brightest of them all was Betelgeuse. PROBLEM II. WHY DO THE STARS APPEAR TO MOVE? The Earth Is Moving through Space. We must go back to our geography to answer this question. The earth is a nearly spherical body which rotates on its axis once in every 24 hours. We also know that it revolves around the sun once every year. If we think of the size of the earth and remember that it is about 25,000 miles in circumference at the equator, we may imagine a city there whirling around the earth's center at a rate many times as fast as the fastest mail plane can travel. If we bear in mind the rotation of the earth on its axis, we can understand The fact that the earth is revolving is shown in this photograph. The fixed stars make trails on the plate. Can you locate the position of the polar star ? In what hemisphere must this photograph have been taken ? WHY DO THE STARS APPEAR TO MOVE? 197 why it is that the sun, moon, and stars appear to rise and set. The earth also rushes through space around the sun at a rate of about 1100 miles a minute. If we also remember that we are moving rapidly through space, we can see why constellations do not always appear to be in the same place in the heavens. Those of us who are scouts know that certain groups of stars called constella- tions are visible in the winter and that six months later others have come above the horizon and occupy the places held by those we saw in the winter. The reason for this is evident when we recollect that in the summer our earth is in quite a different place in space than it is in winter. We have moved along to the other side of the sun in a circular path whose diameter is 186,000,000 miles. Demonstration 1. How the Rotation of the Earth Causes Stars to Appear to Move. Hang a large round umbrella in the room so that the supporting rod is in direct line pointing to the North Star. A compass will show you north. There are 90° from the equator to the north GETTING ACQUAINTED WITH THE STARS pole. Paste a paper star around the umbrella rod where it passes through the cover of the umbrella. As you look up into the umbrella, you see this star where the North Star would be. Place other paper stars in positions to represent the Big Dipper and one or two other constellations. Make holes at the poles of a small globe, place it on the umbrella rod so that it will rotate under the umbrella. The North Star is now directly in line with the axis of the earth represented by the rod of the umbrella. In place of a globe, a ball, an apple, or an orange may be used. The latitude of the place where you live equals the number of degrees it is north of the equator. Mark the spot on the globe where you live. Now imagine you are on the earth. Hold the umbrella still. Rotate the globe and observe the direction in which you would look to see the North Star at different times. Observe the direction in which you see the end star in the Big Dipper. Rotate the globe from west to east far enough to represent six hours' time, or one-fourth of a revolution. Now observe the direction in which you would look to see the same star. In what direction would the star appear to have moved? Why Do Stars Rise and Set ? Suppose we are standing at a certain place on the surface of the earth as it rotates on its axis. After a complete revolution on its axis during a period of 24 hours, we are brought back to the same place. This turning as we look at the stars gives them the appearance of rising and setting. If you walk up a Explain by means of this diagram why stars appear to rise and set. long hill behind which is a factory with a tall chimney, the higher up the slope you go, the more you see of the chimney. It appears to rise. If you go backwards down the hill, you see the chimney gradually disappearing be- WHY DO THE STARS APPEAR TO MOVE? 199 hind the hill. We may think of it as setting. When the moon comes up or sets, it just means that we have traveled past it as we dash by objects on a railroad train. It is in the same way that we move past stars of the constellations. Stars seem to move across the sky from east to west, but the earth is really rotating from west to east. Consequently they appear to rise and set. There is one star, however, that does not appear to move. This is Polaris, the North Star. The reason for this is that it is in line with the axis of the earth, as is shown in the demonstration we just performed. Now, because the earth rotates, the stars appear to describe circles around the earth. If the earth is held still while the umbrella is rotated east to west, and you imagine yourself at a fixed spot on the earth, you will readily see the apparent motion of the stars. SELF-TESTING EXERCISE Select from the following list those words which best fill the blank spaces in the sentences below and arrange the words in proper numerical order. A word may be used more than once. always north move spherical never south motion earth hallucination east movement star illusion west rotates equator near sun speeds axis distant moon revolves poles latitude The earth in form is a (1) body. It (2) on its (3) and (4) around the (5) The axis of the earth points towards the (6) (7) which (8) appears to move. All the other stars appear to (9) from (10) to (11) during the night. But this (12) is really due to the (13) of the (14) The fact that we do not see the same stars at different seasons is explained by the (15) of the earth to (16) parts of the heavens as it revolves around the sun. 200 GETTING ACQUAINTED WITH THE STARS STORY TEST SYBIL HAS A UNIQUE WAY OF EXPLAINING WHY THE STARS APPEAR TO MOVE Read car ef ally and critically. List all the errors and suggest corrections. I play that I am the earth and my eye is a person on the earth. I stand near one end of the room. I name different objects in the room " stars." Directly over my head is the North Star. Un- fortunately my eye does not extend out from the surface of my face as people stand out above the surface of the earth, and so my eye cannot see the North Star. I play it is sunset in September. I rotate slowly. When halfway around it is sunrise and the night is over. The objects representing stars passed before my sight just as if they had been moving and I had been still. I then move to the opposite end of the room. It is now sunrise in March. I rotate halfway to represent the night. I see some of the stars (objects) that I saw before and some different ones. But the positions in which I see them appear quite different. After this experiment it is quite easy to understand how the two movements of the earth can produce the common illusions of the movements of the stars. PROBLEM III. HOW TO GET ACQUAINTED WITH THE CONSTELLATIONS If you live in the northern hemisphere and look towards the north on any clear night, you will find the Big Dipper. The two stars on the side of the dipper away from the handle are called "the pointers.7' If you use these for direction and follow this line from the bottom of the dipper into space, you will presently come to a star not quite so bright as those forming the bowl of the dipper. This is Polaris, the polar or North Star. It is the star that has guided travelers since ancient times. When we see it, we should remember that the light which enters our eyes is believed to have left that star more than 450 years ago. The light by which you see the North Star left it before Columbus, guided by that same star, discovered America. That starlight has been traveling at the rate of 6,000,000,- 000,000 miles a year all these long years. Since the North HOW TO GET ACQUAINTED WITH CONSTELLATIONS 201 Star is practically in line with the axis of the earth and all other stars keep the same relative position to the North Star, there is ap- parent rotation of all the other stars about Polaris in the center. How the Stars Got Their Names. Many boy and girl scouts may have studied the stars enough to know the names of some of the constellations. Ancient peoples in their study of the i ^ „ Star map of the region about the North Star (pole heavens saw many star)> If you face north at 8 PM and hold this map Wonderful Crea- in front of you with the name of the present month at +IIT-OG tViorP rlrao- the bottom, you will find these five constellations in ie, i i d&- the relatiye positions indicated on the map. ons, horses, lions, dogs, as well as many mythological characters. These groups of stars have been called constellations. There are 48 constellations named by ancients and about 40 more have been added in later times. Some are called by very ordinary names such as the Big Dipper and the Little Dipper, which you have all seen. But these same constellations have also been given other names, the Great Bear and the Little Bear. Many of the star groups have Greek or Roman names which have come down from the ancient times because of the stories that the ancient peoples told about these figures in the sky. It is interesting to know that certain constellations known to the Egyptians, Chinese, the Greeks, and our American Indians had the same names given them by these different peoples. For 202 GETTING ACQUAINTED WITH THE STARS example, the constellation we call the Great Bear was so named by the Chaldeans, Greeks, and American Indians : Is this a modern or an ancient map of a portion of the heavens ? Give the reason for your answer. groups of people who had no connection with each other at any time during their existence. The Big Dipper. One of the most conspicuous star groups or constellations is the Big Dipper. From it you can find the North Star and then work out to other groups. Polaris, also a second-magnitude star, is at the end of the handle of the Little Dipper. The two second-magnitude stars in the end of the bowl away from the handle are HOW TO GET ACQUAINTED WITH CONSTELLATIONS 203 called " pointers." They point to the polar star, Polaris. The position of these and other constellations differs with the season. As the earth moves along its orbit to new positions in the heavens, the stars overhead at 8 P.M. will vary greatly at different times of the year. If you observe the Big Dipper in early evening as soon as visible, and again the same evening three or four hours later, you can see that its position in the heavens changes. How to Tell Some of the Constellations. We can easily find a number of the constellations if we know the position of the Big Dipper and the Little Dipper. A study of any good star map will show you that if you follow the pointer of the Big Dipper to the North Star and then continue about an equal distance beyond, you will see a little to the right a constellation whose bright stars roughly form the letter W. This is the constellation Cassiopeia. If you go from the pointer to Polaris and turn at right angles and travel nearly twice the distance, you will come to a very bright red star, called Capella. From the pointer at the open end of the bowl draw a straight line to the handle side of the bowl one- third of the distance down from the rim of the bowl and continue in the same direction to a bright star which is twice as far from the North Star as the bowl of the Dipper is. This is Arcturus in the constellation Bootes. Arcturus is a first-magnitude star 500 times as large as our sun and gives a white light. We have already seen that it takes about 40 years for its light to reach the earth. By studying the star maps shown on pages 204 and 205, you can locate a number of the more common constella- tions such as Orion, with its three-starred belt, and the bright stars Rigel and Betelgeuse ; the Twins ; the Great Dog Star, Sirius, which is the brightest star in the sky; and many others. Remember that the maps made for use here show you the situation in the sky during the JANUARY FEBRUARY 204 JUL.V AUGUST NOVEMBER. SEPTEMBER DECEMBER 205 206 GETTING ACQUAINTED WITH THE STARS months of November, January, March, and June in the northern hemisphere, and that if you see the same heavens six months from these dates, the constellations will have quite a different position in the the sky, as can be seen by comparing the maps on pages 204 and 205. What Is the Milky Way? If you look up into the sky on a clear moonless night, you will see an irregular belt-like luminous cloud extending clear across the sky which varies in brightness in different places. It seems like a pathway in the heavens, and for this reason has been called the Milky Way. This is best seen in September. In ancient times the Milky Way was thought of as a pathway to heaven over which those who died had to travel. It has also been called by such names as Jacob's Ladder and the Pathway of the Souls. Of late years our powerful tele- scopes have revealed much more about the true nature of the Milky Way. It is made up of millions of stars, masses of incandescent matter, and perhaps bodies like our planets, moons, and material out of which comets are made. All the stars that we see through telescopes are luminous bodies like our own sun. This great system of stars that we see in the Milky Way is called a galaxy, and since our own sun is a member of this galaxy, we belong to it also. Many other galaxies have been discovered in the very distant heavens, of which we will learn something later. SELF-TESTING EXERCISE Select from the following list those words which best fill the spaces in the sentences below and arrange the words in proper numerical order. A word may be used more than once. earth north Big first handle cloud northwest south Little second bowl Polaris sun east medium third dipper Cassiopeia stars west Great thousands trillions pointers planets up Small millions northeast constellation galaxy down magnitude billions fourth luminous HOW TO GET ACQUAINTED WITH CONSTELLATIONS 207 The two second (1) stars on the side of the (2) (3) opposite the handle are called the (4) They show the direc- tion to (5) Almost opposite the Big Dipper on the other side of the North Star is the (6) called (7) Polaris is the star at the end of the (8) of the (9) (10) If the handle to the Big Dipper points southeast at 6 P.M., it will point (11) at 9 P.M. and (12) . at 12 midnight. Polaris is a (13) magnitude star and Sirius and Arcturus are (14) magnitude stars. The Milky Way seems like a (15) (16) but in reality is chiefly a cluster composed of (17) of (18) . and is called a (19) of which our own (20) is a member. STORY TEST EVELYN LIKES TO STUDY THE STARS. HAS SHE PROFITED BY HER STUDY? Read carefully and critically. List all the errors and suggest cor- rections. The heavens are just full of stars grouped together in consterna- tions. The largest of these is the Milky Way. Last night I saw Orion. I recognized it by the 3-star belt and the 2 bright stars, Altair and Arcturus. I also saw Procyon in the Little Bear, and the brightest of all stars, Sirius, in the Great Bear. In the early evening the pointers in the Big Dipper pointed northwest and towards Polaris, but six hours later they pointed northeast and away from Polaris. Cassiopeia appears to travel a complete circle around the North Star every 12 hours, but stars farther from the polar star like Sirius require 24 hours to make the circuit because of the greater distance the star has to travel. If we stood over the north pole in winter, Polaris would be directly overhead, but in summer it would be 23^ degrees farther south. THE REVIEW SUMMARY We might study astronomy all our life and still know very little about the stars. However, scientists have agreed that there are a few general facts or generalizations that almost any one can learn about these wonderful neighbors of ours in space. These gen- eralizations are : 208 GETTING ACQUAINTED WITH THE STARS 1. There are many more stars than we can see. 2. The stars are so far away it takes light from them many years to reach us. 3. The rotation of the earth on its axis causes an apparent daily rotation of the stars. 4. Stars vary greatly in size, brightness, and distance. 5. All the stars we ever see with the unaided eye make up a small part of a huge group called a galaxy. Before making your review summary, test your knowledge of the facts of the unit by checking over the text so as to be sure you know the facts underlying the generalizations. Then, using the generalizations, the material in the text, and everything you have read, seen, or done yourself, make a summary outline for your notebook. This outline you may use when you make a recitation. TEST ON FUNDAMENTAL CONCEPTS Make two vertical columns in your workbook. Head one CORRECT and the other INCORRECT. Under the first place the numbers of all state- ments you believe to be correct. Under the second place all the numbers of the statements you believe to be incorrect. Your grade = right answer X2i I. The process which discloses the largest number of stars is : (1) counting them on a very clear night ; (2) looking through a powerful telescope ; (3) by photography ; (4) by using an enlarging camera. II. By the magnitude of a star is meant : (5) its distance away ; (6) its size ; (7) its apparent brightness ; (8) its real brightness compared to the sun. III. When a star gives a white or bluish white color, it is evidence that the star is : (9) very hot ; (10) very near ; (11) a young star ; (12) hot, but not so hot as our sun. IV. The stars in the sky: (13) keep their positions almost unchanged year after year; (14) really move across the sky daily ; (15) would not appear to move if the earth were still; (16) con- stantly change their relative positions as do the drops of water in the ocean. V. The Big Dipper: (17) is a galaxy; (18) contains "the pointers" for locating Polaris; (19) revolves around the sun; (20) appears to revolve around the North Star every 24 hours. VI. There are stars so far away that: (21) their discovery awaits the building of more powerful telescopes ; (22) the light leaving them today will not reach the earth for a hundred thousand HOW TO GET ACQUAINTED WITH CONSTELLATIONS 209 years; (23) follow different physical laws from those of our own system ; (24) they must be cold bodies. VII. When we look into the sky at 8 P.M. in December, we do not see the same constellations that we do at 8 P.M. in June because : (25) it is colder weather ; (26) the nights are longer ; (27) the earth has moved halfway around the sun, changing the heavens which we see at night ; (28) the stars have rotated halfway around the North Star. VIII. The North Star is : (29) about vertically over the north pole of the earth ; (30) visible to all people on the earth, because of its great distance above the earth; (31) more than two million billion miles from the earth ; (32) also called the Little Bear. IX. The light year is : (33) the time it takes light to come to earth from the sun ; (34) the unit of measuring distances of heavenly bodies ; (35) the distance light travels in a year ; (36) about six million million miles. X. The Milky Way is: (37) a constellation; (38) a galaxy; (39) a solid heavenly body ; (40) is seen by reflected light just as the moon is. THOUGHT QUESTIONS 1. Why do stars appear to move in a certain direction during the night ? 2. Why do certain stars appear to change their positions from month to month? 3. Calculate how long it will take the light from a star selected by yourself to reach the earth ? 4. Compare an atom of matter and our own solar system. Show how you will use facts, theories, and imagination in making this comparison. 5. How would you say that future discoveries in astronomy will be made ? 6. How can we tell the age of a given star? 7. We say that the axis of the earth points very nearly towards the North Star. Can you explain how, in reality, this statement is very far from the actual fact ? REPORTS ON OUTSIDE THINGS THAT I HAVE READ, DONE, OR SEEN 1. Report upon an article related to some topic discussed in this unit. The article may be from a current number of a science magazine or from some popular science book you have read. H. & w. sci. i — 15 210 GETTING ACQUAINTED WITH THE STARS 2. The value of Galileo's telescope. 3. Ideas of ancient peoples about the heavens. 4. Kinds of telescopes. 5. Famous observatories. SCIENCE RECREATION 1. WHAT PROGRESS HAS SCIENCE MADE ON THE EARTH SINCE THE BEAM OF LIGHT BY WHICH You MAY SEE ARCTURUS LEFT IT? Ask your grandparents about the wonders of science 40 years ago. Write up the story of scientific progress that has been made on the earth during the time that beam of light traveled through space. 2. MAKE A LUMINOUS STAR CHART. Fit a box approximately four inches on a side over the end of a hand flash lamp. The side of the box opposite the lamp bulb is open to hold the star charts. These are cut out of black paper a trifle larger than the opening in the box. The center of the box cover is cut out nearly to the edge. When this is put on the box over the star chart, it will hold it securely in place. Consult a good star map. Mark on the black paper the relative positions of the principal stars in a constellation. Prick holes through. When in place on the box, the light shines through and shows you just what to look for in the sky. Make as many constellation charts on separate sheets of paper as you desire to locate. The following constellations are suggested as interesting groups to locate : The two dippers, Cassiopeia, Orion, the Northern Cross, Pegasus, Sickle, Lyra, and the Pleiades (Seven Sisters). SCIENCE CLUB ACTIVITIES 1. MAKING STAR TRAILS Have the club meet in the evening. If in the city, get permis- sion to use the roof of some tall building, but it is better to go out into the country where no artificial lights will cast a haze, and so dim the light of the stars. Have at least two cameras loaded with very fast film, such as supersensitive phenachrome. Open the diaphragms wide, and set the lever for time exposures. Point one camera directly at Polaris and the other at the brightest star nearly overhead. Fix the cameras so that they cannot move. Open the shutters and allow them to stay open one and one-half to two hours. You can go away and have an indoor meeting and HOW TO GET ACQUAINTED WITH CONSTELLATIONS 211 make a luminous star chart, or study the star groups with your chart, if you have one already made. When your film has been developed and printed, you will find curved paths circling part way around the polar star but nearly straight paths in the picture taken overhead. You should be able to explain why these trails are not alike. 2. WHAT Is YOUR SPEED AND WHERE ARE You GOING? In addition to considering and making the calculations sug- gested here, ask members to look up and report to the club any information — facts or theories — that has to do with our move- ments in space. a. If you were at the equator, how far would the rotation of the earth on its axis carry you in twenty-four hours? 6. If you were right over the North Pole of the earth, how far would the rotation of the earth carry you in twenty-four hours ? c. If you live about halfway from the North Pole to the equator, how far will you travel in twenty-four hours? d. If you are moving at the rate of eighteen and one-half miles per second, along the orbit of the earth around the sun, how many miles do you travel in a day of twenty-four hours ? 3. Make a star map for the present month. 4. Make a simple telescope. 5. Report on the beginnings of astronomy. 6. Report on a modern astronomical observatory. REFERENCE READING Baker, R. H., The Universe Unfolding, Williams and Wilkins, 1932. Barton, S. G., and Barton, W. H., A Guide to the Constellations. Mc- Graw-Hill, 1928. Book of Popular Science. Universe, page 453 ; Motion, page 871 ; Worlds, page 1305 ; Star Land, page 4167 ; Milky Way, page 4767. Chant, C. A., Our Wonderful Universe. World Book, 1929. Moseley, E. L., Other Worlds. Appleton-Century, 1933. Washburne, H., and Reed, F., The Story of Earth and Sky. Appleton- Century, 1933. SURVEY QUESTIONS If the earth was once all molten rock, how can you account for the soil and water now formed on its surface ? Did you ever find a fossil ? How do you think it was made ? What are some evidences of the force of water ? How are the active forces of nature of vital importance to a farmer? Do you know what kinds of soil hold water ? What kinds are porous ? What kinds make the best soil for growing crops ? Wliy are fertilizers added to soil? Photo by E. S. Shipp. Courtesy U. S. Forest Service UNIT IX ROCKS AND SOIL PREVIEW How many of you have ever been to the top of a high mountain ? You remember how it looked — a great mass of solid rock with perhaps a few trees clinging here and there in places where there was a little soil. If you worked your way down the mountainside, you would probably follow the course of a tiny brook which, as you descended, you would notice had cut its way deeper and deeper between rocky walls and slopes of broken particles of rock. Look at those rocks carefully. They all seem to be angular bits, not rounded like the pebbles you find in the valley at the foot of the mountain or on the beach. The rocks on the mountainside look as though they might have been cracked off and broken up by some force, perhaps great heat or cold. Let us scramble down a lit- tle lower. Trees, shrubs, and plants begin to be more numerous, the rocks are giving place to soil, some of it black and rich. You find more inhabitants of the forest - birds, squirrels, and other small animals. If you dig in the ground, you may find earthworms, beetle larvae, and other living things. The brook is inhabited, too : insect larvae in the water, flies and mosquitoes hovering over its surface, and perhaps small fish, even trout, lurking in its pools. And now the rocks and pebbles over which the brook rushes show the familiar rounded look of those stones which we know were polished by the action of water. At the foot of the mountain we may find the 213 214 ROCKS AND SOIL forests giving place to fertile farms instead of rocky slopes. The story of soil making goes back a long, long way into the past history of the earth. We must look back millions upon millions of years to an earth with no life, no soil, nothing but water and masses of rock. It would be too long a story to tell how all the different kinds of rocks were formed, for soil was made gradually from the rocks. Frost and heat chipped the rocks, winds blew particles against them, glaciers gouged them out and de- posited the ground- \\Tigntfierce j. . ,-. A mountain stream. Why are the rocks rounded ? UP Sediment in the streams formed from their melting ice. Streams of water tore their way down mountainsides and ground up particles of rock as they went. All these forces slowly but effectively did their work and helped make the first soil. Then after plants appeared on the earth, their dead bodies decayed and went to help form soil. Thus two kinds of soil could be found : that made from the original rocks and that containing the decayed bodies of plants and animals. But under the layers of humus or decayed organic matter and the various layers of loam, clay, or gravel, we THE STORY TOLD BY FOSSILS 215 come at last to bed rock, the material out of which the original soil was made. All of these changes on the earth have taken a very long time. Nature works slowly, but Nature is always working. Everywhere the forces of running water, the wind, ice, heat, and cold, are at work changing the rocks into soil, just as they have been at work in past ages. The earth's surface is constantly changing, and some of the changes take place within our own life span. One very interesting evidence of these changes on the earth comes from the story told by fossils, or remains of former life found imbedded in some rocks. Not only do these remains show us that very different plants and animals once lived on the earth, but they also show us that great changes in life have been brought about through the changes in climate and the alteration of the earth's surface. The purpose of this unit is to tell the story of Wright Pierce Which of these pebbles was taken from the brook? Which from rocks on the mountainside ? how the earth became a place fit for living things to grow on, how the living things have changed, and how and why the earth has become fitted for life today. 216 ROCKS AND SOIL The great mass of rock below the mountain jutting out into the forest is a lava flow Once it was molten lava, now it forms what kind of rock ? PROBLEM I. HOW WERE THE ROCKS FORMED? Three Ways in Which Rocks Were Formed. Let us go out into the field to answer this question. You will find, depending upon where you happen to look, various kinds of rock. Rocks of one kind appear to be made up of pieces of different kinds of substance, all mixed up to- gether as if a giant had stirred them all up while hot and they had cooled quickly. Probably the original rocks of the earth were formed as molten masses of semifluid material, like lava that flows from a volcano during an eruption. Such rocks are called igneous, of which granite is an example. Others look as if they were formed in layers. Such rocks, like sandstone, shale, or limestone, were actually formed from particles of ground-up rock being deposited under water. Layers upon layers were made ; the lower layer may have been carried down miles below the surface of the earth, and when subjected to heat, pressure, and chemical action the particles were cemented into solid HOW WERE THE ROCKS FORMED? 217 rock. Perhaps a million years later this part of the earth rose, the surface layers were worn off, and this layer of material is back at the earth's surface once more, but now solid sandstone and not loose particles. Such rocks are called sedimentary. Another kind of rock seems to be in layers, but these layers are greatly curved or folded, like the rock shown in the picture. These look as if they might have been made like sedimentary rocks and then pressed together by some great force. Possibly they might have been the igneous rocks partly remeltetl, and pressure caused a movement so that particles appear in bands somewhat resembling layers. People who have made a study of rocks believe both of these processes have been in action and have caused these rocks to be changed from the original condition. They are called metamorphic rocks. Examples of such rocks are gneiss, marble, and slate. Rocks and Minerals. Geologists call the material out of which the solid part of the earth is formed rock. But if you look at some rocks carefully, you will see they are Geographical Survey, G. K. Gilbert Negative Geographical Survey, T. N. Dale Negative Sedimentary and metamorphic rock. How does the right-hand picture differ from the left-hand one ? What seems to have happened to the metamorphic rock ? 218 ROCKS AND SOIL made up of particles, some large, some tiny. Each of these substances out of which rock is formed has a different chemical composition and is called a mineral. Sulphur is a mineral containing a single chemical element, while table salt or a grain of white sand is a mineral each made of two elements combined in compounds. Granite, on the other hand, is made up of several minerals in which quartz and feldspar are always present. Rocks usually contain several minerals, but some, like the rock salt, are single minerals. The name of the mineral, salt, is halite, and when freed from impurities, we use it to season our food. Mica is an interesting mineral. Some mica is white and some is black in color. It has the remarkable quality of splitting off in very thin almost transparent sheets. It is often incorrectly called isinglass. It is used as an insulator in electric devices and for windows in doors of stoves. Rocks and Minerals Are of Different Hardness. If you take a number of different minerals, such as quartz, feldspar, mica, rock salt, talc, gypsum, and others, you Wright Pierce This shows how the hardest rocks (granite) may be weathered to form soil, has probably caused this rock to break down ? What HOW WERE THE ROCKS FORMED? 219 will find that your knife blade will scratch some and not others. You can scratch your knife blade with quartz, while the blade will easily scratch such a mineral as talc or rock salt. Minerals, evidently, differ in hardness. They also differ in other respects, such as color, chemical composition, the kind of crystals they form, and other ways. Because of these differences, the rocks out of which they are made also greatly differ. Some are hard, others relatively soft ; some strong, others brittle. Rocks Change to Soil. If what has just been said is true, then the change from rock to soil must go on much faster in some rocks than in others. Soils also vary in differ- ent places, depending on the kind of rock they are made from. Quartz, for example, is harder than feldspar. When granite breaks down to form soil, the quartz par- ticles, being harder, grind the rest of the rock to fine powder, while they remain as grains of pure quartz. SELF-TESTING EXERCISE Select from the following list those words which best fill the blank spaces in the sentences below and arrange the words in proper numerical order. A word may be used more than once. hard heat sedimentary ice soft cold durability clouds softer igneous loose metamorphic rock cut quartz scratch solid molten soil melting mineral vaporized water chemical mud solidified air layers Granite is an example of an (1) rock which formed from a (2) condition. Sandstone is a (3) rock and was once (4) particles which eventually were brought into (5) , probably through the action of (6) After being buried deep in the earth loose material may under the action of (7) , pressure, and cementing by (8) action be changed into solid (9) Both sedimentary and (10) rocks may undergo a partial (11) and be changed greatly in form. This class of rock resulting is called (12) Most rocks are made up of two or more 220 ROCKS AND SOIL minerals. Rock salt is both a (13)_ is a very (15) mineral. It will even (16) and a (14) Quartz . steel. Rocks vary greatly in (17) The brittleness of rock determines in large measure how quickly it is changed to (18) In many places the beach sand is almost wholly (19) because the (20) rock has been ground to a powder. STORY TEST RALSTON HAS A FINE COLLECTION OF ROCKS AND MINERALS Read carefully and critically. List all the errors and suggest corrections. It has been great fun to make this collection, and I never tire of showing them. First, I'll show you the minerals. This glass- like stone is quartz. It is quite hard but you see I can just scratch it with my knife blade. Here is a white mineral feldspar, easily scratched by quartz. It breaks with more even surface than quartz. See this beautiful specimen of isinglass. I put my knife point under a thin edge and peel off a large transparent sheet. These minerals that I have shown you all came from sedimentary rocks. This piece of marble is an igneous rock because heat helped to form it. Granite is a typical mineral that has been formed by the slow cooling of molten rock; the more slowly it cooled, the larger the crystals in it. Here is a piece of gypsum ; you can scratch it with your thumb nail. This smooth pebble is found in the bed of a brook. This chip was probably broken off by ice. The colored streaks in this rock are prob- ably due to the light which reached it while the rest was covered with soil. PROBLEM II. WHAT IS THE STORY OF THE FOSSILS ? What Are Fossils ? Someone has likened the earth to a book whose pages tell its life story. The leaves of this book are the layers A fossil fern-like plant. In what kind of rock would you look for such a fossil? WHAT IS THE STORY OF THE FOSSILS? This fossil fish lived in recent geological time. Wright P How do we know this ? of rock, and the characters we read are the imprints left by the living things that inhabited the earth in past ages. Moving water deposited sediments in oceans, ponds, and pools of streams. Plants and animals living near these places were often buried in these sediments and as time went on and the sediment became rock, the remains of the living things were preserved. Sometimes they were the undecayed parts of plants and animals, sometimes the skeleton, often only an impression, such as a footprint or a space once occupied by the soft body. Any such trace or remains of former life is called a fossil. The story told us by these fossil remains is not very complete, but it is plain enough to show us a number of very interesting things. The first is that the earth has been inhabited by living things for a very, very long time. Geologists used to think it was millions of years, but they now believe it a much longer period. New ways of esti- mating the age of the earth have been found, one by 222 ROCKS AND SOIL National Park Service A fossil tree of the Arizona desert. These trees are found by the hundreds in some parts of the west, in some cases having been changed to agate or other semi- precious stones. This one is now held up by a concrete base. figuring the amount of time it took to carry salt to the oceans to give them their present saltiness. This estimate is about 500,000,000 years. Another and newer estimate has just been completed by a group of scientists appointed by the National Research Council in Washington, and they, basing their calculations on radio activity of certain rocks, have estimated the age of the earth at the incredible figure of over 2,000,000,000 years. Of course life did not exist on the earth at first, and nobody knows how the first life came. But we do get this much evidence from the fossils. The very oldest igneous rocks, which we have learned were formed when the earth was very young, do not contain any fossils. The earliest evidences of life come from bacteria, and following them we find tiny plants and animals, all of which lived in water. What Fossils Tell. The character of the fossil tells whether it was deposited in salt sea water or fresh lake WHAT IS THE STORY OF THE FOSSILS? water. Land animals and the stems and leaves of plants could only be deposited close to the shore. Corals could only be buried in deposits in warm water. Plants which grow only in arctic regions indicate cold water. Thus fossils can tell something of the climate of regions of the earth millions of years ago. Fossils of salt-water life dis- close the fact that there have been seas where now it is land. The relative positions of different layers of rock often tell the relative ages of the different kinds of life on the earth. In some parts of Arizona and other places, you can visit petrified forests. Great trees which have been changed to solid rock lie here and there. Some are formed of beautiful agate or other precious materials. These trees were buried by volcanic material, and the mineral matter dissolved in the water replaced the woody fiber and pre- served the form of the tree. In many parts of the country, various animal remains, such as corals, shell, and These animals were trapped in the famous tar pits of La Brea, near Los Angeles. An elephant and wolves have been caught in the soft tar and the saber-toothed tiger will soon suffer the same fate. ROCKS AND SOIL This huge reptile-like Brontosaurus lived on plants and grew to be 60 feet long. It must have weighed 30 to 40 tons. Notice the skeleton of the man in the upper picture. bones, are found in the rock. In the far west, great skeletons of extinct animals have been dug up. One of these is that of a huge vegetarian called the Brontosaurus, which was 60 feet long and weighed 30 tons. But skeletons of still larger animals have been uncovered ; for example, a great elephant-like creature, the Atlantosaurus, 100 feet long and weighing 100 tons. In some parts of the world the fossils of flying reptiles and even ancient insects have been discovered. Some of the dragon flies found had a wing spread of two feet. Changes in Life on the Earth. One very evident thing comes from the study of these fossils. That is, that the earliest forms of animals were very simple. Then the earth became peopled with many water-living forms, mostly >t took to duz.v/eAop cKo.rcxc.tee-ist.ic. •modern -forms of lif YictveWk oiztlze f nom, 5 to 5 million. forerunners o modern. 5 to lo "million ears to ancient/ ancestors of plants' ancC animals took 15-25 million years to develop , naost forms are nov"