UC-NRLF 
 
 'fiicago Nature-Study Series 
 
 am 
 
 FIELD AND LABORATORY 
 . GUIDE IN PHYSICAL 
 
 NATURE-STUDY 
 
 ELLIOT R. DOWNING 
 
 sociate Professor of Natural Science in tl 
 
 Ec'ucaticm of the University of Chicago 
 
 THE UNIVERSITY OF CHICAGO PRESS 
 CHICAGO, ILLINOIS 
 
A FIELD AND LABORATORY GUIDE 
 IN PHYSICAL NATURE-STUDY 
 
"V) 
 
 PREFACE 
 
 It is unfortunate that the term "nature-study" has come to connote 
 experience with living things chiefly and that in practice the nature-study 
 work largely neglects that rich field of physical science that lies so close to 
 the child, the stars that stimulate his wonder, the rocks and minerals 
 which he collects with such delight, the toys and home appliances from 
 which he may obtain such a wealth of useful experience that will clarify 
 in his mind fundamental science concepts. The present volume attempts 
 to organize this more or less neglected material for the use of the teacher. 
 
 The author has used the material here presented with his own teacher- 
 training classes for many years. It is in the hope that it will serve normal- 
 school teachers who are also preparing pupils to teach nature-study in the 
 grades that the book is published. If a short title were given to the book 
 it might well be "How to Make" as the companion volume, The Field and 
 Laboratory Guide in Biological Nature-Study, might be designated "What to 
 See." I can do no better than repeat here the sentiment expressed in the 
 Preface to the preceding volume. It is expected that the book will prove 
 helpful to that large and increasing group of teachers, both actual and 
 prospective, who are earnestly trying to use in the schools that scientific 
 method and accumulated knowledge so important in modern life. Further- 
 more, it is hoped that through the teachers it will serve those boys and girls 
 who, by acquaintance with nature, will come to adjust themselves more 
 intelligently to their environment, use the forces of the universe more 
 effectively, and be happier in their enlarged outlook. 
 
 ELLIOT R. DOWNING 
 THE UNIVERSITY OF CHICAGO 
 THE SCHOOL OF EDUCATION 
 September 29, 1919 
 
CONTENTS 
 
 PAGE 
 
 INTRODUCTION 5 
 
 COMMON MINERALS AND ROCKS . . -6 
 
 THE STARS AND OUR SOLAR SYSTEM . . 15 
 
 SOME TOYS THAT WORK BY AIR 28 
 
 TOP, SLING, AND Bow . . . . .43 
 
 THE HOT-AIR BALLOON AND SOME EXPERIMENTS TO SHOW How IT 
 
 WORKS 51 
 
 SOME COMMON APPLIANCES THAT OPERATE BY HEAT 56 
 
 MAGNETIC AND ELECTRIC TOYS 67 
 
 THE CAMERA, TELESCOPE, MAGIC LANTERN, AND SOME EXPERIMENTS IN 
 
 LIGHT 81 
 
 THE HOMEMADE ORCHESTRA 90 
 
 How TO MAKE THE PHONOGRAPH AND TELEPHONE . ., . . . . 95 
 
 How TO MAKE A PAIR OF SCALES AND USE OTHER MECHANICAL CON- 
 TRIVANCES 101 
 
 APPENDIX 103 
 
 415689 
 
INTRODUCTION 
 
 Look over some good courses of study in nature-study to see that 
 you will be expected as a teacher to lead pupils into those experiences that 
 give them contact with essential scientific facts and phenomena. If pos- 
 sible visit nature-study classes so that you may see that the sort of thing 
 here presented is what you will need when as a teacher you face actual 
 schoolroom work. 
 
 Before the pupil has completed the junior high school he should be 
 assured of a range of experience with commonplace science that will habit- 
 uate him to see and to attempt the solution of problems in a scientific 
 way, that will give him command of the most important principles of science 
 and that will make him appreciative of the wonders to be found in his 
 commonplace environment. This book attempts to prepare the teacher 
 to intelligently use the physical materials of interest to the pupil to achieve 
 such ends. 
 
 It is suggested that not all of the projects outlined be undertaken by 
 each student-teacher but that some be assigned to particular students to 
 work out before the class or undertaken by the instructor as class demon- 
 strations. The author suggests from his experience in handling this work 
 that the projects listed in the Appendix be so assigned and that the remain- 
 ing ones be done by each student of the class. There is also given in the 
 Appendix an estimate of the apparatus required for the course on the 
 foregoing basis with a class of twenty students. 
 
 All projects are to be written up by the individual student as if performed 
 by himself, so that each one may feel responsible for those done for him, 
 to save time, by other members of the class. Write up the notes as directed 
 in ink on the blank pages provided, answering all questions asked. Make 
 such diagrams and sketches as are called for, also in ink, preferably Hig- 
 gins' water-proof drawing ink. 
 
 Follow carefully the directions given for making and operating the 
 appliances and toys. Put yourself as far as possible in the place of the 
 child who is having these experiences. See in them the problems he would 
 see and think them through on the basis of your own observations. It is 
 more important that you cultivate the scientific attitude of mind than that 
 you amass much information. Be neat, accurate, and thoroughgoing in 
 your work; cultivate a workman-like pride in the product of your own 
 handwork. 
 
COMMON MINERALS AND ROCKS 
 
 The collection. i. Make two cardboard, wooden, or tin trays, each with 
 thirty-six compartments, 2 by 3 inches and 2\ inches deep, to hold your 
 minerals and rocks. Obtain from some dealer, like Ward's Natural History 
 Establishment, at Rochester, New York (or collect for yourself), the 
 following minerals and rocks for study. 
 
 Minerals. Amphibole or hornblende both (i) massive and (2) crystal- 
 lized; (3) apatite; augite or pyroxene, both (4) massive and (5) crys- 
 tallized; calcite (6) massive and (7) crystallized as dogtooth spar; (8) 
 chalcopyrite; (9) chalk; (10) chlorite; (n) corundum; (12) dolomite or heavy 
 spar; feldspar is the name of a family of minerals including (13) orthoclase 
 and several plagioclases, such as (14) albite, (15) anorthite, (16) oligoclase, 
 (17) labradorite; (18) fluorite; (19) galenite; when massive gypsum is 
 called (20) alabastine if clean and fine-grained, (21) selenite when crystal- 
 lized; (22) hematite; (23) kaolin; (24) limonite; (25) malachite; mica both 
 (26) biotite and (27) muscovite; (28) olivine; (29) pyrite, crystallized; 
 quartz occurs in a variety of forms (30) massive, (31) crystal, (32) agate, 
 (33) amethyst, (34) chalcedony, (35) flint, (36) jasper, (37) rose quartz; 
 (38) serpentine; (39) sphalerite; (40) tin ore, cassiterite. 
 
 Rocks. {i) Amygdaloid of copper; (2) andesite; (3) basalt; (4) breccia; 
 (5) conglomerate; (6) diabase and (7) olivine diabase; (8) diorite and (9) 
 porphyritic diorite; (10) gabbro; (n) gneiss; (12) granite and both (13) 
 biotite and (14) hornblende granite; (15) limestone and (16) fossiliferous 
 limestone; (17) marble and (18) dolomitic marble; (19) obsidian; (20) 
 pumice; (21) quartzite; (22) sandstone; schist both (23) chloritic and (24) 
 micaceous; (25) syenite; (26) shale; (27) slate. 
 
 The school may provide these type minerals and rocks for study and 
 the pupils may use the trays for local collections properly labeled. 
 
 Characteristics of minerals. -Define (opposite page) a mineral. Define 
 a rock. Minerals are distinguished by several characteristics. They crystal- 
 lize in definite shapes. Study a crystal of quartz. Note that it is a six- 
 sided prism with a six-sided pyramid at each end (if perfect). Note the 
 cubical or dodecahedral crystals of iron pyrite. 
 
 2. Melt some sulphur in an evaporating dish over the Bunsen burner. 
 Let it cool until it begins to solidify about the edges. Then pour out most 
 of it and what is left will set in crystal form. What is the shape of the 
 crystals? 
 
COMMON MINERALS AND ROCKS 7 
 
 3. Make a strong solution of alum in hot water. Let it stand in an 
 open dish so that the water will evaporate. The alum will deposit in 
 crystal form. 
 
 Many minerals split easily along certain planes so that the fragments 
 are bounded by smooth surfaces. This is called the cleavage and the planes 
 the cleavage planes. Study galenite and note how it cleaves into cubes; 
 study feldspar or calcite and see how these cleave into rhombs. Are the 
 angles of the rhombs constant and are they the same for calcite and feld- 
 spar? 
 
 Some minerals break in characteristic ways other than along cleavage 
 planes. Note that the surfaces of broken flint are curved like a shell. It is 
 said to have a conchoidal fracture. 
 
 Luster is the appearance of the mineral when seen in good light on a 
 freshly exposed surface. Observe the vitreous luster of obsidian, the pearly 
 luster of selenite, the waxy luster of chalcedony, the metallic luster of 
 galenite. 
 
 When a mineral is scratched or rubbed on a piece of unglazed porcelain 
 so as to leave a mark it shows a color known as its streak. Thus limonite and 
 hematite are frequently very similar in appearance but are easily dis- 
 tinguished by their streak. 4. Try them and see what streak each gives. 
 
 Then within narrow limits each mineral has a characteristic hardness. 
 This is so valuable a distinguishing character that a scale of hardness has 
 been fixed. Thus talc has a hardness of i, gypsum 2, calcite 3, fluorite 4^ 
 apatite 5, orthoclase 6, quartz 7, topaz 8, corundum 9, diamond 10. 5. In 
 so far as you have these in your collection try scratching them with finger- 
 nail, a knife, or with each other to get some first-hand knowledge of their 
 relative hardness. Frequently similar appearing minerals are distinguished 
 by their hardness. Thus chalcopyrite and pyrite at times look much 
 alike, but the former has a hardness not to exceed 4, while the latter has 
 at least a hardness of 6. 
 
 Table of distinguishing characters. 6. Fill in the following table of 
 the minerals listed above, arranging them now not alphabetically but in 
 the order of their hardness. Obtain the information called for from the 
 minerals themselves, or from any good book on minerals (see Appendix) 
 when you are in doubt. Some spaces must be left blank, as not every 
 mineral will have the characters called for. 
 
GUIDE IN PHYSICAL NATURE-STUDY 
 
 JO 
 
 o< 
 
 II 
 
 8 8 
 
COMMON MINERALS AND ROCKS 
 
10 GUIDE IN PHYSICAL NATURE-STUDY 
 
 Familiarize yourself with the minerals in your collection until you are 
 reasonably sure that you can identify each. 7. Then try to name the 
 unnamed specimens that will be furnished you. 
 
 Ores. In the list of minerals given" above are several ores of the com- 
 mon metals. Galenite, limonite, hematite and pyrite, malachite and 
 chalcopyrite, sphalerite and cassiterite. Your table will show the chemical 
 composition of each. Galenite, pyrite, and sphalerite are found in grains 
 and small masses in the limestone of this region, the lead and zinc blende 
 in paying quantities in immediately adjacent territory. 8. Look up- the 
 method of reduction of some one of these ores by means of which the metal 
 is obtained from it and briefly write it up on the blank page opposite. 
 
 Valuable minerals. Many of the other minerals are commercially 
 valuable. Corundum because of its hardness is the essential ingredient of 
 grinding- wheels. Chalk is familiar in the schoolroom. Gypsum yields 
 plaster of Paris. Kaolin is the clay from which our fine table china is made. 
 Mica is a valuable electrical insulator and is common also in stove doors. 
 The feldspars and the clays which result from their disintregration yield 
 aluminium. Several varieties of quartz serve as valuable gems, such as 
 amethyst and rose quartz, while the clear .crystals are the "Hot Springs 
 diamonds." 
 
 Rocks are classified according to the method of formation into sedi- 
 mentary, igneous, and metamorphic. 9. Briefly state the method of forma- 
 tion of each on the blank page that follows. 
 
 Sedimentary rocks are laid down as (i) beds of more or less waterworn 
 fragments of shells, corals, or other calcareous material, (2) beds of angular 
 rock fragments, (3) beds of gravel, (4) beds of sand, or (5) beds of clay, 
 (6) beds of vegetable material. 
 
 What is sand? gravel? clay? 
 
 These beds are then transformed into stone by pressure, heat, and the 
 action of various cementing substances, working separately or two or more 
 in unison. The calcareous material transforms to limestone, or dolomite 
 if magnesium carbonate predominates rather than the calcium carbonate. 
 The angular fragments are cemented together into breccia, the gravel into 
 conglomerate, sand transforms to sandstone, clay into shale, and vegetable 
 material into peat and coal. 
 
 Tests for rocks. 10. Study your specimens of limestone. Is it easily 
 scratched? Put a drop of chlorhydric acid on it and note the rapid 
 discharge of carbon dioxide, a gas that bubbles up through the drop of acid 
 (effervescence). Try the same on dolomite; on sandstone. What are the 
 results on these? Examine breccia, conglomerate, and shale. The latter 
 flakes easily and emits an earthy odor when you breathe upon it. 
 
COMMON MINERALS AND ROCKS n 
 
 Rocks in formation. Visit the lake shore or river margin where deposits 
 of sand, pebbles, or clay are being made. Dig down into such deposits or 
 study the face of railroad cuts or other excavations to see how .such material 
 is laid down. n. Make a drawing on the opposite page to show this. 
 Do you find any evidence that the material is cementing together or solid- 
 ifying to make rock? 
 
 The stone quarry. 12. Visit a stone quarry and answer the following 
 questions: 
 
 Is the stone in layers? 
 
 Are the layers or strata horizontal ? 
 
 If not, what is the angle of their "dip"? 
 
 1 What is the "dip" ? 
 
 What do you mean by the "strike" of the strata?. 
 
 Are the layers folded at all? 
 
 What are bedding planes and are they apparent? . 
 
 Are joints apparent? . . . 
 Are fossils to be found? 
 What is a fossil?.. 
 
 13. Sketch one or two that you find. 
 
 Geological time. Sedimentary rocks have been forming through many 
 ages and contain in their fossils an exceedingly interesting record of the 
 changing life on the earth. The history of the earth's past is divided into 
 great eras. Just as human history is divided into the modern era, the 
 medieval, the ancient, an earlier era of dim myth, and a still earlier era of 
 which we know nothing, so the geological history of the earth partially 
 revealed by the rock record is divided into the modern or Cenozoic era, 
 the Mesozoic, the Paleozoic, the Proterozoic, and the Archeozoic. This 
 entire geological time spans many millions of years. The historian, for 
 convenience, divides the great eras into periods; thus the ancient era is 
 made up of the Babylonian period, the Egyptian, the Grecian, the Roman. 
 So the geologist subdivides the great geological eras into periods each 
 characterized by its own peculiar living forms. 
 
 Niagara limestone. The bedrock of the Chicago region is the Niagara 
 limestone formed during the Paleozoic era. 14. Visit the Walker Museum 
 (or similar institution) to see some of the many fossils found in this Niagara 
 limestone and to get a glimpse also of the many animals and plants that 
 existed in the Paleozoic and other eras of the earth's geologic past. 
 
12 
 
 GUIDE IN PHYSICAL NATURE-STUDY 
 
 Igneous rocks are subdivided into volcanic and Plutonic rocks. 
 15. Give the method of formation and the distinguishing characters of 
 each on the opposite blank page. It will be evident from their method of 
 formation that no hard-and-fast line can be drawn between these two 
 sorts of igneous rocks. They form a continuous series from the coarsely 
 crystalline Plutonic rocks to the glassy and more or less porous volcanic 
 rocks. Igneous rocks differ greatly also in chemical composition. If the 
 molten material from which the rock formed contained an excess of silica 
 and only bases of low valence like potassium, the rock is acid and contains 
 silicates of the bases together with much free quartz. If on the other hand 
 the molten material contained bases of high valence like calcium or iron, 
 the resulting rock is said to be basic and contains silicates of the bases 
 but little or no free quartz. Potassium is monovalent and can take up in 
 combination relatively little silica when it forms its silicate, so that much 
 free silica is to be expected. Iron, however, is quadrivalent and can take 
 up a large amount of silica to form its silicate, so little free quartz is found 
 in these basic rocks (see p. 62). 
 
 Classification of igneous rocks. On the basis of these two things, the 
 texture of the rocks and their basidity, the classification of the igneous 
 rock is made. In the table below, reading from left to right, the families 
 
 GRANITE-RHYOLITE 
 FAMILY 
 
 SYENITE -TRACHYTE 
 FAMILY 
 
 DlORITE-ANDESITE 
 
 FAMILY 
 
 GABBROBASALT 
 FAMILY 
 
 PERIDOTE 
 FAMILY 
 
 Quartz and orthoclase 
 dominant 
 
 Orthoclase domi- 
 nant. No quartz 
 
 Plagioclase 
 dominant 
 
 Labradorite and 
 pyroxene dominant 
 
 No feldspar 
 present 
 
 Rhyolite pumice 
 Rhyolite obsidian 
 
 Granite 
 Biotite-granite 
 
 Trachyte 
 Syenite 
 
 Andesite 
 
 Basalt-tuff 
 Basalt 
 Dolerite 
 
 
 Horneblende- 
 bearing biotrte, 
 granite, etc. 
 
 
 Diorite- 
 porphyry 
 
 Diabase 
 
 Peridote 
 
 
 
 Diorite 
 
 Olivine- 
 diabase 
 Gabbro 
 
 
 are made of rocks that contain less and less free quartz and whose constit- 
 uent minerals are increasingly basic silicates. The members of each family, 
 reading down in the series, are less porous, less glassy, the crystals of the 
 constituent minerals are larger, and the rocks are heavier, since elements, 
 like iron, of great specific gravity are replacing lighter ones, like potassium. 
 What is a porphyry? an amygdaloid? 
 
COMMON MINERALS AND ROCKS 13 
 
 Study of samples. 16. Study now the igneous rocks in your collection 
 with the explanation in mind and place them in the table. Try to 
 make out the constituent minerals and to recognize them by the characters 
 already studied. Use a lens to assist you in this work. Note the texture 
 and the relative weights of the rock specimens. Verify with your specimens 
 the following additional distinguishing characters that will help in the 
 separation of these rocks. The granites contain quartz and the alkaline 
 feldspars, often with some hornblende, mica, or augite. The composition 
 of gneiss is the same, but it shows evidence of stratification (see below). 
 If any one or two minerals in addition to the essential quartz and feldspar 
 are. especially conspicuous the granite is named accordingly as biotite- 
 1 hornblende-granite. 
 
 Syenite contains an abundance of orthoclase, usually of the red varieties, 
 and no quartz. Hornblende, mica, and augite may one or all be present. 
 It is a Plutonic rock and therefore usually coarse-grained. The correspond- 
 ing volcanic rock is trachyte, finer grained, more porous, and lighter in weight. 
 
 In the diorites the dark feldspars predominate, though sometimes the 
 light-colored plagioclases are abundant. Quartz is present and also often 
 mica and hornblende, but not in predominating quantities. The diorites 
 are Plutonic, the corresponding volcanic rocks being the andesites. 
 
 Gabbro and basalt are respectively the Plutonic and volcanic members 
 of the next family. They are dark, heavy rocks with labradorite and 
 augite as the predominant minerals. The gabbro is distinguished from 
 the diabase by its coarse crystallization and by the large quantity of 
 plagioclase that it contains. The presence of chlorite in these rocks often 
 gives them a distinct green color and they are then known as greenstones. 
 The peridote contains neither quartz nor feldspar, but consists of such 
 minerals as augite and amphibole. 
 
 Metamorphic rocks were originally either sedimentary or igneous, but 
 have been altered greatly by heat, pressure, crumpling, and other agencies, 
 acting singly or in unison, so that their characteristics have been materially 
 changed. Thus limestone and dolomite have been transformed to marbles 
 (the acid test still distinguishes them). Sandstone has been metamor- 
 phosed to quartzite, which is recognized by its hardness and conchoidal 
 fracture. The shales have been changed to slates that beak into thin layers. 
 The granitic rocks have been altered to gneiss or schist, the former showing 
 evidence of layering while the latter is flakey. The schists are named 
 from their dominant mineral: micaceous schist, choritic schist, etc. 
 
 Specimens of metamorphic rocks. Study now the metamorphic rocks 
 in the collection 17. Indicate by an S, I, or M placed beside each rock 
 in the list whether it is sedimentary, igneous, or metamorphic. 
 
14 GUIDE IN PHYSICAL NATURE-STUDY 
 
 Glacial drift. -While the bedrock of the Chicago region and of the 
 adjacent area is sedimentary, the glacial drift the soil and rock debris 
 that overlays the bedrock for the most part contains many bowlders and 
 fragments of igneous and metamorphic rocks brought to our region from the 
 north by the great glaciers that invaded this territory during the glacial 
 epochs in relatively recent geological time. The northern part of Min- 
 nesota, Wisconsin, the Upper Peninsula of Michigan, and much of Canada 
 are occupied by these igneous and metamorphic rocks of the Proterozoic and 
 Archeozoic eras. 18. Go to the lake shore, the gravel pit, or the piles of 
 bowlders found in the fields, and with a hammer break off samples of these 
 glacial rocks and try to identify them. It is too much to expect, with the 
 brief instructions given here and the limited facilities at the hands of the 
 student, that he will be able to identify all these with certainty. Some of 
 them with clear characters and readily recognized mineral ingredients will 
 be easily identified. Still the attempt will help him to gain some facility 
 in recognizing the component minerals and in judging relative weights and 
 textures. Possibly, too, it may serve as an incentive to more thorough 
 courses in this fascinating study of minerals and rocks. 19. Name and 
 label such as you can identify with reasonable certainty and make a list of 
 these on the opposite page, at the same time classifying them as sedimen- 
 tary, igneous, and metamorphic. 
 
 Rocks of commercial value. Some of the rocks listed are of large 
 commercial value. Much of the copper in the famous mines of northern 
 Michigan occurs as amygdaloidal grains or as a cement in a conglomerate 
 rock. Granite and syenite are familiar as building stones. Limestone, 
 marble, and sandstone serve a similar purpose. Slate is a common roofing 
 material, replaced now largely by tile or asbestos (fibrous serpentine) 
 shingles. One variety of serpentine, verd antique, is used as an ornamental 
 stone. Limestone is heated and transformed to CaO, the CO 2 being driven 
 off by the heat. This is the "unslacked lime" used in making plaster. 
 
THE STARS AND OUR SOLAR SYSTEM 
 
 The polar constellations. 
 
 The Big Bear. See in the northern sky the Big Dipper. The two 
 stars forming the side of the Dipper's bowl farthest from the handle are 
 commonly called the pointers, for if a line be drawn through them and 
 extended northward it leads to Polaris, the polestar. Find this in the sky 
 and 20 draw on the opposite page the Big Dipper as it is seen now when 
 
 FIG. i. Principal stars of Ursae Major. The long tail is a late addition to the old 
 mythological figure. Dots are fifth-magnitude stars, crosses fourth-magnitude, etc. 
 
 you are facing north about 9:00 P.M. Draw the polestar also on the 
 same diagram, showing its relation to the Big Dipper both in direction and 
 distance. 
 
 The middle star of the Dipper handle is a doublet, both members being 
 visible to the naked eye. Can you see them both? They are named 
 Mizar and Alcar, the Horse and Rider, the latter being identified in Greek 
 legend with the lost Pleiad (see p. 19). The polestar is at the end of the 
 
 15 
 
1 6 GUIDE IN PHYSICAL NATURE-STUDY 
 
 handle of the Little Dipper, most of the stars of which are dim. With the 
 aid of the diagram (Fig. i) identify the stars of the constellation of the 
 Big Bear, Ursa Major. 
 
 Polaris. 21. Cut a piece 8 inches square from a f-inch board to 
 serve as a baseboard. At the midpoint of the opposite sides fasten two 
 i -inch- wide 1 2-inch uprights of light stuff. Cut a square strip of the 
 f -inch stuff 8 inches long and tack to this, at the midpoint of each, a 1 2- 
 inch strip of light stuff an inch wide so that they will lie at right angles to 
 each other. Run brads through corresponding points near the upper ends 
 of the uprights and into the centers of the opposite ends of the f-inch 
 square strip. Cut an 8-inch semicircle out of cardboard and fasten to the 
 i2-inch strip so that the diameter of the semicircle will run through the 
 axis line on which the f-inch strip rotates. Fasten on one of the uprights 
 a Wire pointer so that when the 12 -inch strip is level (after leveling the base- 
 board, see below) its point will stand at the midpoint of the semicircle. 
 Mark this point O. 
 
 Float the baseboard on a bucketful of water that has been set out of 
 doors on some support, like a soap box. This will insure that the base- 
 board is perfectly level. The same result may be achieved by laying a 
 cheap level first on one, then on the other of the two adjacent edges of the 
 baseboard and blocking up the corners when set on the box until level. 
 With the axis of the apparatus turned east and west set the 1 2-inch strip 
 so that it points to the polestar; sight along the strip to make sure that it 
 is pointed exactly. Mark the point on the semicircle which the pointer 
 now indicates. Measure the area between this point and O in degrees. 
 (Use a protractor a small semicircle divided into degrees and fractions 
 of a degree.) How does the angle between the two points agree with the 
 latitude of the place where you live as you find it from the map? Why 
 this relation? 
 
 Constellation of Bootes. Extend the curved line of the Big Dipper 
 handle in a direction away from the bowl, and about the length of the 
 Dipper from the end of its handle is a first-magnitude star, Arcturus, in the 
 constellation of Bootes, the Hunter. The other stars of Bootes (Fig. 2) 
 are shown in relation to Arcturus. The two northernmost are near the 
 star at the end of the Dipper handle. 22. On the opposite page give the 
 legends of Ursa Major and Ursa Minor and Bootes, the Hunter. 
 
 Cassiopeia. On the opposite side of the pole from the Dipper and about 
 as far from Polaris is Cassiopeia's Chair, an open W of rather bright stars 
 which with the addition of one rather dim one becomes a chair. Find this 
 constellation and 23 diagram it on the opposite page, showing its relation 
 to Polaris, in a way similar to the diagram of Bootes, Figure 2. 
 
THE STARS AND OUR SOLAR SYSTEM 17 
 
 Cephas. A line drawn through the stars at the tips of the chair legs 
 in an anti-clockwise direction reaches a star of the third magnitude in the 
 constellation Cephas, half again as far from Cassiopeia as the full length of 
 the W. Between this and the polestar and directly in line with the two 
 
 FIG. 2. Bootes and the Hunting Dogs, showing the principal Stars 
 
 is another third-magnitude star, also in Cephas. These two serve as pole- 
 star pointers quite as well as the two in the Dipper. The other stars of 
 Cephas are arranged somewhat as in Figure 3. Identify the constellation 
 in the sky. 
 
 Perseus. The star at the base of the back of Cassiopeia's Chair and 
 the one in the angle of the back may be used as pointers to find the con- 
 stellation Perseus. The line through these, extended in the opposite direc- 
 tion from Cephas about as far from Cassiopeia as are the polar pointers 
 of Cephas, reaches the brightest star of Perseus (a Perseus). Run a 
 
i8 
 
 GUIDE IN PHYSICAL NATURE-STUDY 
 
 line from the pole through this star and extend it about as far as the two 
 stars at the bottom of the Dipper are from each other and it reaches Algol, 
 the demon star, a variable, also a bright star of Perseus. 24. Draw on 
 the opposite page the principal stars of Perseus as you find them on a star 
 map and identify them in the sky at the place indicated. 
 
 Andromeda. From the polestar draw a line through the end of the W 
 
 farthest from the back of the 
 chair in Cassiopeia and extend 
 it about as far from Cassiopeia 
 as the latter is from the pole 
 and it reaches a bright star, one 
 of the four that form a great 
 quadrilateral known as "the 
 square of Pegasus." The one 
 first noted is really in Androm- 
 eda, the other three in 
 Pegasus. A diagonal of "the 
 square" drawn through the star 
 of Andromeda and extended 
 toward Perseus about the 
 diameter of the square en- 
 counters another bright star 
 of Andromeda. 25. Copy on 
 the opposite page, from a star 
 map, the principal stars of 
 Andromeda and try to identify 
 
 them in the sky, now that you 
 know where to look for them. 
 Include them in an outline 
 figure of Andromeda similar to 
 that of Bootes in Figure 2. 
 
 FIG. 3. The figure of Cephas and the prin- 
 cipal stars of the constellation. The king stands 
 on the North Pole. 
 
 The Dragon. Draw a line from the star at the base of the chair back 
 through the northernmost one of the pair of polar pointers in Cephas and 
 extend it about as far toward Cephas as Cassiopeia is distant from him to 
 a bright star in the head of the Dragon (a Draco or Theban) . This Dragon's 
 Head is made of four stars, two of which, the eyes, are quite bright. The 
 body of the dragon runs back toward Cephas, then turns in the opposite 
 direction to partly encircle the Little Dipper. Its tail lies between the 
 Big and Little Dippers. 26. Draw a diagram of Draco. 
 
 The Swan. Draw a line from the star in the angle of the back of the 
 chair through the one at the base of the back and extend it in the opposite 
 
THE STARS AND OUR SOLAR SYSTEM 19 
 
 direction from Perseus about twice as far as the latter is from Cassiopeia 
 and a first-magnitude star is reached, Deneb, in the constellation Cygnus, 
 the Swan. 27. Copy, on the first blank page following, the figure of the 
 Swan from some star map showing the constellation, indicate the principal 
 stars, and also show why this constellation is sometimes known as the 
 Northern Cross. 28. On the same page give briefly the legend of Cygnus. 
 
 Other first-magnitude stars. Imagine a line drawn from the polestar 
 to Deneb. Through Deneb at right angles to this line draw a line on the 
 side opposite that which faces the square of Pegasus, to a first-magnitude 
 star about half as far from Deneb as the latter is from the pole. This 
 star is Vega in the constellation of the Lyre. 
 
 "On the opposite side of the polestar from Vega and nearly as far from 
 it lies Capella, a first-magnitude star of the constellation Auriga the Char- 
 ioteer. Why was Auriga given a place among the immortals? 
 
 How many first-magnitude stars lie within 50 of the North Pole and 
 what are they? 29. Make a list of them here and of the constellations 
 in which they are found. 
 
 The zodiacal constellations in December evenings (or early mornings 
 of September). 
 
 Taurus. The Pleiades is a group of six naked-eye stars close together 
 in the form of a very little dipper on the meridian about 9:30 toward the 
 close of December. Find it in the sky. Very good eyes make out seven 
 stars; the "lost one" is identified now as Alcar of the Dipper (see the Source 
 Book of Physical Nature-Study}. 
 
 To the east of the Pleiades notice a V-shaped group, the Hyades, one 
 star of which, Aldebaran, is of the first magnitude. Both the Pleiades and 
 Hyades are in the constellation of Taurus, the Bull. 30. On the following 
 blank page sketch the outline of Taurus and show the principal stars, 
 copying the figure from some star map or other source. 
 
 Orion. Run a line from the Pleiades through Aldebaran and farther 
 to the east to a line of three bright stars, the belt of Orion. To the north 
 of this is a bright reddish star, Betelgeuse, and to the south another first- 
 magnitude star of bluish cast, Rigel. The constellation of Orion is the most 
 brilliant one in the sky. 31. On the blank page that follows copy the 
 outline of Orion from some star map and show also the principal stars. 
 Identify as many as possible in the sky. If possible see the middle star 
 of the dagger handle hanging from Orion's belt through a telescope. It is 
 imbedded in the famous nebula of Orion. 
 
 Canis Major and Canis Minor. The most brilliant single star in the 
 heavens is Sirius. It lies to the east of (below) Orion in the constellation 
 of the Great Dog, Canis Major. Make Betelgeuse and Sirius the basal 
 
20 
 
 GUIDE IN PHYSICAL NATURE-STUDY 
 
 corners of an equilateral triangle, the apex a bright star to the north, and 
 so locate Procyon in the constellation of the Lesser Dog, Canis Minor. 
 The two dogs are supposed to be following the hunter Orion, who stands 
 with club uplifted facing the bull. 32. On one of the blank pages following 
 briefly give the legend connected with these constellations. 
 
 The Twins. Make Aldebaran and Sirius the basal corners of a larger 
 equilateral triangle with the apex to the north and so locate one of a pair 
 of bright stars, Pollux of Castor and Pollux, the twins, in the constellation 
 of Gemini. 33. Diagram the stars of Gemini and identify as much of 
 the constellation as possible in the sky. 
 
 Taurus and Gemini are both among the zodiacal constellations. What 
 is the zodiac? 
 
 34. Fill in the following tabulation: 
 
 NAME OF THE ZODIACAL CONSTELLATIONS 
 
 SIGN OF THE 
 CONSTELLATION 
 
 I 
 
 
 2 
 
 
 7 
 
 
 4 
 
 
 z. . 
 
 
 6 
 
 
 7 
 
 
 8 
 
 
 9 
 
 
 10 
 
 
 ii 
 
 
 12 
 
 
 
 
THE STARS AND OUR SOLAR SYSTEM 21 
 
 From Aldebaran through the Pleiades draw a line and extend it beyond 
 the Pleiades half again as far as Aldebaran is from the Pleiades to a fairly 
 bright star, Alpha, of the constellation Aries the Ram. Near this star directly 
 toward the pole is a group of three stars, the Triangle, which will help to 
 locate Aries. This is the first of the zodiacal constellation. The last, the 
 constellation of the Fishes, is also now visible, though the stars that make 
 it are dim. It is an irregular line of stars that starts south of Andromeda 
 about halfway between Alpha Aries and the square of Pegasus, runs to a 
 point due south of Aries, about as far from the pole as is the belt of 
 Orion, and thence down toward the horizon to the west of the square 
 of. Pegasus. 
 
 Southern constellations in December (or early mornings of late July). 
 Early in the evenings of December (6:00 P.M.), when the square of Pegasus 
 is about on the meridian, a line drawn from the pole, past the westernmost 
 star of the square and continued to the southern horizon, reaches a first- 
 magnitude star, Formalhaut, in the constellation of the Southern Fish. The 
 other stars of this constellation are just visible. On the line from Formal- 
 haut to Deneb and about halfway between the two is a line of three third- 
 magnitude stars that mark Aquarius, the Water Bearer. This constellation 
 is pretty well spread out but may be identified by the aid of the plani- 
 sphere (p. 23), which should be put together now to help locate the 
 constellations that follow. 
 
 To the east of the meridian, also low down in the south, is a nearly hori- 
 zontal group of three pairs of moderately bright (one second-magnitude, five 
 third-magnitude) stars in the constellation of Cetus, the Whale. Five other 
 stars grouped together farther to the east also lie in the constellation. 
 Note that in this region of the sky where Aquarius lies there are also to 
 be found the fishes of the zodiacal constellations, the Southern Fish, the 
 Whale. What is the legend connected with these several constellations ? 
 35. Outline it briefly on the opposite page. The series of constellations 
 connected with this legend continues to pass in review evenings through 
 the spring and early summer. 
 
 Eridanus. In January, when the Pleiades is on the meridian, there is 
 a widespreading constellation zigzagging back and forth across the meridian 
 in the south near the horizon, the great river Eridanus. Trace it westward 
 from Rigel nearly to the Whale, then east again past the meridian west of 
 south to the horizon. 36. Copy the constellation from some star map, on 
 the blank page opposite. 
 
 More zodiacal constellations visible in March evenings (or early morn- 
 ings of October). When Castor and Pollux are on the meridian in the 
 evenings of the middle of March locate a group of stars shaped like a 
 
22 GUIDE IN PHYSICAL NATURE-STUDY 
 
 reversed 2, to the east of them and about a third of the way to the horizon. 
 At what time could you see it now ? Regulus, a brilliant first-magnitude 
 star, is at the end of the base of the figure. Regulus, Procyon, Betelgeuse, 
 and Pollux make a diamond-shaped figure, while Regulus, the star in the 
 bottom of the Dipper farthest from the handle, and Denebola, another 
 bright star, make an isosceles triangle. Denebola is in line with the pole- 
 star and the star in the bottom of the Dipper nearest the handle and about 
 as far from this star as it is from the pole. Denebola and Regulus are both 
 in the constellation of Leo, the Lion. 37. Sketch the figure of the Lion 
 and show the chief stars. 
 
 Southern sky in March. The whole southern sky, close to the horizon, 
 is now occupied by the constellation of the Ship or Ark. All the stars 
 from east to west south of the Great Dog are in this constellation. Identify 
 it with the aid of the planisphere. 38. Sketch the Ship or Ark, copying 
 the figure from some star map and show the principal stars. 
 
 Zodiacal constellations in April (or early mornings in November): 
 About 8 : 30 P.M. in the latter part of April, when the pointers of the Dipper 
 are on the meridian, draw a line from the lip of the Dipper through the 
 star in its bottom near the handle and extend it across the sky to a first- 
 magnitude star, Spica, in the constellation Virgo, the Virgin. Spica and 
 Arcturus are at the basal corners of an isosceles triangle with Denebola at 
 the apex. 39. Copy here the chief stars of this constellation. Try to 
 identify them in the sky. When can you see Spica now ? 
 
 Southern constellations in April. South of Spica and a little west 
 also, in a line from the pole through the star in the top of the Dipper's 
 bowl near the handle and extended nearly to the southeastern horizon, 
 is a semicircular group of quite bright stars, Corvus, the Crow. 40. Draw 
 the group on the next blank page. From east of Corvus running west 
 across the southern sky see a line of stars, mostly faint, that leads nearly 
 over to Procyon, the sea monster, Hydra. 
 
 The zodiac in May. Late in the evening in the latter part of May, 
 when Arcturus is on the meridian, draw a line through the pointer of the 
 Dipper farthest from the polestar and the star at the end of the Dipper's 
 handle. Continue it across the sky to the southeastern horizon to a bright 
 star, An tares, in the constellation of the Scorpion. 41. Sketch the other 
 stars of this constellation on the blank page opposite and identify them in 
 the sky. This is easy because of their arrangement in triplets. 
 
 A southern constellation. On either side of the meridian close to the 
 southern horizon are two second-magnitude stars that locate the Centaur 
 or Noah of the earlier legends. All the stars that stretch along the southern 
 sky west of these two are in this constellation. 
 
THE STARS AND OUR SOLAR SYSTEM 23 
 
 A planisphere. 42. It is quite a feasible undertaking for grade pupils 
 to construct a planisphere which will enable them to determine which stars 
 are visible at any time of the night throughout the year and to see their 
 relative positions. It is well for the teacher to construct one so that she 
 may be competent to give directions. Proceed as follows: Cut a card, 
 board circle of 3! inches in radius. With pencil compass draw light con- 
 centric circles every J inch. The outer J inch will serve as a border for 
 the names of the month to be filled in later. These concentric lines will 
 be 10 apart and will extend down 40 below the equator, which will 
 include all stars we see in our latitude. Draw ink circles to represent 
 Arctic Circle, Tropic of Cancer, Equator, Tropic of Capricorn. With the 
 compass set at 3^ inches start at any point on the circle of that radius 
 and mark six points on the circle, each distant from the adjacent ones by 
 this amount. From the center draw light ink lines through these points, 
 thus dividing the circles, except the outermost, into six sectors. Bisect 
 these sectors, making twelve divisions of each circle. Fill in the con- 
 stellations, showing only the principal stars, copying them from star maps 
 such as those given in the Source Book of Physical Nature-Study or from 
 some published planisphere. The o line radiating from the pole is the 
 one that just touches the tip of the front leg of Cassiopeia's Chair. The 
 30 line goes through Aries. Continue labeling each radiating line 60, 90, 
 etc. The o line falls at March 22, the 90 line at June 21, the 180 line 
 at September 20, and the 270 line at December 21. Subdivide the s'pace 
 between the two outer circles into twelve equal lengths so that the dates 
 given in these months will fall at the points indicated and put the name of 
 a month in each space. 
 
 Cut two other cardboard circles of 3^ inches in radius. In one cut 
 a hole, marking the outline for it as follows: Draw a radius of this circle 
 on the cardboard: 2 inches from the circumference of the circle, mark a 
 point on this radius, and draw a cross-line at right angles to the radius at 
 this point. On the radius extended to make it a diameter mark points 
 J and 4^ inches from the point where the radius meets the circumference 
 of the circle. The portion of the radius between these will be the minor 
 axis of an ellipse that is to be cut out. On the line drawn at right angles 
 to the radius mark points 2\ inches on each side of the radius. The line 
 5 inches long between these will be the major axis. Stick two pins into 
 the major axis, one on each side of the minor axis and i^ inches from it 
 Tie a loop of string of such length that when it is slipped over the two 
 pins and extended by a pencil point the latter will just reach an end of the 
 minor axis. Move the pencil about the pins as if trying to draw a circle. 
 An ellipse is drawn that is J inch distant at its nearest approach from the 
 
24 GUIDE IN PHYSICAL NATURE-STUDY 
 
 circumference of the circle. With a sharp penknife cut this out from the 
 circular card. 
 
 Stick a pin through the center of the circular star map, the head on 
 the side showing the stars. Stick it also through the center of the whole 
 cardboard circle. Bend it close to the head so that the star map will revolve 
 about the pin, the other card serving as the back. Paste a piece of paper 
 over the pointed end of the pin to hold it in place. 
 
 Lay the circle in which the elliptical hole has been cut on the star 
 map -so that its edge will coincide with the outermost circle drawn on the 
 star map. The names of the months should show beyond it. Paste four 
 narrow strips of paper at 90 intervals from the edge of the upper circle 
 to the edge of the lower, folding them snugly around the edge of the star 
 map so that it will move freely. Mark the point where the radius crosses 
 the narrow strip of card 12 noon, the opposite edge of this upper circle 
 12 midnight. With the latter point near you and the former away from 
 you, mark the midpoint of the left-hand semicircle 6:00 P.M., of the right- 
 hand semicircle 6:00 A.M. The interval between noon and 6:00 P.M. may 
 be divided into six equal portions and marked with the hours and so on 
 for each other quarter of the circle. 
 
 If the star map be rotated between the two smaller cardboard circles, 
 the area that shows in the ellipse is the portion of the sky that is visible. 
 If it is turned so that mid-December coincides with 6:00 P.M., the elliptical 
 opening will show what constellations are then visible. Stand out of 
 doors facing north. Hold the planisphere overhead, face down, the North 
 Pole turned north, noon to the south. The morning side now shows the 
 eastern horizon, the evening the western. 
 
 A small model of the planisphere as described is figured here and 
 may be put together as follows: 43. Remove the sheets on which 
 Figures 4 and 5 are printed. Paste both sheets to thin cards and cut 
 them out. Cut out another circular card the same size as Figure 5, with- 
 out the four flaps, but do not cut out the elliptical hole. Run a pin 
 through the center of Figure 4, then through the center of the addi- 
 tional circular card. Finish the planisphere as directed above, using the 
 strips projecting from the margin of Figure 5 to fold around the edge of 
 Figure 4 and paste to the circular back. 
 
 Planets. Consult the almanac and find in what constellations Mars, 
 Jupiter, and Saturn are now in, and through what constellations they will 
 move the remainder of this year. 44. Record the findings on the opposite 
 -blank page. 
 
 Find and 45 record also the morning and evening stars for the 
 year. 
 
THE STARS AND OUR SOLAR SYSTEM 
 
 FIG. 4. The star map for the planisphere 
 
26 
 
 GUIDE IN PHYSICAL NATURE-STUDY 
 
 FIG. 5. Diagram of the front of the planisphere 
 
 To put the planisphere together paste Fig. 4 smoothly on a thin card and cut'it out. 
 Do the same for Fig. 5, but after it is pasted on the card, with a sharp penknife, cut 
 out the ellipse from the card. Cut a second card circle the size of the circle of Fig. 5 
 and mark its center. Run a pin through the center of Fig. 4 and through the center of 
 this circular card placed below Fig. 4. Lay Fig. 5 on Fig. 4 5 its circular edge just inside 
 the strip bearing the names of the months. Bend the four flaps on Fig. 5 over the edge 
 of Fig. 4 and paste them to the circular card below. Bend the pin so that its end will 
 lie down against the circular card back and hold it in place by a piece of paper pasted 
 over it. 
 
THE STARS AND OUR SOLAR SYSTEM 27 
 
 Changes in the moon. Keep record for a month of the change in the 
 moon. 46. Make a calendar for a month by ruling the opposite page so 
 as to give an inch square for each day. In each square draw a figure to show 
 the shape of the moon for that date in so far as it is visible; or on a still 
 larger sheet of paper, similarly ruled, paste figures cut from paper to show 
 the shape of the moon. 
 
 When the moon is new, how long after sundown does it set? 
 
 When it is at first quarter? 
 
 When it is full, how long after sunset does it rise? 
 
 When it is at third quarter? 
 
 47. Draw a diagram to show the relations of the shape of the moon 
 to the relative positions of sun and moon. Why do we not have an eclipse 
 of the sun every time the moon is new? 
 
 The sun. 48. Fasten a coarse wire horizontally across a south window- 
 pane. Lay a good-sized piece of brown paper down on the floor so that 
 the shadow of the wire about crosses its middle. Draw pencil lines on the 
 floor at the corners of the paper when it is spread out so that it may be 
 laid down repeatedly in the same position. Draw a pencil line on the 
 paper to coincide with the shadow of the wire and date it. Every few 
 days through the school year repeat this observation. What do the series 
 of records show? Can you explain the results? 
 
 49. Smoke a piece of glass by holding it over a candle flame until 
 it is covered with a thin layer of soot. Through this look at the sun 
 and see if you can see any sun spots. Draw a 2-inch circle to represent 
 the sun and indicated the position of the sun spot on it. Date it and 
 record the time of your observation. Repeat the observation on several 
 successive days and see if the spot changes its position. You may be able 
 to watch a spot cross the disk of the sun. If so, twice the time required 
 for such a passage is equal to what? Confirm your results from the time 
 given in the astronomies. 
 
SOME TOYS THAT WORK BY AIR 
 
 To make the paper windmill. 50. Take a 6-inch square of paper, 
 preferably colored paper. If the paper is not already cut in such form, 
 proceed as follows to cut a 6-inch square out of any rectangular sheet of 
 larger size. From any corner of the sheet measure 6 inches along each 
 adjacent side, and mark the points. Fold the corner over and crease the 
 paper along the line connecting the marked points. With the scissors, 
 cut the paper close to the folded-over edges. 
 
 Draw lines on the 6-inch square, running from each of two adjacent 
 corners to the diagonally opposite corners. Cut in from the corners along 
 these lines to within a half-inch of the intersecting lines. Lay the left 
 hand, back down, on the paper, the fingers about at the center. With 
 the right hand fold in any one corner and hold it with thumb and finger 
 of the left hand. In the same way fold in every alternate corner around the 
 square, and when all are in hand run a pin through the four infolded corners 
 and also through the center of the square. Thrust this pin into a wood 
 handle and the windmill is complete. 
 
 51. An eight-point windmill may be made in place of the four-point, as 
 follows: It makes the mill more attractive if paper of two colors is used. 
 Cut a 6-inch square of paper of each color, and cut in from the corners as 
 before. On one paper make a half-inch cut at the inner end of each diagonal 
 cut on the left-hand blades, making it at right angles to the edge. Lay 
 this square upon the table, the second square upon it so that the centers 
 coincide and so that the corners of the upper sheet are midway between 
 the corners of the lower sheet. Then insert each alternate edge of the 
 upper blades into the cuts on the lower blades. Then fold over all the inner 
 points as before and run the pin through them and through the centers 
 of the two sheets. Stick the pin into a handle. 
 
 To make the wooden windmill. 52. Cut two 8-inch lengths of wood 
 | inch square. Find the middle of each piece and mark a cross-line at 
 this point. Draw two lines parallel to this, one at each side of it, T V inch 
 distant from it. Saw into the strip on each of these two lines, cutting 
 halfway through the strip. Cut out the central block. The two strips 
 may now be put together at right angles to each other, the space formed 
 by cutting out the block fitting over the remaining section of the other 
 stick. See that they fit well. 
 
 28 
 
SOME TOYS THAT WORK BY AIR 29 
 
 With a knife shave off the opposite angles of one arm until a thin blade 
 of wood is left. The central region is not cut away, but bevels on the thin 
 blade. Cut each of the other arms in the same way, so that the blades 
 are inclined in the same direction. Fasten the mill thus formed securely to 
 a cylindrical stick somewhat larger than a pencil. 
 
 The base of the windmill is built thus: Cut a 3-inch length of J-inch 
 stuff that is i inch wide. At each end with small brads fasten on a 2-inch 
 length of the same material at right angles to the 3-inch strip, the two 
 shorter strips parallel to each other and on the same side of the 3-inch 
 strip. Bore a hole near the top of each 2-inch piece, the holes in line so 
 that the cylindrical piece fastened to the windmill may be run through 
 them. Bore a hole in the middle of the 3-inch piece. This is fastened to 
 the upright piece which should be f inch square and 8 inches long. Cut a 
 thin piece of wood out of a cigar box or similar material to form the vane 
 of the mill. Let this be 6 inches long and 4 inches wide, with a projecting 
 piece sticking out from the 4-inch side, the projection to be i inch long 
 and J inch wide. Tack this projection to the 3-inch strip that makes the 
 base of the structure that carries the mill so that the vane projects from 
 the base in a vertical plane parallel to the cylindrical strip that serves as 
 the axle for the mill. 
 
 When this vane is on the basal strip, fasten the base to the upright sup- 
 port by running a flat-headed wire nail through the hole bored in the basal 
 piece; drive it in through the center of the end of the supporting upright. 
 Put the axle of the mill through the holes bored in the supports and drive 
 a couple of small brads through the axle, one on either side of one of the 
 supports, so that the mill will be held in place. 
 
 Gearing for work. Put a spool, like a small silk spool, on the axle, 
 so that it will serve as a pulley wheel, on which a string belt may be run 
 to couple up the mill with any piece of machinery that you may want to 
 run with wind power. The machine must of course be set on a base that 
 will revolve with the mill. 
 
 How is the ordinary windmill attached to a pump, for instance, that 
 the connections may be maintained as the wind veers? 
 
 Cut out a 2-inch circle of |-inch wood, or a section from a large spool. 
 Fasten this eccentrically to one end of the axle. Run a thin strip of wood 
 to serve as driving rod from this to work a wooden doll with jointed arms 
 and legs. One of the uprights supporting the mill may be lengthened so 
 that the figure can be attached to it, and the doll will dance as the mill 
 goes around. Other contrivances can be added to the mill and pupils may 
 use their ingenuity in devising such attachments. 
 
30 , GUIDE IN PHYSICAL NATURE-STUDY 
 
 Why the windmill goes around. It is evident that the force of the wind 
 blowing against the diagonally placed arms of the windmill drives the wind- 
 mill around. If the arms of the windmill were turned so that the wind 
 struck them squarely a perpendicular blow, there would be no rotation of 
 the mill; the wind would simply tend to force the windmill back in the 
 direction toward which the wind is blowing. But with the arms of the mill 
 inclined to the wind so that the wind strikes a glancing blow, a part of the 
 pressure acts in the direction of the rotation of the mill. In other words, 
 the wind pressure is decomposed into elements, one of which serves to 
 drive the mill around. The principle involved in the composition or de- 
 composition of forces may be illustrated by the following experiment: 
 
 An experiment showing the composition or decomposition of forces. 
 53. Drive three tacks into the top of a table or in the floor, at the points 
 of a triangle, each side of which is at least two feet long. By means of a 
 short string tie the ring of a spring balance to each of the tacks. Take 
 three strings about 10 inches long; tie the three together by a single knot 
 at the ends of the strings leaving three free ends. Fasten one of these 
 free ends to each of the hooks of the three scale balances. In tying the 
 strings to the spring balances, make the length of the string short enough 
 so that each balance will register some pull. 
 
 It is evident that the amount registered on any one scale is the resultant 
 of the pulls of the other two; that is, the force pulling on one string is 
 equivalent to the counter-pull on the other two. 
 
 Graphic calculation. The relation between these forces may be graphi- 
 cally calculated in this way: 
 
 54. Lay a good-sized sheet of paper on the table underneath the three 
 strings, its center about under the knot. With a ruler draw lines im- 
 mediately under and parallel to the three strings, the three lines meeting 
 in a point immediately under the central knot. Mark beside each line the 
 amount registered by the corresponding scale, then remove the paper. 
 Suppose one scale is registering 6 ounces. Measure off 6 inches from the 
 point of intersection of the three lines along the line that led to this scale 
 and mark the point. Suppose the adjacent scale registered 8 ounces. 
 Measure off and mark a point 8 inches distant from the intersection. 
 From the point marked on the first line draw a line parallel to the second ; 
 and similarly from the point marked on the second line draw a line parallel 
 to the first, the two lines intersecting. A parallelogram is thus drawn, and 
 the third line, when continued through the point of intersection of the 
 three lines, should be the diagonal of the parallelogram, and its length in 
 inches will be equal to the number of ounces registered by the third scale. 
 Thus, knowing the strength and direction of the pull of two combined 
 
SOME TOYS THAT WORK BY AIR 
 
 3 1 
 
 forces, the resultant may be determined; or, knowing the resultant and the 
 direction of the pull of the component forces, the latter may be determined. 
 Application to windmill. To apply this to the windmill, suppose that 
 line AB in the diagram (Fig. 6) represents the end of the blade of the 
 windmill, and line CD represents the direction of the wind, and its length 
 the force of the wind. CE will represent the push given to the windmill 
 to cause its rotation. The other factor into which the force of the wind 
 is resolved is represented by the line CF; and the parallelogram of forces 
 is completed by the other lines of the figure. Relative lengths of the lines 
 
 FIG. 6. Diagram of the decomposition of the force of the wind to turn the mill. 
 Note that the sum of the components is greater than the original force of the wind. 
 What force is added to that of the wind to make the kite fly (see p. 34), and so should 
 be considered in the diagram ? Draw a diagram like this one and add this other force. 
 
 CD and CE are entirely hypothetical and will of course have to be deter- 
 mined in any given case by the velocity of the wind that is blowing and by 
 the amount of friction to be overcome in the turning of the windmill and 
 the amount of work that the mill is doing. How is it possible for the sum 
 of the two elements into which the wind is decomposed to be apparently 
 greater than the whole force of the wind? 
 
 A simple flier. 55. That the push of the air on the blades of a wind- 
 mill develops enough force to lift the blade if it is free to move is shown 
 by this simple flier. Cut a piece of wood about 5 inches long and i inch in 
 diameter to serve as a handle. An inch from one end make a circular cut 
 with a saw and then cut away the wood so as to leave projecting from the 
 
GUIDE IN PHYSICAL NATURE-STUDY 
 
 center of the end a round wooden peg an inch long and just large enough 
 to fit loosely into the hole of a spool. If it projects beyond the spool saw 
 it off so that its end is flush with the end of the spool. Shape the handle 
 
 now so that it can be held comfortably in the 
 left hand. Drive two brads into one end of 
 lj the spool, placing them on opposite sides of the 
 central hole, and let their heads stick up about 
 .B i inch. Cut from light-weight tin, like that of 
 
 5 a tomato can, a flier shaped like a pair of pro- 
 peller blades similar to this pattern (Fig. 7). 
 Punch two holes near its center large enough to 
 
 ^ easily slip over the brads on the end of the 
 spool. Twist the ends of the blades so that 
 
 O 
 
 Z they are inclined to the central portion and 
 
 6 curve in opposite directions, similar to the wood 
 propeller of the aeroplane (Fig. 9). 
 
 Wind a yard or so of good stout string on 
 the spool. Set it on the peg of the handle and 
 J place the flier on the end of the spool, the brad 
 | heads in the holes, and in such a way that 
 I when the string is pulled so as to whirl the spool 
 $ rapidly the blades will cut the air so as to 
 .Jj lift the flier off the spool. Grasp the handle in 
 m the left hand, flier up; with the right hand take 
 % hold of the free end of the string and give it a 
 '', strong pull, unwinding it all. As the spool re- 
 a volves the whirling motion is imparted to the 
 
 flier and it rises into the air. 
 
 "% To make the kite. 56. Cut a thin strip 
 
 of bamboo, or other light wood, 3 feet long. 
 If of white pine or cedar make it about J inch 
 square. The bamboo may be even thinner. 
 Cut a second piece 20 inches long. With small 
 > brads tack the shorter piece at its midpoint on 
 to the long piece, one foot from one end. Bind 
 the joint with coarse thread. Tie the end of a 
 piece of string to one end of the long piece, then 
 fasten it tautly to one end of the short piece, 
 then to the other end of the long piece, to the 
 other end of the short piece, and fasten it at 
 the original point of tie at the end of the 
 
 
 
SOME TOYS THAT WORK BY AIR 33 
 
 long piece. Thus the border of the kite is outlined in tightly stretched 
 string. The sharpest angle marks the bottom of the kite. 
 
 Lay the kite frame down on a piece of tissue paper (newspaper will do, 
 or strong wrapping paper that is not too heavy) . With shears cut the paper 
 parallel to the string, about 2 inches from it and outside of the string. 
 Put library paste, or homemade flour paste, on this projecting 2 inches, 
 and turn it over the string, pressing it on the paper. Let it dry. 
 
 Tail and bridle. Tear some old cloth up into inch-wide strips and tie 
 these together so as to make a tail about 12 feet long. Tie one end of this 
 to a short string attached to . the lower point of the kite. Cut a strong 
 string 30 inches long, and tie one end of the string to the cross-piece of 
 the kite, 8 inches from its intersection with the upright. Pass the other 
 end of the string through a small hole punched in the paper at a point 
 just above this tie point. In a similar way punch a hole 8 inches from 
 the upright on the opposite side of the kite, so that the other end of the 
 string may be tied to the cross-piece in corresponding position. On the 
 upright, 8 inches above its intersection with the cross-piece, tie one end 
 of an 1 8-inch string. There are now three strands of string tied at three 
 points of the kite. Bring these together and knot them so that the knot 
 stands directly above the upright and so that when the kite is flying it 
 will be held inclined to the wind, the tail end of the kite slanting back- 
 ward. This arrangement of strings is called the bridle, and the flight of 
 the kite depends on the accuracy with which it is adjusted. The string 
 for flying the kite is now tied at the point of the bridle where the three 
 strands intersect, and the kite is ready to fly. 
 
 Flying the kite. One person holds the kite in the right hand, the fingers 
 grasping the point of intersection of the two sticks. The kite should face 
 the wind. The second person lets out 35 or 40 feet of string and prepares 
 to run against the wind. The first person gives the kite a toss into the air 
 as the second person starts to run. As the wind catches the kite, let out 
 more string, but not too rapidly. If the kite tends to turn somersaults, 
 dashing its nose into the ground, it needs more tail, and this should be 
 added until it flies steadily. 
 
 Bits of colored paper or windmills made of colored paper may be 
 slipped on the string to blow up to the kite, the windmills whirling as they 
 go. The kite may be ornamented with a face drawn upon it in bold out- 
 lines so that it is visible when it is flying. 
 
 57. A bow kite is made by taking a straight upright 24 inches long 
 as before and fastening to its top nearly half of a barrel hoop shaved down 
 so that it is J inch square. This is fastened at its midpoint to the top of 
 the upright, the curve of the bow in a plane at right angles to the upright. 
 
34 GUIDE IN PHYSICAL NATURE-STUDY 
 
 A string runs from one end of the hoop to the opposite end, thence to the 
 lower point of the upright and back again to the first point. The tissue 
 paper is pasted on as before, but loosely, and since the kite frame will not 
 lie flat it must be pasted to one side, then rolled over to be pasted to the 
 opposite side. It is also pasted over the hoop. This kite flies without a 
 tail, the convex side toward the wind; the string is attached at a point on 
 the upright 8 inches below its top. 
 
 For making the box kite. 58. Out of pine, spruce, or cedar, that is 
 free from knots, cut four pieces of f-inch stuff 32 inches long, four 18 inches 
 long, four 9 inches, and four 20 inches. Fasten two of the 32-inch strips 
 and two of the i8 : inch strips together, so as to make a rectangle, the short 
 strips between the long ones. Do the same with the other pair of 32-inch 
 and 1 8-inch strips. Cut two strips of cambric 10 inches wide and 55 inches 
 long. Sew the ends of these together, overlapping i inch, thus making 
 two lo-inch bands of the material. Lay the two rectangles made out of 
 the wood strips together so that they coincide, and put one of the cloth 
 bands around each end, the bands on the outside of the wood rectangles. 
 Spread the rectangles apart, thus stretching the cloth bands, insert the 
 g-inch' strips between the corners of the rectangle, and brace them to pre- 
 vent their collapse with the 20-inch strips, the latter crossing each other 
 diagonally. Cut some J-inch-wide strips of light tin to bind on and rein- 
 force the corners. 
 
 The bridle for this kite is made by fastening a 3o-inch piece of string, 
 tying one end just below the band to one of the 3 2 -inch strips and the 
 other at the opposite side of the same large rectangle, close to the same 
 border of the cloth band. The string for flying is tied to the midpoint of 
 this bridle. The box kite flies without a tail. 
 
 Why the kite flies. It is very evident that the kite is kept up by the 
 force of the wind. The wind of course is blowing horizontally, that is, 
 parallel to the surface of the earth. The kite tends to fall directly down, 
 pulled by the force of gravity. In some way the wind blowing horizontally 
 is made to overcome this pull of gravity and so keep the kite in the air. 
 When the kite is flying it will be noted that the kite is inclined to the 
 direction of the wind, so that the wind strikes the face of the kite a glancing 
 blow. The string serves to hold the kite in a fixed position. The force of 
 the wind is broken into components in much the same way that the force 
 of the wind is broken in running the windmill. 59. Draw a diagram that 
 will show the elements involved and how the wind pressure is decomposed 
 into two elements, one of which overcomes the force of gravity and keeps 
 the kite in the air. Why will the kite not fly except when it is held by 
 the string? 
 
SOME TOYS THAT WORK BY AIR 35 
 
 To make an aeroplane. 60. A simple but very effective type of aero- 
 plane is made as follows: Cut a f-inch square strip of white pine 22 
 inches long (or use a piece of bamboo f inch wide). This strip should be 
 straight-grained and free from knots, for it serves as the backbone of the 
 machine and must bear the strain of the twisted rubber bands that serve 
 to run the propeller. 
 
 Cut a strip of tin 4 inches long and f inch wide. Bend it 2 inches 
 from one end into a sharp V. Holding it with the long arm to the left 
 bend this long arm i inch from its end so that the bent portion turns to 
 the right and lies at right angles to the rest of this side of the V. Bend the 
 other arm of the V in the same direction i inch from its end so that the 
 bent portion is parallel to that of the first arm of the V. These two parallel 
 parts are now to be bound tightly with coarse linen thread to the end of 
 the backbone, their long axes coincident with its long axis. This end is 
 the front end of the machine. Near the tip of this V and in its midline 
 punch a hole through both sides so that, a stiff wire axle that bears the 
 propeller may run through the hole parallel to the long axis of the backbone. 
 
 The skids. -Cut two thin strips of bamboo | inch wide and 6 inches 
 long and one 4^ inches long. Bind these together with the linen thread 
 in the form of a triangle letting their ends overlap J inch. Bind this to 
 the backbone i inch back of the tin propeller bearing, the juncture of the 
 two long sides above the backbone and on the opposite side from the 
 point of the tin strip. Let the plane of the triangle be at right angles to 
 the backbone. Cut two more such thin strips 5 inches long and bind one 
 end of one to the midpoint of one of the long sides of the triangle, the 
 other end to the backbone about 2\ inches back of the point to which 
 the apex of the triangle is affixed. The other strip will be bound to brace 
 the other side of the triangle in a similar way. 
 
 Cut two more thin strips 5 inches long. Set one on each side of the 
 backbone i inch from its rear end at right angles to the backbone and 
 perpendicular to the base of the forward triangle. Bind them on tightly 
 at their midpoints. Fasten a brace of bamboo from the upper end of this 
 pair of strips to the backbone about 3 inches in front of the point where 
 the pair of 5-inch strips is bound to it. 
 
 Cut three strips of bamboo 3 inches long and so thin that each can be 
 bent into a U over the end of the finger without breaking. Bind one of 
 these by its ends to the lower end of each side of the bamboo triangle and 
 one to the lower end of this last support near the rear, the plane of each U 
 parallel to the longitudinal axis of the backbone. These three loops form 
 skids on which the aeroplane stands and they slip along the floor or side- 
 walk as the machine takes flight (Figs. 8 and 9). 
 
36 GUIDE IN PHYSICAL NATURE-STUDY 
 
 Propeller. Shape a g-inch propeller out of the tin of a coffee can similar 
 to the one cut for the flier (p. 32). If the longitudinal axis of the propeller 
 is made to coincide with the length of the can the curve of the tin will 
 give about the right curve to the propeller after it is bent according to the 
 instructions there given. Or a propeller may be fashioned out of white 
 pine, white wood, or cedar that is straight-grained and free from knots. 
 Cut the block of |-inch stuff 9 inches long and 2 inches wide. Bore a hole 
 at the middle of one broad face just large enough to take the stiff wire 
 that must be used as the axle for the propeller. Draw a square i inch on 
 
 FIG. 8. The aeroplane frame. (In this the forward legs are part of a quadrangular 
 frame instead of a triangular one as described.) 
 
 each side, its center coincident with the hole, its sides parallel to the sides 
 and ends of the block. Draw lines from its corners to points on the adjacent 
 sides 2 inches from each corner of the block. Cut away the sides of the 
 block along these lines. Mark the ends of the block according to the 
 diagram (Fig. 10) and saw away the wood from both sides of the diagonal 
 strip down to the central square. By sandpaper held over the thumb to 
 give a curved surface or with bits of broken glass having rounding edges 
 work away the wood of the blades to make them thin and curved according 
 to the heavy line of the diagram. The blades may be shaped so that their 
 outlines are similar to these of the flier. Cut away the corners of the central 
 block so that it joins the blades in flowing surfaces. 
 
 Pass one end of a 6-inch length of stiff wire through the hole in the 
 center of the propeller so that it protrudes f-inch. Bend this protruding 
 end down to the wood center and tack it securely. If the tin propeller 
 is to be used stick the wire through one hole ij inches, bend it so that the 
 end can be thrust back through the other hole and twisted on the long wire 
 so as to hold the propeller securely. A short block of wood set on the back 
 
SOME TOYS THAT WORK BY AIR 
 
 37 
 
 of the propeller between the holes and included in the loop of wire will 
 help to hold the propeller solidly. 
 
 Put a flat good-sized bead on the free end of the wire, then pass the 
 end through the holes in the tin propeller bearing and make a triangular 
 loop on the wire just back of the ^bearing to take the strands of rubber 
 that make the motor. The bead used helps to reduce friction. Make 
 another small triangle of wire and bend the free ends so that they can be 
 bound securely to the front of the rear skid strut about i inch from the 
 
 FIG. 9. Front view of frame and propeller 
 
 backbone. Pass the long strand of rubber that can be bought for this 
 purpose through this rear wire loop, then through the one on the rear 
 end of the propeller shaft, and so back and forth until about ten strands 
 are laid on. Tie the ends of the rubber together to complete the last strand. 
 Planes. Cut two thin bamboo strips f inch wide and 22 inches long 
 and two 5 inches long, and bind their crossed ends together so as to make a 
 rectangular parallelogram of the strips that will serve as the frame for the 
 forward plane. In the same way make the rear frame for the plane 10 by 4 \ 
 inches. Cover the frames with strong but light paper, folding the paper 
 over the edge of the frame i inch and gluing it down. Fasten the forward 
 plane horizontally to the backbone, its long axis at right angles to the 
 latter, its front edge just back of the struts that support the forward skids. 
 
GUIDE IN PHYSICAL NATURE-STUDY 
 
 Tack it lightly in place with thread. The rear plane is fastened similarly 
 with its hind edge just in front of the brace that supports the rear strut. 
 When the planes are in place balance the machine on the forefinger placed 
 
 under the backbone near its center. 
 If the planes do not lie horizontally 
 but tend to dip to one side or the 
 other their position may need to be 
 changed slightly. When they do 
 balance well fasten them securely in 
 place, daubing the bindings with 
 glue so that they will not slip. Guy 
 
 FIG. 10. Diagram of end of block, 
 showing method of cutting and curve of 
 blade of wood propeller for aeroplane. 
 
 threads may then be run from the 
 outer tips of the planes to the ad- 
 jacent struts to help hold them in place (Fig. n). 
 
 Observe which way the propeller, which is at the front of the machine, 
 should turn in order to carry the machine in the air, then turn it about 
 
 FIG. 1 1 . The aeroplane complete 
 
 150 times in the opposite direction. Head the aeroplane into the wind, 
 set it down on a smooth surface, like a cement sidewalk, release the pro- 
 peller and it should rise and fly. If at first it is not successful try shifting 
 the planes slightly forward or back or changing their inclination. Possibly 
 you can reduce the weight of the machine. It is imperative to keep in 
 mind while building the aeroplane that it must be exceedingly light in 
 order to fly and that the parts must not be made any heavier than is abso- 
 lutely necessary. 
 
 Another model. 61. A still larger aeroplane with two propellers is 
 made by making a triangular frame of f-inch square strips 42 inches long 
 with a lof-inch strip of the same stuff for the base of the triangle. The 
 
SOME TOYS THAT WORK BY AIR 39 
 
 apex of the triangle is in this case to be the front end of the plane and is 
 provided with a pair of hooks to take the rubber bands, one set of which 
 runs along under each long side to the propeller bearing at its hind end. 
 The forward plane is small, about 12 by 4 inches, and is fastened in the 
 plane of the triangle about 6 inches back of its tip, its longitudinal axis 
 perpendicular to the altitude of the triangle. The rear plane is 36 by 5 
 inches and attaches in a similar position 6 inches from the hind end of the 
 triangular frame. This plane takes two Q-inch propellers. If the pull of 
 the tightly twisted rubber bands tends to bend the long sides of the triangle, 
 run fine wires one from the rear of each side to the apex of the triangle 
 over a 2-inch upright of light stuff set on the middle of each side and bound 
 in place. Skids may be provided as in the other plane, but they are not as 
 necessary, for this plane is started off from the hands, each hand holding 
 one propeller and letting go as the plane is launched by a shove out from 
 the shoulders as the person launching it stands upright. 
 
 62. A very simple aeroplane propelled from a sling shot instead of by 
 a propeller, is made thus: Split a J-inch square wood strip, 10 inches long, 
 at one end. Insert a light card i J by 3 inches so that the ends of the card 
 stick out equally on either side of the stick and its rear edge is i| inches 
 from the end of the stick. Bind it in place. Tack another card on the 
 stick, the same size as this, its surface at right angles to the first, its rear 
 edge at the end of the stick, its ends projecting equally from the sides of 
 the stick. Parallel to this card, at the other end of the stick, fasten one 
 8 by ij inches, its middle on the stick. Notch the stick under this near 
 the end. Bend a piece of telephone wire in the form of a Y. Tie one end 
 of a rubber band to the tip of each arm of the Y. Tie one end of a 6-inch 
 string to the free end of one band, the other end to the other band. Hold 
 the base of the Y in the left hand. Hold the aeroplane by the end near 
 the small cards, between thumb and finger of the right hand, the string 
 of the sling in the notch near the front end. Pull it back, stretching the 
 rubbers, and release it for its flight. 
 
 To make and operate a sailboat. The sailboat is another thing that, 
 like the aeroplane, kite, and windmill, depends on the decomposition of the 
 force of the wind for its propulsive power. Both sailboat and windmill are 
 very old contrivances. A very simple sailboat may be made with little 
 trouble. 63. Take a block of f-inch stuff 6 inches long and 3 inches wide. 
 Draw a line down the middle of one broad side. Mark points on this line 
 i J, 2 J, and 3! inches from one end. Draw cross-lines at these points at right 
 angles to the central line. Mark off on either side of the central line on 
 the first of these cross-lines points i inch from the central line, on the second 
 and third i J inches, and at the rear end of the block points i J inches from 
 
4 o 
 
 GUIDE IN PHYSICAL NATURE-STUDY 
 
 the center. Connect these points with flowing lines to mark the sides of 
 the boat. Then with a sharp knife cut along these lines to shape the boat. 
 Cut a thin strip of wood 6 inches long and i inch wide. Fasten this on 
 edge with brads along the midline of the bottom of the boat to serve as a 
 keel. On the opposite side from the keel, the deck of the boat, bore a hole 
 in the midline ij inches from the prow of the boat and set tightly in this 
 a round stick 5 inches long and about J inch in diameter for the mast. 
 
 Cut out a rudder shaped as in Figure 1 2 and fasten it vertically in the 
 midline at the stern of the boat with two double-pointed tacks set about 
 
 the round rudder post just tightly enough so 
 that the rudder may be turned into the desired 
 position but still held in place when so set. 
 The blade of the rudder should be under water 
 when the boat is floating. 
 
 Across the stern of the boat set a stiff wire 
 so that it lies parallel to the deck and about 
 | inch above it, the ends of the wire bent down 
 and fastened on either side by means of tacks. 
 The sail. To make the sail cut a piece of 
 cloth 4! inches long at its lower edge, which 
 fastens to the boom; 3^ inches long on the side 
 next to the mast, which side is at right angles 
 to the lower edge; 2\ inches long on its upper 
 edge, which lies at an angle of 45 to the edge 
 
 next the mast, thus making the edge opposite the mast about 6 inches long. 
 Turn in and hem down \ inch all around the sail. 
 
 Cut two round sticks T \ inch in diameter, 5 inches and 2 J inches long, 
 respectively. Bind a round loop of stiff wire on one end of each of these 
 spars, large enough to slip readily over the mast. Sew these spars to the 
 lower and upper edges of the sail by looping the thread over the spar at 
 each stitch. Slip the wire loops on the ends of the spars over the mast, 
 the long spar next the deck. Tie one end of a short string to the tip of the 
 upper spar and an end of another string at its base near the ring of wire. 
 Tie the other ends of these strings to the upper end of the mast so that 
 the sail will be hung with its long spar or boom about \ inch above the 
 deck/ 
 
 Tie one end of a 5-inch string to the outer end of the boom and fasten 
 the other end loosely to the wire at the stern of the boat, which is ready to 
 sail now. It is well to keep a long string tied to the stern of the boat while 
 sailing it until you have mastered the art of adjusting sail and rudder 
 sufficiently well to make sure that the boat will arrive at the desired port 
 
 FIG. 12. Rudder of sailboat 
 
SOME TOYS THAT WORK BY AIR 41 
 
 when it is started off on a voyage. Set the rudder in various positions 
 until you learn what its effect is on the movements of the boat. The 
 length of string between the end of the wire and the tip of the boom must 
 be varied according to the direction of the wind in relation to the course 
 of the boat. You may readily figure out these things, keeping in mind the 
 principle of the composition of forces. Can a boat ever sail faster than 
 the rate at which the wind is blowing? 
 
 Sailors in the olden times found it necessary to wait for a favoring 
 wind, one going in the general direction which they wished to pursue in 
 their journey. But the modern sailor has learned how to tack into the 
 teeth -of the wind. How close to the wind can you make your boat sail? 
 
 The motor boat. 64. The sailboat may be transformed to a motor 
 boat or a motor boat may be built on the same lines as the sailboat just 
 described. The motor boat needs no sail or mast. Cut the keel away 
 from in front of the rudder for a space of i inch, and slope it from this 
 point to the front of the boat, where it may be J inch high. Carefully 
 punch four or five small holes in the keel near its stern end, and by 
 means of strong thread or fine wire run through these holes bind to the 
 keel at the stern end a short piece of glass tubing, the ends of which 
 have been heated enough in the flames to melt down their sharp edges 
 and leave them rounded. A small piece of brass tubing may be used in 
 place of the glass or a small screw-eye may be set in the keel at its stern 
 end. Drive a brad into the keel at its front end, leaving the* head project- 
 ing so that the rubber band for motive power may be attached to it. 
 
 Propeller. Cut two pieces of tin like the flier on page 32, only make 
 these smaller, about 2 inches long. Lay one on top of the other in the 
 form of a cross with equal arms. Punch two holes in their common center 
 and wire them together with one end of a stiff wire set through the holes 
 and twisted to fasten them, leaving the other end of the wire projecting 
 several inches from their midpoint at right angles to the plane in which 
 they lie. Bend the blades of this propeller so that they will be inclined 
 like the vanes of the windmill. Thus all of them will exert their thrust in 
 the same direction when the propeller is turned in the water. 
 
 Slip on the wire a rather flat glass bead of about the same diameter as 
 the outside of the glass tubing on the keel, pass the wire through the tube 
 from the stern end forward. Make a loop on the wire just in front of the 
 tube and cut off the excess wire. Fasten the ends of several 4-inch rubber 
 bands to this wire loop and their other ends to a similar wire loop that is 
 attached firmly to the brad at the bow end of the keel. 
 
 Turn the propeller wheel many turns until the rubber bands are tightly 
 twisted. (Figure out in which direction they must be twisted to drive 
 
42 GUIDE IN PHYSICAL NATURE-STUDY 
 
 the boat forward as the propeller is turned by their untwisting.) When 
 the boat is set in the water and the propeller released it should move with 
 considerable speed. 
 
 The boat, for the making of which directions have been given, is not 
 a very graceful model. One worked out of a thicker block of wood with 
 curving sides instead of straight and with a hold hollowed out of the block 
 is much more shipshape. But this is a good first model to attempt. The 
 boy or girl who wants to make a better type, a real racing motor boat or 
 a speedy sailboat with more elaborate rig and numerous sails, may consult 
 such books as those on boats given in the Appendix. 
 
 To make a water wheel and use it. 65. Cut four strips from a cigar- 
 box cover 5 inches long and f inch wide. At the center of each bore a 
 ^-inch hole with a bit and brace. Fasten two of these together at right 
 angles to each other tacking them with small brads, thus making a cross 
 with a hole at its center. Fasten the other two together in the same way. 
 Cut four more strips if inches wide and 3 inches long for the paddles. 
 Fasten one of these to the edges of corresponding arms of the foregoing 
 crosses, its long edge flush with the end of the arms, the short edge flush 
 with the f-inch outer face of the arm. Fasten the other three in corres- 
 ponding positions on the other arms. Make a round axle slightly more 
 than J inch in diameter and 6 inches long. Force it into the holes of the 
 two crosses and let it stick out on either side of the wheel. Cut two up- 
 rights of the cigar-box wood i inch wide and 5 inches long. A half-inch 
 from the end of each of these latter and in the midline have a -jVinch 
 hole. Put the axis into these holes and tack the uprights to the end of a 
 fooard 4 inches wide. Set the board in the sink and let the water from the 
 faucet strike the paddles. 
 
 Fasten a small spool to one of the projecting ends of the axle. Make 
 this serve as a wheel over which a loop of string may be run as a belt to 
 connect with any mechanical toy and furnish the power for its propulsion. 
 At what angle will the water strike the paddle when it exerts its greatest 
 force in turning the wheel ? How is a water turbine built ? 
 
TOP, SLING, AND BOW 
 
 To make and spin tops. 66. Saw the beveled end off of a spool. 
 Whittle out a peg long enough to stick through this and project J inch 
 below the bevel and i inch above the flat side of the spool end. Make 
 the peg round and large enough to fit the hole of the spool end snugly. 
 Drive it into the hole, thus making the top. Hold the blunt end of the 
 peg between thumb and finger and give it a vigorous whirl, letting go so 
 that the top will drop on the sharp end of the peg and keep turning. Make 
 a hemispherical hole in the middle of a soft pine board by pounding in 
 the head of a brass upholstery tack. Set the top spinning in this depression. 
 Then incline the board. Does the top incline too or remain upright ? Why ? 
 
 The peg top. The ordinary wooden peg top is so cheaply bought at 
 the store that it is not worth while to make one. 67. To spin such you 
 first loop one end of the string around the upper end of the top, .then carry 
 it to the peg, and wind it on firmly over the loop of string first made, up to 
 the beginning of the curved portion. Hold the top in the hand with the 
 peg on the ball of the thumb, the upper end of the top covered by the 
 first three fingers. The end of the string has a button on it and this end 
 is held between the first and second fingers, the button on the back of these 
 fingers. Throw the top down on the ground with an overhand throw as 
 if the top were a ball. The string unwinding sets it spinning, and it con- 
 tinues to spin after it strikes on its peg end. The instructions seem easy, 
 but you may have to practice some time before you acquire the art of 
 spinning a top. 
 
 Inertia. Can you balance a top on its peg when it is not spinning? 
 What happens when it ceases to spin? The top illustrates beautifully a 
 law of motion, namely that when a body is once in motion it tends to remain 
 moving in the same line or plane unless some force is used to change the 
 direction of its motion. If a very heavy disk is made to spin it requires a 
 very great force to move it out of the plane in which it is whirling. Such 
 whirling disks are used to keep boats steady so they will not rock in a sea 
 and to keep the car upright on the rail in the monorail railroads. 
 
 The top on a tight rope. 68. Get the spinning top on the palm of 
 your hand; you can scoop it up while it is spinning, spreading your fingers 
 so that it will climb up on your hand over the web between the second 
 and third fingers. While holding it as it spins incline your hand. Does it 
 remain upright? While it spins on your right hand hold the string with 
 
 43 
 
44 GUIDE IN PHYSICAL NATURE-STUDY 
 
 the button between the second and third fingers of the right hand. Hold 
 most of the string in the left hand, but have a couple of feet of it stretched 
 between the hands. Then incline the hand so that the top will spin off 
 on the string, the left-hand end of which is somewhat lower than the right. 
 Let the side of the peg be supported by the string not its tip. The top 
 will spin along the string, standing out in a nearly horizontal position 
 without falling, because a body in motion resists being pulled out of the 
 plane in which it is moving. Thus the top, while spinning, apparently 
 defies gravitation. 
 
 The sling. 69. Fill a pail partly full of water. Hold it in the hand, 
 arm down, then swing it rapidly with a full arm swing over the head and 
 to its first position. Swing it several times. Why does not the water 
 spill out when the pail is upside down over the head? When a wagon or 
 carriage is being driven rapidly over a muddy road in what direction does 
 the water fly off the wheels and why? 
 
 The force illustrated in the foregoing experiment with the pail is utilized 
 in a very old weapon, the sling. 70. Cut a piece of leather 2 inches wide 
 and 5 inches long. Make a hole in the middle of each end near the edge, 
 large enough to fasten in a string. Cut two limp strings one 2 feet, the 
 other 2\ feet long. Tie one end of the string to the leather at one hole, 
 an end of the other into the other hole. Wrap the free end of the longer 
 string about the third and fourth fingers of the right hand a couple of 
 times. Hold the free end of the other string between thumb and first 
 finger and place a good-sized pebble in the leather. When the arm is 
 hanging free at the side the leather with its contained stone should be 
 just off the ground. Swing the sling around and around the head rapidly, 
 then suddenly let go the string between thumb and first finger when you 
 think the position is about right to send the stone toward the object at 
 which it is aimed. Some practice will be required to gain skill in throwing 
 the stone in the right direction, and it is well to practice in the open, away 
 from windows and people. 
 
 Centrifugal force. Sometimes flywheels or grindstones break while 
 in motion. How do the fragments fly? How does the cream separator 
 work? Which way do you lean in riding a bicycle around a corner and 
 why? How do you play crack-the-whip and on what does the game depend 
 for the fun in it? 
 
 To make bow and arrow. 71. Select a piece of wfell- seasoned white 
 cedar or arbor vita that is straight-grained, i inch wide, \ inch thick, and 
 4 feet long, or use oak, hickory, ash, Osage orange. Round off the middle 
 6 inches and then round off the rest, tapering to each end. Make the ends 
 about \ inch in diameter. Trim each end and cut a groove in it to hold 
 
TOP, SLING, AND BOW 45 
 
 the cord. Tie a permanent loop in each end of a stout cord large enough 
 to slip over the tip and lie in the groove. Make the cord with its loops 
 about 2 inches less than 4 feet long. To string the bow slip one loop 
 over the end and past the groove, the other loop over the other end and 
 into the groove. Set this end of the bow on the ground. Press the knee 
 against the 'bow, held nearly upright by the hand near the other end, 
 thus bending the bow until the other loop can be shoved up into the groove. 
 Always slip the loop out of the groove when the bow is not in use so that 
 it will not be permanently bent out of shape. 
 
 The arrow. Cut an arrow out of straight-grained light wood, like 
 cedar or pine, 30 inches long and make it about as large around as a pencil, 
 except the head end, which for a distance of 3 inches may be made f inch 
 in diameter. Or the head end may be left the same size as the shaft of the 
 arrow and sharpened. Then a bit of thin brass tubing may be forced on 
 the head end just back of the point or regular arrow tips may be fastened on. 
 
 The string end of the arrow's shaft is notched so as to set on the string. 
 To feather it split a chicken's wing or tail feather in two, cut the quill 
 off J inch from the web and cut the web off from the shaft inch from the 
 other end. Bind these pieces to the shaft i inch from the string end, one 
 on the top of the shaft, the other below it. 
 
 The operation of the bow and arrow depends upon the fact that the 
 wood of the bow is elastic. When a body is distorted by pressure and then 
 tends to resume its normal shape, exerting a force in the attempt to do so, 
 this is known as elasticity. Thus the bent bow tends to straighten itself 
 and exerts a pressure through the string on the arrow equal to the force 
 used to bend the bow. When a rubber ball is dropped on the sidewalk it 
 is distorted by hitting the hard walk. It hits back as it reassumes its 
 normal shape and so throws itself back into the air or bounces from the 
 walk. 
 
 When muscular energy is used to bend the bow it is stored in the 
 curving wood as potential energy. When the string is released this potential 
 or static energy becomes at once active or kinetic and is imparted to the 
 arrow, starting it on its flight. Thus muscular power is transformed and 
 stored as elasticity, then reappears as mechanical motion, an illustration of 
 the principle of conservation of energy that will be repeatedly seen in the 
 work that follows. This principle, briefly stated, is that energy cannot be 
 created or destroyed but may be transformed from one sort to another. 
 
 It is an instructive thing to fire the arrow straight up in the air. It 
 leaves the bow with a certain velocity and momentum which decrease 
 gradually as gravity tends to pull the mounting arrow back to earth. The 
 arrow stops its upward flight as the force of gravity equals the waning 
 
GUIDE IN PHYSICAL NATURE-STUDY 
 
 momentum. Then it begins to fall slowly at first, then with increasing 
 velocity as gravity continues to act upon it, and finally it strikes the earth 
 with sufficient energy to bury its head in the ground. 
 With what amount of energy does it strike? 
 
 To make the target. 72. Take an old gunny sack 
 or other bag made of coarsely meshed cloth. Lay it 
 down flat on the floor and mark one side of it with 
 bull's-eye and concentric circles, using a grease 
 pencil or express- marking pencil for the purpose. 
 Stuff the bag partly full of straw or excelsior, held 
 in place by occasional stitches of darning cotton 
 through the bag. Tie the target up between two 
 upright sticks set in the ground. 
 
 In using the bow it is held vertically in the left 
 hand just below its center. The notch in the end 
 of the arrow's shaft is placed at the center of the 
 bowstring. The end of the shaft is held between 
 the thumb and bent forefinger of the right hand. 
 The shaft of the arrow lies next the bow on the base 
 g of the thumb of the left hand. Draw the arrow 
 ^ back to its head, sighting along it at the target, 
 | then when it is pointed at or a little above the 
 % bull's-eye release it for its flight. 
 
 The bow gun. The same force, developed from 
 ^ the elasticity of the wooden bow, is seen in several 
 ^ other interesting toys. Long before the days of 
 - the modern gun, the bow gun was in use and was 
 ^ called the cross-bow. It is not a difficult weapon 
 to make. 
 
 73. Take a piece of f-inch stuff, 6 inches wide 
 and 3 1 feet long. Saw out the general form of a 
 gun, laying it out by the working plan (Fig. 13). 
 The barrel of the gun is left square at the outset. 
 It may be rounded off below after carrying out the 
 following directions, if it is desired. With a groov- 
 ing plane or a gouge cut a shallow groove along the 
 top of the barrel. Cut a hole through the bulge 
 near the end of the barrel to receive the bow. The 
 . bow already made may be used, fastening it at its 
 mid-point in this hole and wedging it with wooden 
 wedges to hold it in place. 
 
TOP, SLING, AND BOW 47 
 
 The arrow, some 1 8 to 20 inches long, should have a rounded head so 
 that it will slip along the groove easily, and the opposite end must be made 
 wide with a generous notch to catch the string from the bow when the 
 former is released in firing the gun. 
 
 The trigger. At the point where the stock of the gun and the barrel 
 meet cut a slot from top to bottom of the gun in the midline ij inches 
 long and J inch wide. In this set a trigger whose upper end comes but 
 slightly above the upper face of the barrel. The trigger is held in place 
 by a nail passed through it and also through the sides of the gun barrel 
 and then bent on one side to keep it in place. Drive a tack in the middle 
 of the bottom of the barrel a few inches in front of the trigger. - To this 
 attach a small rubber band the other end of which is set in a notch near 
 the lower end of the trigger to keep this end drawn forward. Notch the 
 top of the trigger to receive the bow string when the bow is drawn back. 
 If the trigger will not hold it add a stronger rubber band to the lower end 
 of the trigger. 
 
 Shooting. Set the arrow in the groove on the upper side of the gun 
 barrel. Aim the gun as you would an ordinary piece and pull the trigger 
 to shoot the arrow. The muzzle velocity is, of course, not very high. 
 The trajectory is therefore a line that curves rapidly down toward the 
 earth's surface when the gun is fired horizontally; still, a little experience 
 will make one fairly expert in allowing for the pull of gravity by sighting 
 somewhat above the mark, as one must do even with a high-powered rifle 
 when firing at long range. 
 
 A toy pistol. 74. Cut a f-inch square piece of wood 6 inches long 
 and fasten another piece of the same wood 3 inches long at one end to serve 
 as the handle or pistol grip, or the whole pistol may be cut out of a block 
 of wood in the rough and then shaped more exactly with a knife. Rig a 
 trigger as in the cross-bow. Fasten two rubber bands to the pistol, one 
 on each side by a tack driven in near the end of the barrel farthest from 
 the handle. Tie the ends of a short string to the free ends of these rubber 
 bands, so that when they are stretched it will catch in the notch of the 
 trigger. Just in front of the trigger on the upper surface of the barrel 
 make a little longitudinal slot with the end of the knife. A piece of card- 
 board f inch square is set by one of its corners in this slot and is fired as the 
 "bullet" when the stretched rubber bands are released by the trigger. 
 
THE HOT-AIR BALLOON AND SOME EXPERIMENTS TO SHOW 
 
 HOW IT WORKS 
 
 How to make a hot-air balloon. 75. Cut sixteen strips of tissue 
 paper 8 inches wide and 5 feet long. These may be all of the same color 
 or, if it is desired to have the balloon striped, half of one color and half of 
 another. Fold each piece down the center so as to make a double strip 
 4 inches wide and 5 feet long. Cut a strip of newspaper or heavy brown 
 paper to serve as a pattern, as follows: Cut the strip 5 feet long and 4 
 inches wide. Mark on one long edge a point at every foot. At the first 
 from the tip mark a point 3 inches from this edge as measured along a 
 line perpendicular to it. At the second point mark a point on the other 
 edge opposite it. At the third point mark another point 3 inches from this 
 edge; at the fourth, a point midway between the two edges. At the end 
 mark a point ij inches from the edge. Beginning at this last point draw 
 a flowing line to connect these several points and run out finally to the corner 
 aj: the opposite end from the start adjacent to the side on which the points 
 were spaced a foot apart. This pointed end of the pattern makes the top 
 of the balloon. Lay the pattern on the folded strips and the straight edge 
 on the fold and so cut the sixteen strips. 
 
 When all the strips are cut according to pattern lay one of the folded 
 strips down on the table, unfold another strip, and lay it on the folded 
 strip, their edges parallel, but the folded strip extending J inch beyond the 
 open strip. Put paste on the projecting edge of the folded strip and then 
 turn this edge back so as to paste it on the unfolded strip. Refold the 
 strip that was opened, open a third strip and lay it on the refolded one, 
 and proceed to paste as before. In this way all of the strips can be fastened 
 together, making the balloon. Let this much of the balloon dry before 
 proceeding with the next step. 
 
 The strips cannot be made to meet exactly at their upper sharp ends, 
 so that there will be a small hole in the top of the balloon. Cut two circular 
 patches of paper 8 or 10 inches in diameter, and paste these on, one inside 
 and one outside of the hole so as to cover the hole. 
 
 Bend a thin piece of bamboo J inch wide so as to make a hoop just 
 large enough to fit inside the mouth of the balloon. Fasten the ends of 
 the strip by binding with string. Fasten the hoop in by folding the tissue 
 paper up over it and pasting it on the inside of the balloon. Run two light 
 iron wires across the mouth of the balloon, fastening their ends to the bam- 
 
 48 
 
THE HOT-AIR BALLOON AND SOME EXPERIMENTS 49 
 
 boo hoop and placing them so that they cross each other at right angles at 
 the center of the hoop. 
 
 Pass the ends of a loop of string through the center of the circular 
 patch on the top of the balloon and fasten these ends by pasting paper 
 over them on the inside of the balloon. This loop will serve to hang up 
 the balloon, and to hold the balloon when it is being inflated with hot air. 
 It is well now to hang the balloon up after the fastenings of the loop are 
 dried and examine it to see that there are no holes, covering them with 
 pieces of paper pasted on if any are found. 
 
 Bend a piece of wire 6 inches long into the shape indicated in the diagram 
 (Fig. 14) ; on the center of this wind a ball of lamp wick or cotton batting. 
 This to be saturated with alcohol, slipped on one of the cross-wires at the 
 mouth of the balloon, and lit just before the balloon is sent up so as 
 keep the air inside the balloon hot. To prevent the flame setting the balloon 
 afire make a cylinder of asbestos paper 6 inches long 
 and 3 inches in diameter. Cut four slots 2 inches 
 long in one end of this so that this chimney will set 
 down on the cross-wires around the ball of wicking. 
 Inflating it. The balloon must be filled with hot 
 air before it is sent up. To do this take a length of 
 stovepipe, cut a piece out of one end and set this 
 end down in the ground, forcing it into the ground 
 for some distance. A wood fire is then built in the 
 stovepipe, the hole at the bottom serving as a draft ^ ^ Bent wire 
 
 to let in the air. When the fire has died down f or hanging wicking to 
 some, so that the flames are no longer coming from balloon frame, 
 the top of the pipe, hold the mouth of the balloon 
 
 over the top of the pipe. It is best to place a stick through the loop 
 at the top of the balloon, one person holding this while a second person 
 holds the mouth of the balloon. Pull out the sides of the balloon to 
 straighten out folds so that it will inflate to its capacity. When the 
 balloon is well distended with hot air, take it away from over the stove- 
 pipe, put on the ball of wicking saturated with alcohol and the asbestos 
 chimney, light the alcohol. Remove the stick now from the loop. Let 
 the person who is holding the mouth continue to hold it until the balloon 
 begins to tug a bit, then let go and it will rise and probably drift out of sight. 
 
 It is well not to try to send the balloon up on a windy day. Fill it in a 
 sheltered position, but select a place where it will not get tangled among 
 tree branches, telephone wires, or blow against a building as it rises. 
 
 The remainder of this chapter will consist of experiments to make clear 
 why the balloon rises. Incidentally some other things will be explained. 
 
50 GUIDE IN PHYSICAL NATURE-STUDY 
 
 Water seeks its own level. 76. Slip a ij-foot length of rubber tubing 
 on the end of a good-sized funnel and put a smaller funnel on the other 
 end of the rubber tubing. Hold the two funnels in the left hand, and 
 pour water into one of them until it rises into the other. Take one funnel 
 in one hand and one in the other and vary their relative levels. It will be 
 noted that the level of the water is the same in the tube even when the 
 large funnel is quite well filled, thus having a large water surface, while 
 the level of the water in the small funnel may be only part way up the 
 stem of the funnel. 
 
 The fountain. 77. Substitute for the small funnel a piece of glass 
 tubing, drawn out into a fine point. To do this cut an 8-inch length of 
 glass tubing as follows: 
 
 78. To cut glass tubing make a scratch on the glass with a triangular 
 file at the point at which you want it to break. Hold it in the hands, with 
 the thumbs, nail to nail, opposite the scratch, the fingers on the scratched 
 side of the tube. Press up with the thumbs and down with the fingers, 
 when the tubing will easily break straight across. 
 
 79. Hold the glass tube by its ends and let the middle of it heat in 
 the gas flame or the flame of the alcohol lamp, turning it slowly until it 
 is red hot and bends easily. Then quickly pull the ends apart. Break off 
 the tip when cool. Hold the large funnel and the tube in the left hand 
 and fill the apparatus with water. Cover the tip of the tube with the 
 finger and lower it, the tip pointing up. When the finger is removed 
 the water plays like a fountain, rising approximately to the level of the 
 water in the funnel. Why not to the level? The principle illustrates the 
 method by means of which water is conducted into houses through 
 pipes, when the water gets its pressure from some reservoir that stands at 
 an elevation. 
 
 Water pressure. 80. With a nail set or large wire spike, make a 
 round hole in the top, one side, and the bottom of a tin can with a very 
 tight cover. Put small rubber corks, each with a hole, into these openings. 
 Pass a small funnel through the hole of the cork in the top of the can, a 
 glass tube with a right-angled bend through the hole in the side of the can, 
 and one with two right-angled bends both on the same side of the straight 
 portion, through the hole at the bottom of the can (see Fig. 15). To 
 bend the glass tubing proceed as follows: 
 
 81. Heat the tubing, at the point where the bend is to be made, in the 
 flame of an alcohol lamp or a Bunsen gas burner. Hold it up near the tip 
 of the flame and turn it slowly so that it will heat on all sides. Glass is 
 a poor heat conductor, so that it may be held in the fingers while this is 
 being done. Soon the glass will soften so that it can be slowly bent. If the 
 
THE HOT-AIR BALLOON AND SOME EXPERIMENTS 51 
 
 bending is done rapidly the hole through the tube is likely to be closed, 
 and we want it open. 
 
 Seal the cover on the can by putting on a strip of surgeon's adhesive 
 tape, which can be bought at the drug store. Pour water into the funnel, 
 filling the can, and continue to pour it in until the water stands in the funnel 
 2 or 3 inches above the top of the can. Tilt and jar the can to get out all 
 air bubbles. Note the water level in the tubes and observe in what direc- 
 tion the pressure must be exerted in the can to maintain it at this level. 
 What determines with what force the water strikes the 
 paddles in project 64? 
 
 Pumps. In any city water-supply system in which 
 there is no large reservoir, the supply pipes are kept 
 filled and the pressure is maintained by a force pump; 
 and in the ordinary well the water is obtained by a 
 lift pump. 
 
 82. The lift pump is made readily as follows: Take 
 a length of good-sized glass tubing 12 inches long, a 
 
 parafinned mailing- tube, or a piece of bamboo. Cut a FlG - 15. Diagram 
 
 piece of wood 15 inches long and about as large of can with tubes to 
 
 illustrate water pres- 
 around as a lead pencil, for the plunger handle. At sure 
 
 one end of this fit a slice of cork for a plunger and 
 fasten it securely. The cork should fit the tube snugly. Punch a hole 
 through the cork and then with a small tack fasten a flap of leather so 
 that it will cover the hole on the handle side, the tack being placed at 
 one side of the hole. The cork should be free to slip up and down 
 rather tightly in the tube when worked by the lift handle. Put a 
 cork in the lower end of the tube, having first made a hole in it and 
 covered the hole with a leather flap held by a tack, the flap being on the 
 inner face of the cork. Put this corked end of the tube in the water and 
 work the plunger back and forth. If properly constructed the water rises 
 in the tube and is pumped out at the top. A tube made of rolled 
 paper may be set in the mailing tube or bamboo with glue, to serve as 
 a spout. 
 
 The force which impels the water up the tube is the pressure of the air. 
 
 83. Take a piece of glass tubing, fill it with water by simply laying it 
 down in a pan of water; put the finger over one end of the tube and raise 
 this out of the water, leaving the other end in the water. The water re- 
 mains up in the tube but drops the minute the finger is taken off the open 
 end. Why? 
 
 The leather sucker. 84. Cut a circular piece of leather (as from the 
 top of an old boot or shoe) 2 inches in diameter. With a heavy needle 
 
52 GUIDE IN PHYSICAL NATURE-STUDY 
 
 pass a 2-foot length of string through its center. Tie a knot in one end 
 of the string and draw the knot up to the leather. Soak the leather in water 
 for some time. Apply the leather, knot side down, closely to a smooth 
 surface, like that of glass, and pull on the string. The disk should adhere 
 vigorously, resisting quite a strong pull before it detaches from the surface. 
 Why? 
 
 An experiment. Try this experiment and explain what happens: 
 
 85. Pass a i -foot length of glass tubing through a rubber cork that 
 will fit into the mouth of a flask. Draw out the end of the tube projecting 
 from the small end of the cork in the flame, so that it is a fine tube. Break 
 off the excess of glass tubing. Put a tablespoonful of ;water into the flask. 
 Let the water in the flask boil for a minute, then insert the cork. Handling 
 the flask with tongs, turn it upside down and stick the free end of the glass 
 tube into a vessel full of cold water. 
 
 To make a squirt gun. 86. Fit a cork into one end of a good-sized 
 glass tube or length of bamboo, but before inserting it file or cut a groove 
 on one side. Make a plunger, as was done for the pump, except that there 
 will be no valve in this. Put the head of the plunger into the free end of 
 the tube or length of bamboo, drive it down nearly to the cork, put the 
 corked end under water, draw the plunger back slowly, lift the corked 
 end above the water, and drive the plunger rapidly down. This squirt 
 gun illustrates the principle of the force pump. 
 
 The force pump. As the stream of water comes from the force pump 
 into the faucets in the house, or from the hose nozzle connected to the 
 fire engine, the stream is a steady stream and not a succession of spurts. 
 This change is brought about by the addition of an air chamber, which 
 has an inlet and an outlet. The water coming in, in a succession of spurts, 
 crowds up against the cushion of elastic air, the pressure of which sends 
 the water out in a steady stream. 87. Replace the cork in the squirt 
 gun with one having two holes, one for intake, one for outlet. Put short 
 lengths of glass tubing in each so that the ends are flush with the small 
 end of the cork. Attach a leather valve over the intake tube so that it 
 will let water in but not out. Attach a rubber tube to the intake pipe 
 and let its free end set in a glass of water. Fit a cork with two holes into 
 a 4-ounce wide-mouthed bottle. Put short lengths of glass tubing into the 
 cork, their ends flush with the inner end of the cork. Put a valve over 
 one so that it will let water in. Connect this one by a short length of 
 rubber tubing to the outlet of the squirt gun, now to be used as a force 
 pump. Connect a short rubber tube to the outlet of the small bottle and 
 put a pipette glass into the other end of this rubber tube. Then operate 
 the pump and a steady stream will issue from the pipette "nozzle." 
 
THE HOT-AIR BALLOON AND SOME EXPERIMENTS 53 
 
 Why lead sinks but cork floats. 88. Cut a piece of plasticine or 
 putty into the shape of a rectangular solid i by i by 5 centimeters, or 
 hammer a piece of lead into this shape. Tie a string about it so that it 
 hangs with its long axis vertical. Then let it down into a glass cylinder 
 graduated to 100 c.c. or more tha't is all filled with water up to the 50 c.c. 
 mark. When the block of plasticine is under water what is the level of 
 
 the water in the cylinder? The water has risen c.c. 
 
 What is the volume of the plasticine block? c.c. A solid 
 
 body then when immersed in water displaces volume 
 
 of water. 
 
 89. Tie a small glass cylinder or bottle to a spring scale or set it on 
 a balance. Note how much it weighs in grams. Pour into it 10 c.c. of 
 
 water. Weigh again. The water weighs how much? grams. 
 
 One cubic centimeter of water weighs grams. Fasten the 
 
 string to which the plasticine block is tied to the hook of the spring scale. 
 
 What does the block weigh? Let it down into the water. 
 
 When it is in water it weighs grams. When immersed in water 
 
 it loses grams of its air weight. But this is the weight of the 
 
 water Since water pressure at 
 
 a given level is equal in all directions, the pressure on the opposite vertical 
 faces of the quadrangular block must be equal, for they are identical in 
 area and in position point for point. But the upward pressure on the bottom 
 of the block will not be equal to the downward pressure on the top of the 
 
 block, though their areas are equal, but it will be by the 
 
 weight of a column of water, which is the size of block sustained by the 
 scales. 
 
 90. Cut a cube 2 centimeters on each edge from a good-sized cork or block 
 of wood and weigh it. Then let it float in water and mark the level to which 
 it sinks in the water. Measure the depth to which it sinks and calculate (or 
 measure) the volume of water it displaces when floating. The weight of this 
 
 water the weight of the cork or in other words the 
 
 upward pressure on the lower surface of the cork cube is 
 
 than that on the upper surface by an amount 
 
 Why does a boat float even when made of iron, which so readily sinks? 
 How much of a load can you put into a boat without danger of its sinking? 
 Archimedes' problem. 91. Squeeze the block of plasticine used above 
 out of shape so that it is no longer rectangular but is irregular in shape. 
 Again immerse it in the 50 c.c. of water in the graduate. How much 
 water does it displace? How could you find the volume of a key? Find 
 out how many times heavier than water it is. Archimedes was once given 
 
54 GUIDE IN PHYSICAL NATURE-STUDY 
 
 a problem to work out on an examination and if he flunked he was told 
 by the king that he would lose his head! Some motivation! What was 
 his problem and how did he solve it? If you wear a plain gold ring can you 
 tell if it is pure gold? (First find out from a book how many times pure 
 gold is heavier than water.) 
 
 Why the balloon rises. The hot-air balloon goes up for the same 
 reason that the cork floats. It floats in air. The fluid in which it is immersed 
 is a gas instead of a liquid. It will be well to have experience with some 
 characteristic gases. 
 
 To make chlorine gas. 92. Fit a cork into the mouth of a good-sized 
 test tube. With a rat-tail file punch and file out a hole through the center 
 of the cork so that it will take tightly one end of an 8-inch length of glass 
 tubing. (To cut glass tubing see p. 50.) 
 
 Bend the tubing into the shape of a hook, making a bend about two 
 inches from one end (see p. 50). 
 
 Put the short end of the tube through the cork. Put about a teaspoon- 
 ful of strong chlorhydric acid into the test tube and mix with it half as 
 much granular manganese dioxide, or you may use a heaping teaspoonful of 
 chloride of lime in place of these. Then put the cork with its tube into the 
 mouth of the test tube and hang the bend of the tube over the ring of a 
 ring stand or hold the test tube with a test-tube holder. Apply the flame 
 of the alcohol lamp or Bunsen burner to the lower end of the test tube. 
 As the material heats the yellowish chlorine gas is given off and passes 
 out through the tube. Put a bottle under the mouth of the tube. This 
 gas is heavier than air and sinks to the bottom of the bottle, forcing the 
 air out. Be careful not to inhale any quantity of the gas for it is irritating 
 and tends to choke you. It is this chlorine gas that was used in the early 
 "gas attacks" in the war. This gas is chosen for our experiment because 
 it is colored and can so readily be seen. 
 
 To make hydrogen. 93. Use the same sort of a test-tube generator 
 as was used above for the chlorine, but run the free end of the glass tube 
 through a cork that fits a wide-mouthed bottle of about 8-ounce capacity 
 so that the end of the tube will be close to the bottom of the bottle. Cut a 
 second hole in the cork of this large-mouthed bottle and run through it a 
 3-inch length of glass tubing. Put a short length of rubber tubing on this 
 glass tube and the other end of it on the stem of an ordinary clay pipe. 
 Fill the wide-mouthed bottle about half full of water. Fill the test tube 
 one-sixth full of granulated zinc. Cover this with water and then pour 
 enough chlorhydric acid in so that the hydrogen gas will begin to bubble up 
 freely. The hydrogen is colorless and odorless. .If the test tube is fitted 
 to the cork that carries the delivery tube the hydrogen will flow through 
 
THE HOT-AIR BALLOON AND SOME EXPERIMENTS 55 
 
 the latter into the water, will bubble up through the water, and will escape 
 out of the wide-mouthed bottle through the rubber tube and the clay 
 pipe. Have ready some soap suds, the sort that you would use to blow 
 bubbles. Dip the mouth of the pipe in the suds, then lift it so that the 
 bubbles may form at the mouth of the pipe. Shake the bubble off when 
 it is fairly large. If it does not shake from the mouth of the pipe, remove 
 the pipe, blow the bubble on the end of the rubber tube. The result will 
 tell you whether hydrogen is lighter or heavier than air. It is advisible 
 to keep flame away from the neighborhood of this experiment as hydrogen 
 forms an explosive mixture with air. 
 
 Heat expands things. We will need to make clear why the hot air 
 on the inside of the balloon is lighter than the surrounding air to under- 
 stand why the balloon goes up. 94. Cut a 1 2-inch length of small glass 
 tubing and run it through a perforated cork that just fits the mouth of 
 a small flask. Fill the flask one-fourth full of water and put the cork in so 
 that the water will rise a bit in the tube. Hold the flask in the hand or 
 heat it over the flame. What happens and what does this show? What 
 common instrument about the home or in the schoolroom illustrates 
 the same thing? You may demonstrate this in another interesting way. 
 95. Take a good-sized iron bolt that fits a nut. Heat the bolt and then try 
 to get the nut on. Can you tell how iron tires are put on wooden wheels so 
 that they will fir tightly? Now can you tell why the air in the balloon 
 was heated before the balloon was released? And why heating the air 
 made that inside of the balloon lighter than an equal volume outside of 
 the balloon? 
 
SOME COMMON APPLIANCES THAT OPERATE BY HEAT 
 
 Air currents. 96. Set a lighted candle or a Bunsen burner on the 
 table and then put a lamp chimney over it. Support the chimney on 
 blocks of wood or the ring of a ring stand. Bring a smoking joss stick 
 or a tightly rolled wisp of paper that is smoking near the base of the 
 chimney. Notice the direction taken by the smoke. Why does it move 
 thus? Draw a diagram of this apparatus, showing how the smoke moves. 
 Can you see how this principle applies to the heating of a house with a 
 hot-air furnace ? Suppose the region where you live were very hot, the sun 
 heating the land intensely. Suppose, further, that some nearby region 
 were protected from the sun's rays by clouds so that the area was not as 
 hot. What would happen? 
 
 Making ice. 97. Put a drop of chloroform or ether on the back of 
 your hand with a medicine dropper. What becomes of it immediately? 
 How does the spot on your hand feel? 98. Put some water in a small tin 
 pan or evaparating dish and heat it. Keep the bulb of a thermometer that 
 registers at least 212 F. in the water as it heats. When the water boils 
 what does the thermometer register? As you apply more heat does the 
 temperature of the water continue to rise? Why? 
 
 99. Take a 3-inch square piece of clean sheet zinc. Lay a piece of sheet 
 copper on a drop of water placed on the zinc. Drop ether or chloroform 
 on the copper and blow on it. In a few moments the water between the 
 two is frozen. Why? 
 
 100. Put a piece of ice in a tin pan or evaporating dish and apply heat 
 to it. As it melts put the thermometer bulb in the water that forms. 
 Note what the thermometer registers. Continue to heat. Does the tem- 
 perature of the water rise? Why? Could you determine where the 32- 
 point and the 2i2-point should go on a thermometer if you were making 
 one? 
 
 To make a cloud. 101. Fit a rubber cork with two holes in it to the 
 mouth of a large flask of at least 2 -liter capacity or to a large bottle. Insert 
 one long straight glass tube through the cork so that it will run within an 
 inch of the bottom of the flask and project above the cork i inch, and a 
 short one through the other hole so that it will project i inch on both sides 
 of the cork. Equip another flask or bottle of the same size in the same way. 
 Connect the two flasks with a 3-foot length of rubber tubing, the ends of 
 which slip on the protruding ends of the short tubes in the two bottles. 
 
 56 
 
SOME COMMON APPLIANCES OPERATED BY HEAT 57 
 
 Put a compression clamp on this tube and close it. Slip short lengths of 
 rubber tubing to the outer ends of the two long tubes and have compression 
 clamps ready to close these. 
 
 Fill one flask five-sixths full of water, and after putting the cork in 
 tightly set it mouth down in a large ring on a stand placed near the edge of 
 a table in strong light. We will designate this flask A the other one, B~ 
 Fill B one-third full of water, cork tightly, and hold it mouth down in the 
 left hand at about the level of A . Hold a smoking joss stick or wisp of 
 paper near the free end of the long glass tube of flask A and let a second 
 person open the compression clamp. Water runs from A to B and at the 
 same time smoke is drawn into the space above the water in A . Put the 
 compression clamps on the short rubber tubes on the flasks and close them, 
 removing the clamp on the long connecting tube. 
 
 Raise flask B as far as the rubber tube will permit. The pressure on 
 the air and its contained water vapor in A is increased. Lower B as far 
 as possible and look for a "cloud" as a slight haze over the water in flask A. 
 The smoke was drawn into A so that its particles might act as condensa- 
 tion nuclei for the vapor. Do you see why decreasing the pressure on the 
 air and vapor in A produces condensation to form the cloud? 
 
 Why the ice-cream freezer freezes. 102. Chop about a pound of ice 
 up into pieces as big as peas. Mix some coarse salt with this and put 
 the mixture in a tumbler. Set the tumbler on a few drops of water on a 
 piece of glass. Put a thermometer bulb in the salt and ice mixture. Note 
 at intervals what it registers. Probably the tumbler will freeze to the 
 glass on which it sets in a short time. What happens gradually to the ice? 
 When salt stands in the salt shaker at home it cakes and is hard to get out. 
 Does this happen most quickly in moist or dry weather? Why? Pile a 
 half-teaspoonful of salt on a piece of ice. What happens? What did we 
 find above was needed to make ice melt? Now can you tell why the cream 
 freezes in the freezer? 
 
 Why do you have a wooden or woven wire handle on the poker 
 or stove lifter? 103. Cut a piece of No. 18 copper wire 8 inches long 
 and one of iron wire of the same size and the same length. Twist them 
 together at one end so as to form a V. Fix a little ball of paraffin or bees- 
 wax on each wire halfway from the point of the V to the end. Hold the 
 point of the V in the flame, the arms horizontal, with the wax balls down. 
 Continue heating until both balls fall off. What do you learn? 104. Try 
 the same experiment with two similar wires of copper or iron, one coarse 
 and one fine. Hold a 4-inch length of iron rod in the hand and an equal 
 length of glass rod, of the same size in the other hand. Hold the other ends 
 together in the flame until one or the other is distinctly hot at the end 
 
58 GUIDE IN PHYSICAL NATURE-STUDY 
 
 that you are "holding. What do you learn? Is dry wood a good or a poor 
 conductor of heat? 
 
 Why put a storm sash on a window? 105. Hold the bulb of a thermom- 
 eter 6 inches to one side of the flame of the Bunsen burner or the stove 
 for a minute and see what rise the mercury makes in that time. Take 
 two old photograph plates that have been cleaned, or similar pieces of 
 glass, and tie them together with a couple of strips of wood between to 
 separate them J inch. Interpose these glass plates, held vertically be- 
 tween the flame and the bulb of the thermometer again held 6 inches 
 to one side of the flame. .How much does the mercury rise now in one 
 minute. 106. Light a candle and with a concave mirror focus the light 
 from the flame on the bulb of a thermometer. Is the heat focused there 
 
 too? Evidently the surface of a mirror heat as 
 
 well as light. 107. Interpose an electric light bulb between the flame and 
 the bulb of the thermometer held 6 inches to one side of the flame. What 
 is the rise of the mercury now in one minute? Is there any air inside the 
 bulb? 108. To find out, break the tip of the bulb off while holding it 
 under water. This can readily be done if a scratch is filed part way across 
 the base of the tip and then the tip is twisted off with pliers. 
 
 The icy-hot bottle. 109. Examine a thermos bottle, a broken one if 
 possible. Note the space between the inside and outside walls of the glass 
 jacket. This is a more or less complete vacuum in good makes of bottles. 
 Can you tell why? Why are the glass walls of the jacket mirrored? 
 
 To make a tireless cooker. no. Procure one or two aluminum or 
 tin pails, the size you want to use in the cooker, say, four quarts. Take 
 a wooden box in which the pail or pails may be set and leave 6 inches 
 between them and as much space between the pail and the outside of the 
 box all around. Cut a if -inch strip from the top edge of the box and fasten 
 this with brads or small nails to the cover as a rim all around it. Line the 
 bottom of the box with asbestos board. Put J-inch strips across 
 each end of the bottom. Set on these a false bottom of J-inch stuff, 
 covered both sides with asbestos board. Set the pails 6 inches apart on a 
 |-inch board that is as long as the box is inside and with a pencil draw a 
 mark on the board around the bottom of the pail, thus making a circle 
 about f-inch larger than the pail all around. Tack cleats across the ends 
 of the box i inch below the upper edge, and on these lay the board out of 
 which the holes have been cut. Fit additional boards on either side of it 
 to make an inside cover, the holes about in the midline lengthwise. Lay the 
 circular boards on the bottom of the box, their centers directly under the 
 centers of the holes, and fasten them in place. Line the box with asbestos 
 board, covering also the bottom of the cover except the circular 
 
SOME COMMON APPLIANCES OPERATED BY HEAT 59 
 
 holes. Cut a strip of asbestos board long enough and wide enough to make 
 a cylinder of double thickness that will fit about the circular block on the 
 bottom of the box and extend up through the circular holes in the inside 
 cover flush with its top. Tack these onto the circular boards. Fill the 
 space between them and the asbestos-lined sides of the box with chopped 
 straw or excelsior. Put the inside cover in place and tack the asbestos 
 cylinders to the inside of the holes. Line the cover of the box with asbestos 
 board and tack a piece as large as the cover to the bottom of the rim all 
 around so that there will be an air space between it and the asbestos lining 
 of the cover. Hinge the cover to the box. Set the pails in the asbestos 
 cylinders and the cooker is ready to use. Castors may be put on it to 
 facilitate moving it about. Why are so many air spaces provided in the 
 construction? Why pack it with chopped straw? Would straw be better 
 than excelsior or the reverse, and why? Which would be the warmer, 
 tightly woven or loosely woven clothing, weight for weight? Why are 
 bed quilts lined with a cotton batting? Would wool batting be any better? 
 Why? 
 
 Heating the house. When holding the thermometer bulb beside the 
 flame in the experiment above, the heat went to the bulb directly through 
 the air, and such a process is called heating by radiation. When you held 
 the glass and iron rods in the flame, the heat came to your fingers by con- 
 duction. In the experiment with the flame in the lamp chimney we have 
 seen how the heated air rises and the cooler air comes in to take its. place, 
 as indicated by the movement of the smoke. In holding your hand above 
 the chimney it is warmed by the heat conducted to it as the particles of 
 air bump against it. But the moving air currents are called "convection 
 currents," and the hand is so warmed by convection and conduction. These 
 convection currents can easily be rendered visible as water is heated. 
 in. Set a good-sized beaker of cold water on a ring stand or other support 
 and put the flame of the alcohol lamp below it so that the tip of the flame 
 is below the middle of the beaker's bottom. Dust in some finely powdered 
 carmine or some starch and see how the powder rises over the flame, moves 
 up to near the top of the water, then to one side and down again. When 
 you stand in front of an open fireplace by what process are you warmed? 
 What process of heat transfer is involved in warming yourself by a hot-air 
 furnace? By a hot- water system? 112. Draw a diagram of a hot-air furnace 
 in a house, showing the course of the pipes. 113. Construct a model of a 
 hot-water system for heating a house. (Optional.) 
 
 What is fire. 114. Examine a 6-inch strip of magnesium ribbon or 
 wire. Note that it is a metal, fairly tough, lustrous, and elastic. Weigh 
 it as accurately as possible (see p. 97). Hold one end of the piece in a pair 
 
60 GUIDE IN PHYSICAL NATURE-STUDY 
 
 of forceps and light the other end with a match. Hold the burning metal 
 over a piece of dark paper to catch the product. Weigh this stuff accu- 
 rately together with any unburned ribbon still held in the forceps. Examine 
 this, rubbing it between the thumb and fingers. In what ways is it different 
 from the original metal? Evidently something has been going on that 
 completely changes the nature of the substance involved. This is a chemical 
 change. You know that air is usually necessary for a fire. When you 
 want the fire in a stove or furnace to burn more briskly you do what? 
 But we may readily show that not all the gases of the air are involved 
 when something burns. 115. Crumple up a sheet of paper in your hand. 
 Fk>3,t it on a saucer nearly full of water. Light it and when it is burning 
 well set an empty tumbler down over it, into the water, and let the mouth 
 rest on the saucer. What happens? Can you tell why? What fractional 
 part of the tumbler is filled with w,ater? Evidently only a part of the 
 
 air is used up in the burning, and this is about per cent of the volume 
 
 of air. (Why is this estimate not accurate?) The gas that is usually 
 involved in burning or combustion is oxygen. Which was heavier, the 
 magnesium strip or the product produced by burning it, and why? 
 (Answer this after the next experiments are completed.) 
 
 To make oxygen. 116. Make a bend in each end of a 1 5-inch length 
 of glass tubing, about ij inches from the end. Let each bent portion 
 stand at an angle with the long portion of the tube that is distinctly less 
 than a right angle, and have the bent ends stick out on opposite sides of 
 the long portion. Fit one end of this delivery tube through a cork that 
 fits the mouth of a good-sized test tube. Put a teaspoonful of pulverized 
 potassium chlorate mixed with half as much manganese dioxide into the 
 test tube. Hang this on a ring stand so that the flame can be applied to 
 its lower end. Let the other end of the delivery tube lie on the bottom of 
 a fairly deep pan, its open end pointing up. Fill this pan nearly full of 
 water. Sink a wide-mouthed 8-ounce bottle in this water so that it will 
 fill full. Then lift it up, keeping the mouth below water, and support it 
 in position with the mouth over the end of the delivery tube. Heat the 
 mixture in the test tube. The air will bubble out first. Move the end of 
 the delivery tube so that this can escape. Oxygen gas will bubble out, 
 shortly, in a steady stream. Catch this in the bottle. Fill three bottles. 
 Cover the mouths with small glass plates; and lift them out of the water, 
 setting them right side up on the table. 117. Light a splinter of wood 
 and when burning well blow out the flame, leaving a glowing ember on 
 the end. Slide the glass cover of one bottle to one side and stick the splinter 
 in. What happens, and why? 118. Take a J-inch piece of soft-cored 
 electric-light carbon and dig out one end so as to make a depression. Fasten 
 
SOME COMMON APPLIANCES OPERATED BY HEAT 6 1 
 
 this piece on a wire to serve as a handle in letting the carbon down into 
 another jar of oxygen. Put a bit of sulphur as large as a half-pea in the 
 depression of this "spoon," ignite it and lower the "spoon" into the jar 
 of gas. What happens? 
 
 119. Unravel slightly one end of a 6-inch length of woven iron wire 
 picture cord. Fasten a bit of wood, like a piece of broken match, in the 
 ravelings. Light the wood and when it is burning well stick it into the 
 third jar of oxygen. What happens, and why? 
 
 Spontaneous combustion. What do you have to do to an ordinary 
 match to start it burning? Rub your hand briskly over your coat sleeve 
 or any rough cloth for a minute. What is noticeable? How did the Indians 
 start a fire? 120. Let some member of the class make the Indians' fire 
 stick and try to produce fire with it. Some substances take fire at ordinary 
 temperatures. Phosphorus is one such. 121. Take a small piece of 
 this out of the fluid in which it is kept in a bottle, using a forceps with which 
 to handle it, and lay it in an evaporating dish on the table. In a few minutes 
 it begins to smoke perceptibly and promptly bursts into flame. The igni- 
 tion point is below ordinary room temperature. The ignition point of 
 wood is relatively high so that the bit that is to be a match is dipped into 
 a substance that has an ignition point low enough to be attained by brief 
 friction. The ignition point of sulphur is low enough so that it may be 
 ignited with a match. It burns much more freely in an atmosphere of pure 
 
 oxygen. The greater the supply of oxygen the 
 
 combustion occurs. The ignition point of iron is so high that it will not 
 burn in ordinary air at all readily but does burn in an atmosphere of oxygen. 
 
 When the sulphur burned in the atmosphere of oxygen dense fumes 
 filled the bottle. When magnesium was burned in air a new substance 
 was formed. The chemist tells us that when the temperature is sufficiently 
 high to start up the action the tiny particles of sulphur unite with the 
 tiny particles of oxygen and thus form a new substance, a combination of 
 sulphur and oxygen known as an oxide of sulphur. This constitutes the 
 dense fumes in the bottle. Thus the magnesium and oxygen unite and 
 form an oxide of magnesium. Iron and sulphur and magnesium and 
 oxygen are called elements because they cannot be broken up ordinarily into 
 simpler substances. But the potassium chlorate used in making oxygen is a 
 compound, for we could get oxygen from it and still have a residue left. 
 Thus when the hydrogen was made to fill our soap bubbles the granulated 
 zinc shoved the hydrogen out of its combination with chlorine gas of the 
 chlorhydric acid (HC1) and took its place, making chloride of zinc. 
 
 We think then of a chunk of potassium chlorate as a thing which can 
 be subdivided into smaller bits of potassium chlorate and then into smaller 
 
62 GUIDE IN PHYSICAL NATURE-STUDY 
 
 and smaller. Finally we think of a little bit smaller than we can see that 
 cannot be broken apart and still be potassium chlorate. This is what the 
 physicist calls a molecule. Chlorhydric acid may be separated into hydro- 
 gen and chlorine; these still smaller units which unite to make a molecule 
 of chlorhydric acid are atoms, and in this case one atom of hydrogen unites 
 with one of chlorine (HC1). 
 
 Such a union is not always a one-and-one affair, for atoms seem to 
 have hands or bonds or lines of force by which they take hold of other 
 atoms. Some atoms have two, others four, some only one. Thus oxygen 
 has two, hydrogen only one. When hydrogen burns the substance formed 
 is H 2 O or water. Sulphur has four. When it burns the substance formed 
 is SO 2 . Chemists have devised a sort of shorthand for writing out these 
 reactions and indicate the elements by the initial letter of their English 
 or sometimes their Latin names. In case two or more elements begin with 
 the same letter, it is necessary to use in such cases two letters from the 
 name; thus C is carbon; Cl, chlorine; N is nitrogen; Na, sodium (Latin, 
 natrium). Thus when sulphur burns the reaction is written: 
 
 the crinkled line over the latter symbol showing that it is a gas. 
 
 = ZnCl 2 +2H. 
 
 The burning candle. 122. Light a candle and observe (i) that the 
 solid material of the candle is changed to a liquid; (2) that this liquid is 
 conducted up the wick of the candle; (3) that it is changing to a bluish 
 substance at the center of the flame; (4) as this burns it forms the outer 
 part of the flame. Lay a piece of white paper on the flame and hold it 
 just long enough for it to scorch a bit without burning. What do you 
 learn from examining the scorch on the paper? 123. Hold a short length 
 of quite small glass tubing with one end in the bluish part of the flame 
 and the other end above and to one side of the flame. The purpose is to 
 conduct some of this blue material through the tubing. Can you light it 
 as it comes out of the upper end of the tube? Here evidently the solid 
 material of the candle is first changed to ..................... , then to ................... , 
 
 and when burned it goes off into the air as gas. Set a piece of candle in 
 the bottom of a wide-mouthed bottle. Light it with a long splinter and 
 cork the mouth of the bottle. What happens, and why? 
 
 124. Put a piece of slacked lime as large as a bean into a tumbler of 
 water. Let it stand for one hour, stirring it occasionally, then let it stand 
 
SOME COMMON APPLIANCES OPERATED BY HEAT 63 
 
 to settle until the water is clear. Pour off the clear water into a tumbler. 
 125. Pour half of this into the bottle with the candle. Uncork the latter 
 as little as possible to accomplish this. Shake it up and then note the 
 color of the limewater. This is a commonly used test for one of the gases 
 resulting from the burning of carbon, namely, carbon dioxide. 
 
 126. Blow through a length of glass tube, the end of which is dipped 
 into the remainder of the limewater. What do you learn? 
 
 Gunpowder. Sometimes the volume of gas formed when solid sub- 
 stances burn is very great. 127. Mix one part of sulphur, one of powdered 
 charcoal, three of potassium chlorate. Put as much of this as will go on 
 a penny on a piece of iron. Touch a match to it. The potassium chlorate 
 is mixed with the sulphur and charcoal to furnish an abundant supply of 
 oxygen so that the charcoal and sulphur can burn very freely, forming a 
 great volume of gas. This substance that we have made is really gunpowder. 
 If set off in a confined space the gases formed will break out, their pres- 
 sure is so great. 
 
 Making coal gas. 128. Break up a small piece of soft coal (or pine 
 wood) into bits and fill the bowl of an ordinary clay pipe, such as children 
 use for blowing soap bubbles, two- thirds full. Then plug the opening of 
 the bowl with a piece of clay or with plaster of Paris mixed with water to 
 the consistency of putty. If the latter is used, let it stand for a few minutes 
 to harden in the pipe. Heat the bowl of the pipe over the flame of the 
 Bunsen burner or alcohol flame. At first, water vapor will pour out of the 
 opening in the stem of the pipe; soon, however, gas will be delivered. 
 Light this and note that it burns with a flame much like a candle flame. 
 Soft coal contains much carbon and some hydrogen. As these substances 
 burn, what would be the products of combustion ? After the gas is all 
 driven off, take out the clay or plaster plug and examine the residue in 
 the pipe. What is it? 
 
 Gas burns ordinarily with a yellow flame because the air is not thor- 
 oughly mixed with the gas and some of the unburned carbon freed from 
 the gas glows in the heat. If air is mixed with the gas before lighting the 
 mixture then the combustion is much more complete and the flame is much 
 hotter, hence the mixer on the gas burner that produces the blue flame. 
 129. Turn the collar on the Bunsen burner to see the effect and explain 
 the result. Introduce an old saucer into the flame both when it is blue 
 and when it is yellow. What deposits on the saucer? 
 
 The gas engine. The gas generated above burns steadily in the open 
 air. If, however, gas and air are mixed in a confined space before the gas 
 is ignited, the combustion takes place instantly, quantities of hot gas 
 are formed, and the result is an explosion. Advantage is taken of this 
 
64 GUIDE IN PHYSICAL NATURE-STUDY 
 
 in the gas engine, in which the force of the explosion is used to furnish 
 motive power. This may be readily illustrated as follows. 130. Make a 
 hole in the side of a small tin coffee or tea pot near the bottom, through 
 which may be run the metal tube of the Bunsen burner. On the opposite 
 side, halfway up, punch another hole as large as a pencil. Insert the 
 Bunsen burner in the lower hole. Tie a piece of clock spring to the handle 
 so that it will press lightly on the cover to keep it closed. Turn on the 
 gas and hold a candle flame or match beside the small hole, halfway up 
 the side. Successive explosions blow the cover up, but the spring closes 
 it each time. 
 
 Toy gas engines are commonly sold as children's toys. 131. Operate 
 one. These are single-cylinder engines; therefore the wheel goes around 
 with a rather jerky motion. The automobile gas engine has several cylin- 
 ders, the explosions occurring in them in succession, so that power is applied 
 to the crank at such frequent intervals as to produce a steady motion. 
 The mixture of gas (vaporized gasoline) and air is ignited by an electric 
 spark. Write to some automobile concern for a catalogue that will illustrate 
 their engine. Insert it on the opposite page, or else draw your own diagram 
 of such an engine. 
 
 Steam engines. In the steam engine the piston is driven back and 
 forth by the expansive force of steam under pressure, operating on the 
 piston head. It is necessary that there be some device to cut off the inlet 
 of steam at one end of the cylinder when the piston head has been driven 
 as far as possible, and to let in the steam at the opposite end to drive the 
 piston head back again. Furthermore, there must also be some way of 
 letting the steam out from the end of the cylinder toward which the piston 
 head is moving. 
 
 See a toy steam engine work. Examine the model of the working 
 parts of an engine or see the paper model in Nelson's Encyclopedia article 
 "Steam Engine." 132. Make a cardboard model with movable parts to 
 illustrate the method of operation of the piston in the cylinder, the 
 eccentric cut-off and the exhaust valves. 
 
 A glass model may be made and operated by air blown into it as follows : 
 
 133. Select a 6-inch length of large glass tubing an inch or so in 
 diameter, or use an 8-dram, wide-mouthed homeopathic vial. Bore four 
 holes in the side of the tube or vial, two on one side, two on the other, 
 setting them about i inch from the ends. The hole may be bored by using 
 the tip of a round file or drill kept wet with camphor gum dissolved in 
 turpentine. Pulverize the camphor gum coarsely and put it into the 
 turpentine, letting it stand for several hours before using. Two of these 
 holes will be inlets for the air and two will be outlets for the exhaust. 
 
SOME COMMON APPLIANCES OPERATED BY HEAT 65 
 
 Steam chest. Cut glass so as to make a small box, the inside dimensions 
 of which will be as wide as the outside diameter of the tube or vial, and 
 nearly as long as the vial. File out the ends of the box in a curve to fit 
 the curve of the tube or vial, keeping the file wet with the camphor solution. 
 Fasten the box together with glass or china cement. Let this harden for 
 twenty-four hours. Then reinforce all corners of the box with strips of 
 surgeon's adhesive tape. Cut from a piece of bamboo fishing-pole of about 
 the same diameter as the vial two strips an inch shorter than the distance 
 between the holes bored in the tube or vial. These will serve as the sliding 
 valves to open and close these holes. Bevel their upper edges. Bevel the 
 under edges of four narrower strips of the same length as the inside of the 
 box and glue these latter to the outer surface of the tube or bottle so that 
 they will hold the wider strips between them when these latter strips are 
 laid on the surface of the tube or vial between the holes. These strips 
 should be held loosely, so as to allow back and forth movement. 
 
 Piston. Fit a slice of cork or a short section of a spool to the end of 
 a wooden piston rod, the spool or cork being of sufficient size to move 
 back and forth in the bottle, which it must fit fairly snugly. Cut a groove 
 with a round file in the edge of the cork or wooden piston head and bind 
 with string so as to make the contact between the inside of the bottle 
 and the piston head fairly air-tight. The wooden piston rod should be 
 slightly longer than the bottle. If a tube has been used, cork both ends 
 with a thin cork so that the holes bored in the tube or vial will not be 
 covered. Bore a hole in the center of one of these just large enough to 
 allow the round piston rod to slip through. 
 
 Fasten a block of wood about ij inches square and J inch thick by 
 one side to one end of a board that is i foot long and about 3 inches wide. 
 Cut a V-shaped notch down to the middle of this block on its upper edge. 
 The ends of the V should be close to the corners of the block. Fasten 
 the tube or vial about its midpoint to this block, setting it in the V, with 
 two of the holes down and two up. In line with the center of the tube 
 or vial toward the other end of the board set up a block on which may be 
 mounted vertically a wheel of thin wood, its diameter in the plane of the 
 long axis of the vial. Attach a driving rod to this wheel ij inches from 
 its center and connect the other end of the driving rod with the piston 
 that protrudes from the cork in one end of the tube or vial. 
 
 Devise eccentric rods that will run from the wheel or its axis to the 
 sliding valves that cover and uncover the holes. Think out how these 
 sliding valves are going to work before you make your attachment, so as 
 to have them work at proper intervals. File out the front end of the glass 
 box a bit to make room for the rod that attaches to the sliding valve. 
 
66 GUIDE IN PHYSICAL NATURE-STUDY 
 
 Bore a hole in the top of the glass box large enough to admit a small glass 
 tube. Cement in an inch length of glass tubing, the end of it flush with 
 the inside of the box. Through this tube air will be blown into the steam 
 box. Cement the box to the top of the vial and reinforce the joint with 
 surgeon's tape. The engine should be ready to operate now by blowing 
 through the glass tube, to which a length of rubber tube may be attached 
 for convenience. Since the apparatus is made of glass it is easy to see the 
 working of all parts. 
 
MAGNETIC AND ELECTRIC TOYS 
 
 The compass. 134. Take a compass in hand and note how it is 
 made, and if the needle assumes a fixed position when at rest. 135. Take 
 a couple of bar magnets and note how they behave with reference to each 
 other. Present an end of one magnet to an end of the other; try the opposite 
 end. Repeat the operation several times until you can state a law that 
 governs the behavior of the magnets with reference to each other. 
 136. Suspend a bar magnet so that it will hang freely by a very fine wire 
 or a strand of non-twisted fiber. Let it stand until it comes to rest. What 
 position does it assume? 137. Present the end of a bar magnet to the 
 compass needle and note what happens. Try the other end. What did 
 you make when you hung the bar magnet on the fine wire? How would 
 you state the law governing the movement of the compass needle when 
 influenced by the bar magnet? When the bar magnet is suspended, what 
 influences its position, determining the direction it assumes when quiet? 
 What, then, would you call the earth? 
 
 To make a magnet out of a bar of soft iron. 138. Dip a bar magnet 
 into iron filings. What happens? Present the end of a bar magnet to the 
 head of a nail. What happens? Present the tip of this nail to the head of 
 a second nail. Try touching the tip of the second nail to the head of a third 
 nail. 139. Take a knitting needle and rub one end of it vigorously on one 
 end of a magnet, the other end of the needle on the other end of the magnet. 
 Dip one end of the knitting needle into iron filings. What happens, and 
 what does this show? 140. Take a piece of soft iron, like an ordinary bolt; 
 hold it parallel to the earth's axis and hit it repeatedly with a hammer. 
 Can you get any evidence that it is magnetized? (Think of what will be 
 the most delicate test for this.) Summarize the methods by which magnets 
 are made. Can you suggest a reasonable explanation of what occurs in 
 the soft-iron bar to change it to a magnet? 
 
 Lines of magnetic force. 141. Put a bar magnet under a piece of 
 stiff card that is sufficiently large to cover the magnet; sprinkle fine iron 
 filings on the surface of the card and tap the card gently so that the iron 
 filings will have a chance to arrange themselves under the influence of the 
 magnet. 142. After you have learned how to accomplish this fasten a 
 piece of blueprint paper on a thin drawing board; lay the drawing board 
 on the bar magnet and tap the board gently until the iron filings are well 
 arranged. Put the drawing board with the blueprint paper on it in strong 
 
 67 
 
68 GUIDE IN PHYSICAL NATURE-STUDY 
 
 sunlight and let it stand until the paper begins to assume a bronzed tint. 
 Remove the iron filings and at once put the blueprint paper in a large dish 
 of water and let it wash in running water for ten minutes. Then take it 
 out and spread it on the table or hang it up to dry. 
 
 The mysterious pith balls. 143. Fasten two little balls of elder pith 
 each on a fine strand of silk. Hang them so they will be side by side and 
 free to move. Rub a glass tube with a piece of silk and bring it near the 
 balls. What happens? After the balls have touched the glass tubing, 
 how do they behave with reference to each other? Again rub the glass 
 with the silk, touch the surface of the glass to the pith balls, and then rub 
 a stick of sealing wax with the silk and bring it near to the balls. What 
 happens? Bring the surface of the silk used in rubbing the sealing wax 
 near to the balls. What happens? Try rubbing the glass and the sealing 
 wax with flannel, and touch the pith balls with the glass. Then bring the 
 sealing wax, also rubbed with flannel, near them. Continue the experi- 
 ment until you can state the law that governs the phenomenon. Test out 
 your law to see if you can always tell what will happen when the balls 
 are brought near to a surface that has been rubbed with the silk or the 
 flannel. What conclusion would you draw from these experiments regard- 
 ing electricity? 
 
 A more delicate test. 144. Run a piece of naked copper wire through 
 the cork of a small bottle so that it will stick down halfway in the bottle, 
 with 3 or 4 inches of wire above the cork outside of the bottle. Make a 
 right-angled bend J inch from the end of the wire, inside the bottle, and 
 hang on the bent portion a strip of thin tin foil 2 inches long, suspending 
 it from about its midpoint. The halves of the strip will then lie face to 
 face. Bend the free end of the wire above the cork so as to make a little 
 ball of wire at the end. Rub the glass rod with the silk and bring the 
 surface of the rod close to the ball on the end of the wire. What happens? 
 Touch the wire ball with the glass rod; then bring the rubbed surface of 
 the silk close to the wire ballr Try rubbing the glass with silk, touch the 
 ball, then rub the sealing wax with flannel and bring it near the ball. This 
 piece of apparatus is known as an "electroscope." How would you use it? 
 
 Dancing dolls. 145. Cut out of tissue paper some little dolls, f inch 
 long. Lay them on the table and support between the leaves of a couple 
 of books a piece of window glass of good size above the dolls and about 
 i inch from the table. Rub the upper surface of the glass with the silk- 
 What happens? Can you explain it. 
 
 The electrophorus. 146. Fasten an old phonograph record to the 
 underside of the. bottom of a tin pie plate. This may be done thus: Make 
 three V-shaped cuts in the tin plate near the margin with the point of the V 
 
MAGNETIC AND ELECTRIC TOYS 69 
 
 out. Bend these points up over the edge of the record so as to hold it in 
 place. Set the tin, rim down, on the table and rub the face of the record with 
 silk. Test both the surface of the record and of the silk with the electro- 
 scope. What is your conclusion? Again rub the record with the silk and 
 present your knuckle to the edge of the record. A slight shock may be felt 
 and if the air is dry a small spark may be drawn from the record. 
 
 To make lightning. Frictional electricity may be accumulated until 
 quite a strong charge is obtained by means of the Ley den jar. 147. To 
 construct this take a wide-mouthed 8-ounce bottle and cover its sides and 
 bottom inside and out with tin foil, pasted on. Pass an 1 8-inch length of 
 naked copper wire through the cork, leaving 4 inches protruding from the 
 top. Roll up 3 inches of this to make a little ball. Bend the wire below 
 the cork so that it will be in contact with the tin-foil lining when the cork 
 is in the mouth of the bottle. 
 
 148. Rub the electrophorus with the silk and then, holding the 
 Leyden jar in the hand, present its knob to the edge of the record on the 
 electrophorus. The latter will discharge into the Leyden jar, possibly 
 showing a spark. Repeat this a number of times. Why does the charge 
 in the jar get stronger constantly, and why does an equally strong charge 
 of the opposite sort develop on the outside of the jar? Strip the insulation 
 from 8 inches of one end of a 1 5-inch insulated copper wire and from i 
 inch at the other end. Bend the 8 inches of naked wire about the tin 
 foil on the outside of the jar and, holding the wire by the insulated portion, 
 bring the other end close to the knob on the jar. What happens, and why? 
 Why call this lightning? 
 
 The frictional electrical machine usually consists of a revolving glass 
 disk against which brushes rub to generate the electricity. Other metal 
 brushes take off the positive and negative electricity to two Leyden jars. 
 When quite a charge has accumulated, the knobs of the two jars are brought 
 close enough together to permit the discharge of a zigzag spark. 149. Such 
 a machine may be built by the pupils, using an old, large-sized phonograph 
 record in place of the glass disk, and homemade Leyden jars. The details 
 of construction may be learned from descriptions and figures in any book 
 on physics. (Optional.) 
 
 To make a simple battery. -150. Take a strip i by 3 inches each of 
 sheet copper and sheet zinc. Punch a hole with a nail near one end of 
 each and fasten in the naked end of a 6-inch length of insulated copper 
 wire, in one strip, of an 1 8-inch length in the other. Twist it in tightly so 
 as to make intimate contact of the wire and the sheet metal, or, better 
 still, solder it in. (A cheap soldering set with directions can be obtained 
 from any hardware house.) Fill a tumbler two-thirds full of water and 
 
70 GUIDE IN PHYSICAL NATURE-STUDY 
 
 add two tablespoonfuls of chlorhydric acid (or twice as much vinegar). 
 Hang the metal strips over the opposite sides of the tumbler so that they 
 are below the surface of the acidulated water. Hydrogen gas promptly 
 begins to discharge from one metal strip. If not add more acid. Bring 
 the ends of the wires together and note if there is any spark visible. Hold 
 the ends between the moistened tips of thumb and finger and note if you 
 feel any electric current. 
 
 From which metal plate is the hydrogen given off most freely when 
 the tips of the wires are in contact? Do some of the bubbles move from 
 one plate to the other in the acidulated water? If so, from which to which? 
 
 The chemistry of the reaction. -We have already noted how elements 
 combine to produce new substances (see p. 61). The metal or positive 
 element usually combines with the non-metal or negative element to form 
 a salt. Thus the zinc and the chlorine combine in this case, the zinc re- 
 placing the hydrogen, which is forced out of the chlorhydric acid (HC1) , and 
 ZnCl 2 is formed. The chemical equation showing the reaction is 
 Zn+2HCl=ZnCl 2 -h2H. 
 
 Hydrogen is a substance whose atoms have each a single bond or 
 line of attraction by which it is held to other atoms, or, as the chemist 
 says, it is monovalent. Zinc is bivalent. Chlorine is monovalent. To 
 write chemical equations one must know the valency of the elements. 
 He must also know the formulas for the acids that enter into a reaction. 
 If we had used sulphuric acid (H 2 SO 4 ) instead of chlorhydric the substance 
 formed would have been zinc sulphate, ZnSO 4 , instead of zinc chloride. 
 The acid radical, SO 4 , is known to have a valence of two because it combines 
 with two atoms of H, each with a valence of one. Acids are named accord- 
 ing to the amount of oxygen present. 
 
 The hydro- acids, like hydrochloric or chlorhydric, have no oxygen. 
 What is the name of HBr, HI, H 2 S? Knowing the -ic acid, like HC1O 3 , 
 chloric acid, you can always give the formulas of others of the same series, 
 
 for the per ic acid, like HC1O 4 , perchloric acid, has one more atom of 
 
 O than the -ic acid; the -ous acid, like HC1O 2 , or chlorous acid, has one 
 
 less atom of O, and the hypo ous acid, like HC1O, or hypochlorous 
 
 acid, has two less than the -ic acid. 
 
 The salts formed from the acids are readily named: 
 
 Hydr- acids give -ide salts. NaCl is sodium chloride, 
 -ous acids give -ite salts. NaClO 2 is sodium chlorite, 
 -ic acids give -ate salts. NaClO 3 is sodium chlorate. 
 
 per ic acids give per ate salts. NaClO 4 is sodium perchlorate. 
 
 hypo ous acids give hypo ite salts. NaCIO is sodium hypochlorite. 
 
 Name ZnCl 2 , ZnSO 4 , ZnSO 3 , ZnSO 2 , ZnSO 5 . 
 
MAGNETIC AND ELECTRIC TOYS 71 
 
 Movement of the electrons. We conceive of the atom as a sort of solar 
 system. It has a central positively charged nucleus around which revolve 
 particles of negative electricity or electrons. Some substances tend to lose 
 one or more of these electrons, in which condition they can hold more nega- 
 tive electricity and so manifest an attraction for it, and are said to be 
 positive. Others take on extra negative particles and so attract the posi- 
 tive substances. The number of electrons lost or gained is indicated in 
 terms of valence (see p. 70). Thus if the positive nucleus of the atom of 
 some substance holds two less electrons than it has positive charges, that 
 substance is said to be positive and to have a valence of two. In the 
 violent chemical action going on in the battery electrons are set free. They 
 pass to the zinc plate, up the wire, and back to the solution by the copper 
 plate. The zinc plate is usually designated the negative electrode and the 
 copper plate the positive electrode. Furthermore it has become customary 
 to regard the current as flowing outside the cell from the positive to the 
 negative electrode, though the electrons move in the opposite direction. 
 
 Why the simple battery stops working. The simple battery made above 
 soon ceased to give a current. The copper strip becomes covered with 
 hydrogen bubbles that are bad conductors of electricity. Then, too, 
 impurities in the common sheet zinc or copper set up local currents between 
 the impurity and the pure metal. These difficulties are avoided by using 
 purer strips of metal, by surfacing the zinc with mercury, and by using 
 other solutions than the sample acid, solutions which contain an excess of 
 oxygen that unites with the liberated hydrogen and so prevents its accumu- 
 lation on the copper or other negative plate. 
 
 The gravity cell is made as follows: 151. Attach insulated wires to 
 the zinc and copper strips as before. Lay the copper strip on the bottom 
 of the tumbler and throw on it a heaping teaspoonful of copper sulphate 
 crystals. Fill the tumbler nearly full of water and add a few drops of 
 sulphuric acid. Suspend the zinc strip in the upper part of the water. 
 The sulphuric acid acts upon the zinc, making zinc sulphate, which dis- 
 solves. The zinc sulphate solution is light and remains in the top of the 
 tumbler above the heavy copper sulphate solution. The liberated hydrogen 
 moves toward the copper plate, but before reaching it drives out the copper 
 of the copper sulphate, the copper depositing on the copper plate. The 
 zinc and copper sulphate waste away and must be renewed occasionally; 
 the zinc sulphate increases and deposits as crystals, which must be removed. 
 
 Another type of battery uses potassium bichromate, K a Cr 2 O 7 , to take up 
 the hydrogen. 152. Make enough strong solution of potassium bichromate 
 to nearly fill a tumbler. Add about a half-teaspoonful of strong sul- 
 phuric acid. Fasten insulated wires, bare at one end, to a rod of zinc 
 
72 GUIDE IN PHYSICAL NATURE-STUDY 
 
 or zinc strip and a piece of electric-light carbon. Immerse these in the 
 solution and note the current. The sulphuric acid attacks the zinc. The 
 liberated H starts toward the carbon but on the way unites with some of 
 the O of the potassium bichromate solution, reducing the bichromate to 
 a chromate. 
 
 The dry cell. 153. Pull an old worn-out dry cell to pieces. The 
 black powdery substance inside is largely carbon and manganese peroxide, 
 which was originally mixed with ammonium chloride. What are the metals 
 in the battery? 154. Make a dry battery for yourself. 
 
 To detect an electric current and determine the direction of its flow 
 one may make a simple form of the galvanoscope. 155. Set a compass 
 on the table and bring a wire through which a current is running over the 
 needle and parallel to it. What happens to the needle? Turn the wire 
 about so that the current is flowing over the needle in the opposite direc- 
 tion. How is the needle affected? Try the wire in both positions under 
 the compass needle. Make a statement in writing on the opposite page 
 indicating the relation of the behavior of the needle to the direction of the 
 flow of the current. 156. When you are riding in a street car take a 
 compass along to see if its needle is deflected by the current passing along 
 the trolley wire overhead. 
 
 157. Wrap insulated wire a dozen times about some cylindrical object, 
 like a quart fruit jar, so as to make a circular coil of the wire, leaving free 
 ends to attach to the battery. Cut a strip of wood wide enough for the 
 compass to stand on and as long as the diameter of the coil. Fasten this strip 
 into the coil, tying the coil to its ends, the face of the strip at right angles 
 to the plane of the coil. Connect the free ends of the wires to a battery and 
 place the compass on the middle of the wood strip. Is the needle deflected 
 more vigorously than before? Reverse the direction of the flow of the 
 current through the coil. How does the needle behave? Write out a 
 statement to cover the relation of the needle's behavior to the direction of 
 the current's flow in the coil. 
 
 Electroplating. 158. Fasten a wire to a strip of copper, as was done 
 in making the simple battery (p. 69), and also fasten a wire to a 3-inch 
 length of old electric-light carbon by winding it tightly about one end. 
 Hang these in a tumbler two-thirds full of diluted sulphuric acid. This 
 again makes a battery. Test its current with the galvanoscope. Connect 
 the wires so that a current will flow. The acid acts rapidly on the copper, 
 not at all on the carbon. Which is now the positive and which the nega- 
 tive electrode? In what direction is the electric current moving in the 
 wires connecting the electrodes ? In what direction is it moving in the 
 solution in the tumbler ? Let the current run for some time and then note 
 
MAGNETIC AND ELECTRIC TOYS 73 
 
 the deposit on the carbon. What is it? Evidently the electric current 
 passing through the solution is capable of carrying the metal from one 
 point and depositing it at another. Advantage is taken of this in 
 electroplating. 
 
 159. Fasten a strip of copper and an iron nail each on a length of copper 
 wire. Suspend them in a tumbler containing a strong solution of copper 
 sulphate. Connect the wires to the poles of the battery so that the current 
 will flow in the solutipn from the copper-plate to the iron nail. In time the 
 nail will be copper-plated. Use two pieces of electric-light carbon in 
 place of the copper strip and iron nail in the experiment. Does the copper- 
 plating go on as before ? If a silver salt in solution instead of the copper 
 sulphate solution were used in the experiment with the carbons, what 
 would be the effect ? How would one replate a spoon the silver on which 
 was wearing off ? 
 
 To make an electromagnet. 160. Wind an insulated copper wire 
 (not too fine) around an iron spike or bolt a few times. Attach the ends 
 of the wire to the poles of the battery so that a current will flow through it. 
 See if the bolt will pick up iron filings. Which end of the spike is the N 
 end of the magnet? (Devise a way to find out.) Unfasten the ends of 
 the wire on the battery and reverse them so that the one formerly attached 
 to the positive pole is now attached to the negative pole. Is the same end 
 of the spike the north end now? What is the effect of many turns of wire 
 on the bolt instead of few ? 
 
 . To make a telegraph instrument. -161. Cut two blocks of J- to f- 
 inch-thick wood 3 inches wide, making one 6 inches long, the other 3 inches. 
 Nail the shorter one on one end of the larger so that it stands upright when 
 the longer one is laid flat on the table. Cut a J-inch-wide strip of springy 
 sheet metal 3 inches long. To one end tack a slice of cork or a small block 
 of wood. Lay the strip, cork up, on the midline of the upper surface of 
 the long block, the base end 2 inches from the upright block. Tack down 
 the base end and bend the strip so that the cork end is J-inch above the 
 wood strip. Set a tack part way in the wood under the cork end of 
 the metal strip so that when the strip is pressed down it will rest on the 
 head of the tack. 
 
 Wrap a copper wire about the upper two- thirds of a 3-inch wire nail 
 many times, leaving the free ends of the wire i foot or so long. Drive the 
 nail into the baseboard close up to one edge of the upright. Another nail 
 is to be fastened horizontally, its head just over the head of the upright 
 nail. Fasten the sharp end of this nail into a loop of string tacked to the 
 upright. Hold the head just off of the upright nail by a small rubber band 
 also tacked to the upright. 
 
74 GUIDE IN PHYSICAL NATURE-STUDY 
 
 Fasten one naked end of the wire that is wound about the upright nail 
 to the tacked-down end of the metal strip, the other end to one pole of the 
 battery. Connect the other pole of the battery by a wire to the tack under 
 the cork end of the metal strip. As the "key" is pressed down on the tack 
 the "sounder" should click. Why? If it does not work at first, adjust 
 it so that it will. 
 
 162. Work with a second person who also has made such an instru- 
 ment and change the wiring so that by the addition of a "switch" on each 
 instrument, which switch you will devise and apply, the sounder of one 
 instrument will sound when the key on the other is operated, and vice 
 versa. 
 
 163. Set up a pair of commercial telegraph intruments, if these are 
 available, and operate them. Look up the Morse alphabet code and try 
 sending a message. 
 
 Some common electric appliances. 164. Examine the electric bell to 
 see how it works. Connect it up with a battery to see it operate. Follow 
 the course of the current to see how the clapper is made to strike the bell. 
 How is the current broken so that the clapper springs back? Draw a 
 diagram and write an explanation to accompany it. 
 
 165. Examine the electric buzzer and connect it up with a battery to 
 see how it operates. 
 
 166. Examine a "knife switch" to see how it serves to "break" a 
 current when open, to "make" the current when it is closed. 
 
 Introduce the knife switch between the battery and the electric bell, 
 wiring properly so that bell will ring when the switch is closed. 
 
 167. Examine a push button to see how it operates to make or break 
 the current. Draw a diagram and write out an explanation of the way 
 the button operates. Connect up the push button with the battery and 
 bell (or buzzer) so that it will ring the bell when it is pressed. 
 
 To make an electric motor. 168. Cut a block of ^- to f-inch-thick 
 wood 3 inches wide and 4 inches long. This block will serve as the base. 
 Drive a wire nail about i\ inches long clear to the head through its center, 
 perpendicular to the face. At the midpoint on each side set up a 3-inch strip 
 of J-inch stuff about J inch wide, fastening the upright strips to the base by 
 means of brads so that they stand upon the same side of the base as the 
 wire nail. Bend ten or a dozen p-inch lengths of soft-iron wire or an iron rod 
 into U-shapes. Tie these U-shaped wires together at two or three points. 
 Then wind insulated copper wire many times around one end of the (J, 
 covering perhaps i inch from the end of the U. Leave the end of the in- 
 sulated wire free for a foot or more of length, so that it may be attached 
 as indicated below. Carry the insulated wire across to the other end of 
 
MAGNETIC AND ELECTRIC TOYS 75 
 
 the U, carrying it down the wooden upright under the base and up the 
 upright on the other side. Then wind it around the other end of the U, 
 making the turns in the reverse direction from those on the first winding. 
 Leave a foot of wire free again to make attachment. Take a cork about 
 an inch in diameter and punch a hole through the middle large enough to 
 receive a short length of glass tube. 
 
 Cut a 4-inch length of glass tube of sufficient size to slip on the upright 
 nail. Heat this at its midpoint in the Bunsen burner until it is soft. Then 
 pull the ends apart, heating the top of one of these pieces until it is rounded 
 off. Shove this rounded end of the glass tube into the big end of the cork 
 and let it go nearly through the cork. The open end of the tube is to be 
 slipped on the nail, the end of which is to be sharpened. This makes a 
 nearly frictionless bearing. Cut eight or ten 2-inch lengths of the soft- 
 iron wire (or one of iron rod) and bind them together by wrapping the insu- 
 lated copper wire around them many times. Leave the ends of the wire 
 sticking out about i inch. Fasten this coil with its wire core on the small 
 end of the cork so that its axis is at right angles to the glass tube. The 
 coil with its contained wire should be bound on so that it balances as nearly 
 as possible when the cork is on the nail. 
 
 The commutator. Cut two strips of sheet copper half as wide as the 
 cork is long and a little shorter than half the circumference of the cork at 
 its midpoint. Strip the insulation off from the ends of the copper wire of 
 the coil on the cork; bring these down, one on either side of the cork, and 
 place on top of each of them one of the strips of sheet copper bent to con- 
 form to the curve of the cork. With thread bound on close to the edge of 
 the copper strips fasten these latter on the cork so that together they 
 nearly encircle it. Their ends must be separated by a distinct space and 
 each must be in contact with only one of the wire ends. Cut two strips 
 of sheet copper about \ inch wide and if inches long. Tack one of these 
 on each of the uprights by one end. The other end should lie on the copper 
 strips on the cork. Fasten a 6-inch length of copper wire with the insulation 
 removed from each end to each of these copper strips at the point where 
 it is tacked to the upright. Twist together the other end of one of these 
 wires to the free end of the wire coming from the end of the U that lies on 
 the same side of the apparatus. Solder to this juncture of the two wires 
 one end of the wire that is to run to the switch or batteries furnishing the 
 current. 
 
 If the motor has been properly made it should run when the current 
 is sent through. It may need considerable current if the parts are not 
 nicely adjusted so as to avoid friction. This current may be taken from 
 an ordinary electric-light wire by unfastening the wires from the electric- 
 
76 GUIDE IN PHYSICAL NATURE-STUDY 
 
 light circuit and attaching them to a knife switch. For fear this current 
 may prove too strong and burn out some of the connections it is well to 
 introduce resistance. This may be done as follows: 
 
 Resistance. 169. Fill a beaker or large tumbler with water to which 
 eight or ten drops of hydrochloric acid are added. Fasten one wire from 
 the motor to the knife switch and let the other dip into the acidulated water 
 in the tumbler. Take a short length of insulated wire and remove the insu- 
 lation from an inch of each end. Fasten one end of the wire to the knife 
 switch and put the other end in the tumbler of acidulated water at the 
 opposite side from the wire that brings in the current. If enough current 
 does not flow to run the motor, add a little more acid and bring the wires 
 gradually nearer together until there is sufficient current. 
 
 * Examine a small dissectible model of the commercial motor to see how 
 it is wired and how it works. 
 
 To make a dynamo. 170. The motor made above may be altered to 
 serve as a dynamo. Break the connections between the wires running to 
 the U-shaped magnet and those running to the commutator. The former 
 are to be connected directly to the battery. Before this is done, however, 
 arrangements must be made to rotate the cork bearing its coil. Put a 
 small spool on the glass tube just below the cork, or use a thick slice of 
 cork the edge of which is grooved to take a string belt. Clamp the base- 
 board of the motor to the table or nail it to a board. Saw out a circular 
 board from f-inch stuff, making it 8 or 10 inches in diameter. Groove 
 its edge with a round file so that it will take the string belt. Bore a hole 
 in its center and fasten it by a nail horizontally to a block that may be 
 clamped to the table or nailed to the same board that the motor is on. 
 Set it near the motor so that a string or a leather shoe string may be tied 
 about its edge and about the spool or cork on the motor axle to serve as 
 a belt. Put a nail near the edge of this wood wheel for a handle so that the 
 wheel may be turned rapidly. This will make the coil on the cork of the 
 old motor whirl very rapidly. Connect up the wires to the U-shaped 
 magnet with a battery. Connect the wires from the commutator to the 
 galvanoscope. Turn the wheel to rotate the coil in the cork. The 
 galvanoscope will show a current if all connections are good. 
 
 The principle upon which the dynamo works may be readily illustrated 
 by the following experiments: 
 
 171. Roll a piece of paper 4 inches wide and 10 or 12 inches long so as 
 to make a paper tube 4 inches long and i inch in diameter. Wind insulated 
 copper wire (about No. 18 or finer) thirty or forty times around the paper 
 tube, thus making a wire coil on the outside of the tube. Connect the 
 ends of this wire with the galvanoscope, set a yard or so from the coil. 
 
MAGNETIC AND ELECTRIC TOYS 77 
 
 Watching the needle of the galvanoscope, thrust a bar magnet quickly 
 into the paper tube. Pull it out again. 'Reverse the magnet and thrust 
 in its other end. Try thrusting the magnet in the reverse end of the coil. 
 Record the results for each of these tests. This shows in general that 
 when the turns of a wire coil cut through the lines of force of a magnetic 
 field, a current is generated. Can you state the relation of the direction 
 of the current to the way in which the turns run in the coil? 
 
 172. Take a strip of paper 6 inches long and 2 inches wide. Make a 
 paper tube 2 inches long on your pencil. Remove the pencil and wind 
 upon the tube a coil of insulated wire, leaving ends 3 inches long. Stick 
 these ends through a large flat cork so that the coil stands above its upper 
 surface and parallel to it. Attach to the bare ends of the wires, close to 
 the bottom of the cork, strips of copper and zinc. Set the cork on the 
 surface of dilute sulphuric acid in a tumbler. A current should now be 
 flowing through the coil. Present the end of a bar magnet to one of the 
 coil ends. What happens? Try the other end of the magnet. What 
 position does the axis of the coil assume if allowed to stand for a few 
 moments undisturbed? State your conclusion. 
 
 Can you explain now how the dynamo above works, and can you 
 predict in what direction the current is flowing from it? 
 
 173. Examine a small commercial dynamo and follow the course of 
 the wiring. Can you explain how it works, and why? 
 
 To make an electric toaster. 174. Take a block of f-inch wood about 
 6 inches square and tack a 6-inch square of asbestos board to one face. 
 Cut two strips of the heavy asbestos board ij by 6 inches. Tack one of 
 these to each end of the board so that the 6-inch edge will stand up about 
 | inch above the asbestos board. Make j-inch-deep cuts every half-inch 
 on these edges. Take about 90 inches of No. 24 iron wire and, leaving 
 3 inches free at one end, insert the wire into the cut nearest the end of one 
 6-inch strip. Carry the wire to the corresponding cut on the strip at the 
 other end. Bend the wire and put it into the next cut at this end and 
 carry it back to the corresponding cut at the end where the wiring began. 
 Continue to weave the wire back and forth until all the cuts are filled. 
 Fasten insulated copper wires to the free ends to connect with the current 
 which is to heat this iron wire. Take 5^ feet of No. 18 iron wire and make 
 four turns of this wire around the board from end to end, spacing the 
 turns ij inches. These wires will rest on top of the asbestos strips, not 
 set in the cuts. They will be J inch above the wire that is to be heated and 
 on them the bread to be toasted will be laid. 
 
 Connect up the apparatus with the incandescent current, putting in 
 resistance as was done in case of the motor. The iron wires should heat 
 
78 GUIDE IN PHYSICAL NATURE-STUDY 
 
 red hot. The principle here used is the same as that applied in electric 
 heaters, electric irons, etc. 
 
 An experiment. 175. Make a coil of a dozen turns of No. 30 or 
 finer insulated copper wire around the bulb of a thermometer. Let the 
 current flow from a battery through the wire for one minute, noting the 
 rise of the mercury in that time. Use the same length of No. 18 wire and 
 make the same number of turns around the bulb. Connect with the same 
 battery and let the current run one minute. What is the rise in temperature 
 now? State your conclusion. 
 
 Resistance. An electric current in passing through a body meets 
 some resistance, somewhat as water passing through a pipe is retarded by 
 the friction on the sides of the pipe. (Remember that in the fountain we 
 made, p. 50, the water did not rise as high as its level in the funnel.) The 
 greater the resistance the more energy is used in overcoming it, and so is 
 transformed into heat. Why do we use iron wire in the toaster and why 
 does the experiment with the thermometer above give the results seen? 
 (Recall the experiments on heat conduction, p. 57.) 
 
 Pressure and rate of flow. Name some substances that you know to be 
 good electrical conductors, some that are non-conductors. In the latter the 
 
 is so high that practically no current flows through them. 
 
 Resistance is expressed in terms of ohms. The ohm is about the resistance 
 offered by 9 . 3 feet of No. 30 (American gauge) copper wire. To overcome 
 high resistance, high electric pressure must be used. Electric pressure is 
 expressed in terms of volts. Just as with liquids, the greater the pressure 
 the more the flow, so with electric currents, other things being equal. 
 The unit that measures the rate of flow is the ampere, and it is defined as 
 that amount of current which flowing through a standard solution of 
 silver nitrate (as in silver-plating) will deposit a specified amount of silver 
 (0.001118 grams) per second. The electric pressure or electromotive force 
 that will give a current of one ampere against a resistance of one ohm is 
 called a wit. 
 
 It is found that a current of one ampere working under a pressure of 
 one volt will do work equivalent to 1/746 of one horse-power. This unit 
 is known as the watt. Therefore, volts X amperes -4- 746 = horse-power. 
 
 The instrument used for measuring the amount of current flowing in a 
 wire is called an ammeter. It is built like the galvanoscope except that the 
 end of the compass needle moves over a graduated scale marked in amperes. 
 The voltage of the current is measured by a similar instrument, the -voltmeter. 
 In this the wire used is fine, so as to offer higher resistance. The greater 
 the voltage the more the current that flows, and so the more the needle is 
 deflected. Both instruments may be combined in one, the wltammeter . 
 
MAGNETIC AND ELECTRIC TOYS 79 
 
 Batteries may be set up either in series or parallel. In the former case 
 the positive element in one is connected with the negative element of the 
 next, and the wires bringing off the current connect with the remaining 
 positive pole and negative pole. When connected parallel, the wires from 
 all negative poles are twisted together, those from all positive poles are 
 similarly twisted together, and the current is taken from these bunches of 
 wires. 176. Connect up two batteries, first in series, secondly parallel, 
 and measure the amperage and voltage of the current obtained in each 
 case. Record the results. 
 
 Electric lights. -177. Connect up a small incandescent electric light 
 with a battery (or several batteries in series if necessary to light it). Why 
 is the filament in the light so small? What is the advantage of using a 
 nitrogen-filled bulb? Measure the voltage and amperage of the current 
 that is used to light the little incandescent light above. Then introduce 
 the voltammeter between the lighted bulb and the negative pole of the 
 battery. How do the voltage and amperage now compare with that of 
 the battery when the light is not in the circuit? Connect up two small 
 incandescent electric lights with the battery, first wiring them "in series," 
 then ' 'parallel." In which case do they burn most brightly? Introduce 
 the voltammeter as before in each case. Which sort of wiring uses up most 
 current? Which reduces the voltage most? 
 
 The arc light. 178. Sharpen two soft lead pencils. Cut away the wood 
 from each for a half-inch back from the point, thus laying bare the lead. 
 Twist an end of No. 18 copper wire tightly around the lead near the 
 wood on each pencil. Connect the other ends of the wires to the dynamo 
 (or to a series of batteries). Holding one pencil in each hand, bring the 
 points together and then separate them the least bit. You thus produce 
 a miniature arc light. What makes the light in this case? 
 
 Examine the arc light on the projection lantern. 179. With a pair of 
 forceps, the handles of which are covered with glass tubes or rubber, hold 
 a sliver of iron ore in the flame of the arc between the carbons. What 
 happens, and why? Could you "weld" two pieces of iron in the flame? 
 
 The induction coil. -This is a somewhat expensive bit of apparatus to 
 make, yet it is exceedingly interesting, for it is one of the essential pieces 
 in the wireless outfit and may be made to yield brilliant electric sparks 
 and vigorous electric shocks. 
 
 180. Obtain a pound spool of No. 36 insulated copper wire, all in one 
 piece, and a 4-ounce spool of No. 14. Cut a dozen or so lengths of large- 
 size soft-iron wire as long as the pound spool and tie them together in a 
 round bundle. Wind on this, in close-set turns, the No. 14 wire three 
 layers deep, leaving the ends of the wire sticking out a foot. Cover this 
 
8o GUIDE IN PHYSICAL NATURE-STUDY 
 
 coil with a layer of bicycle tape. This should make a roll about as large as 
 the core of the spool on which the No. 36 wire is wound. Saw off one end 
 of this spool as close to the wire as you can without cutting its insulation- 
 Finish trimming off the wood with a knife so that the wire can be slipped 
 off the spool and on the tape-wound coil made above. As this is done get 
 hold of the inner end of the fine wire and pull it out a foot to make connec- 
 tions. Cut off the other end of the spool and slip the two ends, their centers 
 cut out somewhat if necessary, on the ends of the coarse wire coil to keep 
 the fine wire in place as it was on the spool. 
 
 Mount the double coil on a base horizontally, carrying the ends of the 
 fine wire to two binding-posts set 6 inches apart on the baseboard, each 
 post with openings and screws for two connections. Set in one of these 
 openings on each post a coarse copper wire, its end tipped with a ball of 
 solder, the wires adjusted so that their balls are close together but not 
 quite in contact. 
 
 Rig a windlass somewhere on the baseboard, made of a spool, and set 
 at intervals a row of tacks in a line all around the spool, their heads sticking 
 up so that as the spool is rotated the tacks catch and lift one end of a springy 
 metal strip off the head of an upright nail. The other end of this strip is 
 fastened to the top of an upright post set near the windlass and one of the 
 coarse wires from the coil is connected to it. The other coarse wire runs to 
 one pole of the battery of two dry cells connected in series. The other pole 
 of the battery is connected to the wire nail, on the head of which rests the 
 metal strip. 
 
 As the windlass is turned the current sent through the primary coil of 
 coarse wire is constantly made and broken. The lines of magnetic force 
 appearing and disappearing constantly cut the secondary coil and induce 
 a current of high voltage which will send sparks between the terminals. 
 If your moistened finger tips are put on the binding-post of the secondary 
 coil you will receive quite a shock. 
 
 181. This coil can be made to break its own current. Devise and 
 apply a modification of the apparatus that will accomplish this. 
 
THE CAMERA, TELESCOPE, MAGIC LANTERN, AND SOME 
 EXPERIMENTS IN LIGHT 
 
 To measure the candle power of an electric light, the brightness of its 
 light is compared with that of the flame of a "standard" candle. Any 
 candle flame may be used to show the method, though the results will 
 not be accurate unless a "standard" candle is used. Two or three pre- 
 liminary experiments are necessary to show the principles involved. 
 
 Experiments. 182. Make a cut in the small end of each of two corks 
 perpendicular to the end. Set two similar cards, one in each cork, and make 
 a pinhole in the middle of each. Set them on the table i foot apart and 
 set up a candle so that when looking through the two holes you can see 
 the candle flame. Move one of the corks a little to one side. Why can 
 you no longer see the light of the flame? If the shades in a room are 
 drawn when the sunlight is on the windows and a small hole in one shade 
 admits a ray of light, the course of the beam of light may be seen as it 
 lights up floating dust particles. What sort of a path does it have? Why, 
 then, does an object throw a shadow? 
 
 183. Cut an inch-square piece of cardboard. Hold it 3 inches from 
 a candle flame or an electric light. Hold another large piece of card or 
 paper 6 inches from the light. How large is the shadow of the inch square? 
 Hold the larger card or paper 9 inches away. How large is the shadow 
 now? The light that is thrown on the one-inch square of card would, if 
 
 the card were not there, cover square inches of surface at twice the 
 
 distance of the card from the candle, square inches of surface at three 
 
 times the distance of the card from the candle. The intensity of the illu- 
 mination from any source of light varies, then, inversely as the square of 
 the from the 
 
 184. Set a nail vertically into a small block of wood. Stand this on 
 a white sheet of paper on the table. Light an electric light and set it 
 several feet from the nail so that the latter will cast a shadow on the white 
 paper. Light a candle and move it nearer to or farther from the nail 
 until the shadow it casts is just as dark as that cast by the electric light. 
 Measure the distance to the candle at this point in inches and the distance 
 to the electric light in inches. What is the candle power of the electric 
 light? 
 
 To make a candle burn in a glass of water. 185. Set a large clear 
 piece of window glass vertically on the table and support its edges. Set 
 
 81 
 
82 GUIDE IN PHYSICAL NATURE-STUDY 
 
 a box with one side open on the table, its open side in front of the glass. 
 Hang a black cloth back of the glass about as far as the open side of the 
 box is in front of the glass. Set a tumbler of water on the table just in 
 front of the black cloth and opposite the open box. Light a short length 
 of candle and set it in the middle of the bottom of the box. Looking down 
 over the top of the box against the glass plate, you may move the tumbler 
 of water until the candle appears burning in its center. This will seem 
 mysterious to any person who does not know how the apparatus is set up. 
 Explain the phenomenon yourself. Measure the distance to the glass 
 plate from the middle of the tumbler and the distance from the candle to 
 the glass plate. State the relative positions of an object and its mirror 
 image. 
 
 Some such arrangement as that in the foregoing experiment is some- 
 times used in the theater to produce the ghost in such plays as Hamlet. 
 The actor impersonating the ghost is strongly illuminated in a room over 
 or below the stage and opening toward it. The room is lined with black. 
 A large plate of glass near the front of the stage reflects the image to the 
 audience. The "ghost" can walk through tables and chairs on the stage, 
 just as the candle flame goes into the water. 
 
 The angle of reflection. 186. Set up a mirror on a sheet of white 
 paper on the table. Stand the nail on the block on the table. Look along 
 the surface of the table, your eye at its level, until your eye is in position 
 to see the nail in the mirror. Draw a line on the paper from the image 
 toward your eye, one from the image toward the nail, and one along the 
 front edge of the mirror. The angle made by the line from the object to 
 the mirror with the front of the mirror bears what relation to the angle 
 made by the line to your eye and the front of the mirror? Find out by 
 comparing these angles drawn on the paper, cutting one out and laying it 
 on the other. 
 
 Can you write thus? 187. Set a mirror up vertically on the table. 
 Lay a sheet of white paper in front of it. With a pencil in hand place 
 your hand on the paper. Then hold a card in your left hand in front of 
 your face so that you cannot see your hand but can see its reflection in the 
 mirror. Write: "I see the image of my hand," watching the formation 
 of the letters in the mirror. Why is it so hard to do? Who can learn to 
 do it in the shortest time? 
 
 Your image in a spoon. 188. Look into the bowl of a shiny silver 
 spoon and then turn it over and look on the back. Can you see why your 
 image is so misshaped? Draw a diagram to show why. You may use 
 the convex and concave mirrors furnished in the laboratory for this quite 
 as well as the spoon. 
 
THE CAMERA, TELESCOPE, MAGIC LANTERN 83 
 
 The engine headlight. 189. Hold a concave mirror in the sunlight 
 and see at what distance in front of the mirror the sun's rays are brought 
 to a point by the mirror. This is the focal point of the mirror. What is 
 the focal length of this concave mirror in inches? If a candle flame is set 
 at the focal point, how are the rays of light reflected? Try the experiment, 
 holding a piece of white paper up at a couple of feet from the mirror and 
 catching the light upon it. When the flame is moved nearer to the mirror, 
 what is the effect on the beam of light? Where is the light placed with 
 reference to the focus of the mirror in an engine or automobile headlight? 
 
 The magnifying mirror. -190. Hold a concave mirror nearer to your 
 eye than its focal length. Look at your eye in the mirror. Why does the 
 dentist use a concave mirror in his work? 
 
 The kaleidoscope. 191. Take two strips of mirror about i inch wide 
 and 6 or 8 inches long, or use two strips of glass, one side of each of whic^i 
 is covered with a strip of black paper pasted to the glass along the edges. 
 Cut a strip of dark cardboard or blackened wood as long as the^lass 
 strips and sufficiently wide so that when it is placed between tHe long 
 edges of the mirrors and their other long edges are in contact the 
 faces of the glass strips will make an angle of 30. Paste dark paper over 
 the outside of this so that it will be held together and form a triangular 
 tube. Cut two triangular pieces of glass of sufficient size to cover the 
 end of the triangular tube and place between them along their edges 
 some narrow strips of glass; fill the space between them, bounded by 
 this edging, with broken bits of colored glass. They should be small enough 
 to move around freely between the glasses. Bind these triangular glasses 
 together and fasten them to one end of the triangular tube over its opening, 
 pasting black paper over the end so that only the light going through the 
 opening in which the bits of colored glass are will enter the tube. Look 
 through the apparatus now, holding the end containing the, colored glass 
 toward the light. While looking, rotate it on its axis so that the bits of 
 glass will change their relative positions. Can you explain what you see? 
 
 Cameras. To make a pinhole camera. 192. Cut out one end of a 
 pasteboard box, like a shoe box. Cover the hole thus made with paraffin 
 paper or tracing paper, pasting it in place. With a pin make a small hole 
 in the center of the opposite end of the box. Set the box on the window 
 sill, pinhole end out; throw a dark cloth over the inner end of the box and 
 at the same time over your head. The image of the landscape will be seen 
 on the paraffin paper. (Draw a diagram to show why.) 
 
 193. Cut a piece of blueprint paper the size of the end of the box on 
 the inside, or use a photographic negative. Fasten either by means of 
 pins inside the box against the end that is covered with tracing paper, 
 
84 GUIDE IN PHYSICAL NATURE-STUDY 
 
 the sensitive side of paper or plate toward the pinhole. Blueprint paper 
 must be handled in dim light and the photographic negative must be put 
 in place in a dark room lighted by a red light (see below). The pinhole 
 camera may be set on the window sill on a bright day and left for a half- 
 hour if the blueprint paper is taken, for five minutes if the negative is 
 used. Then the blueprint paper may be washed, or the negative developed 
 (see below), and the image of the outdoor scene will appear. 
 
 The camera obscura. 194. A camera for sketching may be made by using 
 a larger wooden box with one side off. Set the box on the table in front 
 of the open window, the open side toward you. In the middle of the side 
 away from you, 8 inches or so from the top of the box, bore a small hole. 
 Fasten a mirror to the top of the box opposite this hole and a foot from it, 
 so that the light will be reflected down to the bottom of the box. Throw a 
 dark cloth over the open side of the box and put your head under the cloth. 
 Place a white paper on the bottom of the box. The image of the out-of- 
 door scene is thrown on this white paper and may be sketched in outline. 
 
 The lens camera. So little light comes in through the pinhole in the 
 camera above that it takes a very long exposure to affect the sensitive 
 plate. 195. If the hole is made larger, the image is blurred. (Show by 
 a diagram why this is so.) But if a lens is set in the opening a clear image 
 may be obtained, even with a wide opening. 
 
 To make a lens. 196. Smear a little vaseline on the edges of two 
 watch crystals. Be careful not to get the vaseline on the outside. Put 
 these under water and bring them together accurately, edge to edge. 
 Hold them firmly together with the left thumb and fingers and bring them 
 out of water. The vaseline prevents the water running out. Dry them 
 off, particularly the edges, and bind the edge of this "lens" with surgeons' 
 tape, seeing that it adheres closely so that the water will not escape. You 
 have thus a double convex lens. 
 
 Images formed by the lens. 197. Hold the lens up in the right hand 
 in front of a sheet of white paper tacked up in a darkened room, and in 
 the left hand hold a candle. Move the lens nearer to the candle or to 
 the paper, as may be necessary, to throw a clear image of the candle flame 
 on the paper screen. Note the size of the image. Measure the distance 
 from the paper to the lens and from the lens to the candle. Set the lens 
 twice as far from the screen and move the candle back and forth until the 
 image is clear again. Is the candle nearer to the lens or farther from it 
 than before? Repeat the experiment, setting the lens half as far from the 
 screen as in the first case. Is the image smaller or larger? 
 
 The nearer the object is to a convex lens, the the screen 
 
 must be from the lens to get the clear image and the the 
 
THE CAMERA, TELESCOPE, MAGIC LANTERN 85 
 
 image is. You will see then why, in the ordinary cameras, the lens is 
 mounted so that its distance to the sensitive plate may be altered in order 
 to focus the image sharply. 
 
 The lens as a burning glass. 198. Hold the lens in the sunlight so 
 that the light will shine through it. Focus the light in a tiny point on a 
 sheet of white paper. Not only is the light focused but the heat also, and 
 the paper may be set on fire. Measure the distance from the lens to the 
 paper when the point of light is as small as you can get it. This is the 
 focal length of the lens. 
 
 The camera. 199. Enlarge the pinhole in the pinhole camera so that 
 the lens can be set in the hole. Fasten it in with dark paper pasted around 
 the opening and on the lens. Make a wooden frame that fits snugly as 
 it stands up in the inside of the box. Remove the tracing paper from the 
 back of the box and fasten it to the front of the frame. Set the frame in 
 the box back of the lens, about as far from it as the focal length of the lens. 
 Set the camera on the window and cover the open end with the dark cloth, 
 covering your head also. Look on the paraffin paper for the image of the 
 objects out of doors. If the image is not clear, move the frame back and 
 forth until it is reasonably clear. Load the camera as before with a sensi- 
 tive plate, keeping the lens covered until the exposure is made. The 
 exposure now may be short, a second or two, to get a good negative. 
 
 Camera plates. 200. Examine a sensitive plate in the light. Take it 
 out of the box in the dark room (see below) and close the box before opening 
 the door. Note that one surface of the plate is covered with a gelatine 
 film in which are held certain substances sensitive to light. These are 
 salts of silver. When light acts on silver salts they often break down, 
 depositing grains of metallic silver that look black in the mass. 
 
 201. Take a crystal or two of silver nitrate and dissolve in a test tube 
 in a tablespoonf ul of hot water. Dip a piece of filter paper or white blotting 
 paper in this and place it in strong sunlight. The paper darkens as the silver 
 is deposited. 
 
 The dark room. -Sensitive plates and print papers must be handled 
 in a room lighted by red light that does not act at all rapidly on the sen- 
 sitive surface. 202. To make a safe dark-room light, a sheet of red 
 tissue paper, doubly thick, may be tied over the electric light, or a lighted 
 candle may be set in a shoe box, one side of which has been cut out and 
 the opening covered with red tissue paper. Punch holes near the bottom 
 and in the top of the box for ventilation and screen these also with red 
 paper. 
 
 To develop the plate. A plate exposed in a camera does not show the 
 image when removed, for the light has acted for so short a time that the 
 
86 GUIDE IN PHYSICAL NATURE-STUDY 
 
 process of disintegration of the silver salts has only just begun. It is 
 completed by "developing." 203. At some photo supply store buy a 
 package of hydrochinone developing powders (six for twenty-five cents), 
 and a half-pound of acid fixer. Dissolve the fixer in one quart of water 
 and put it in a pan in the dark room. Dissolve one of the powders in 
 4 ounces of water, dissolving the content of the blue paper first, then adding 
 that of the pink. Put this in a small pan or a soup plate in the dark room. 
 Remove the exposed sensitive plate from the camera in the dark room. 
 Handle it by its edges. Dip it in water, then put it in the developer, 
 sensitive side up, promptly wiping off its face with a bit of absorbent 
 cotton wet in the developer, and see that the whole face is covered 
 instantly with the developer. Rock the pan or plate so that the 
 developer will move about in the pan. The image should appear in a few 
 seconds. When it begins to show through on the back of the plate, take 
 the plate out of the developer and put it in the fixer, face up. Leave it in for 
 ten minutes, or until all the white has disappeared from it. Then wash it 
 in running water for thirty minutes or put it through a dozen changes of 
 water, leaving it in each for two or three minutes. Set it up on edge to dry. 
 
 The negative. This gives a negative, so called because all light areas 
 in the object before the camera are dark in the negative and all dark areas 
 are light. The negative is used to make the picture. 
 
 Printing. 204. In the dark room place a sheet of print paper like 
 "Cyko" or "Solio," of the same size as the negative with its sensitive 
 face against the film side of the negative. Cover the back of the paper 
 with a piece of cardboard or wood (or the back of the printing frame). 
 Expose the paper to the light by letting the light fall on the negative. At 
 6 feet from a sixteen-candle-power electric light an exposure of three to 
 six seconds is enough for a negative of ordinary density. The print is 
 developed like a plate, using 8 ounces of water for a package of developer, 
 and metol developer is better than hydrochinone for this. It is fixed in the 
 fixing bath, washed and dried as was the plate. 
 
 The good camera. 205. Hold a lens, such as we have made, up to 
 the light and look through it at some object, like the window. It will be 
 noticed that the image is more or less distorted, straight lines appearing 
 curved, and the image is surrounded by more or less of a halo of color. 
 These defects of a lens are in part overcome by using only the central 
 portion of the lens; hence a lens is usually "diaphragmed down" in a camera. 
 Examine a good camera to see its parts lens, diaphragm, bellows, rack- 
 and-pinion focusing adjustment, ground-glass back, plate holders, etc. 
 
 Refraction. 206. Put a coin in a cup or bowl which sets on the 
 table. Stand back from the table so that you can just see the coin on the 
 
THE CAMERA, TELESCOPE, MAGIC LANTERN 87 
 
 bottom over the edge of the bowl. Step back one step farther, until the 
 coin is no longer seen. Have someone pour water into the bowl slowly 
 so as not to disturb the coin. What happens? Evidently the ray of light 
 from the coin going over the edge of the bowl, a ray that would go over 
 your eye, is bent down by the water to your eye. 207. Hold a prism of 
 glass in your hand, the base of the triangle down and horizontal, the edge 
 up, and look at a lighted candle on the table. Trace the course of the ray 
 of light. Draw a diagram of it. As the ray enters the glass is it bent 
 toward or away from the line that is perpendicular to the surface at this 
 point? As the ray comes out of the glass or water, how is it bent with 
 reference to the perpendicular? It is this refraction of the light, passing 
 through a lens, that makes it form an image. 208. Diagram the forma- 
 tion of an image by a lens. 
 
 To make a telescope. 209. Wrap several thicknesses of stiff paper 
 blackened on one side, black face in, on the outside of a cylindrical stick 
 of wood and paste down the edges so as to make a paper tube, black inside, 
 when it is slipped off the stick of wood. Make another similar loose tube 
 on the outside of this so that they will telescope into each other. Fasten 
 one of the homemade lenses or a plane convex glass lens on the end of the 
 larger tube. This will be the objective of the telescope. Have this tube 
 about as long as the focal length of the lens used. Fasten another lens, 
 the eyepiece, on one end of the smaller tube and let this tube be two- 
 thirds as long as the longer one. Cut a circular hole of about f-inch dia- 
 meter in a piece of black paper and fasten this over the eyepiece so as to 
 cover all but its central portion. Slip the open end of the short tube into 
 the open end of the larger tube. Look through the eyepiece, shoving the 
 small tube in or out until you see the outdoor object. The image formed 
 by the objective is examined by the eye looking through the eyepiece. 
 The tubes are really unessential. You may hold two lenses, one in each 
 hand, and looking through both held in line with the eye change their 
 relative position so as to get the telescope effect. 
 
 Magnifier and microscope. -210. The homemade double convex lens 
 can be used as a simple magnifier. Try it. Must the object to be magni- 
 fied be nearer to the lens or farther from it than its focal length when it is 
 seen enlarged? 
 
 211. To make the compound microscope, proceed as in making the 
 telescope, only make the larger tube three tunes as long as the focal length 
 of the lens. The object to be seen must be an inch or so from the objective 
 and in strong light. Move the eyepiece up or down until the magnified 
 object is seen. 
 
88 GUIDE IN PHYSICAL NATURE-STUDY 
 
 To make the magic lantern. 212. Use the homemade camera for the 
 body of the lantern. Set it horizontally on the table. Fasten an electric 
 light inside the box so that it is about as far from the lens as the focal 
 length of the latter. This lens now serves as a condenser. With India 
 ink draw a picture on a piece of glass or on tracing paper. Fasten this up 
 in front of the condenser. Hold another homemade lens an inch or so in 
 front of the picture. Move a sheet of white paper, held a few feet in front 
 of the lens, nearer to and farther from the lens until the image of the picture 
 appears on the paper. A block of wood with a hole bored in it with a 
 large auger, opposite the condenser, may be set on the table to serve as a 
 slide carrier for magic-lantern slides. The objective lens may also be 
 mounted on a similar block and the magic lantern may be set up at any 
 time for use. Much better results can be obtained if well-ground glass 
 lenses are used in place of our homemade lenses, but the latter will show 
 the method of construction. 
 
 The rainbow. 213. Look through the prism at some well-lighted 
 object, like the window sill, and note that the rays of white light are 
 evidently broken up or dispersed into their component colors. It is this 
 dispersion of sunlight as it passes through the raindrops that produces 
 the rainbow. 214. Let a beam of light into a darkened room through a 
 slot in the shutter or in a board set below the curtain and set the prism 
 just inside the slot so that the beam of light passes through it. The band 
 of color will be seen on walls or ceiling. , 
 
 Mixing colors. The reverse of this is true, that colors may be blended 
 to produce new ones, even to produce white. Send for a sample book of 
 educational colored papers (Thomas Charles and Co., 2249 Calumet Ave., 
 Chicago). 215. Cut two circular pieces of paper from these samples, 
 one blue and one yellow. Slit each disk from its margin to its center. 
 Slip the edge of one of these cuts into the other and adjust the two disks 
 so that about half of each disk shows its color. Punch a hole in the middle 
 of the disks and slip them on the stem of the peg top (p. 43). Punch a 
 hole in the center of a slice of a small cork and slip this on the stem to hold 
 the papers in place. Spin the tip and note the color. Change the relative 
 amounts of color exposed, letting one blue disk show two-thirds and the 
 yellow one- third. Spin again and note the results. 216. Add a third disk 
 of white paper, exposing one- third of each disk, blue, yellow, and white. 
 What is the effect when the top is spun? 217. Try disks of white and 
 black paper, each half-exposed. Try disks of red and yellow, or red and 
 green. 218. Can you recombine by means of the top the rainbow colors 
 (violet, indigo, blue, green, yellow, orange, red) to make white? How 
 would the color top be useful in mixing paints? 
 
THE CAMERA, TELESCOPE, MAGIC LANTERN 89 
 
 Optical illusions. There are many interesting optical illusions that 
 show that you do not always see what you think you see. 219. Draw 
 two parallel lines i^ inches apart and 6 inches long. At intervals of a 
 half-inch on each line draw half -inch lines into the space between the lines, 
 these short lines all pointing one way and standing at an angle of 45 to 
 the parallel lines. Do the long lines still appear parallel? 
 
 220. Draw two inch squares near together, one of light lines, one of 
 heavy. Draw two half-inch squares inside the inch squares, their sides 
 separated from those of the larger squares by half-inch spaces. Make 
 the inner square of heavy lines in the larger square of light lines, and vice 
 versa. Connect each corner of the inner square to the adjacent corner of 
 the outer square. How do the resulting figures compare? 
 
 221. Draw two lines a few inches apart, one i inch long, the other 4^ 
 inches long. In the middle of each mark off by short cross-lines ^ inch. 
 Do the marked-off portions look equal? On the same paper several inches 
 apart draw two lines each 2 inches long. At the end of each line draw two 
 half-inch lines making a V, its point coincident with the end of the line. 
 Let the open ends of the V on one line be toward each other, on the other 
 away from each other. Do the two 2-inch lines appear now of equal 
 length? 
 
THE HOMEMADE ORCHESTRA 
 
 A ukelele. 222. Cut a 2-inch square hole in the middle of the cover 
 of a cigar box. Cut a strip of f-inch pine 2 inches wide and 18 inches 
 long. In one end of this saw out two slots the long way of the strip, each 
 f inch wide and 2 inches long and f inch from the edge of the strip. Through 
 the walls of each of these slots and at right angles to them bore J-inch 
 holes about i inch apart. Have those on one slot alternate with those on 
 the other. Cut out four round pegs i^ inches long with flat heads like 
 those on the violin, so that the pegs will fit these holes tightly. With an 
 awl make a hole in the middle of each peg. Nail the other end of this 
 long strip on the middle of one end of the cigar box, the face of the strip 
 flush with the top of the box. Fasten four wires, about Nos. 32, 28, 24, 
 1 8, by tacks to the end of the cigar box opposite the long strip to serve 
 as strings. Tack a piece of thin wood to serve as a bridge on the cover of 
 the box below the hole and parallel to its lower edge. Pass a string over 
 the bridge, making a little notch in the top edge of the bridge to hold it 
 and put the free end of the wire through the hole in a peg. Turn the peg so 
 as to wind the wire about it and tighten the string. Do the same for the 
 other strings. Tighten the strings so that they will sound do, mi, sol, do 
 on the scale. Can you play a tune? 
 
 Banjo. 223. Make a similar instrument, using a round cheese box in 
 place of the cigar box. A string band might easily be improvised if boxes 
 of various sizes are used to make the instruments and these are tuned so 
 as to be in harmony. The larger instruments could be tuned an octave or 
 two lower than the small ones. 
 
 Why some strings on the piano are long and coarse. 224. Fasten two 
 tacks 3 or 4 inches apart in one end of the table or in one end of a board 
 as long as the desk. Tie the ends of strings, one coarse and one fine, each 
 to one of these two tacks. Make two bridges and set one near each 
 end of the table or board so that the strings can pass over them. Hang 
 equal weights of a pound or two to each string. Pluck the strings so. that 
 they will sound a note. What do you learn? Double the weight- on each 
 string and pluck the strings again. What additional fact can you record? 
 Move the bridges closer together and then pluck the strings. Record the 
 
 results. The coarser the string, the the note it gives off. 
 
 The longer the string, the the note omitted. The greater the 
 
 tension of the string, the the note it gives. 
 
 90 
 
THE HOMEMADE ORCHESTRA 91 
 
 Why the violin has a box. 225. Set a large cigar box with a hole cut 
 in its lid under the strings on the table and put the bridges on its top, one 
 at either end, setting the two strings over them. Then pluck the strings. 
 How does the sound compare with that given off when the cigar box is 
 not used but the bridges are set at the same distance on the table top or 
 board? The thin wood of the box also is set in vibration as well as the 
 air in the 'box. 226. Roll up some stiff paper to make a flaring conical 
 trumpet. Talk into the small end. Why is the sound of your voice 
 so loud? 227. Hold your nose shut and then talk. You change the 
 character of the sound by cutting off certain resonance chambers. How 
 can you change the pitch of the note given off by a stretched string? The 
 intensity of the sound? The quality? 
 
 To make a whistle. 228". Cut an 8-inch length of good-sized bamboo 
 open at both ends. Fit a cork plunger at one end, on the end of a 
 stick, as if making a squirt gun (p. 52). Cut a transverse notch i inch 
 from the other end, a third of the way through the bamboo, the edge of 
 the notch toward the near end, inclined to the long axis of the bamboo 
 about 45, the other edge vertical to this long axis. Cut off the end of the 
 bamboo near the notch parallel to the adjacent edge of the notch, i.e., 
 at an angle of 45. Plug this end of the bamboo down to the notch with 
 a cork, cut off to conform to the inclination of the end. On the side of 
 the cork where the notch is, cut off a thin slice so as to make a slot through 
 which to blow. When blowing through this the whistle should operate 
 and the note may be changed by pushing in or drawing out the plunger. 
 This instrument may be added to the orchestra. 
 
 Sound due to vibrations set up by the sounding body. 229. Fold an 
 inch strip of light-weight paper in half so as to make a little rider. Drop 
 it on the middle of a stretched string that is emitting a sound. What 
 happens and what does it show? Set a bell to ringing and bring a pith ball 
 suspended by a fine string against its edge. What happens and why? 
 
 230. Draw the edge of a piece of stiff card, like a post card, held 
 between thumb and finger, over the teeth of a comb. Can you feel the 
 vibrations? Draw it over rapidly, then very rapidly. The more frequent 
 the vibrations, the the pitch of the note emitted. 
 
 In the whistle it is the column of air that is made to vibrate. The 
 
 shorter the vibrating column, the the pitch of the note. 
 
 From which pipes do the bass notes of the pipe organ come? 
 
 A rattler. -231. From the wood of a cigar box cut two strips 6 by ij 
 inches. Cut a block of f-inch stuff ij inches wide and J inch longer than 
 an empty spool. With brads fasten the two strips to the equally wide 
 ends of the block so that they are parallel to each other, the block between 
 
92 GUIDE IN PHYSICAL NATURE-STUDY 
 
 them. Cut another 6-inch strip just wide enough to fasten on the block 
 and the first two strips with brads, and so close one side of this long box, 
 the other side and one end of which are still open. Cut a piece of wood 
 about i inch square and 6 inches long to serve as a handle. Whittle down 
 2 inches at one end of this so that it will fit tightly into the hole of the 
 spool, but do not put the spool on yet. Cut deep notches in the ends of 
 the spool so as to make the ends toothed all around. Bore two holes 
 slightly larger than the hole in the spool, one in each of the ij-inch-wide 
 strips about f inch from the ends opposite the blocks. Place these holes 
 near enough to the uncovered side of the box so that when the round end 
 of the handle that carries the spool is put through them the teeth on the 
 spool ends will project above the edges of the adjacent strips. Put the 
 round end of the handle through one hole, then force it through the hole 
 in the spool far enough to stick through the second hole. Cut a strip of 
 real thin wood as a tongue, making it as wide as the spool and long enough 
 so that when one end is fastened by brads to the block the other will press 
 against the teeth of the spool. 
 
 While holding the handle in your hand rotate the hand so as to whirl 
 the box about the handle. The teeth on the spool lift the tongue and drop 
 it repeatedly with incessant clatter. If the piece of wood used for the 
 tongue is too stiff to spring up as the teeth lift it file or sandpaper the base 
 away near the attachment to the block until it is springy. This may not 
 be a very musical instrument to add to the orchestra, but it does show 
 well that sound is produced by the vibration of the sounding body, in this 
 case the tongue of the rattler. The box serves as a resonator to increase 
 the volume of sound. 
 
 The triangle. 232. Bend an i8-inch-long piece of J-inch round iron 
 or very heavy wire into the shape of an equilateral triangle, the ends of 
 the wire not quite touching. Hang this on a string by one angle and play 
 it by tapping it with a large nail. 
 
HOW TO MAKE THE PHONOGRAPH AND TELEPHONE 
 
 The phonograph. 233. In the making of a phonograph record a sharp 
 stylus borne on a thin disk at the small end of a receiver horn makes a series 
 of impressions in a spiral line on a rotating plastic plate as the disk is 
 caused to vibrate by the sound waves entering the horn when the per- 
 former sings or speaks into it. This wax plate is then used as a pattern to 
 mold hard-rubber plates, exact duplicates of itself, and these are the records. 
 When the sharp needle of the phonograph travels over the line of little 
 hills and valleys it causes the disk to which it is attached to vibrate and 
 reproduce the same succession of sound waves that caused the impression 
 on the original plate. 
 
 When one understands the principle in accord with which the phono- 
 graph works it is not difficult to make one that will operate fairly well. 
 Use a planed board 9 by 1 2 inches as the base. Draw a line down through 
 its center. One inch from one end of this line bore a hole large enough to 
 take a hardwood upright peg that will fit the hole of a spool, so that the 
 latter can revolve on the peg smoothly. Let the peg be long enough to 
 project slightly above the end of the spool when the lower end of the peg 
 is set securely in the hole in the baseboard. Sharpen off the top of the peg 
 to a blunt point. 
 
 The turntables. Cut a lo-inch square of J-inch board that is perfectly 
 flat and draw upon it the diagonals of the square so as to find its center. 
 At this point make a depression into which the upper end of the peg may 
 fit. Fasten the spool on this same side of the board, its hole directly over 
 the hole on the board. The square board on the spool will revolve on the 
 peg. On the top of this board at its center glue a short round peg, just 
 large enough to fit the hole in the record to be used. If it tends to slip, 
 the record may be fastened in place by thumb tacks placed so as to lap 
 over its edge. 
 
 Place the baseboard on the table in front of you so that the turntable 
 is at its distant end. Then at the left-hand corner near you draw a square 
 with i-inch sides, the corner of the board being one corner of the square. 
 By means of a nail driven into the corner of this square opposite the corner 
 of the baseboard fasten a wheel not exceeding 9 inches in diameter. This 
 may be a wheel taken from an old rubber- tired doll carriage or a cart, the 
 rubber tire removed so that the rim is grooved, or it may be a wheel cut 
 out of J-inch board, the edge grooved with a round file. Near the rim of 
 
 93 
 
94 GUIDE IN PHYSICAL NATURE-STUDY 
 
 this wheel fasten a handle so that it may be revolved horizontally. Tie a 
 heavy cord or long leather shoe lace about the rim of this wheel and the 
 spool under the turntable so that it will serve as a belt. 
 
 The vibrating disk and the arm that carries it. Take a small tin or glass 
 funnel the mouth of which is not over 2 inches in diameter. Cut a circular 
 piece of mica, split very thin, the same size as the mouth of the funnel and 
 glue its edge to the rim of the funnel's mouth all round. At the center 
 of this mica disk glue a small piece of cork large enough to hold the butt 
 end of the stylus, usually used on the phonograph, or the end of a machine 
 needle broken in half. 
 
 Cut a strip of J-inch pine i inch wide and 1 2 inches long. A half- 
 inch from one end bore a hole large enough to take the stem of the funnel; 
 at the other end, one to take a long brad. Two inches from the end where 
 the funnel goes cut the strip square across and refasten the cut-off portion 
 to the long part by a hinge set on the i -inch- wide side of both. Put a bit 
 of rubber tube or a rubber washer on the stem of the funnel close to the 
 flare. Set the stem of the funnel into the hole of the wood strip, its tip 
 protruding on the same side to which the hinge is affixed. Slip a 6-inch 
 length of rubber tubing on the stem of the funnel and push it down until 
 the end is pressed against the wood strip. 
 
 A piece of |-inch wood 2 inches wide is to be fastened as an upright to 
 the end of the baseboard, its edge ij inches from the corner opposite the 
 wheel. It must be sufficiently long so that when the arm bearing the funnel 
 is attached to its top by the long brad in a horizontal position the tip of 
 the stylus will rest on the record. After this upright and the arm are in 
 place an additional support for the arm is rigged so that the stylus may not 
 bear too heavily on the record. Bend a stiff wire into a 2-inch-wide U 
 with sides long enough to straddle the arm, the curve of the U several 
 inches above the arm. Shove the tips of the U down into holes bored in 
 the baseboard 2 inches apart. Dent the top of the U and fasten a loop 
 of string from the dent to the arm so as to hold it up and still leave it 
 free to swing from side to side. 
 
 The horn. Roll a piece of stiff paper into the form of a good-sized horn. 
 Glue it so that it will stay in shape. Glue into its small end a cork through 
 the center of which runs a short length of glass tubing. On this slip the 
 end of the rubber tube, which also attaches to the funnel. On the side of 
 the base fasten an upright on top of which is fixed a small hoop to hold 
 the horn. 
 
 When the record is placed on the turntable the tip of the stylus in its 
 outermost groove must be rotated very steadily by the wheel in the direction 
 opposite to that in which the hands of a clock move. The proper speed 
 
HOW TO MAKE THE PHONOGRAPH AND TELEPHONE 95 
 
 of rotation will have to be determined by trial until the reproduction 
 sounds natural. 
 
 Pan's pipes. 234. Cut glass tubing with about J-inch bore so as to 
 make eight pieces 3^, 3!, 4, 4j, 4!, 5}, sJ, and 6} inches long. Plug one 
 end of each with a cork plug J inch long set in flush with the end. Fasten 
 these pipes to a block of wood, their open ends at the "same level and far 
 enough apart so that you can blow across the end of each to produce a 
 note. They should give the successive notes of an octave. 
 
 The flute. 235. Take one joint of bamboo as long as is obtainable, 
 with one end closed, the other open. Near the closed end bore a hole on 
 one side about J inch in diameter. Blow across this to get a tone. Measure 
 the distance from this hole to the open end. Bore another hole on the same 
 side one-half of the distance from the mouth hole to the open end. Locate 
 the other holes in a row on the same side, nine-eighths of the distance from 
 the mouth hole to this central hole, five-fourths, four-thirds, three-halves, 
 five-thirds, fifteen-eighths, respectively. You now have another instrument 
 for the orchestra. To play it hold the thumbs on the side of the flute opposite 
 the holes, the first, second, and third fingers of the left hand on the hole 
 nearest the mouth hole and the next two holes, the fingers of the right 
 hand on the other four holes. Blow across the mouth hole, lifting first one 
 finger, then another, off the holes. The notes rendered should be those of 
 the scale if you have located the holes accurately. 
 
 The echo. Sound may be reflected from a surface like a hillside or 
 the wall of a room as light is reflected from a mirror. Such reflection 
 out of door gives the echo. 236. Try reflecting sound and focusing it 
 with a mirror like that used on bracket lamps. Hold a watch a few inches 
 in front of the mirror that is held so as to reflect the sound toward a second 
 person. Hold a candle beside the watch and focus the light on the person's 
 ear. The sound should also be focused and the person will hear the watch 
 r tick with concentrated loudness. Hold your hands up behind your ears, 
 curving the hands so as to focus the sound waves into the openings of the 
 ears. Let someone talk in a uniform voice while you do this, then take 
 your hands away. Why do partially deaf people'use an ear trumpet? 
 
 The string telephone. -237. Punch a small hole in the middle of the 
 bottom of two tin cans, like baking-powder cans. Fasten one end of a 
 long (50 feet or more) heavy string in each can by passing the end in through 
 the hole and tying a knot so that the string will not pull out. Let each of 
 two persons hold a can in hand and stand far enough apart so that the 
 string is pulled taut. Then one may talk into the can and the other use 
 the can as a telephone receiver. If two lamp chimneys are used in place 
 of the cans, one end of each being covered by tightly stretched bladder or 
 
g6 GUIDE IN PHYSICAL NATURE-STUDY 
 
 parchment paper, the results will be better. The string may turn corners 
 and still carry the sound, if it is passed through empty spools that are 
 suspended from convenient objects. You can thus connect two rooms in 
 the house or two houses that are not too far apart. 
 
 The electric telephone. 238. Examine the parts of an old telephone. 
 Bear in mind what we found out in handling* induced electric currents 
 (P- 77)> that moving a magnet into or out of a coil of wire produces a 
 current in the wire. Changing the strength of the magnet in a coil will 
 of course have the same effect. 239. After looking over the telephone 
 and finding out how it works, could you devise a plan of making one for 
 yourself ? Try it. 
 
HOW TO MAKE A PAIR OF SCALES AND USE OTHER 
 MECHANICAL CONTRIVANCES 
 
 To make a pair of balances. 240. Cut a block of J-inch wood 4 
 inches square, to serve as a base. At its midpoint fasten an 8-inch upright 
 of the same stuff ij inches wide. Saw or shave off the sides at its upper 
 end so as to make a wedge with a i^-inch edge. Cut a J-inch square 
 piece 15 inches long and drive a tack two-thirds to the head in the center 
 of each end. At the midpoint of this piece cut a notch straight across 
 one side and balance the stick on the upright, the edge of the wedge in 
 the notch. The scale pans may be made of the covers of baking-powder 
 or similar cans. Punch three holes in the edge of each cover at intervals 
 of a third of the way around the cover. Tie short strings in these holes 
 and knot their ends together so that the covers will hang from the tacks 
 at each end of the balanced stick. If now the stick does not balance 
 exactly, shave off one end or the other so that it will. At the midpoint 
 of the balanced stick opposite the notch fasten an 8-inch wire by a tack, 
 then bend it an inch from the tack so that it will hang vertically in front 
 of the upright. Make a mark upon the upright at the lower end of the 
 wire when the scale beam is horizontal. The end of this pointer and the 
 mark should coincide when the scale pans just balance. 
 
 241. To make the weights, take a pound of sheet lead and cut it in 
 half. Cut one-half in half again, and so proceed to make weights of 8-ounce, 
 4-ounce, 2-ounce, i-ounce, and two J-ounce; weights may be made also, if 
 preferred, by using small cloth bags filled with small shot, weighing them 
 on some reliable scales. Such scales and weights will make a valuable 
 addition to the outfit of the boy or girl who wants to play store. 
 
 An experiment with the scales. '242. Make another notch on the 
 scale beam on the same side as before, but 5 inches from one end. Set 
 the beam on the upright at this notch and pour fine shot into one scale 
 pan until the scales balance. If the 2-ounce weight is now put in the pan 
 with the shot, what weight must be put in the other pan to balance it? 
 Try the 4-ounce weight and note what is required to balance it. What is 
 the relation between the weights in the two pans in each case? What is 
 the relation between the lengths of the arms of the scale beam now? 
 
 243. Cut another notch 3 inches from one end and again get the 
 scales balanced by pouring shot in one pan. Put the 2-ounce weight in 
 this pan again and note what weight is needed in the other pan to balance 
 
 97 
 
g8 GUIDE IN PHYSICAL NATURE-STUDY 
 
 it. The number representing the weight in one pan multiplied by that 
 showing the length of the opposite arm always equals what? 244. Devise 
 and make a pair of scales on which you can weigh yourself. 
 
 The lever. The balance is merely one form of the simple machine 
 called a lever. The unmoved point upon which the beam balances is 
 the fulcrum. One arm is called the weight arm, the other the power 
 arm, because they bear, respectively, the weight and the power. We may 
 state our findings above, then, in this form: weight arm times the power 
 equals what? 
 
 There are evidently only three possible relations of fulcrum, weight, 
 and power. The fulcrum may be between the weight and power; the 
 weight may be between the fulcrum and power; power may be between 
 fulcrum and weight. 
 
 There are many applications of the lever, as, for instance, a hammer 
 used for drawing a nail, a tack claw, a can opener, scissors used in cutting, 
 a nut cracker, a lemon squeezer. 245. Draw diagrams of each of these 
 indicating the location of fulcrum, power, and weight. 246. List some 
 other common household utensils that involve the use of a lever. 
 
 247. Fasten a spring scale to the end of a hammer handle. Insert 
 the hook of a second spring scale in the claw of the hammer. Set the 
 hammer head down at the edge of a table and take hold of one spring 
 scale with the right hand, the other with the left. Pull on the scale attached 
 to the handle as if the other spring scale were a tack you were drawing. 
 Note what each spring scale registers. Measure the weight arm and power 
 arm of this lever and note if the amounts registered by the spring scales 
 figure out properly in relation to the length of power arm and weight arm. 
 
 The sprocket wheel on the bicycle. 248. Cut a piece of |-inch stuff 
 2 inches wide and 2 inches long for a base. At one end fasten on with 
 brads two uprights, one on each side, each upright of light stuff and about 
 i inch by 3 inches, the two parallel to each other and at right angles to 
 one broad side of the base. Whittle a 4-inch stick round and sufficiently 
 large to tightly fit the hole in a spool. Bore a hole a little larger than this 
 round stick in each of the uprights near their upper ends so that the round 
 stick can set in them and turn as an axle, the spool turning with it. Square 
 off one protruding end of the axle and at right angles fit on it an arm of 
 light wood with a square hole at one end to receive the square end of 
 the axle. At the other end of the arm, which may be a couple of inches 
 long, drive a peg into a small hole to make the handle to this crank on the 
 windlass. The crank is like the pedal bar on the bicycle, the spool compa- 
 rable to the sprocket wheel. Let us see what mechanical advantage such 
 a mechanism affords. Tie one end of a string tightly around the spool and 
 
HOW TO MAKE MECHANICAL CONTRIVANCES 99 
 
 then, turning the handle of the windlass, wind several turns of the string 
 upon the spool. Tie the free end of the string to the hook of a spring scale, 
 the other end of which is fastened to a tack on the table. Fasten the base 
 block to the tablfe also. Throw the hook of another spring scale over the 
 handle of the crank and by means of it apply force to turn the crank. 
 As you thus wind the string slowly on the spool note the reading of both 
 scales. Then let the string unwind a very little and again note the reading 
 of both scales. * If you divide the sum of the readings of each scale by two 
 the results should be the force applied on the crank to pull a given weight 
 on the string; the element of friction is also eliminated. Do you know 
 why? 
 
 Do you see also that this machine is merely an application of the lever? 
 What is the power arm, the weight arm? Are these constantly changing 
 their relative lengths as the windlass is turned, or do they remain constant? 
 Measure these arms of the lever and calculate to see how closely your 
 measure of the force applied and the resistance overcome agrees with the 
 amounts determined from the application of the law of the lever. 
 
 Bearing down with a pressure of twenty pounds on the pedal of your 
 bicycle what pull is given on the chain by the teeth of the sprocket wheel? 
 
 There is such a crank and axle on the coffee mill, the wringer, and the 
 ice-cream freezer. 249. Can you figure out in either of these how much 
 the power applied to the crank handle is multiplied by the machine? 
 
 Wheel and axle on the sewing machine. If the crank on the end of 
 the axle is replaced by a wheel the machine is known as a wheel and axle. 
 But the principle involved is merely that of the lever again, for, of course, 
 when the crank handle on the windlass is turned around it describes the 
 circumference of a circle just as does the rim of a wheel. The steering 
 wheel of a boat works as a wheel and axle. Are there any on the sewing 
 machine? Can you think of any others in common use? 
 
 To make a pulley. 250. Cut two thin wood strips from a cigar box 
 each ij inches by | inch. Bore a hole in the center of each through 
 which may be set an axle on which revolves an empty silk spool. With 
 small brads fasten a block of wood in each end thick enough for the spool 
 to revolve freely. Fasten in each end of this pulley a small screw hook or 
 a brad bent into a hook. 
 
 Why pulleys can help lift a load. 251. Fasten up a single pulley, 
 pass a string over the wheel and tie one end to the hook of a spring scale 
 and a weight of 8 ounces to the other end. What does the spring scale 
 register? What would be the advantage in using such a pulley then? Can 
 you determine how much of the pull exerted by the scale in raising the 
 weight is used up in overcoming friction? 
 
ioo GUIDE IN PHYSICAL NATURE-STUDY 
 
 252. Fasten one end of the string to the bottom of the pulley, already 
 hung, from which the string has been removed, pass the string over the 
 wheel of a second pulley so as to suspend it below the first, thence over 
 the wheel of the first. Fasten the hook of a spring scale to the free end of 
 the string and hang a half-pound weight on the hook of the lower pulley. 
 See what the spring scale registers. What should it register if friction were 
 eliminated? Can you devise a way to eliminate friction in your results? 
 How many strings are now supporting the weight? If you raise the weight 
 6 inches how much must you lower the end of the string fastened to the 
 spring scale? Make the measurement to find out. 
 
 253. Try a system of a double pulley above and a single pulley below. 
 Fasten the end of the string to the upper end of the lower pulley, pass 
 it over one of the wheels of the upper pulley, then over the wheel of 
 the lower pulley, then over the other wheel of the upper pulley. Fasten the 
 hook of the spring scale to the free end of the string and a weight to the 
 lower hook of the lower pulley. See what the relation is between the weight 
 raised and the power required to raise it after making allowance for friction. 
 254. Try a system of two double pulleys and find out the same thing. 
 Do you see any relation between the weight raised, the power applied, 
 and the number of strands of cord that support the weight, remembering 
 that one strand of string merely serves to change the direction of the applied 
 power, as in the single pulley. Would it be possible for a man to lift him- 
 self with a rope and a couple of pulleys? 
 
 Why the grocer uses an inclined plank to load the barrel of sugar into 
 his wagon. 255. Cut a small block of f-inch wood 3 inches wide and 
 4 inches long. At the middle of one end drive a tack. By means of nails 
 fasten four small spools to the block to serve as wheels, thus making a 
 small wagon. Fasten a string to the block by means of the tack at the 
 front end. Load the wagon with some weights and then by means of a 
 spring scale attached to the string weigh the wagon and its load. 
 
 Support one end of a smooth 5-foot board on blocks so that it is 3 feet 
 higher than the other end, which rests on the table or the floor. Draw the 
 wagon up the inclined board and note the pull registered on the spring 
 scale. Note the pull on the scales when the wagon is allowed to roll, back- 
 ward, down the inclined board. In pulling the wagon up the board the 
 scale registers the pull of the wagon plus the resistance due to friction of 
 the wheels; when the wagon rolls back the scale registers the pull of the 
 wagon minus the friction. How, then, will you get the pull due to the 
 loaded wagon and eliminate the element of friction? What is this amount? 
 How far has the weighted wagon to move horizontally in going from one 
 end of the board to the other? How far must it move vertically? If the 
 
HOW TO MAKE MECHANICAL CONTRIVANCES 101 
 
 wagon and its weight equaled one pound and it were lifted directly from 
 the table or floor to the raised end of the board the energy used would 
 evidently be three foot pounds. What energy was used in raising the wagon 
 in the experiment? The pull registered on the scale, leaving friction out 
 of consideration, is what part of the weight of the loaded wagon? But 
 this pull was working through how many horizontal feet of movement of 
 the wagon? Do you see that the proportion existing between the weight 
 raised and the pull on the scale is the same as that between the vertical 
 distance and the horizontal distance through which the weight moves? 
 Can you explain why this is so? 256. Suppose the end of the board 
 were raised 2 feet instead of 3 feet, then what would be the pull on the 
 scale required to get the wagon up the inclined board? Figure this out 
 first and then verify your conclusion by trying the experiment. Can you 
 now state the law of the inclined plane? Would the grocer best use a long 
 or a short board to roll his barrel of sugar up into the wagon? When a 
 railroad goes up a mountain why must it wind back and forth around 
 the mountain? The grade must not exceed 2 per cent if an engine is to 
 pull a train of cars. What does such a statement mean? Why must the 
 gradient be so small? Why is it so hard to ride a bicycle up a hill? 
 
 Why a knife blade cuts so easily. Do you see that a knife blade is 
 just another application of the machine called the inclined plane? Instead 
 of pulling the weight up the inclined plane the plane is forced in against 
 the resistance caused by the cohesion of the particles of wood or other 
 object cut. Though this simple machine is simply a new application of 
 the old inclined plane it is called the wedge. 257. Can you measure your 
 knife blade and calculate what amount of force is acting to push the wood 
 fibers apart if you are exerting a pressure of five pounds on the handle of 
 the knife? Name five other tools that use the wedge as a means of accom- 
 plishing their work. 
 
 Why even a child can raise an automibile with a jack. 258. Cut a 
 long right triangle out of paper, making one side of the right angle 
 6 inches, the other, i inch. Lay the i-inch end on a pencil parallel to its 
 length and roll the paper strip on the pencil. The longest side of the triangle, 
 the hypotenuse, makes a spiral like a screw thread. It is evident, then, 
 that the screw, another simple type of machine, is really only an applica- 
 tion of the principle of the inclined plane, for the longest side of the tri- 
 angle is comparable to the edge of an inclined plane. The screw, then, is 
 merely a coiled inclined plane and of course works in the same manner. 
 The power applied to a screw jack is also usually applied by means of a 
 long handle that acts as a lever to further increase the efficiency of the 
 machine. 
 
102 GUIDE IN PHYSICAL NATURE-STUDY 
 
 If we take a coarse wooden screw, like that on a carpenter's bench vise, 
 it will be easy to measure the elements in the inclined plane. 259. With 
 a tapeline measure the circumference of the screw. Evidently when the 
 handle of the vise is turned around once, the resistance, whatever it is, 
 has moved horizontally over a distance equal to that measured. It has 
 at the same time moved vertically, to adopt the same phrasing as used 
 above for the inclined plane, a distance equal to that between correspond- 
 ing points on successive turns of the screw. Measure this distance. We 
 now have the two essential elements in an inclined plane. What should 
 be the increase in power accomplished through the use of this screw? 
 Probably the bench screw operates by means of a handle that acts as a 
 lever to further increase the power. Measure the length of power arm 
 and weight arm and calculate what its mechanical efficiency is. 
 
 We may experimentally verify our calculations. 260. Cut two sticks 
 of J-inch stuff an inch or so wide and fasten them together loosely by 
 a nail or bolt set through them at their midpoints, thus making a crude 
 pair of shears. Bore holes through the ends of the sticks that may be 
 called the tips of the shears. Fasten the other ends of the sticks, the handles 
 of the shears, to the jaws of the bench vise by means of brads, so that when 
 the vise is opened by turning the screw the tips of the shears will be spread. 
 Fasten a spring scale between these tips by strings tied in the holes. Hook 
 another spring scale over the handle of the bench vise and turn the screw 
 so as to open the shears. Note the reading on both scales. Is the power 
 applied increased by the machine as much as you calculate it should be? 
 If not, why not? 
 
APPENDIX A 
 
 It is suggested that the following list of projects, outlined in the pre- 
 ceding pages, be done by individual students or the instructor as class 
 demonstrations and that all others be done by every student in the 
 class: 21, 42, 44, 48, 52, 57, 58, 60, 61, 63, 64, 65, 72, 73, 74, 75, 76, 80, 
 81, 85, 87, 92, 93, 96, 98, 100, lor, 102, 105, 106, 107, 108, no, in, 113, 
 114, 116, 117, 118, 119, 120, 121, 124, 125, 127, 128, 130, 133, 144, 146, 
 147, 149, 151, 152, 168, 169, 170, 174, 178, 179, 180, 185, 194, 200, 202, 
 
 203, 214, 222, 223, 232, 233, 234, 235, 237, 239, 240, 241, 242, 243, 244, 
 
 248, 255, 260. 
 
 103 
 
APPENDIX B 
 
 The following list of apparatus and supplies is required to work out 
 the projects suggested in this book, the foregoing list of experiments to 
 be performed by one member of the class for the benefit of all. The 
 estimate is based on a class of twenty students. It does not include 
 drawing material, extra paper, cardboard, etc., that would naturally 
 be supplied by the pupils. 
 
 Alcohol lamps or Bunsen burners, 10. 
 Asbestos paper, thin, i sq. ft. 
 Asbestos sheet, -rV in., 2 sq. yds. 
 Bamboo poles, 2. 
 
 Beads, 2 doz., J in. with large hole. 
 Beakers, 500 c.c., 6. 
 Bolts, 3 by | in., 20. 
 Bottles, 8-oz., wide-mouthed, 6. 
 Brads, f lb., \ in. 
 \ lb., f in. 
 i lb., 1 1 in. 
 
 Bunsen burners or alcohol lamps, 10. 
 Candles, 2 standard. 
 Cheese cloth, 5 yds. 
 Chemicals: 
 
 Acid chlorhydric, 8 oz. 
 
 Alcohol, 4 oz. (more if alcohol lamps are used). 
 
 Alum, \ lb. 
 
 Ammonium chloride, 4 oz. 
 
 Calcium oxide, | lb. 
 
 Camphor, 2 oz. 
 
 Carmine, powdered, \ oz. 
 
 Charcoal, pulverized, 4 oz. 
 
 Copper sulphate, 8 oz. 
 
 Ether, 2 oz. 
 
 Magnesium ribbon, i oz. 
 . Manganese dioxide, granular, 4 oz.; pulverized, 4 oz. 
 
 Phosphorus, yellow, 2 oz. 
 
 Potassium chlorate, 4 oz. 
 
 Salt, coarse, i lb. 
 
 Silver nitrate, \ oz. 
 
 Sulphur, 8 oz. 
 
 Turpentine, 4 oz. 
 
 Zinc, granulated, 4 oz. 
 Clay pipes, 3. 
 Compasses, 10. 
 
 104 
 
APPENDIX 105 
 
 Compression clamps, 4. 
 Copper, sheet, i sq. ft. 
 
 Corks, rubber, to fit flasks 2-holed and 10 small i -holed. 
 Corks, assorted sizes, 50. 
 Electric bell. 
 
 Electric binding-posts with two openings, 4. 
 Electric buzzer. 
 Electric dry batteries, 10. 
 Electric dynamo, toy. 
 Electric knife switch. 
 Electric lights, old incandescent. 
 Electric lights, i-candle power, and sockets, 20. 
 Electric motor, toy. 
 Electric push button. 
 Evaporating dishes, 5 of 100 c.c. 
 Flasks, 3 of 2 liters. 
 5 of f liter. 
 20 of 100 c.c. 
 
 Filter paper, i package, 5 in. diameter. 
 Funnels, 2 of i in. diameter, 
 
 2 of 3 in. diameter. 
 Gas engine, toy. 
 Glass cutter, wheel, 2. 
 Glass stirring rods, i dozen. 
 Glass tubing, i Ib. soft, iVin. bore. 
 i Ib., j-in. bore. 
 5 of 6-in. length, |-in. bore. 
 5 of 4-in. length, i-in. bore. 
 Glass, window, 3 pieces 8 by 10. 
 Gunnysack, i. 
 
 Iron, round, -& in., 10 linear ft. 
 Joss sticks, i package. 
 Knitting needles, 10 steel. 
 Lamp chimneys, 2. 
 Lead, sheet, i sq. ft. 
 Leather, i sq. ft., thin. 
 Lemon squeezer. 
 Level, 2 detached. 
 Lumber, 10 linear ft., f in., 3 in. wide, white pine. 
 
 10 linear ft., f in., 9 in. wide, white pine. 
 
 10 linear ft., \ in., 9 in., white pine. 
 
 30 |-in. square strips, 3 ft. long, white pine. 
 
 20 |-in. square strips, 4 ft. long, oak or cedar. 
 Magnets, bar, 10. 
 Mica, i piece, 2 in. square. 
 Minerals and rocks (specimens listed, p. 6). 
 
io6 GUIDE IN PHYSICAL NATURE-STUDY 
 
 Mirrors, 10 pieces 6 in. square. 
 10 concave. 
 
 40 strips about i by 6 in. 
 Nails, assorted wire, 2 Ibs. 
 Nut cracker. 
 
 Paper, colored, i package assorted colors, about 2 doz. sheets. 
 Paper, tissue, 40 sheets, assorted colors. 
 Phonograph record, 2 old, i good one. 
 Photograph material: 
 
 Blueprint paper, 5 by 8, 2 doz. sheets. 
 4 by 5, 2 doz. sheets. 
 
 Fixer, acid, i Ib. 
 
 Hyjdrochinone developer, 6 powders. 
 
 Metol-hydrochinone developer, 3 tubes. 
 
 Plates, i box, 4 by 5, Cramer's medium or equivalent. 
 
 Print paper, 2 doz. sheets 4 by 5 Normal Cyko or equivalent. 
 Picture cord, i package. 
 Pie plates, tin, 2. 
 Pipettes, i doz. straight. 
 Pith balls, 20. 
 Plasticine, i Ib. 
 Pneumatic trough. 
 Prism, 2-in., 2. 
 
 Protractor, 3-in., brass or horn. 
 Ring stands, 2. 
 Rubber for aeroplane, 40 ft. 
 Rubber bands, 2 doz., 2 in. 
 
 Rubber tubing, 10 ft., to fit glass tubing of iVin. bore. 
 Saucers, 10. 
 
 Scales, spring, 8 oz., 20, 
 Scales, spring, 2 Ib., 2. 
 Sealing wax, 10 sticks. 
 Shot, i Ib. 
 
 Silk, several pieces large enough to rub glass tubing. 
 Silk, i spool fine. 
 Spikes, i doz. 
 String, 5 balls. 
 
 Surgeons' tape, i in. wide, 10 yds. 
 
 Tacks, i package each, small, carpet, and double-pointed. 
 Teapot, i small tin. 
 Telegraph instruments, 2. 
 Telephone, i old one. 
 Test tubes, 20. 
 
 Thermometers, 3 registering 10 to 220 F., or equivalent in C. 
 Thermos bottle broken one is best. 
 
APPENDIX 107 
 
 / 
 
 Tin foil, 4 oz. 
 Tin, sheet, i sq. ft. 
 Tools: 
 
 5 awls. 
 
 5 triangular files. 
 
 2 round files. 
 
 10 hammers. 
 
 20 knives, Sloyd. 
 
 5 pliers. 
 
 2 saws, cross, and i split, i keyhole, i hack. 
 10 pairs scissors. 
 
 5 screw drivers. 
 
 i pair tinners' shears. 
 
 i bench vise. 
 
 Tumblers, 20. 
 Voltammeter, i. 
 Watch crystals, not the laboratory dishes of this name but real watch crystals, 
 
 3 doz. 
 
 Wire, No. 12, soft-iron, 2 Ib. 
 
 iron, 1 8 and 24, i spool each. 
 * copper, 1 8 and 24, i spool each. 
 
 copper insulated, 18, f Ib. 
 
 copper insulated, 36, i Ib. 
 Zinc, sheet, i sq. ft. 
 
APPENDIX C 
 
 There is given herewith a brief list of books that will be found useful 
 if it is desired to extend the list of projects to be carried out by the pupils. 
 A more complete bibliography will be found at the ends of the chapters 
 in the forthcoming Source Book of Physical Nature-Study, which it is 
 intended shall serve as a reading text to accompany this laboratory and 
 field guide. 
 
 Bayley, W. S. Minerals and Rocks. New York: D. Appleton & Co., 1915. 
 
 $2 . OO . 
 
 Beard, Dan C. The American Boy's Handybook. New York: Charles Scribner 
 
 & Sons, 1914. $1.50. 
 
 . Boat-Building and Boating. ' New York: Grosset, Dunlap & Co., 1914. 
 
 $0.50. 
 
 . Handicraft for Outdoor Boys. New York: Grosset, Dunlap & Co., 1915. 
 
 $0.50. 
 Bond, Alexander R. The Scientific American Boy. New York: Munn & Co., 
 
 1905. $1.50. 
 Chadwick, M. L. Pratt. Storyland of Stars. Chicago: Educational Publishing 
 
 Co., 1906. $0.50. 
 Collins, Archie F. Easy Lessons in Wireless. New York: Theo. Audel & Co., 
 
 1915. $0.50. 
 Collins, Francis A. The Boy j s Book of Model Aeroplanes. New York: The 
 
 Century Co., 1910. $i . 20. 
 Crosby, W. O. Common Minerals and Rocks. Boston: D. C. Heath & Co., 
 
 1881. $0.64. 
 
 Fairbanks, H. W. Stories of Rocks and Minerals. Chicago: Educational Pub- 
 lishing Co . , 1 903 . $o . 60 . 
 Griffith, Alice M. The Stars and Their Stories. New York: Henry Holt & Co., 
 
 1-913. $1.25. 
 Hall, A. N. Homemade Toys for Boys and Girls. Boston: Lothrop, Lee & 
 
 Shepherd, 1915. $1.35. 
 
 . Handicraft for Handy Boys. Boston: Lothrop, Lee & Shepherd, 1911. 
 
 $2.00. 
 Hobbs, W. H. Simple Directions for the Determination of the Common Minerals 
 
 and Rocks. New York: The Macmillan Co., 1914. $o. 25 . 
 Hopkins, George M. Experimental Science. New York: Munn & Co., 1906. 
 
 $7.00. 
 Hubbard and Turner. The Boys' Book of Aeroplanes. New York: F. A. 
 
 Stokes & Co., 1913. $i..75. 
 
 108 
 
APPENDIX 109 
 
 Johnson, G. F. Toys and Toy Making. New York: Longmans, Green & Co., 
 
 1912. $1.00. 
 Olcott, William T. Star Lore of All the Ages. New York: G. P. Putnam's 
 
 Sons, 1911. $3.50. 
 
 . A Field book of the Stars. New York: G. P. Putnam's Sons, 1907. 
 
 $1.00. 
 Porter, J. G. The Stars in Song and Legend. Boston: Ginn & Co., 1901. 
 
 $0.50. 
 Proctor, Richard A. Myths and Marvels of Astronomy. New York: Longmans, 
 
 Green & Co., $1.75. 
 . Stars in Their Season. New York: Longmans, Green & Co., 1907. 
 
 $2.00. 
 
 Rowe, J. P. Practical Mineralogy, Simplified. New York: John Wiley & 
 
 Sons, 1911. $i .25. 
 St. John, Thomas M. Real Electric Toy Making for Boys. New York: Thomas 
 
 M. St. John, 1911. $1.00. 
 Serviss, Garrett P. Astronomy with the Naked Eye. New York: Harper Bros., 
 
 1008. $1.40. 
 
 . Round the Year with the Stars. New York: Harper Bros., 1910. $i . oo . 
 
 Sloane, Thomas 0. Electric Toy Making for Amateurs. New York: Norman 
 
 W. Henley Publishing Co., 1914. $i .00. 
 Spencer, L. J. World's Minerals. New York: F. A. Stokes & Co., 1916. $2.75. 
 
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