,,rollo',s ,,philosophy4 ,,air4 ,,the ,,rollo ,,series ,,is ,,composed ,,of ,,fourteen ,,volumes1 ,,viz ,rollo ,learning to ,talk4 ,rollo ,learning to ,read4 ,rollo at ,work4 ,rollo at ,play4 ,rollo at ,school4 ,rollo's ,vacation4 ,rollo's ,experiments4 ,rollo's ,museum4 ,rollo's ,travels4 ,rollo's ,correspondence4 ,rollo's ,philosophy--,water ,rollo's ,philosophy--,air4 ,rollo's ,philosophy--,fire4 ,rollo's ,philosophy--,sky4 ,a ,,new ,,edition1 ,,revised ,,by ,,the ,,author4 ,,boston3 ,,phillips1 ,,sampson1 ,,and ,,company ,entered1 according to ,act of ,congress1 in the ,year #ahee1 by ,,phillips1 ,,sampson1 ,,co41 ,in the ,clerk's ,office of the ,district ,court of the ,district of ,massachusetts4 ,,preface4 ,the main design in view1 in the discussions which are offered to the juvenile world1 under the title of ,,the ,,rollo ,,philosophy1 relates rather to their effect upon the little reader's habits of thinking1 reasoning1 and observation1 than to the additions they may make to his stock of knowledge4 ,the benefit which the author intends that the reader shall derive from them1 is an influence on the cast of his intellectual character1 which is receiving its permanent form during the years to which these writings are adapted4 ,the acquisition of knowledge1 however1 though in this case a secondary1 is by no means an unimportant object2 and the discussion of the several topics proceeds accordingly1 with regularity1 upon a certain system of classification4 ,this classification is based upon the more obvious external properties and relations of matter1 and less upon those which1 though they are more extensive and general in their nature1 and1 therefore1 more suitable1 in a strictly-scientific point of view1 for the foundations of a system1 are less apparent1 and require higher powers of generalization and abstraction2 and are1 therefore1 less in accordance with the genius and spirit of the ,rollo philosophy4 ,as teachers have1 in some cases1 done the author the honor to introduce some of the preceding works of this class into their schools1 as reading books1 c41 considerable reference has been had to this1 in the form and manner of the discussion1 and questions have been added to facilitate the use of the books in cases where parents or teachers may make the reading of them a regular exercise of instruction4 ,,contents4 ,,chapter ,i4 ,page4 ,,lost ,,in ,,the ,,snow1 #i ,,chapter ,,ii4 ,,flying1 #ai ,,chapter ,,iii4 ,,valve ,,making1 #dj ,,chapter ,,iv4 ,,experiments1 #ea ,,chapter ,v4 ,,pressure1 #fd ,,chapter ,,vi ,,ballooning1 #gi ,,chapter ,,vii4 ,,philosophical ,,discussion1 #id ,,chapter ,,viii4 ,,tasks1 #ajh ,,chapter ,,ix4 ,,burning1 #aba ,,chapter ,x4 ,,gravitation1 #adc ,,chapter ,,xi4 ,,air ,,in ,,motion1 #aeh ,,chapter ,,xii4 ,,air ,,at ,,rest1 #agh ,,chapter ,i4 ,,lost ,,in ,,the ,,snow4 ,one pleasant morning1 very early in the spring1 ,rollo's cousin ,lucy came to call for ,rollo to go on an expedition1 which they had planned the day before4 ,it was near the end of ,march1 and the snow had become so consolidated by the warm sun in the days1 and the hard frosts at night1 that it would bear the children to walk upon it4 ,the children called it the crust2 but it was not1 strictly speaking1 a crust1 for the snow was compact and solid1 not merely upon the top1 but nearly throughout the whole mass1 down to the ground4 ,rollo and ,lucy were going to have an expedition upon the crust4 ,rollo had a sled1 and they were going to put upon the sled such things as they should need1 and ,rollo was to draw it1 while ,lucy and ,nathan1 ,rollo's little brother1 were to walk along by his side4 ,rollo's sled was ready at the back door1 when ,lucy came4 ,lucy brought with her some provisions for a luncheon1 in a basket4 ,this was her part of the preparation4 ,rollo got his axe1 and one or two boards a little longer than the sled1 which he said were to make seats4 ,he also had a tinder-box1 and some matches1 to enable him to make a fire4 ,when all things were ready1 the three children set out together4 ,rollo drew the sled1 with the boards1 the basket1 and some other things upon it1 all bound together securely with a cord4 ,the load appeared to be considerable in bulk1 but it was not heavy1 and ,rollo drew it along very easily4 ,they were not obliged to confine themselves to the roads and paths1 for the snow was hard in every direction1 and they could go over the fields wherever they pleased4 ,in one place1 where the snow was very deep on the side of a hill1 they went right over the top of a stone wall4 ,it was a cloudy day1 but calm4 ,this was favorable4 ,the sky being overcast1 kept the sun from thawing the snow2 but yet their father told them that probably it would begin to grow soft before they came home1 and1 if so1 they would have to come home in a certain sled road1 which ,jonas had made that winter by hauling wood4 ,he advised them not to encamp at any great distance from the sled road4 ,they came at last to a pleasant spot on the margin of a wood1 near where there was a spring4 ,the rocks around the spring were all covered with snow1 and the little stream1 which in summer flowed from the spring1 was frozen and buried up entirely out of sight4 ,but the spring itself was open1 which ,rollo said was very fortunate1 as they might want some water to drink4 ,here they encamped4 ,rollo cut some stakes1 which he drove down into the snow1 and contrived to make a rude sort of table with his boards4 ,he also cut a large number of hemlock branches1 which ,lucy and ,nathan dragged out and spread around the table for them to sit upon4 ,then ,rollo built a fire of sticks1 which he gathered in the wood4 ,the ground was covered with snow1 so that it would have been very difficult for him to have found any sticks1 were it not that some kinds of trees1 in the woods1 have a great many small branches near the bottom1 which are dead and dry4 ,these ,rollo cut off1 and ,lucy and ,nathan dragged them out1 and put them on the fire when he had kindled it4 ,the fire was a little way from the table1 with the carpet of hemlock boughs between4 ,there was a high hill covered with snow at a little distance1 and1 after they had eaten their luncheon1 ,rollo said1-- ,o ,lucy1 we will play go up the mountains4 ,there is a hill for us4 ,that shall be ,chimborazo4 ,well1 said ,lucy1 if you will cut us some long staves4 ,accordingly ,rollo went into the wood1 and selected some tall and slender young trees1 about an inch in diameter1 and cut two for ,lucy1 two for ,nathan1 and two for himself4 ,these he trimmed up smoothly1 and each of the children took one in each hand4 ,they played that ,rollo was the guide1 and ,lucy was the philosopher4 ,nathan was the philosopher's servant4 ,rollo conducted them safely to the summit2 but just after they got there1 it began to snow4 ,the snow descended in large flakes1 and ,rollo was delighted to see it2 but ,lucy seemed a little anxious4 ,she said that1 if there should be much snow1 it would make it hard for ,nathan to get home1 and she thought that they had better go down the mountain immediately1 and set out for home4 ,rollo was rather unwilling to go1 but he allowed himself to be persuaded1 and so they all came down the mountain together4 ,they packed up their things as quick as they could1 leaving the fire to burn itself out1 only ,rollo first piled on all the hemlock branches1--which made a great crackling4 ,the snow began to fall faster4 ,the air was full of the large flakes1 which floated slowly down1 and lodged gently upon the old snow4 ,the children went along very successfully for some time1 but at length ,rollo lost his way4 ,the air was so full of snow-flakes1 that he could see only a very little way before him2 and the old snow covered the ground1 so as to hide all the old marks1 and to alter the general aspect of the fields so much1 that ,rollo was completely lost4 ,he1 however1 did not say anything about it1 but wandered on1 ,lucy and ,nathan wondering all the while why they did not get home2 until at length they came across a track in the snow4 ,o6 see this track1 said ,rollo4 ,here is a track1 where somebody else has been along with a sled4 ,yes1 said ,lucy1 some boys1 who have gone out to slide1 perhaps4 ,the track was partly obliterated by the snow which had fallen upon it since the boys that made it had gone along4 ,rollo wondered whose track it could be4 ,he said that he thought it very probable it was ,henry's4 ,lucy thought that it might be the track of some children1 that had gone out to find them4 ,at any rate1 said ,rollo1 we will follow the track a little way1 and see what it leads to4 ,perhaps we shall overtake the boys4 ,accordingly ,rollo turned along in the track1 but ,lucy stopped4 ,no1 ,rollo1 said she1 we must go the other way if we want to find the boys2--the track is going the other way4 ,but never mind1 she added1 ,i don't want to find the boys2 ,i want to go home2 so we will go this way4 ,rollo went on1 secretly pleased to find the track1 for he supposed that by retracing it1 as he was doing1 it would lead him back home4 ,he had1 however1 a great curiosity to know who could have made it2 and in fact the mystery was soon unraveled4 ,for1 after following the track a short distance1 they saw before them a large1 dark spot upon the snow1 and1 on drawing near to it1 to see what it was1 they found it was the place of their own encampment2 and the track which they were following was their own track1 leading them back to the mouldering remains of their own fire4 ,they had gone round in a great circle1 and come back upon their own course4 ,rollo looked exceedingly blank and confused at this unexpected termination of the clew1 which he had hoped was to have led him out of his difficulty4 ,what he was to do now1 he did not know4 ,the fact1 however1 that they were lost1 was no longer to be concealed2 and ,lucy proposed that they should go into the woods1 where the tops of the trees would act as a sort of umbrella1 to keep the snow from falling upon them1 and wait there until it stopped snowing2 and then the air would be clear1 and they could find their way out4 ,o1 said ,rollo1 ,i can easily make a hut of hemlock branches1 and we can go into that for shelter4 ,but1 ,rollo1 said ,nathan1 how do you know but that it will snow all day8 ,we can't stay in the woods all day4 ,no1 said ,rollo2 when it snows in great flakes1 it is not going to snow long4 ,jonas told me so4 ,so the children went into the woods1 and ,rollo began to make his hut2 but he was soon interrupted1 and the attention of all the children was called off by a little bird1 which they saw there1 hopping about1 and appearing benumbed with cold4 ,after some effort1 ,rollo succeeded in catching her in his cap4 ,we'll carry her home1 said ,nathan2 we'll carry her home1 and show her to mother4 ,yes1 said ,rollo1 ,i'll carry her in my cap4 ,no1 said ,lucy1 you must have your cap on your head1 or you will take cold4 ,let me carry her in my hands4 ,no1 said ,rollo1 you will have to lead ,nathan4 ,i'll tell you what we will do4 ,we will put her into the basket1 for a cage4 ,lucy1 on the whole1 liked this plan1 and they accordingly put the bird in the basket1 and ,rollo contrived to make a cover of boughs1 to keep her from getting away4 ,by the time that this was all arranged1 the children found1 to their great satisfaction1 that it had ceased snowing2 and they immediately set out for home4 ,rollo drew the sled1 with the basket and bird upon it1 secured as before with the cord2 and ,lucy led ,nathan4 ,they now had no difficulty in finding their way1 and soon reached home in safety4 ,they kept the bird until the next day1 and then1 as it was mild and pleasant1 they let her fly away4 ,,questions4 ,by what process had the snow become hardened at this time8 ,did ,rollo's father expect that it would continue hard till noon8 ,why not8 ,did it continue hard8 ,what prevented its melting8 ,how did ,rollo get sticks for his fire8 ,what name did he give to the hill which they ascended8 ,what occasioned the difficulty in the way of ,rollo's finding his way home8 ,what conversation took place when he found the track8 ,was this track in the new snow1 or in the old snow8 ,how had it become partly obliterated8 ,how did they carry the bird home8 ,,chapter ,,ii4 ,,flying4 ,nathan became very much interested in the bird1 and that evening1 as his father was sitting by the fire1 with a book in his hand1 which he had been reading1 ,nathan came up to him1 and said1-- ,father1 are you busy now1--thinking1 or anything8 ,no1 said his father4 ,because1 said ,nathan1 if you are not1 ,i want to read you something out of my little book4 ,so ,nathan's father took him up into his lap1 and ,nathan opened his little book1 and began to read as follows3-- ',with fins for the water1 and wings for the air1 ,and feet for the ground1 ,i could go everywhere4' ,isn't that funny8 said ,nathan4 ,rather funny1 said his father4 ,i wish ,i had wings1 said ,nathan4 ,why8 said his father4 ,why1 then ,i could fly4 ,that is not certain1 said his father4 ,there are two difficulties which prevent boys from flying4 ,one is1 they have no wings2 and the other is1 they have not strength to use them4 ,o father1 said ,nathan1 ,i could use them2 ,i am pretty strong4 ,i can wheel ,rollo's wheelbarrow4 ,his father smiled4 ,very possibly1 said he2 but ,i do not think that you would be strong enough to use wings1 even if you had them4 ,why1 at any rate1 ,i am stronger than a bird1 said ,nathan4 ,yes1 said his father1 you have more actual strength than a bird1 but not more in proportion to your size4 ,you are absolutely stronger1 but not relatively4 ,what do you mean by that8 said ,nathan4 ,why1 you have actually more strength than a bird1--a robin1 for instance2 you could hold him so that he could not get away2 and you could lift more than he could too4 ,but then you are a great deal larger1 and you are not as much stronger than he is1 as you are larger4 ,if you are a hundred times as heavy as he1 you are not a hundred times as strong4 ,that's what ,i mean by saying that you are absolutely stronger1 but not relatively4 ,that is1 you are not as many times stronger1 as you are larger and heavier4 ,you are absolutely stronger1 but not relatively2 that is1 in proportion to your size and weight4 ,now ,i can prove to you1 continued his father1 that you would not be strong enough to fly with wings1 even if you had them4 ,suppose there was a pole fastened across the room1 and another pole just above it2 could you pull yourself up1 from one pole to the other1 by your hands alone1 without touching your feet8--,or a ladder1 continued his father1--it will be better to suppose a ladder4 ,now1 if there was a ladder leaning up against a building1 could you climb up on the under side by your hands1 drawing yourself up1 hand over hand1 without touching your feet8 ,here ,rollo1 who was reading in a little chair at the back part of the room1 when his father first commenced the conversation with ,nathan1 but who had been listening for a few minutes past to what his father had been saying1 jumped up1 and came across the room to his father1 and said1-- ,yes1 sir1 yes1 sir2 ,i can4 ,i have done it often in the barn4 ,how high up could you go8 said his father4 ,o1 almost up to the loft1 said ,rollo4 ,only1 you see1 father1 the rounds are too far up4 ,i can't reach up very well4 ,if they were nearer together1 ,i could climb up so1 very well4 ,well1 said his father1 a bird1 when flying1 has to climb up in much the same way4 ,he has to pull himself up by the air1 with his wings1 just as you do with your hands and arms1 by the rounds of the ladder2 only the air is not fixed1 like the ladder1 but constantly gives way under his wing2 and so1 to make the case the same1 you must suppose that the ladder is not firm1 but is floating in the air1 and sinks down with your weight1 so that you have to climb up faster than you pull the ladder down4 ,do you think you would have strength enough in your arms to do that8 ,rollo and ,nathan looked very much interested in what their father was saying1 but they both admitted that they could not climb up such ladders as those4 ,the air1 added their father1 gives way continually under the bird's wing2 and yet they have to pull themselves up by it4 ,and this is very hard4 ,they must either have very large wings1 and prodigious strength to use them1 so as to pull upon the air with very hard and heavy strokes1 or else1 if they have small wings1 they must have strength to strike very quick and often with them4 ,the wings of sparrows move so quick1 that you cannot count the strokes2 and those of humming-birds1 which are smaller still1 so fast that you cannot see them4 ,they make a hum4 ,i could make my wings go so fast1 said ,nathan2 and he began to imitate the flapping of the wings of a bird1 with his arms1 as rapidly and forcibly as he could4 ,so can ,i1 said ,rollo2 and he made the same motions4 ,that is as fast as crows' wings move1 when they are flying4 ,yes1 said his father1 crows move their wings as fast as that1 whereas you only move hands and arms4 ,if you had great wings1 as long1 in proportion1 as the crows1 you could not move them so fast4 ,how large would they be8 said ,rollo4 ,o1 ,i don't know1--perhaps as big as the top of the dining-table4 ,o father1 said ,rollo1 ,i don't think they would be as big as that4 ,the crow's wings are not longer than his body1 and so mine would not be longer than my body4 ,perhaps you never saw a crow's body1 said his father4 ,his feathers and his tail1 which are very light1 swell out his body1 and make it appear much larger than it really is4 ,i presume his wings1 when they are spread1 are twice or three times as long as his body4 ,if you had wings in proportion1 it would be with the utmost difficulty that you could use them at all4 ,you certainly could not strike the air with them fast enough to pull yourself up by them4 ,i did not think that the birds pulled themselves up by the air1 said ,nathan4 ,i did not know that the air was anything real4 ,o yes2 it is something real1 said his father4 ,i've seen birds fly without moving their wings at all1 said ,rollo4 ,yes1 said his father1 and so have ,i seen a stone4 ,a stone6 repeated ,rollo4 ,what1 a stone fly8 said ,nathan4 ,yes1 replied his father2 did you never see a stone fly through the air1 without any wings at all8 ,why1 yes1 said ,rollo1 when somebody threw it4 ,very well1 said his father4 ,if you set the stone in motion1 it will continue in motion for some time1 without any wings2 and so will a bird4 ,but1 father1 they don't throw birds1 said ,nathan2 and he laughed aloud at such an idea4 ,birds throw themselves1 said his father2 that is1 they strike their wings upon the air1 hard and quick1 and thus get into very quick motion1 and then they can keep their wings still for a time1 and go on1 as long as the impulse they have given them lasts4 ,this shows what prodigious strength they have in their wings4 ,they can not only strike the air hard and frequently enough to raise themselves up1 and move along1 but they can do it so easily1 as to get such a velocity1 that they can rest their wings for some time1 and sail away through the air1 only expending the impulse they had accumulated4 ,rollo and ,nathan were silent4 ,rollo was thinking how he had seen the swallows sailing swiftly round and round in the air1 with their wings spread out motionless by their side4 ,so1 you see1 continued his father1 the difficulty in the way of a boy's flying1 is not the want of wings1 but the want of strength to use them4 ,it would be very easy to make wings4 ,would it8 said ,nathan4 ,yes1 said his father4 ,at least it would not be very difficult4 ,ingenious mechanics would soon find out modes of making something to answer the purpose of wings1 to strike upon the air1 if there was the necessary power to work them4 ,the great difficulty in almost all cases in mechanics is1 in getting the power2 there is very little difficulty in applying it to any purpose it is wanted for4 ,so1 you see1 next time1 ,nathan1 when you want to fly1 you must wish1 not that you had wings1 but that you were strong enough to use them4 ,well1 father1 said ,rollo1 men are strong enough to paddle themselves along in the water2 why can't they in the air8 ,because1 said his father1 water supports them by its buoyancy1 and they have nothing to do but to move themselves along upon it4 ,but air cannot support them2 and1 of course1 a great part of the effort which they would make1 would be required to keep them up4 ,and then1 besides1 the water is generally nearly at rest1 but the air is generally in a state of rapid motion4 ,why1 father1 said ,rollo1 ,i'm sure water is sometimes in rapid motion4 ,the rivers run very swiftly1 often4 ,yes1 replied his father2 but then1 when they do1 men cannot paddle1 or row boats upon them4 ,a current that should run at the rate of four or five miles an hour1 would be very hard to row against4 ,but the air is seldom in a state of less motion than that4 ,it is very often moving at the rate of fifteen or twenty miles an hour2 sometimes sixty4 ,so1 you see1 there is a double reason why men cannot fly in the air1 as well as paddle on the water4 ,if we were only light enough1 said ,rollo1 to float in the air1 then we could fly4 ,we could paddle about in it1 when it was calm1 replied his father1 but that would not be flying4 ,is there anything light enough to float in the air8 said ,rollo4 ,no1 said his father1 ,i don't think of any visible substance that is4 ,what do you mean by visible substance8 said ,nathan4 ,why1 anything that you can see1 replied his father4 ,there are some other kinds of air1 which are lighter than common air1 but there is nothing else1 so far as ,i know4 ,why1 father1 there are clouds4 ,they float1 and they are visible1 ,i am sure4 ,yes1 said his father4 ,there is some mystery about the floating of clouds4 ,i don't fully understand it4 ,clouds are formed of small globules or little balls of water2 and water1 ,i should think1 whatever the size of the little drops might be1 would be heavier than air4 ,and yet they seem to float4 ,if they are large1 like rain drops1 they fall quickly to the ground4 ,if they are small1 like mist1 they fall slowly4 ,that ,i should expect4 ,if they are finer still1 like vapor or fog1 ,i should think that they would fall still more slowly2 but still ,i should suppose that they would descend4 ,but they do not appear to descend2 they seem to float1 nearly at rest2 though perhaps all the clouds we see1 may be slowly descending all the time1 while we do not perceive it4 ,the smoke goes up from the top of the chimney1 said ,rollo4 ,yes1 said his father1 there is no difficulty about that4 ,the vapor from a fire is carried up by the warm air1 no doubt4 ,air swells when it is heated1 and so becomes lighter1 and rises2 and the hot air from the top of the chimney carries the vapor up with it1 no doubt4 ,after it rises a little way1 and becomes cool1 it ceases to ascend1 but floats away horizontally4 ,perhaps it begins to descend when it gets cool1 though very slowly2 and perhaps all clouds are really descending all the time1 though too slowly for us to perceive the motion4 ,only1 said ,rollo1 after a little time1 they would get down to the ground4 ,perhaps not1 said his father2 for1 when they get down nearer the earth1 where it is warm1 they may be gradually dissolved1 and disappear1 and thus never reach the earth4 ,i should think they would descend1 being composed of globules of water1 which1 however small1 must1 ,i should think1 be heavier than air4 ,a soap bubble will float in the air1 said ,rollo4 ,i never saw one that would1 said his father1 unless it got into a current1 which carried it up4 ,a soap bubble--make it ever so thin--shows a tendency to descend1 unless you put it out in the open air1 where there are currents to carry it up4 ,it descends very slowly1 but still it descends4 ,it is heavier than the air4 ,i am not absolutely certain1 but ,i believe there is no visible substance that is lighter than the air2 and it is very well for us there is not4 ,why1 father8 said ,rollo4 ,because1 if there were any1 they would immediately rise from the earth1 and float upwards1 till they got up where the air was so light and thin1 that they could not go up any higher4 ,and so1 said ,rollo1 we should lose them4 ,that would not be all1 said his father4 ,they would float about1 above us1 and1 if there were enough of them1 they would form a perpetual cloud over our heads1 to keep out the sun1 and to make the world dark and gloomy4 ,there seems to have been no way to keep all the solid and visible substances of the earth down upon its surface1 but to make them all heavier than the air4 ,and thus1 continued his father1 all solid substances being heavier than the air1 they sink in it1 like stones or iron in water4 ,only those that are very much expanded in surface1 sink very slowly1 and sometimes almost seem to float4 ,what do you mean by expanded1 father8 said ,nathan4 ,spread out1 said his father4 ,an umbrella1 for example1 when it is spread out1 is said to be expanded2 other things are expanded in a little different way4 ,a feather is expanded1 that is1 it is spread out in fine filaments1 which extend1 in every direction1 into the air1 all around the stem of it4 ,things that are expanded take a great deal of air with them when they descend1 and so can only descend slowly4 ,and water is expanded in a soap bubble1 said ,rollo4 ,yes1 replied his father1 and there is a great deal of air included in it1 which all has to be brought down when the bubble itself descends4 ,and thus1 you see1 the bubble must descend slowly4 ,water is expanded1 too1 in clouds2 for1 in that case1 it is divided into millions of small particles1 by which it is spread out over a great deal of air1 and cannot descend without bringing a large portion of the air with it4 ,men have contrived1 on this principle1 to make an apparatus to prevent being hurt by falling from great heights4 ,what is it8 said ,rollo4 ,why1 it is called a parachute4 ,it is a sort of umbrella2 in fact1 it is an umbrella1 only made very large4 ,it is folded up1 and fastened under a balloon1 just over the car1 which the man is in4 ,then1 if the balloon bursts1 or any other accident happens to it1 and the man begins to fall1 the parachute opens and spreads1 and then the man falls very slowly4 ,the reason is1 that the parachute takes hold of a large mass of air1 and brings it down with it2 and so it cannot descend very fast4 99 99 99 99 99 ,a few days after this1 ,nathan said to ,rollo1 as they were playing in the yard1 that he wished that he had a parachute4 ,i know where there is one1 said ,rollo4 ,a parachute1 said ,nathan2 a real parachute8 ,yes1 said ,rollo1 or1 what is the same thing1 a great umbrella4 ,is that just the same8 said ,nathan4 ,yes1 said ,rollo2 for father said that a parachute was in fact only a large umbrella2 and father has got a large umbrella in the closet1 and ,i have a great mind to go and get it for a parachute4 ,but you haven't got any balloon1 said ,nathan4 ,o1 no matter for that1 said ,rollo4 ,then how are you going to get up into the air8 asked ,nathan4 ,why1 ,i can climb up on the shed1 and jump off that1 and hold the umbrella over my head4 ,just at this moment1 ,rollo's cousin ,james came into the yard1 and ,rollo ran to him1 to explain to him about the parachute4 ,after describing to him the construction of it1 and its use by men who go up in balloons1 he said he was going to get his father's umbrella1 which would make an excellent parachute4 ,and then1 continued he1 ,i am going to get upon some high place1 and jump off1 and hold the parachute over my head1 and then ,i shall come down as light as a feather4 ,o ,rollo1 said ,james1 ,i don't believe you will4 ,yes ,i shall1 said ,rollo3 you see the parachute is expanded1 and so brings down a great deal of air with it1 and this makes it come very slowly4 ,air is a real thing1 ,james1 and it keeps the parachute back a great deal4 ,illustration3 ,james and ,nathan both ran towards him1 thinking that he must be hurt4--,page #cg4 ,so ,rollo ran off after the umbrella1 very much interested in proving to ,james1 by actual experiment1 that the air was a real thing4 ,when he came with it1 he was himself inclined to make the first experiment from the low side of the shed4 ,he could climb up1 by means of a fence at the corner4 ,james advised him1 however1 to try it first from the end of a woodpile1 which was pretty high1 but yet not so high as the shed4 ,james was not quite sure that the experiment would succeed1 and he was afraid that ,rollo might get hurt4 ,rollo said that he was not afraid to jump off the shed4 ,he knew the parachute would bear him up4 ,he did not believe but that he could jump off the house with it2 and1 at any rate1 he could jump off the shed1 he knew4 ,he accordingly clambered up1 and1 taking his station upon the eaves1 he spread the umbrella over his head1 and then jumped off4 ,down he came with great violence2 his cap flew off in one direction1 and his umbrella rolled away in another1 as he had to put out both his hands1 to save himself1 when he reached the ground4 ,as it was1 he came down upon all fours1 and in such a way1 that ,james and ,nathan both ran towards him1 thinking that he must be hurt4 ,did you hurt yourself1 ,rollo8 said ,james4 ,no1 said ,rollo1 not much4 ,i don't think the umbrella did you much good4 ,no1 said ,rollo1 as he got up rubbing his elbows1 it didn't1 and ,i don't see what the reason is4 ,you came down just as hard as you would without it4 ,yes1 said ,nathan1 and he almost broke his back2 ,i don't believe the air is any real thing at all4 ,the fact was1 that the umbrella did do some good4 ,rollo did not come down quite so hard as he would have done without it4 ,it retarded his descent a little4 ,but it was not large enough to enable him to descend in safety4 ,when his father said that a parachute was in fact only a large umbrella1 he meant a great deal larger than ,rollo had supposed4 ,a parachute1 such as is used with balloons1 is a great deal larger than any umbrella that ever was made4 ,,questions4 ,what was ,nathan's wish1 after he had read his father something out of his book8 ,did he think that he could fly if he had wings8 ,did his father think so8 ,what deficiency did his father think was even more important than that of wings8 ,did ,nathan think that a boy was stronger than a bird8 ,is a boy absolutely stronger than a bird8 ,is he relatively stronger8 ,what is the meaning of relatively stronger8 ,would a man be strong enough to work wings that were sufficiently large to bear him up into the air8 ,would there be any great difficulty in constructing wings for him if he were strong enough8 ,is any visible substance lighter than air8 ,what would be the consequence if any of the loose substances about the earth's surface were light enough8 ,what are clouds composed of8 ,what difficulty did ,rollo's father point out1 in regard to their floating in the air8 ,what is a parachute8 ,describe ,rollo's experiment with the umbrella4 ,,chapter ,,iii4 ,,valve ,,making4 ,one morning1 when ,rollo awaked1 he heard a sharp clicking against the window4 ,nathan1 said he1 ,nathan1 ,i believe there is a snow-storm4 ,but ,nathan was too sleepy to hear or understand4 ,rollo looked up1 but there was a curtain against the window1 and he could not see very well4 ,he listened4 ,he heard a low1 moaning sound made by the wind1 and a continuance of the sharp clicking which he had heard at first4 ,when he had got up1 and dressed himself1 he found that there was a violent snow-storm4 ,at first he was glad of it1 for he liked snow-storms4 ,but then1 pretty soon1 he was sorry1 for it had been winter a long time1 and he was impatient for the spring4 ,after breakfast1 he and ,nathan read and studied for two hours1 under their mother's direction4 ,when they were released from these duties1 ,rollo proposed to ,nathan that they should go out into the shed1 and see how the storm came on4 ,there was a large door in the shed1 opening towards the street1 where they could stand1 protected from the wind1 and see the drifts of snow4 ,they accordingly put on their caps1 and went4 ,they found that the snow was pretty deep4 ,it was heaped up upon the fence and against the windows2 and there was a curious-shaped drift1 with the top curled over in a singular manner1 running along from the corner of the shed towards the garden gate4 ,ah1 says ,rollo1 when it clears up1 ,i mean to go and wade through it4 ,and ,i too1 said ,nathan4 ,o ,nathan1 said ,rollo1 it is over your head4 ,hark6 said ,nathan2 who is that pounding in the barn8 ,it is ,jonas1 ,i suppose1 said ,rollo4 ,i mean to go out and see what he is doing4 ,how are you going to get there8 said ,nathan4 ,o1 ,i can put on my boots1 said ,rollo1 and go right out through the snow4 ,i wish ,i could go1 said ,nathan4 ,well1 said ,rollo1 ,i can carry you on my back4 ,nathan clapped his hands at this proposal1 being doubly pleased at the prospect of both getting into the barn to see what ,jonas was doing1 and also of having a ride1 on the way4 ,so ,rollo put on his boots1 while ,nathan went and got ,rollo his straps1 to fasten his pantaloons around them4 ,when all was ready1 ,rollo sat down upon the step of the door1 in order that ,nathan might get on easily4 ,we'll play that ,i am a camel1 said ,rollo1 and that ,i'm kneeling down for you to get on4 ,do camels kneel down1 said ,nathan1 when the men want to ride8 ,yes1 said ,rollo2 and so saying1 he rose laboriously1 with his heavy burden upon his shoulders4 ,he staggered along with some difficulty1 but yet safely1 until he came to the great drift2 and1 after wallowing into the midst of it1 he lost his balance1 and both camel and driver rolled over together into the snow4 ,the snow got up under ,nathan's sleeve1 and he began to cry4 ,o ,nathan1 said ,rollo1 don't cry4 ,i'll run and get ,jonas to come and carry you in4 ,so ,rollo ran into the barn1 and called to ,jonas to come quick4 ,jonas laid down his hammer upon the bench1 and followed ,rollo4 ,he found ,nathan in the snow1 and took him up in his arms1 and carried him into the barn4 ,as soon as he got him under cover1 he brushed the snow off1 and told him not to cry4 ,i've got a fire in the shop1 said he1 and you shall see me do my work4 ,i'm mending the bellows4 ,so he led ,nathan through the barn1 and thence along under a shed to a sort of shop-room1 where there was a large fireplace and a fire4 ,rollo put on some sticks1 which made a great blaze2 and so ,nathan soon got warm and dry1 and forgot all his troubles4 ,then ,jonas sat him up1 upon a high stool1 near the bench1 where he could see him work4 ,he was just drawing out some of the nails1 by which the leather of the bellows was nailed to the sides4 ,what is the matter with the bellows8 said ,nathan4 ,the valve is out of order1 replied ,jonas4 ,the valve1 repeated ,nathan2 what is the valve8 ,the valve is a kind of clapper1 said ,jonas4 ,i will show it to you in a few minutes4 ,so ,jonas proceeded to take off the leather from one of the sides of the bellows4 ,there was a hole in one of the sides1 but no hole in the other4 ,nathan had often noticed the hole1 but he did not know what it was for4 ,what is the hole for8 said ,nathan4 ,that is to let the air in1 said ,jonas4 ,what do they want the air to come in for8 said ,nathan4 ,to make wind of1 said ,jonas4 ,do they make wind out of air8 said ,nathan4 ,yes1 said ,jonas1 they get the bellows full of air1 and then blow it out through the nose1 and that makes wind4 ,wind is air1 put in motion1 said ,rollo4 ,i read it in a book4 ,by this time1 ,jonas had taken off the leather so far that ,nathan could see into the bellows4 ,he saw that there was a little clapper over the hole1 in one of the sides of the bellows4 ,is that the valve8 said he to ,jonas4 ,yes1 said ,jonas4 ,what is it for8 said ,nathan4 ,it is to keep the wind from coming out of that hole4 ,why don't they want the wind to go out of that hole8 said ,nathan4 ,because1 said ,jonas1 they want it to go to the fire1--to blow the fire4 ,you see1 said ,rollo1 it can't go out of the hole1 and so it has to go out of the long nose1 which is pointed towards the fire4 ,what makes it go out at all8 said ,nathan4 ,why1 when we blow the bellows1 we press the two sides together1 and that presses the wind out4 ,it can't go out of the hole whence it came in1 because the clapper stops it up1 and so it goes out the long nose1 right into the fire1 and makes the fire burn4 ,by this time1 ,jonas had got the leather off so far1 that he could get at the clapper to mend it4 ,he told the boys that it was old and worn out1 and he must make a new one4 ,how are you going to make it8 said ,rollo4 ,you'll see1 said ,jonas1 if you watch me closely4 ,so ,jonas took some leather1 and cut out a piece1 of an oblong shape1 a little wider than the hole1 and about twice as long4 ,then he laid this down over the hole4 ,it covered it entirely4 ,then he took some small carpet nails1 and nailed one of the ends of the leather down to the board4 ,then ,jonas put his hand down under the board1 and run one of his fingers up through the hole1 and pushed the leather up a little way4 ,there1 said he to the boys1 you see ,i have nailed the leather1 so that1 when it lies down in its place1 it covers the hole completely2 and yet ,i can push it up a little with my fingers1 so that there will be an opening4 ,then ,jonas cut a small leather strap1 and nailed one end of it down upon one side of the clapper1 and the other end upon the other side of the clapper4 ,he put one little carpet nail into each end of the strap4 ,the strap1 when it was nailed1 passed directly across the clapper or valve4 ,it was not drawn tight across1 but it lay upon the clapper loosely4 ,the ends were nailed tight1 but the middle rested loosely upon the clapper4 ,now1 said ,jonas1 ,i can push the clapper up a little way1 but ,i can't push it far4 ,the strap keeps it from coming up far4 ,but why1 said ,nathan1 do you want it to go up at all8 ,to let the air in1 said ,jonas4 ,when ,i get the leather all nailed on again1 ,i'll show you the whole operation of it4 ,and you can be telling us about it in the mean time1 said ,rollo4 ,well1 then1 said ,jonas1 when ,i lift up the upper side of the bellows by the handle1 to blow1 the air comes in by the hole4 ,the clapper lifts up a little way1 and lets it in4 ,then1 when ,i press down the handle again1 it presses the air out through the nose1 because it can't go back through the valve hole4 ,why not8 said ,nathan4 ,because1 said ,jonas1 the valve falls down over the hole1 and stops it up4 ,it is made so as to lift up easily1 and then to fall down and cover the hole exactly1 and prevent the air going out the same way it came in4 ,so1 as it cannot get out by the valve1 it has all to go out through the nose4 ,if the nose were stopped up1 it could not get out at all4 ,and what then8 said ,rollo4 ,why1 then1 replied ,jonas1 you could not bring the two sides of the bellows together again4 ,the air between would keep them apart4 ,i should like to try1 said ,rollo4 ,well1 said ,jonas2 and there are some other experiments you may perform with it too4 ,at length1 ,jonas said that he had got the leather all nailed on1 and they might try the experiment4 ,he took hold of the nose of the bellows1 and held his thumb near the end of it1 ready to stop up the hole4 ,now1 ,nathan1 you may take hold of the handles1 and pull them apart as if you were going to blow4 ,nathan did so4 ,he pulled the handles apart1 and held them open4 ,now1 said ,jonas1 ,i will stop up the nose1 and the valve will close itself2 and then you will find that you cannot bring the sides together again4 ,so ,jonas put his thumb over the hole1 and told ,nathan to blow4 ,nathan pressed hard1 and the sides came together again1 about as easily as usual4 ,what6 exclaimed ,jonas with surprise4 ,he did not know what to make of the failure of his experiment4 ,there must be a leak somewhere1 said he4 ,and he took the bellows out of ,nathan's hand to look for it4 ,he found there was a corner1 on the side opposite to the one where he had been working1 where the leather was open1 he having forgotten to nail it down4 ,ah6 said he1 here is the difficulty4 ,when ,i have nailed this down1 we will try again4 ,is that a leak8 said ,nathan4 ,yes1 said ,jonas4 ,when you worked the bellows1 you pressed the air all out through there4 ,i did not know that that was open4 ,let me nail this down1 and then we will begin our experiment regularly4 ,,questions4 ,what was ,jonas doing in the shop1 when ,rollo and ,nathan went out to find him8 ,what part of the bellows was out of order8 ,how did he make a new valve8 ,how did he fasten it to its place8 ,did he nail down only one edge1 or both edges8 ,why did he want the other edge to be left at liberty8 ,how did he prevent its lifting up too far8 ,what was the first experiment which he performed with the bellows1 after he had finished the mending8 ,did it succeed at first8 ,why not8 ,in working a pair of bellows1 where does the air come in8 ,where does it go out8 ,why cannot the air escape through the valve where it comes in8 ,,chapter ,,iv4 ,,experiments4 ,when ,jonas had finished nailing down the corner1 he said1 ,now there are several experiments1 which we can perform with the bellows4 ,i will be the professor1 and you two shall be my class in philosophy1 and ,i will direct you how to make the experiments4 ,first1 said ,jonas1 you1 ,rollo1 may take hold of the nose of the bellows with your hand1 in such a way as to put your thumb over the end of it1 to stop it up1 and then let ,nathan try to blow4 ,rollo did so1 and ,nathan tried to blow4 ,he found that he could open the bellows very easily2 but when he attempted to press the sides together again1 he could not4 ,he crowded the handle belonging to the upper side down1 as hard as he could1 but it would not move4 ,what makes it do so8 said ,nathan4 ,the air inside1 said ,jonas4 ,we have stopped up all the places1 where it could get out4 ,the valve stops itself4 ,rollo stops the nose with his thumb1 and ,i have nailed the leather down close1 about all the sides4 ,and so the air can't get out1 and that keeps you from bringing the sides together again4 ,nathan tried again with all his strength4 ,the sides came together very slowly4 ,they're coming1 said he4 ,yes1 said ,jonas4 ,they come a little1 just as fast as the air can leak out through the little leaks all around4 ,i thought you stopped all the leaks1 said ,nathan4 ,yes1 replied ,jonas1 ,i stopped all the real leaks1 but still ,i can't make it perfectly tight4 ,some air can escape between the leather and the nails all around1 and just as fast as it can get out1 so fast you can press the sides together1 and no faster4 ,here ,nathan tried again with all his strength2 but he could only bring the sides together very slowly4 ,now comes the second experiment1 said ,jonas4 ,while ,nathan is trying to press the two handles together1 you1 ,rollo1 may run your finger into the hole1 and push up the valve a little4 ,rollo did so4 ,he pushed up the valve a little with his finger1 and that allowed the air to escape through the opening4 ,the consequence was1 that the bellows collapsed at once under the pressure which ,nathan was exerting upon them4 ,there1 said ,jonas1 you see that when the air is kept in1 you cannot bring the sides together2 but when ,i let the air out1 then they come together easily4 ,yes1 said ,nathan2 do it again1 ,rollo4 ,so they performed the experiment again4 ,nathan pulled the handles apart wide1 while ,rollo kept his thumb over the nose1 to keep the air from issuing through4 ,then ,nathan tried to press them together2 but he could not1 until ,rollo put his finger under1 and pushed up the valve a little1 and then they came together again very easily4 ,the air is a real thing1 ,i verily believe1 said ,nathan4 ,yes1 said ,rollo1 ,i know it is4 ,and now for the third experiment1 ,jonas4 ,the third experiment1 said ,jonas1 is this4 ,turn the bellows bottom upwards1 and try to blow4 ,nathan did so4 ,he found that he could work the bellows easily--too easily1 in fact2 but they did not blow4 ,hold your hand opposite the nose1 and see if any wind comes1 said ,jonas4 ,they did so2 there was no wind1 or rather scarcely any4 ,the reason is1 said ,jonas1 that1 when the bellows are bottom upwards1 the valve hangs down off from the hole all the time1 and lets the air all out through the hole in the side2 and it can come out more easily there than through the nose1 and so it don't blow well4 ,well1 ,jonas1 said ,rollo1 that's a pretty good experiment2 but what is the next8 ,let me try the next4 ,nathan1 it is my turn4 ,the next experiment1 which is the fifth1---- ,no1 the fourth1 said ,nathan4 ,the fourth1 then1 said ,jonas1 is to prove what ,i said to you--that the air1 which is blown out at the nose of the bellows1 really comes in through the valve4 ,let me see1--,i want something to make a smoke4 ,will not paper do8 said ,rollo4 ,yes1 said ,jonas1 here is some brown paper1 which will do4 ,so ,jonas rolled it up1 and told ,rollo to set it on fire1 and then1 when it was well burning1 to step on it with his foot1 and put the flame out4 ,rollo did so1 and the paper lay in a heap1 making a great smoke upon the hearth1 just before the fire4 ,now1 said ,jonas1 put the bellows upon its edge1 by the side of the paper1 so as to have the valve near the smoke1 and then hold still a minute1 until the smoke comes up steadily by the valve4 ,when this was done1 ,jonas told ,nathan to take hold of the nose of the bellows1 to steady it1 so that ,rollo could blow4 ,he then directed ,rollo to lean the bellows over a little towards the smoke1 so that the moving side should not rub upon the hearth1 when he began to blow4 ,now1 he continued1 if you work the bellows1 you will see that the smoke will be drawn in through the valve1 and then will come out through the nose4 ,this experiment succeeded perfectly well1 only just in the midst of the interest that they felt1 in seeing the smoke come pouring out through the nose1 they heard a bell ring at the house4 ,they knew at once that this bell was for ,rollo and ,nathan2 and so the two boys jumped up from the hearth1 and ran out to see what was wanted4 ,they went through the shed into the barn1 and thence on till they came to the great barn door1 where they had come in4 ,there ,rollo stopped1--for he did not like to go out into the snow1--and asked ,dorothy1 who was ringing the bell1 what she wanted4 ,where's ,nathan8 said ,dorothy4 ,he's here with me1 said ,rollo4 ,nathan was coming along1 as fast as he could1 through the barn4 ,do you want us8 said ,rollo4 ,no1 said ,dorothy1 only we did not know where you were4 ,you may stay half an hour more1 and then it will be nearly dinner time4 ,dorothy then went in1 leaving the boys at the great barn door4 ,the door opened in such a direction1 that the wind did not blow in2 and ,rollo and ,nathan looked out for some time1 watching the falling snow1 and listening to the wind1 as it roared through the tops of the trees4 ,at last1 when they began to think of returning to the shop1 ,rollo said1-- ,o ,nathan1 let us go and hide1 and then ,jonas will not know where we are4 ,well1 said ,nathan1 we will4 ,the boys accordingly began to look about the barn for a place to hide4 ,it was a large barn1 with stalls for oxen and cows1 and cribs for horses1 and one or two calf-pens4 ,then there was a granary in one corner1 and a tool-room near it1 and lofts and scaffolds above4 ,the boys found plenty of places to hide in1 and it took them some time to decide which to choose4 ,at last1 they found a good warm place1 by some bundles of wheat straw1 up in the barn chamber2 and they amused themselves by choosing out large straws1 and making tubes of them to blow through4 ,they called them their bellows4 ,they entirely forgot that they were hid from ,jonas1 for nearly half an hour2 and then ,rollo proposed that they should creep softly down1 and see what ,jonas was about4 ,so they went down stairs on tiptoe2 ,rollo first1 and ,nathan following4 ,they crept softly along to the door leading out into the shed1 through which they had to pass in order to get to the shop2 and ,rollo was going to open this softly1 when1 to his surprise1 he found it fastened4 ,why1 ,nathan1 said he1 this door is fastened4 ,how came it fastened8 said ,nathan4 ,i don't know1 said ,rollo1 unless ,jonas fastened it4 ,i think he must have finished his work1 and gone into the house2 and so he has fastened this door4 ,and now he won't come and find us1 said ,nathan4 ,no1 said ,rollo1 and we must go out the front door4 ,and ,i don't care much1 he continued1 for it is pretty near dinner time4 ,the boys then went back to the front door of the barn1 and1 to their surprise and alarm1 found that fastened too4 ,what shall we do8 said ,rollo2 ,jonas has fastened us in4 ,as ,rollo said this1 his face assumed an expression of great solicitude1 and ,nathan began to cry4 ,don't cry1 ,nathan1 said he2 we can find some way to get out4 ,but ,i don't see1 ,i confess1 what made ,jonas lock us in4 ,the truth was1 that ,jonas did not know that the boys were in the barn when he fastened it up4 ,as they did not come back after they had gone to answer the bell1 he supposed that they had gone into the house2 and when he was ready to come in himself1 he shut and fastened the back doors of the barn1 as he usually did when he left the shop4 ,he then came around to the front barn door1 and although that was on the sheltered side1 so that the wind did not blow in1 he thought it possible that the wind might change1 and so drive the snow in upon the barn floor2 and therefore1 to make all safe1 he thought that he would shut them1 too4 ,he accordingly shut the great doors1 and put the fid into the staple4 ,the fid is a wooden pin1 to be passed through the staple when the doors are shut1 to fasten them4 ,the doors cannot be opened again until the fid is taken out4 ,rollo went all around the barn1 trying to find some place where he could get out2 but he could not find any place at all4 ,let us go up stairs1 said he1 at length1 to ,nathan4 ,o1 it will not do any good to go up stairs1 said ,nathan4 ,it would kill us to jump out the window4 ,i know we can't jump out the window1 said ,rollo1 but perhaps we can find out some way to get down4 ,o1 there is a ladder2 ,i remember now1 ,nathan1 there is a ladder4 ,we can get down from the window by the ladder4 ,i shall be afraid to go down the ladder1 said ,nathan4 ,o no1 said ,rollo1 ,i will go first1 and see if it is safe4 ,by this time they had reached the barn chamber4 ,there was a window in it1 with glass1 over the great barn door2 but ,rollo could not get it open4 ,he told ,nathan that1 if he could only get it open1 and could find a long pole1 he could reach it down1 and knock the fid out1 and so open the great doors4 ,but1 with all his efforts1 he could not raise the window4 ,there was another window1 which had no glass1 but was closed by a wooden shutter1 which opened upon hinges like a door4 ,rollo said he meant to open this window4 ,now1 it happened that this window was upon that side of the barn which was exposed to the wind and storm2 and1 the moment that ,rollo had pushed open the shutter a little way1 the wind forced it instantly from his hand1 and slammed it back against the side of the barn1 with great violence4 ,it almost pulled ,rollo himself out of the window4 ,nathan looked frightened4 ,rollo himself looked somewhat astonished at such an unexpected effect2 but presently said1-- ,well1 ,nathan1 ,i rather think that1 if you had had hold of that shutter1 you would have thought that air was a real thing4 ,o1 that was the wind1 ,rollo2 that was the wind1 said ,nathan4 ,rollo did not answer1 but went to the ladder1 which was standing up against the hay-loft4 ,it was a pretty long1 but yet a very light ladder2 and ,rollo and ,nathan succeeded1 after some difficulty1 in getting it down1 and in running the end out of the window4 ,when the lower end reached the ground1 the upper end was two or three feet above the bottom of the window2 so that ,rollo could easily get upon it to descend4 ,the wind and storm1 which raged with great violence1 were somewhat terrifying2 but he knew that the ladder was secure1 the upper part being confined in the window2 and so he resolutely descended4 ,when he had fairly reached the ground1 he looked up1 with an expression of great satisfaction upon his countenance1 and said1-- ,there6 now1 ,nathan1 for your turn4 ,but ,nathan was afraid to venture2 and ,rollo himself was half afraid to have him make the attempt4 ,while they were standing in this perplexity1 ,rollo heard a voice behind him1 calling out1-- ,rollo4 ,rollo turned1 and saw ,dorothy standing by the door4 ,what are you doing1 ,rollo8 said ,dorothy4 ,i am trying to get ,nathan out of the barn1 said ,rollo4 ,how came he in the barn8 said ,dorothy4 ,why1 ,jonas locked us in1 and ,i had to come down the ladder2 but ,nathan is afraid1 and ,i can't get him out4 ,why don't you go to the door1 and let him right out8 ,o1 said ,rollo1 laughing1 ,i never thought of that4 ,go down1 ,nathan1 he continued1 to the door1 and ,i will go round and knock out the fid4 ,so ,nathan went down1 and ,rollo1 meeting him there1 knocked out the fid1 and released him from his imprisonment4 ,,questions4 ,what was the first experiment with the bellows1 described in this chapter8 ,why could not ,nathan press the two sides of the bellows together1 while the nose was stopped8 ,what was the second experiment8 ,what was the effect produced by turning the bellows bottom upwards1 as in the third experiment8 ,what was the fourth experiment8 ,what was the use of the smoke of the paper8 ,how were the experiments interrupted8 ,what evidence did ,rollo and ,nathan have that the air was a real substance1 when in the barn chamber8 ,,chapter ,v4 ,,pressure4 ,one evening1 just after tea1 ,rollo came to his father1 who was sitting by the side of the fire1 and said1-- ,father1 ,i wish we could see the air1 as we can the water1 and then perhaps we could try experiments with it4 ,o1 we can try experiments with the air as it is1 said his father4 ,can we8 said ,rollo2 ,i don't see how4 ,we cannot see the air1 it is true2 but then we can see its effects1 and so we can experiment upon it4 ,well1 at any rate1 said ,rollo1 we can't build a dam1 and make it spout through a hole1 like water4 ,no1 said his father1 not exactly4 ,in your dam1 for instance1 when it was full1 you had water on one side of the board1 and no water on the other2 and then1 by opening a hole in the board1 the water spouted through2 but we cannot very well get air on one side of a partition1 and no air on the other2 if we could1 it would spout through very much as the water did4 ,why can't we do that1 sir8 said ,rollo4 ,because1 replied his father1 we are all surrounded and enveloped with air4 ,it spreads in every direction all around us1 and rises many miles above us4 ,whereas1 in respect to water1 you had one little stream before you1 which you could manage just as you pleased4 ,if you were down at the bottom of the sea1 then the water would be all around you and above you2 and there1 even if you could live there1 you could not have a dam4 ,no1 sir1 said ,rollo1 the water would be everywhere4 ,yes1 replied his father1 and the air is everywhere4 ,if1 however1 we could get it away from any place1 as1 for instance1 from this room1 then bore a hole through the wall1 the weight of the air outside would crowd a portion of it through the hole1 exactly as the weight of the water above the board in your dam crowded a part through the hole in the board4 ,i wish we could try it1 said ,rollo4 ,we can try it1 in substance1 said his father1 in this room2 or--no1 the china closet will be better4 ,there was a china closet1 which had two doors in it4 ,one door opened into the parlor1 where ,rollo and his father were sitting4 ,the other door opened into the back part of the entry4 ,rollo's father explained how he was going to perform the experiment1 thus3-- ,if we could1 by any means1 get all the air out of the closet for a moment1 then the pressure of the air outside would force a jet of it in through the key-holes of the doors1 and the crevices4 ,and how can we get the air out8 said ,rollo4 ,we can't1 said his father1 get it all out2 but we can get a part of it out by shutting the door quick4 ,the door will carry with it a part of the air that was in the closet1 and then the outside air will be spouted in1 through the key-hole of the other door4 ,only we can't see it1 as we can the water4 ,no1 said ,rollo2 but ,i can put my hand there1 and feel it4 ,a better way1 said his father1 would be to hold a lamp opposite to the key-hole1 and see if it blows the flame4 ,rollo tried the experiment1 in the way his father had described4 ,he went into the closet with the lamp4 ,he held the lamp opposite to the key-hole1 and pretty near to it1 and then he asked ,nathan to shut the other door suddenly4 ,nathan1 who was standing all ready by the other door1 which was about half open1 put his two hands against it1 and pushed it to1 with all his strength1 producing a great concussion4 ,o ,nathan1 said his father1 you need not be quite so violent as that4 ,it succeeded1 father1 it succeeded1 said ,rollo4 ,i'm glad it succeeded1 said his father2 but ,nathan need not have shut the door with so much force4 ,i wanted to drive out all the air1 said ,nathan4 ,i'll show you how to do it1 said his father4 ,rollo's father accordingly arose1 and came to the closet door4 ,he opened the door wide1 and then explained to the boys1 that the beginning of the movement of the door1 when it was wide open1 did not drive out any air4 ,for1 said he1 there is so large a space between the edge of the door and the wall1 that the air that is put in motion by the movement of the door1 can pass directly round the edge1 back into the closet again4 ,it is only when the door is almost shut1 when the edge of it comes close to the casing all around1 that the movement of the door drives the air out4 ,then he took hold of the latch of the door1 and put it almost to1 very gently4 ,he turned the latch so as to prevent its snapping against the catch1 and then pushed it suddenly into its place three or four times1 opening the door only a very little way every time4 ,now1 said he1 hold the lamp at the key-hole1 and watch the flame1 while ,i shut the door two or three times in this way4 ,rollo did so1 ,nathan standing all the time by his side4 ,they observed that the flame of the lamp was driven into the room every time the door was shut2 proving that1 every time a little of the air was driven out by the door1 a little puff rushed in at the key-hole4 ,let us stop up the key-hole1 said ,rollo1 and then it can't get in4 ,yes1 said his father1 there are a great many little crevices all around the closet1 where the air can come in4 ,couldn't we stop those up too8 said ,rollo4 ,no1 said his father1 not so as to make the closet air-tight4 ,for1 if the crevices could all be stopped exactly1 the air would come in through the very wood itself4 ,how8 said ,rollo4 ,why1 there are little pores in wood1 that is1 little channels that the sap flowed in when the wood was growing1 and the air can pass through these4 ,here ,rollo's father observed that ,rollo was looking very intently at the table2 and he asked him what he was doing3 he said he was trying to find some of the pores4 ,you can't see them there1 said his father4 ,st4 ,domingo mahogany is a very hard and close-grained kind of wood4 ,if it was summer1 and you could dig down and get a small piece of the root of the great elm-tree in the yard1 you could see the pores and channels there4 ,after some more conversation on this subject1 ,rollo asked his father if he could not think of some other experiments for them to try4 ,his father said that he did not just then think of any experiment1 but that1 if ,rollo and ,nathan would come and sit down by the fire1 he would give them some information on the subject4 ,rollo's mother said that she should like to hear too4 ,they accordingly waited until she was ready1 and then1 when all were seated1 ,mr4 ,holiday began thus3-- ,air is in many respects much like water4 ,yes1 interrupted ,rollo1 just like water1 only thinner1 because1 you see---- ,you must not interrupt me1 said his father1 unless to ask some question1 which is necessary to understand what ,i say4 ,it is entirely irregular for a pupil1 instead of listening to his teacher1 to interrupt1 in order to tell something that he knows himself4 ,rollo's father smiled1 as he said this1 but ,rollo looked rather ashamed4 ,then his father proceeded3-- ,there is one very remarkable difference between them4 ,water is not compressible by force2 but air is4 ,what is the meaning of compressible8 said ,nathan4 ,compressible things1 said his father1 are those that can be compressed1 that is1 pressed together1 so as to take up less room than they did before4 ,sponge is compressible4 ,a pillow is compressible4 ,but iron is not compressible1 and water is not compressible4 ,i should think it was1 said ,nathan2 it is very soft4 ,it is very yielding1 replied his father1 when you press it1 but it is not pressed into any smaller space4 ,it only moves away4 ,if you have a tumbler half full of water1 and press a ball down into it1 you could not crowd the water into any smaller space than it occupied at first2 but1 as fast as the ball went down1 the water would come up around the sides of the ball4 ,but suppose1 said ,rollo1 that the ball was just big enough to fit the tumbler all around2 then the water could not come up4 ,and then1 said his father1 you could not crowd the ball down4 ,could not a very strong man8 said ,nathan4 ,no1 replied his father1 the water cannot be sensibly compressed4 ,but now1 if the tumbler contained only air1 and if a ball were to be put in at the top1 just large enough to fit the tumbler exactly1 and if a strong man were to crowd it down with all his strength1 he would1 perhaps1 compress the air into half the space which it occupied before4 ,perhaps the tumbler would break1 said ,nathan4 ,yes1 replied his father1 and the tumbler will answer only for a supposition2 but for a real experiment it would be best to have a cylinder of iron4 ,what is a cylinder8 said ,nathan4 ,an iron vessel1 shaped like a tumbler1 only as large at the bottom as it is at the top1 would be a cylinder4 ,now1 if there was a cylinder of iron1 with the inside turned perfectly true1 and a brass piston fitted to it---- ,what is a piston8 said ,nathan4 ,a piston1 said his father1 is a sort of stopper1 exactly fitted to the inside of a cylinder1 so as to slide up and down4 ,it is made to fit perfectly1 and then it is oiled1 so as to go up and down without much friction1 that is1 hard rubbing4 ,there is a sort of stem coming up from the middle of the piston1 called the piston rod1 which is to draw up the piston1 and to press it down by4 ,now1 continued his father1 if a strong man had a cylinder like this1 with a piston fitted to it1 and a strong handle across the top of the piston rod1 perhaps he might press the air into one half the space which it occupied before4 ,that is1 if the cylinder was full of air when he put the piston in1 perhaps he could get the piston down half way to the bottom4 ,then the air would be twice as dense as it was before2 that is1 there would be twice as much of it in the same space as there was before4 ,it would be twice as compact and heavy4 ,this is called condensing air4 ,the philosophers have ingenious instruments for condensing air4 ,if1 however1 a man condenses air in this way1 by crowding down a piston1 he does not begin the condensation when the piston begins to descend4 ,the air is condensed a great deal before he begins4 ,all the air around us is condensed4 ,how comes it condensed8 said ,rollo4 ,why1 you recollect that1 when you bored a hole through the board in the bottom of your dam1 the water spouted out4 ,no1 father1 said ,rollo1 we pulled the plug out2 ,jonas bored the hole4 ,well1 said his father1 the water spouted out4 ,yes1 said ,rollo4 ,what made it8 said his father4 ,why1 the water above it was heavy1 and pressed down upon it1 and crowded it out through the hole4 ,yes1 said his father1 and the deeper the water1 the more heavily it was pressed4 ,yes1 sir1 said ,rollo1 and the farther it spouted4 ,because it was pressed down by the load of such a high column of water4 ,yes1 sir1 said ,rollo4 ,well1 replied his father1 it is just so with the air4 ,the air all around us is pressed down by the load of all that is above us4 ,we are1 in fact1 down at the bottom of a great ocean of air1 and the air here is loaded down very heavy4 ,how heavy8 said ,rollo4 ,o1 very heavy indeed1 said his father4 ,why1 air is pretty light1 said ,rollo4 ,yes1 replied his father1 but then the column of it is very high4 ,how high8 said ,rollo4 ,why1 between thirty and forty miles4 ,but it grows thinner and thinner towards the top2 so it is not as heavy1 by any means1 as a column of air would be1 thirty miles high1 and as dense all the way up as it is here4 ,what makes it grow thinner and thinner towards the top8 said ,rollo4 ,because1 said his father1 that which is near the top1 has not as much load of air above it1 to press it down4 ,and that which is at the top1 said ,rollo1 has none above it1 to press it down4 ,no1 replied his father4 ,and how thin is it there8 ,nobody knows1 said his father4 ,what1 nobody at all8 said ,nathan4 ,no1 ,i believe not2 at least ,i do not2 and ,i don't know that any body does4 ,how do they know1 then1 how high it is8 said ,rollo4 ,the philosophers have calculated in some way or other1 though ,i don't exactly know how4 ,i believe they have ascertained how great the pressure of the air is here at the surface of the earth1 and have calculated in some way1 from that1 how high the air must be to produce such a pressure4 ,and how high must it be8 said ,nathan4 ,why1 between thirty and forty miles1 said ,rollo2 father told us once4 ,and yet1 continued his father1 water1 thirty or forty feet deep1 would produce as great a pressure as a column of air of thirty or forty miles4 ,that is1 the air around presses about as heavily1 and would force a jet of air through a hole with about as much force1 as water would1 coming out at the bottom of a dam1 as high as a common three-story house4 ,these explanations were all very interesting to ,rollo and to his mother2 but ,nathan found it rather hard to understand them all1 and he began to be somewhat restless and uneasy4 ,at length he said1-- ,and now1 father1 haven't you almost done telling about the air8 ,why1 yes1 said his father2 ,i have told you enough for this time2 only you must remember it all4 ,i don't think ,i can remember it quite all1 said ,nathan4 ,well1 then1 remember the general principle1 at any rate1 said his father1 which is this--that we live at the bottom of a vast ocean of air1 and that the lower portions of this air are pressed down by the load of all the air above2 that1 being so pressed1 the lower air is condensed1--so that we live in the midst of air that is pressed down1 and condensed1 by the load of all that is above it2 and that1 consequently1 whenever the air is taken away1 even in part1 from any place1 as you removed some of it from the china closet1 the pressure upon the air outside forces the air in through every opening it can find4 ,i think that is a little too much for me to remember1 said ,nathan4 ,nathan's father and mother laughed on hearing this1 though ,nathan did not know what they were laughing at4 ,his father told him that he could not expect him to remember all2 and that1 to pay him for his particular attention1 he would tell him a story4 ,so he took ,nathan up in his lap1 and told him a very curious story of a boy1 who went about the yard with a little dog upon one of his shoulders1 a cat upon the other1 and a squirrel on his head4 ,the squirrel was tame4 ,,questions4 ,why cannot experiments be performed upon the pressure of air1 as conveniently as upon the pressure of water8 ,how did ,rollo's father contrive to remove a part of the air from the china closet8 ,where did they expect that the air would be forced into the closet8 ,how were they to make this effect visible8 ,did the experiment succeed8 ,suppose the key-hole had been stopped up2 where would the air have been forced in8 ,suppose all the crevices had been closed4 ,is water compressible8 ,is air compressible8 ,what is the shape of a cylinder8 ,what is a piston8 ,how might air be compressed by means of a cylinder and piston8 ,what was the general principle which ,rollo's father stated1 in conclusion8 ,,chapter ,,vi4 ,,ballooning4 ,the next evening1 ,rollo and ,nathan had another conversation with their father1 respecting air4 ,when they were all seated1 he commenced as follows3-- ,i told you yesterday1 that air may be compressed by force1 while water cannot be4 ,it has another property1 which is in some respects the reverse of this4 ,it springs back into its original bulk1 when the pressure is removed4 ,how8 said ,nathan2 ,i don't exactly understand you4 ,why1 you remember what ,i said about the experiment with the iron cylinder and a piston to fit it4 ,yes1 sir1 said ,rollo4 ,what was the experiment8 said his father4 ,why1 if a man were to press the piston down hard1 he could crowd the air all into the lower half of the cylinder4 ,yes1 replied his father4 ,now1 the property ,i am going to tell you about this evening is this--that1 if the man lets go of the piston rod1 the air that is condensed into the bottom of the cylinder1 will spring up1 and force the piston up again4 ,this property is called elasticity4 ,it is sometimes called the expansive force of the air4 ,for it is a force tending to expand the air1 that is1 to swell it out into its original dimensions4 ,this is another great difference between air and water4 ,now1 as all the air around us1 continued ,rollo's father1 is pressed down very heavily1 and is condensed a great deal1 it is all the time endeavoring to expand2 and it would expand1 were it not that the great burden of the air above it keeps it condensed4 ,but water is not compressed1 and has no tendency to expand4 ,the water of ,rollo's dam1 for instance1 had all the weight of the atmosphere resting upon it1 but it did not compress it at all1 and so it did not tend to expand4 ,and now1 said his father1 ,i cannot perform any experiment1 to show you that air tends strongly to expand or swell out into a great space1 while water does not2 but ,i can make a supposition1 which will illustrate it4 ,suppose we had a large1 but very thin1 glass bottle1 filled with water1 and put down upon the floor in the middle of this room4 ,suppose1 also1 that we had another bottle1 of the same size and shape1 filled with air1 and we put that down upon the floor by the side of the other2 both bottles being stopped very tight4 ,now1 if we could by any means suddenly take away all the air from the room1 so that there should be nothing around the bottles1 then the bottle of water would remain just as it is1 for the glass would have nothing to support but the weight of the water1 and it would be strong enough for that4 ,but the bottle of air would fly all to pieces2 for that would not rest quietly1 like the water1 satisfied with the space which it already has1 and only pressing with its own weight upon the sides of the glass2 but it would immediately expand with so much force as to break the thin glass all to pieces4 ,would it6 exclaimed ,rollo and ,nathan together4 ,and would it make a loud noise8 ,yes1 replied their father1 ,i presume it would make a loud explosion2 that is1 if the air in the room around it could by any means be all at once and suddenly removed4 ,and so you must remember1 he continued1 that there are two very remarkable differences between air and water4 ,air may be condensed by pressure1 and1 as it exists all around us1 is greatly condensed by the pressure of the air above1 and it may be compressed more4 ,and air is expansive1 while water is not4 ,whenever the pressure upon it is removed1 it suddenly expands1 or spreads out in all directions4 ,o dear me6 said ,nathan1 with a sigh4 ,what is the matter8 said his father4 ,why1 ,i can't understand it very well4 ,can't you8 said his father4 ,well1 ,i must admit that you are rather too young to study pneumatics4 ,pneumatics8 repeated ,rollo4 ,yes1 said his father2 that is the name of this science4 ,illustration3 ,then it sailed slowly away4--,page #he4 ,what1 the science of air8 said ,rollo4 ,yes1 said his father1 the science which treats of air1 and of all other compressible and expansive fluids4 ,but let me think4 ,i must try to tell you something which ,nathan can understand and be interested in4 ,if ,i had a very light feather1 ,i could let him perform an experiment4 ,would a little down do8 said ,rollo's mother4 ,yes1 replied his father1 that would be better than a feather4 ,mrs4 ,holiday then went and brought a little down1 and handed it to ,rollo's father4 ,now1 there was a lamp upon the table1 of a peculiar kind1 called a study lamp4 ,it had a glass tube1 called a chimney1 around the wick1 and consequently around the flame itself1 being round1 like a ring4 ,rollo's father told ,nathan to hold the down over the top of this glass chimney1 and then to let it go4 ,nathan did so4 ,the little tuft of down was wafted up into the air1 quite high above the lamp1 and then it sailed slowly away1 and fell down upon the table4 ,i know what makes it rise1 said ,rollo4 ,it is the heat4 ,the heat makes it rise4 ,do you think so8 said his father4 ,then take the down1 and lay it gently upon the hearth1 before the fire1 as near as you can4 ,rollo did so4 ,he had to take his hand away very quick1 for it was quite hot there4 ,the little tuft remained quietly upon the hearth where he placed it4 ,there1 said his father1 is not that a hotter place than it was over the lamp8 ,yes1 sir1 said ,rollo4 ,then1 if it was heat that made it rise1 why does not it rise now8 ,rollo could not tell4 ,i will tell you how it was1 said his father4 ,heat makes air more expansive4 ,when air is heated1 it swells2 when it is cool1 it shrinks again4 ,now1 if it swells1 it becomes lighter1 and so it is buoyed up by the heavier air around it2 just as wood at the bottom of the sea would be buoyed up1 and would rise to the surface of the water4 ,now1 the heat of the lamp heats the air that is in the glass chimney1 and swells it4 ,this makes it lighter2 and so the air around it1 which is heavier1 buoys it up1 and it carries up the feather with it4 ,no1 the down1 father1 said ,nathan4 ,yes1 the down1 said his father4 ,then it seems to me1 after all1 said ,rollo1 that it is the heat which makes it rise4 ,yes1 said his father1 it does1 indirectly4 ,it expands the air2 that makes it lighter2 then the heavy air around it buoys it up1 and1 when it goes up1 it carries up the down4 ,so that it is not strictly correct to say1 that the heat carries it up4 ,the heat sets in operation a train of causes and effects1 the last of which results in carrying up the feather4 ,now1 continued his father1 there is always a stream of air going up1 wherever there is a lamp1 or a fire1 or heat1 which heats the air in any way4 ,the expanded air from a fire goes up chimney4 ,the cool and heavy air in the room and out of doors crowds it up4 ,the air out of doors8 said ,rollo4 ,how can that crowd it up8 ,why1 it presses in through all the crevices and openings all around the room1 and crowds the light air up the chimney4 ,all the smoke is carried up too with it1 and it comes pouring out at the top of the chimney all the time4 ,you can see that the air presses in at all these crevices1 continued ,rollo's father1 by experiment4 ,what experiment is it8 said ,rollo2 let us try it4 ,i will let ,nathan try it1 said his father1 and you may go with him and see the effect4 ,first1 he continued1 you see by the smoke1 that the air really goes up the chimney2 and ,i will show you that other air really crowds into the space1 from other parts of the room4 ,so he took a lamp from the table1--not the study lamp2 it was a common lamp1--and held it at various places in the opening of the fireplace1 by the jambs and near the upper part2 and ,rollo and ,nathan saw that the flame1 in all cases1 was turned in towards the chimney4 ,yes1 said ,rollo1 ,i see it is drawn in4 ,no1 said his father2 strictly speaking1 it is not drawn in2 it is pressed in1 by the cool and heavy air of the room4 ,i thought1 said ,rollo's mother1 that the chimney drew the air from the room into it4 ,that is what is generally said1 replied ,mr4 ,holiday1 but it is not strictly true4 ,the common idea is1 that the hot air rises in the chimney1 and so draws the air from the room to supply its place2 but this is not so4 ,in the first place1 nothing can rise unless it is forced up4 ,the lightest things have some weight1 and would1 if left to themselves1 fall4 ,the hottest and lightest air in a chimney would fall to the earth1 if there was no cooler and heavier air around it1 to force it to rise2--just as the lightest cork1 which would rise very quick from the bottom of the sea1 would fall back again very quick1 if the water was not there4 ,remember1 then1 ,nathan and ,rollo1 that1 when a fire is built in a fireplace1 so as to warm the air in the chimney1 it makes this air not so heavy2 and then the cool air all around it in the room and out of doors1 presses in1 and crowds under the light air1 and makes it ascend4 ,but1 father1 said ,nathan1 you said ,i might perform an experiment4 ,very well1 ,i am ready now4 ,take the lamp1 and carry it around the room1 and hold it opposite any little opening you can find4 ,i can't find any little openings1 said ,nathan4 ,o yes1 said his father2 the key-hole of the door is a little opening1 and there is a narrow crevice all around the door2 and you will find little crevices around the windows4 ,now1 hold the lamp opposite any of these1 and you will see that the air presses in4 ,so ,nathan went with the lamp1 ,rollo following him1 and held the lamp opposite to the key-hole1 and the crevices around the door and windows2 only1 when he came to the window1 his father told him to be very careful not to set the curtain on fire4 ,rollo wanted ,nathan to let him try it once2 and so ,nathan gave him the lamp4 ,he said he meant to make a crevice2 and so he pushed up the window a very little way1 and held the lamp opposite to the opening4 ,the air pressed the flame in towards the room1 in all cases4 ,people commonly say1 that it is drawn in1 said his father1 but that is not strictly correct2 it is really pressed in4 ,there is no power of attraction1 in the air that is in the room1 to draw in the air that is out of doors1 through the crevices2 but the air that is out of doors1 is so heavy1 that it presses in1 and crowds the warm and light air up the chimney4 ,and now1 said his father1 ,i cannot tell you anything more this evening2 but1 if you remember this1 ,i will give you some further instruction another time4 ,well1 sir1 said ,nathan1 only ,i wish you would tell me a little story1 as you did last evening4 ,have not ,i been still8 ,his father had noticed1 that he had been very still and attentive1 but did not think before1 that it was in expectation of being rewarded with a story4 ,well1 said his father1 ,i will tell you a story1 or give you a little advice4 ,how should you like a little advice8 ,well1 father1 a little advice2 just which you please4 ,i advise you1 then1--let me see1--what shall ,i advise you8--,no1 on the whole1 ,i will tell you a story4 ,once there was a man1 and he was a philosopher4 ,he understood all that ,i have been explaining to you about the air being light when it was hot4 ,so he got some very thin paper1 and made a large paper bag4 ,he cut the paper very curiously1 and pasted it together at the edges in such a way1 that the bag1 when it was done1 was round1 like a ball2 and it had a round opening at the bottom of it4 ,in fact1 it was a large paper ball4 ,how large was it8 said ,nathan4 ,it was so large1 that1 when it was swelled out full1 it would have been higher than your head4 ,o1 what a large ball6 said ,nathan4 ,but what was it for8 ,why1 the man thought1 as hot air is lighter than cool air1 and floats up1 that perhaps1 if he could fill his paper ball with hot air1 it would go up too4 ,and did it8 said ,nathan4 ,yes1 said his father4 ,he filled it with hot air2 and the hot air was so light1 that it rose up and carried the paper ball with it4 ,how did he get the hot air into it8 said ,rollo4 ,why1 he held it over a little fire1 with the mouth down4 ,then the hot air from the fire went up into the ball1 and swelled it out full4 ,how high did it go8 said ,nathan4 ,o1 it soared away1 said his father1 away up into the air1 very high2 until at length it got cool1 and then it came down4 ,i should like to see such a ball as that1 said ,nathan4 ,such a ball as that is called a balloon1 said his father4 ,i wish ,i could see a balloon1 said ,nathan4 ,,questions4 ,what is the important difference between air and water1 which was explained in the last chapter1 and mentioned in this8 ,does the air tend to expand again after it is compressed8 ,what is this property of the air called8 ,is the air around us already condensed1 or is it in its natural state8 ,what causes it to be condensed8 ,suppose a thin glass vessel were to be filled with air1 and another with water1 and the air suddenly removed from the room around them2 what would be the effects8 ,what effect does heat have upon the expansibility of air8 ,how may this effect be made to appear over a lamp8 ,in a chimney8 ,what was the story which ,rollo's father told ,nathan8 ,,chapter ,,vii4 ,,philosophical ,,discussion4 ,some time after this1 ,rollo1 and ,nathan1 and ,james1 were playing in the shed1 one pleasant morning in the spring4 ,they were building with sticks of wood1 which they piled in various ways1 so as to make houses4 ,they took care not to pile the wood1 in any case1 higher than their shoulders1 for ,jonas had told them that1 if they piled the wood higher than that1 there would be danger of its falling down upon them4 ,after some time1 ,rollo went into the house a few minutes1 and ,james and ,nathan went to the open part of the shed1 and began to look out of doors4 ,the sun was shining pleasantly1 but the ground was wet1 being covered with streams and pools of water1 and melting snow-banks4 ,what a pleasant day6 said ,james4 ,i wish it was dry1 so that we could go out better4 ,i wish we could fly1 said ,nathan1 for it is very pleasant up in the air4 ,i wish we had a balloon1 said ,james4 ,if we had a balloon1 we could go up in the air1 easier than to fly4 ,o ,james1 said ,nathan1 you could not get into a balloon if you had one4 ,why not8 said ,james4 ,because1 said ,nathan1 it would not be big enough4 ,why1 ,nathan1 said ,james1 a balloon is bigger than this house4 ,o ,james1 it is not higher than my head4 ,it is1 said ,james1 ,i know it is4 ,i have read about balloons bigger than a house4 ,and my father1 said ,nathan1 putting down his foot in a very positive air1 my father told me himself1 that a balloon was about as high as my head4 ,the boys disputed some time longer upon the subject1 and finally1 when ,rollo came out of the house1 they both appealed to him very eagerly to settle the dispute4 ,isn't a balloon higher than ,nathan's head8 said ,james4 ,is it as high as a house8 said ,nathan4 ,why1 ,i know1 said ,rollo1 that a man made a balloon once about as high as ,nathan's head1 because my father said so2 but perhaps it was a little one4 ,yes1 said ,james1 ,i know it must be a little one2 for balloons are big enough for men to go up in them4 ,o ,james1 said ,nathan1 ,i don't believe it4 ,besides1 the fire would burn 'em4 ,what fire8 said ,james4 ,the fire they burn under the balloons1 to make the air hot1 said ,nathan4 ,i don't believe they have any fire1 said ,james4 ,just then ,nathan1 happening to look around1 saw ,jonas standing behind them2 he had just come out of the house1 and was going out to his work4 ,hearing the boys engaged in this dispute1 he stopped to listen4 ,the boys both appealed to ,jonas4 ,jonas heard all that they had to say1 and then replied1-- ,i cannot tell you much about going up in a balloon1 but ,i can tell you something about getting along pleasantly down here upon the earth1 which ,i think may be of service to you4 ,what is it8 said ,james4 ,why1 that you will neither of you get along very pleasantly until you can bear to have any body else mistaken1 without contradicting them4 ,james1 you think ,nathan is mistaken about the size of a balloon1 do you8 ,yes1 ,i know he is1 said ,james4 ,well1 said ,jonas1 now why not let him remain mistaken8 ,why1--,i don't know1 said ,james4 ,he isn't willing to be convinced1 is he1 that a balloon is as big as a house8 ,no1 said ,james1 he is not4 ,then why don't you let him remain unconvinced8 ,why should you insist on setting him right1 when he don't want to be set right8 ,and you1 ,nathan1 suppose that ,james is mistaken1 in thinking that the balloon is so big4 ,yes1 said ,nathan1 and that men can get into it1 and go up in the air4 ,well1 now1 if he wants to believe that balloons are so big1 why are you not willing that he should8 ,why should you insist upon it that he should know that they are smaller8 ,because ,i know1 said ,nathan1 very positively1 that they are small2 and1 besides1 the paper would not be strong enough to bear a man4 ,i did not ask you1 said ,jonas1 why you believed that men could not go up in balloons1 but why you were so anxious to make ,james believe so4 ,why not let him be mistaken8 ,why--because1 said ,nathan4 ,you see1 ,nathan1 continued ,jonas1 the world is full of people that are continually mistaken2 and if you go about trying to set them all right by disputing them1 you'll have a hard row to hoe4 ,a hard what8 said ,nathan4 ,a hard row to hoe1 repeated ,jonas4 ,it's never of any service to attempt to convince people that don't want to be convinced2 especially if they are wrong4 ,especially if they are wrong6 repeated ,rollo1 in astonishment4 ,yes1 replied ,jonas4 ,the very worst time to argue with a boy1 is when he is wrong1 and does not want to be set right4 ,it is a great deal harder to get along in argument with one who is right1 than with one who is wrong2 for the one who is wrong1 disputes2 the one who is right1 reasons4 ,well1 ,jonas1 said ,james1 which of us was disputing8 ,both of you1 said ,jonas4 ,both of us1 said ,james2 but you said that only the one who was wrong1 disputed4 ,well1 replied ,jonas1 you were both wrong4 ,both wrong6 ,o ,jonas6 said ,james4 ,yes1 both wrong1 replied ,jonas2 and so saying1 he was going away to his work4 ,but stop a minute longer1 said ,james1 and tell us how it is about the balloon2 we want to know4 ,o no1 said ,jonas1 you don't want to know2 you want to conquer4 ,what do you mean by that8 said ,nathan4 ,why1 you don't really wish to learn any thing2 but you want to have me decide the case1 because each of you hopes that ,i shall decide in his favor4 ,you want the pleasure of a victory1 not the pleasure of acquiring knowledge4 ,no1 ,jonas1 said ,nathan1 we do really want to know4 ,well1 said ,jonas1 ,i can't stop now to tell you2 perhaps ,i will this evening2 but ,i advise you always1 after this1 not to contradict people1 and dispute with them1 when they say things that you don't believe4 ,do as the gentleman did1 when the man said the moon was a fire4 ,what did he do8 said ,rollo4 ,why1 he let him say it as much as he wanted to4 ,tell us all about it1 said ,james4 ,well1 then1 said ,jonas1 once there was a man1 and he saw the moon coming up behind the trees1 and thought it was a large house burning up4 ,he went along a little way1 and he met a vulgar fellow1 riding in a carriage4 ,riding in a carriage6 repeated ,rollo1 astonished4 ,yes1 said ,jonas1 handsomely dressed4 ',sir1' said the man1 'see that great fire6' ',it isn't a fire1 you fool1' said the vulgar fellow2 'it's nothing but the moon4' ',the moon6 no it isn't1' said the man2 'it is a monstrous great fire4 ,don't you see how it blazes up8' ',it is not a fire1 ,i tell you1' said the vulgar fellow4 ',i tell you 'tis1' said the man4 ',you don't know any thing about it1' said the vulgar fellow4 ',and you don't know the moon from a house on fire1' said the man1 and so passed on4 ,a minute or two after this1 he met a gentleman driving a team4 ,a gentleman driving a team6 said ,james4 ,yes1 said ,jonas1 with a frock on4 ,he was tired and weary1 having driven all day4 ,the man asked him if he did not see that house on fire4 ',ah1' said the gentleman1 ',i thought it was the moon4' ',no1' said the man1 'it is a house on fire4' ',well1' said the gentleman1 ',i am very sorry if it is4 ,i hope they'll be able to put it out6' ,so saying1 he started his team along1 and bade the man good evening4 ,jonas then1 having finished his story1 stepped out of the shed1 and went along towards the barn2 ,nathan called out after him to say1-- ,well1 ,jonas1 ,i don't understand how the gentleman came to be driving a team all day4 ,jonas did not reply to this1 but only began to laugh heartily1 and to walk on4 ,nathan turned back into the shed1 saying1 he did not see what ,jonas was laughing at4 ,the boys wanted very much to have the question about the balloon settled2 and1 after some further conversation on the subject1 they concluded to go in and ask their mother4 ,so they all three went in4 ,rollo proposed this plan1 and he led the way into the house4 ,he found his mother sitting in the parlor at her work4 ,well1 boys1 said she1 have you got tired of your play8 ,no1 mother1 said ,rollo1 but we want to know about balloons3 how big are they8 ,o1 some of them1 said she1 are very large4 ,ain't they as big as this house8 said ,james4 ,yes1 ,i believe they have been made as big1 said she4 ,but1 mother1 said ,nathan1 father told me1 his very self1 that they were no higher than my head4 ,o no1 said his mother2 he said that a man made one which was about as high as your head2 but that was only a little one1 for experiment4 ,when they make large ones1 for use1 they are as high as this house4 ,for use1 mother8 what use8 said ,nathan4 ,men go up in them1 don't they1 aunt8 said ,james4 ,not in them1 exactly1 said his aunt4 ,they could not live in them1 but they go up by means of them4 ,how8 said ,nathan4 ,why1 they have a kind of basket1 which hangs down below the balloon1 and they get into that4 ,i knew they could not get into the balloon1 said ,nathan4 ,then you have had a dispute about it1 said his mother4 ,why1--yes1 said ,nathan1 with hesitation1 we disputed a little4 ,i am sorry to hear that1 said his mother1 for disputing seldom does any good4 ,the fact is1 however1 that men have often been carried up by balloons1 but they never get into them4 ,they could not live in them4 ,they could not breathe the kind of air which balloons are filled with4 ,it is hot air1 said ,nathan4 ,no1 said his mother1 the kind of balloon which your father told you of was filled with hot air2 but the balloons which people generally use to go up with1 are filled with another kind of air1 which is very light when it is cool4 ,they make an enormous bag of silk1 and fill it with this light air1 which they make in barrels2 and then1 when the bag is filled1 it floats away above their heads1 and pulls hard upon the fastening4 ,there is a net all over it1 and the ends of the net are drawn together below1 and are fastened to the basket1 or car1 where the man is to sit4 ,when it is all ready1 the man gets into the car1 and then they let go the fastenings1 and away the great bag goes1 and carries the man with it1 away up into the air4 ,and then how does he get down8 said ,nathan4 ,why1 he can open a hole in the bag1 and let some of the light air out2 and then he begins to come down slowly4 ,if he comes down too fast1 or if he finds that he is coming into the water1 or down upon any dangerous place1 there is a way by which he can make his balloon go up again4 ,what way is it1 aunt8 said ,james4 ,why1 he has some bags of sand in his balloon1 said his aunt2 and the balloon is made large enough to carry him and his sand-bags too4 ,then1 if he finds that he is coming down too fast1 he just pours out some of his sand1 and that makes his car lighter2 and so the balloon will carry him up again4 ,that's a good plan1 said ,rollo4 ,yes1 said his mother2 the reason why he takes sand is1 because that will not hurt any body by falling upon them4 ,if he should take stones1 or any other heavy1 solid things1 and should drop them out of his car1 they might possibly fall upon some body1 and hurt them4 ,so he takes sand in bags1 and1 when he wants to lighten his balloon1 he just pours the sand out4 ,rollo's mother then told the boys that there was a large book1 which had several stories in it of men's going up in balloons1 and that she would get it for them4 ,so she left her work1 and went out of the room2 but in a few minutes she returned1 bringing with her two very large1 square books1 with blue covers4 ,one of them had pictures in it1 and among the rest there were pictures of balloons4 ,she opened the other book1 and found the place where there was an account of balloons1 and she showed the place to ,rollo4 ,she told the boys that they had better go out in the kitchen1 or into the shed1 if it was warm enough1 and read the account4 ,you and ,james1 ,rollo1 said she1 can read by turns1 and let ,nathan hear4 ,then1 when the plates are referred to1 you must look into the other book and find them4 ,yes1 said ,rollo1 we will2 only1 mother1 if you would let us sit down here and read it--and then1 if there is any thing which we cannot understand1 you can tell us what it means4 ,very well1 replied his mother1 you may sit down here upon the sofa4 ,so the boys sat down upon the sofa4 ,they put ,nathan between them1 so that he might look over4 ,rollo and ,james took turns to read1 and they continued reading about balloons for more than an hour4 ,there was one story of a sheep1 which a man carried up in his car1 under a balloon1 and then let him drop1 from a great height1 with a parachute over his head1 to make him fall gently4 ,and he did fall gently4 ,he came down to the ground without being hurt at all4 ,,questions4 ,how was the subject of balloons introduced into the conversation8 ,what was ,nathan's opinion about the possibility of being carried up by a balloon8 ,what was the dispute about the size of balloons8 ,what was ,nathan's evidence8 ,what was ,james's evidence8 ,what did ,jonas say when they appealed to him8 ,what was the story that he related8 ,which of the boys did he finally say was wrong8 ,whom did the boys appeal to afterwards8 ,what did ,rollo's mother say about the size of balloons8 ,how did she say that large balloons were filled8 ,how can they make the balloon come down8 ,how can they make it go up again1 if they wish to do so8 ,,chapter ,,viii4 ,,tasks4 ,a few days after this1 there commenced a long storm of rain4 ,rollo and ,nathan were glad to see it on one account1 for their mother told them it would melt away the snow1 and bring on the spring4 ,the first day1 they amused themselves pretty well1 during their play hours1 in the shed and in the garret2 but on the second day1 they began to be tired4 ,nathan came two or three times to his mother1 to ask her what he should do2 and ,rollo himself1 though1 being older1 his resources might naturally be expected to be greater1 seemed to be out of employment4 ,at last1 their mother proposed that they should come and sit down by her1 and she would tell them something more about the air4 ,how should you like that1 ,rollo8 said she4 ,why1 pretty well1 said ,rollo2 but he spoke in an indifferent and hesitating manner1 which showed that he did not feel much interest in his mother's proposal4 ,i can't understand very well about the air1 said ,nathan4 ,their mother1 finding that the boys did not wish much to hear any conversation about the air1 said nothing more about it just then1 and ,rollo and ,nathan got some books1 and began to read2 but somehow or other1 they did not find the books very interesting1 and ,rollo1 after reading a little while1 put down his book1 and went to the window1 saying that he wished it would stop raining4 ,nathan followed him1 and they both looked out of the window with a weary and disconsolate air4 ,their mother looked at them1 and then said to herself1 ,they have not energy and decision enough to set themselves about something useful1 and in fact ,i ought not to expect that they should have4 ,i must supply the want1 by my energy and decision4 ,then she said aloud to ,rollo and ,nathan1-- ,i want you1 boys1 to go up into the garret1 and under the sky-light you will see a large box4 ,open this box1 and you will find it filled with feathers4 ,select from these feathers three or four which are the most downy and soft about the stem1 and bring them down to me4 ,what are they for8 said ,rollo4 ,i will tell you1 replied his mother1 when you have brought them to me4 ,so ,rollo and ,nathan went up into the garret1 and brought the feathers4 ,they carried them to their mother4 ,she said that they would answer very well1 and she laid them gently down upon the table4 ,then she took up her scissors1 and began to cut off some of the lightest down1 saying1 at the same time1-- ,now1 children1 ,i am going to give you some writing to do1 about the air4 ,writing8 said ,rollo4 ,yes1 said his mother4 ,i am going to explain to you something about the air1 and then you must write down what ,i tell you4 ,but ,i can't write1 said ,nathan4 ,no1 said his mother1 but you can tell ,rollo what you would wish to say1 and he will write it for you4 ,why1 mother1 said ,rollo1 ,i don't think that that will be very good play4 ,no1 replied his mother1 ,i don't give it to you for play4 ,it will be quite hard work4 ,i hope you will take hold of it energetically1 and do it well4 ,first1 said she1 ,i am going to perform some experiments for you1 before ,i tell you what ,i want you to write4 ,by this time1 she had cut off the downy part of several feathers1 and had laid them together in a little heap4 ,then she took a fine thread1 and tied this little tuft of down to the end of it4 ,then she took up the thread by the other end1 and handed it to ,rollo4 ,there1 ,rollo1 said she4 ,now1 do you remember what your father told you1 the other day1 about the effect of heat upon air8 ,it makes it light1 said ,rollo4 ,and why does it make it light8 asked his mother4 ,why1 ,i don't exactly recollect1 said ,rollo4 ,because it swells it2 it makes it expand2 so that the same quantity of air spreads over a greater space2 and this makes it lighter1 ,but cool or cold air is heavier1 because it is more condensed4 ,now1 wherever there is heat1 continued his mother1 the air is made lighter1 and the cool and heavy air around presses in under it1 and buoys it up4 ,this produces currents of air4 ,you recollect1 don't you1 that your father explained all this to you the other day8 ,yes1 said ,rollo1 ,i remember it4 ,well1 said his mother1 now you and ,nathan may take this little tuft1 and carry it about to various places1 and hold it up by its thread1 and it will show you the way the air is moving2 and then you may come to me1 and ,i will explain to you why it moves that way4 ,well1 said ,rollo1 come1 ,nathan1 let us go4 ,first we will hold it at the key-hole of the door4 ,rollo held the end of the thread up opposite to the door1 in such a way1 that the tuft was exactly before the key-hole4 ,the tuft was at once blown out into the room4 ,o1 see1 ,nathan1 how it blows out4 ,the air is coming in through the key-hole4 ,yes1 said his mother2 when there is a fire in the room1 and none in the entry1 then the cold air in the entry runs down through the key-hole into the room4 ,it don't run down1 mother1 said ,rollo2 it blows right in straight4 ,perhaps ,i ought to have said it spouts in1 said his mother1 just as the water did from the hole in your dam4 ,and1 now1 she continued1 come and hold the tuft near the chimney4 ,rollo did so2 and he found that it was carried in1 proving1 as their father had showed them before1 that the heavy1 cold air1 pressing into the room1 crowded the warm1 light air up the chimney4 ,now1 should you think1 said their mother1 that the cold air could come in through the key-hole1 as fast as it goes up the chimney8 ,both ,rollo and ,nathan thought that it could not4 ,then go all around the room1 said she1 and see if you can find any other place1 where it comes in4 ,for it is plain1 you see1 that the light air cannot be driven up chimney any faster than cold and heavy air comes in to drive it up and take its place4 ,so ,rollo and ,nathan went around the room1 holding their tuft at all the places they could find1 where they supposed there could be openings for the cold air to press in4 ,they found currents coming in around the windows1 and by the hinges of the doors2 and at length ,rollo said1 he meant to open the window a little way1 and see if the cold air from out of doors would not press in there too4 ,he did so1 and the tuft was blown in very far1 showing that the cold air from out of doors pressed in very strongly4 ,now1 if all these openings were to be stopped1 said their mother1 then no cold air could crowd into the room2 and of course the hot air could not be buoyed up into the chimney1 and a great deal of the hot air and smoke would come into the room4 ,this very often happens when houses are first built1 and the rooms are very tight4 ,but now1 ,rollo1 she continued1 suppose that the door was opened wide2 then should not you think that more cold and heavy air would press in1 than could go up the chimney8 ,yes1 mother1 a great deal more1 said ,rollo4 ,try it1 said his mother4 ,so ,rollo opened the door1 and held his tuft in the passage-way2 and he found that the air was pressing in very strongly through the open space4 ,wherever he held it1 it was blown into the room a great deal1 showing that the heavy air pressed in1 in a torrent4 ,now1 as much warm air must go out1 said she1 as there is cold air coming in2 but ,i don't believe that you and ,rollo can find out where it goes out4 ,rollo looked all around the room1 but he could not see any opening1 except the chimney and the door1 and the little crevices1 which he had observed about the finishing of the room4 ,he said he could not find any place4 ,his mother then told him to hold his tuft down near the bottom of the door-way4 ,he did so1 and found that the current of air was there very strong4 ,the tuft swung into the room very far4 ,now hold it up a little higher1 said his mother4 ,rollo obeyed1 and he found that it was still pressed in1 but not so hard4 ,higher1 said his mother4 ,rollo raised it as high as he could reach4 ,the thread was of such a length1 that the tuft hung about opposite to his shoulder4 ,the tuft was still pressed in1 but not nearly as far as before4 ,so you see1 said his mother1 that the air pours in the fastest at the lowest point1 where the weight and pressure of the air above it are the greatest2 just as1 in your dam1 the water from the lowest holes spouted out the farthest4 ,yes1 said ,rollo1 it is very much like that4 ,now1 continued his mother1 you see that a great deal of air comes in1 and if you look up chimney1 you will see that there is scarcely room for so much to go up there2--and yet just as much must go out as comes in4 ,get the step-ladder1 said his mother1 and stand up upon it1 and so hold your tuft in the upper part of the door-way4 ,there was in the china closet a small piece of furniture1 very convenient about a house1 called a step-ladder4 ,it consisted of two wooden steps1 and was made and kept there to stand upon1 in order to reach the high shelves4 ,rollo brought out the step-ladder1 and placed it in the door-way1 and then ascended it4 ,from the top he could reach nearly to the top of the door2 but then1 as his tuft was at the end of the thread1 it hung down1 of course1 some little distance below his head4 ,why1 mother1 said ,rollo1 it goes out4 ,yes1 repeated ,nathan1 it goes out4 ,in fact1 ,rollo found that the tuft1 instead of swinging into the room1 was carried out towards the entry4 ,you have found out1 then1 said his mother1 where the hot air of the room goes to1 to make room for the cold air1 that comes in from the entry4 ,yes1 out into the entry1 said ,rollo4 ,through the upper part of the door1 said his mother4 ,suppose the entry were full of water1 and the parlor full of air1 and the door was shut1 and the door and the walls were water-tight4 ,now1 if you were to open the door1 you see that the water1 being heavier1 would flow in1 through the lower part of the door-way1 into the parlor1 and the air from the parlor would flow out1 through the upper part of the door-way1 into the entry4 ,the water would settle down in the entry1 until it was level in both rooms1 and then the lower parts of both rooms would be filled with water1 and the upper parts with air4 ,yes1 mother1 said ,rollo4 ,and it is just so with warm and cold air4 ,if the parlor is filled with warm air1 made so by the fire1 and the entry with cold air1 and you open the door1 then the cold air1 being heavier1 will sink down1 and spread over the floor of both rooms2 and the warm air1 being light1 will spread around over the upper parts of both rooms2 and this will make a current of air1 in at the bottom of the door-way1 and out at the top4 ,now1 continued his mother1 let me recapitulate what ,i have taught you4 ,what do you mean by recapitulating it8 said ,nathan4 ,why1 tell you the substance of it1 so that you can write it down easier4 ,o1 ,i can write it now1 said ,rollo2 ,i remember it all4 ,can you remember it1 ,nathan8 said his mother4 ,perhaps ,i can remember some of it1 said ,nathan4 ,so ,rollo and ,nathan went out into another room1 where ,rollo kept his desk1 and they remained there half an hour4 ,when they returned1 they brought their mother two papers4 ,their mother opened the largest paper1 and read as follows3-- ,we took a tuft of down1 tied to a thread1 and held it in the cracks and places that the air came in at1 to see which way it went4 ,we held it at the window1 and it blew in very strong4 ,at the bottom of the door1 it blew in very strong too2 but at the top1 it blew out1 into the entry4 ,so1 when the entry is full of cold air1 and this room full of warm1 the cold air will press in and drive out some of the warm air1 into the entry4 ,,rollo4 ,the other paper was also in ,rollo's handwriting1 and was as follows3-- ,if the entry was full of water1 and the parlor full of air1 and the walls were water-tight1 and you were to open the door between the two rooms1 the water would flow into the parlor down below1 and the air would flow into the entry up above4 ,we tried it with a tuft4 ,,nathan4 ,,questions4 ,why were ,rollo and ,nathan at first glad to see the rain8 ,what did their mother say to herself on the second day1 when she observed their weary and listless appearance8 ,what did she at first direct them to do8 ,how did she prepare the downy tuft8 ,what experiments did they perform with it8 ,where did they find that the air came in which crowded the warm air up the chimney8 ,what experiments did they perform when the door was opened8 ,which way did they find that the current of air was setting at the lower part of the door-way8 ,which way did the current set at the upper part of the door-way8 ,what did ,rollo write in his exercise8 ,what was written in ,nathan's exercise8 ,,chapter ,,ix4 ,,burning4 ,after the snow had all gone off1 and the ground was dry1 ,jonas piled up a heap of stumps1 roots1 and decayed logs1 in a field1 not far from the brook1 and one sunny afternoon he and ,rollo went down to set the heaps on fire4 ,jonas set one on fire1 and then he told ,rollo that he might set another on fire4 ,after this1 ,jonas employed himself in gathering up sticks1 bushes1 roots1 and other such things that lay scattered about the field1 and putting them upon the fires1 while ,rollo amused himself in any way he pleased4 ,after a time1 ,rollo found1 on the margin of the field1 near the edge of a wood1 an old stump1 taller than he was1 much decayed4 ,there was a hole in the top4 ,rollo climbed up so that he could put a stick in1 and run it down1 to see how far down the hole extended4 ,he found that it extended down very near to the bottom4 ,then ,rollo called out to ,jonas1 with a loud voice1 saying1-- ,jonas1 ,i have found a hollow stump here4 ,it is hollow away down to the bottom4 ,may ,i build a fire in it8 ,yes1 said ,jonas1 if you can4 ,rollo accordingly went to the nearest fire1 and got a quantity of birch bark1 which he had collected there to aid him in kindling his fires4 ,he lighted one piece1 and put it upon the end of a stick1 and carried it to the stump1 with the rest of the birch bark in the other hand4 ,rollo then spent some time in fruitless attempts to make some lighted birch bark go down into the stump1 and burn there4 ,he succeeded very well in getting pieces completely on fire2 but1 after they were dropped into the hole1 they would not burn4 ,rollo could not think what the reason could be4 ,at last he called ,jonas to come and help him set the stump on fire4 ,jonas said that he did not think that it could be set on fire4 ,illustration3 ',jonas1 ,i have found a hollow stump here1' said ,rollo1 calling with a loud voice4--,page #abb4 ,why not8 said ,rollo4 ,because1 said ,jonas1 it is so wet4 ,yes1 but1 ,jonas1 replied ,rollo1 your brush heaps burn1 and why should not this stump8 ,because1 said ,jonas1 the stump is more solid1 and the water soaks into it more in the winter and early in the spring2 and it takes it much longer to dry1 than it does brush and small roots1 which lie open and exposed to the air4 ,well1 then1 replied ,rollo1 why does not my birch bark burn8 that is dry2 but as soon as ,i drop it down into the stump1 it goes out4 ,jonas looked into the stump1 and down around the bottom of it1 and said1-- ,because there is no air4 ,no air8 repeated ,rollo4 ,no1 replied ,jonas2 it is all close and solid around2 the air cannot get in4 ,it can get in at the top1 said ,rollo4 ,jonas made no reply to this remark1 but walked away a few steps1 to a place where he had put down his axe2 he took up the axe1 and brought it to the stump4 ,he immediately began to cut into it1 at the bottom1 as if it were a tree which he was going to fell4 ,o ,jonas1 said ,rollo1 don't cut it down4 ,i am not going to cut it down1 said ,jonas2 ,i am only going to cut a hole into it4 ,what for8 asked ,rollo4 ,to let the air in1 replied ,jonas4 ,jonas continued to cut into the side of the stump1 near the ground1 until he perceived that the edge of his axe went through into the hollow part4 ,then he cleared away the chips a little1 and showed ,rollo that there was an opening for the air4 ,now1 said he1 ,i presume you will be able to make sticks and birch bark burn in the stump1 though you can't make the stump itself burn very well4 ,rollo now dropped a blazing piece of birch bark into the stump1 and1 to his great joy1 he found that it continued blazing1 after it reached the bottom4 ,he then dropped in another piece upon it1 which took fire4 ,he then gathered some dry sticks1 and put in2 and1 finding that the flame was increasing1 he proceeded to gather all the dry and combustible matter1 which he could find around1 and put them in1 so that in a short time he had a fine blaze1 a foot above the top of the stump2 and the inside of the stump itself seemed to be in flames4 ,jonas1 said ,rollo1 it does burn4 ,does it8 said ,jonas2 ,i am glad to hear it4 ,but you said the stump would not burn4 ,you ought to wait until it is all burnt up1 before you triumph over me4 ,why1 ,jonas1 said ,rollo1 ,i didn't mean to triumph over you2 but why would not the fire burn before you cut the hole through8 ,because1 replied ,jonas1 there was not air enough4 ,there was air in the stump1 said ,rollo4 ,yes1 replied ,jonas1 but all the life of it was consumed by the first piece of birch bark which you put in4 ,the life of it8 said ,rollo4 ,yes1 replied ,jonas2 what do you suppose it is1 that makes anything burn8 ,why1 it burns itself1 said ,rollo4 ,no1 answered ,jonas2 the air makes it burn3 it must have good air around it1 or else it won't burn4 ,there is something in the air which ,i call the life of it2 this makes the fire burn4 ,but when this is all gone1 then that air will not make fire burn any longer4 ,it will only burn in good fresh air1 which has got the life in it4 ,i thought fire would burn in any kind of air1 said ,rollo4 ,no1 replied ,jonas2 you can see if you stop up the hole ,i made here4 ,jonas then took a piece of turf from the field1 and put it before the hole1 and crowded it in hard with the heel of his boot4 ,rollo observed that the fire was almost immediately deadened4 ,now1 continued ,jonas1 light a small piece of birch bark1 and put it in4 ,jonas helped ,rollo fasten a small piece of bark upon the end of a stick1 and then ,rollo set it on fire1 and held it down a little way into the stump4 ,it burned very feebly4 ,see1 said ,jonas1 how quick it is stifled4 ,yes1 replied ,rollo1 it goes out almost directly4 ,you see1 said ,jonas1 that the fire already in the stump consumes all the goodness of the air2 and ,i stopped up the hole1 so that no fresh air can come in4 ,why doesn't it go in at the top8 said ,rollo4 ,it does a little1 said ,jonas1 but not much1 because the hollow of the stump is already full of bad air1 and there is nothing to make a current4 ,when there is an opening below1 then there is a current up through4 ,yes1 said ,rollo1 it is just like a chimney4 ,yes1 replied ,jonas1 the stump is the chimney1 and the hole is the fireplace4 ,and the air in the stump1 said ,rollo1 gets hot1 and so the cold air all around is heavier1 and so it crowds down under it1 and buoys the hot air up out of the stump4 ,my father explained it all to ,nathan and me4 ,rollo then wanted to open the hole again1 to see if the effect would be as he had described4 ,then ,jonas pulled away the turf from the hole at the bottom of the stump1 and ,rollo observed that the fire brightened up immediately4 ,he then held a smoking brand near the hole1 and he saw that the smoke was carried in1 in a very strong current1 by the cool air1 which was pressing into the hole4 ,yes1 said ,rollo1 it operates just like a fireplace4 ,so you see1 continued ,jonas1 that whenever you build a fire1 you must see to it1 that there is an opening for air to come up from underneath it4 ,and it must be good fresh air too4 ,what is it in the air1 which makes the fire burn8 said ,rollo4 ,i don't know what the name of it is1 said ,jonas2 it is some part of the air1 which goes into the fire1 and is all consumed1 and then the rest of the air is good for nothing4 ,isn't it good for anything at all8 asked ,rollo4 ,i don't know1 said ,jonas1 how that is2 only ,i know that it isn't good for anything for fires4 ,it stifles them4 ,i should like to know what the name of that part of the air is1 which is good for fires1 said ,rollo4 ,i knew once1 said ,jonas1 but it was a hard word1 and ,i have forgotten it4 ,i mean to ask my father1 said ,rollo4 ,jonas then went on with his work1 gathering up everything that he could find around the field1 to put upon the fires4 ,rollo amused himself by putting large rolls of birch bark around the end of a stick1 and then1 after setting them on fire1 holding them over the fires1 which ,jonas was making1 to see how soon the flame was extinguished3 then he would draw them away1 and see them revive and blaze up again in the open air4 ,at last1 he called out to ,jonas1 once more4 ,jonas1 said he1 ,i have found out what makes the blaze go out4 ,it is the smoke4 ,i don't believe but that it is the smoke4 ,no1 replied ,jonas1 it is not the smoke4 ,i can prove that it is not4 ,so ,jonas came up to the fire where ,rollo was standing1 and pointed out to ,rollo a place1 over a hot part of it1 where there was no smoke1 because the fire under it burned clear1 being nearly reduced to coals4 ,he told ,rollo to hold his blazing bark there4 ,rollo did so1 and found that it was extinguished at once1 and as completely1 as it had been before1 when he had held it in a dense smoke4 ,yes1 said ,rollo1 it isn't the smoke4 ,but perhaps it is because it is so hot4 ,no1 said ,jonas1 it isn't that4 ,it is a difference in the air4 ,they sometimes collect different kinds of air in glass jars1 and then let a candle down in1 and see whether it will go out4 ,and will it go out8 said ,rollo4 ,that depends upon what kind of air it is1 said ,jonas4 ,they all look clear1 just as if there was nothing in the jars2 but when you let a candle down in1 in some it burns just the same as before2 in some it burns brighter2 and in some it goes out4 ,in what kinds does it go out8 asked ,rollo4 ,i only know of one kind1 said ,jonas1 and that is a kind that comes of itself in mines1 and wells1 and other places4 ,what is the name of it8 asked ,rollo4 ,why1 the people in the mines call it choke damp2 but ,i believe it has got another name besides4 ,what do they call it choke damp for8 said ,rollo4 ,because1 said ,jonas1 if the miners get into it and breathe it1 it kills them4 ,it is not any better to breathe than it is to make fires burn4 ,i wish ,i could see some choke damp1 said ,rollo4 ,o1 you can't see it at all1 said ,jonas1 if it was right before you1 any more than you can see common air4 ,if a well or a mine is full of it1 they cannot find it out by looking down4 ,how do they find it out8 said ,rollo4 ,why1 they let a candle down1 replied ,jonas4 ,and will the candle go out8 asked ,rollo4 ,yes1 said ,jonas1 if there is choke damp in the well4 ,sometimes they make a little of it in a tumbler or a jar upon the table1 and so let a little flame down into it1 and it goes out immediately4 ,i wish we could make some1 said ,rollo4 ,do you know how they make it8 ,no1 said ,jonas2 but ,i believe it is pretty easy to do it1 if we only knew how4 ,i will ask my father1 said ,rollo2 perhaps he will know4 ,this conversation took place when ,jonas and ,rollo were about the fires2 but now the fires had pretty nearly burnt out1 and they prepared to go home4 ,that evening1 just about sunset1 ,rollo went out behind the house1 and found ,jonas raking off the yard4 ,the spring was fast coming on1 and the grass was beginning to look a little green2 and ,jonas said he wanted to get off all the sticks1 chips1 and straws1 so that the yard would present a surface of smooth and uniform green4 ,rollo told him that he had found out how to make choke damp4 ,did your father tell you8 said ,jonas4 ,no1 replied ,rollo4 ,who did tell you1 then8 said ,jonas4 ,guess1 answered ,rollo4 ,your mother1 said ,jonas4 ,no1 answered ,rollo4 ,then ,i can't tell1 said ,jonas4 ,it was ,miss ,mary1 replied ,rollo4 ,i met her in the road to-day1 and ,i asked her4 ,and how is it8 asked ,jonas4 ,why1 we make it with chalk and vinegar1 said ,rollo4 ,we pound up a little chalk1 and put it in the bottom of a tumbler4 ,then we pour some vinegar over it4 ,the vinegar takes the choke damp out of the chalk1 and ,miss ,mary says it will come up in little bubbles4 ,she says we can lay a paper over the top loosely1--she said loosely1 but ,i think it ought to be tight4 ,why8 asked ,jonas4 ,so as to keep the choke damp from coming out1 replied ,rollo4 ,no1 said ,jonas4 ,i understand why she said you must put it on loosely2 that's to let the common air out4 ,what common air8 said ,rollo4 ,why1 the air that was in the tumbler before1 replied ,jonas4 ,you see that1 as fast as the choke damp comes up1 it drives the common air out of the top of the tumbler2 and so you must put the paper on loosely1 and let it go out4 ,that evening ,jonas and ,rollo tried the experiment4 ,first they put about two teaspoonfuls of chalk into the tumbler4 ,then they poured in the vinegar4 ,it immediately began to foam4 ,ah1 said ,rollo1 that's the effervescence4 ,the what8 said ,dorothy2 for they were making this experiment upon the kitchen table1 and ,dorothy was standing by1 looking on with great interest4 ,the effervescence1 said ,rollo4 ,miss ,mary said there would be an effervescence1 which would be occasioned by the little bubbles of choke damp1 coming up from the chalk4 ,poh6 said ,dorothy2 it's nothing but a little frothing4 ,it isn't frothing1 said ,rollo1 very seriously2 it isn't frothing1 it is effervescence4 ,don't you think ,miss ,mary knows8 ,jonas1 said ,rollo again after a short pause1 how many of these little bubbles will it take1 do you think1 to fill the tumbler full of choke damp8 ,i don't know1 replied ,jonas2 we will wait a little while1 and then try it4 ,there1 now1 ,jonas1 said ,rollo1 we have not got any candle4 ,o1 ,i will roll up a piece of paper1 and set the end on fire1 and then dip it down into the tumbler1 and that will do just as well4 ,what are you going to do that for8 said ,dorothy4 ,why1 to see it go out1 said ,rollo4 ,it won't go out1 unless you put it away down into the vinegar1 said ,dorothy4 ,yes it will1 said ,rollo2 we are only going to dip it down a little way1 just into the choke damp1 and it will go out4 ,it won't go out1 child1 said ,dorothy4 ,there's nothing to put it out4 ,well1 you'll see4 ,won't it go out1 ,jonas8 ,i don't know1 said ,jonas4 ,don't know8 said ,rollo4 ,why1 you told me that choke damp would put out a blaze4 ,yes1 said ,jonas1 ,i am sure of that2 but there are a great many ways of failing in trying experiments4 ,well1 said ,rollo1 that may be2 but this will not fail1 ,i know1 for ,i can see the little bubbles of choke damp coming up4 ,there are millions of them4 ,by this time ,jonas thought that the tumbler was filled with the gas1 which was rising from the chalk and vinegar4 ,so he rolled up a piece of paper1 and set the end on fire1 and1 when it was well burning1 he plunged the end of it into the tumbler4 ,to ,rollo's great disappointment and mortification1 it continued to burn about as much as ever4 ,the flame crept rapidly up the paper1 and ,jonas had soon to run with it across the floor and throw it into the fire1 to avoid burning his fingers4 ,dorothy laughed aloud2 ,jonas smiled2 and as for ,rollo1 he looked disappointed and vexed1 and appeared to be overwhelmed with chagrin4 ,dorothy continued to laugh at them1 while ,jonas went to the pump and washed out the tumbler4 ,at length she said1-- ,but come1 ,rollo1 don't be so disconsolate4 ,you look as if you had swallowed all the choke damp4 ,yes1 ,rollo1 said ,jonas1 we must keep good-natured1 even if our experiments do fail4 ,well1 said ,rollo1 ,i mean to ask ,miss ,mary again1 and then we can do it1 ,i know4 99 99 99 99 99 ,rollo accordingly went1 the next day1 to ask ,miss ,mary about the cause of the failure4 ,miss ,mary said that she could not think of any thing which was likely to be the cause1 unless it was that they put too large a flame into the tumbler4 ,well1 replied ,rollo1 and what harm would that do8 ,won't the choke damp put out a large flame8 ,yes1 replied ,miss ,mary1 if it only fairly surrounds and covers it2 but1 then1 if you put a large flame into a tumbler1 it makes the first instant1 a great current of air1 and so the choke damp might be blown out1 and common air get in1 and so keep the paper burning4 ,how does it make a current of air8 asked ,rollo4 ,why1 the heat of the flame1 when you first put the paper in1 replied ,miss ,mary1 makes the air that is above it lighter2 and the common air all around crowds in under it1 in buoying it up2 and by that means1 if the flame is too large1 common air is carried into the tumbler4 ,you ought to make a very small flame1 if you leave the top of the tumbler open4 ,how can we make a small flame8 said ,rollo4 ,one good way1 replied ,miss ,mary1 is to roll up some paper into a very small roll4 ,i will show you how4 ,so ,miss ,mary took a piece of paper1 and cut it into the proper shape with her scissors1 and then rolled it up into a long and very slender roll2 one end of it was not much larger than a large knitting-needle4 ,she gave this to ,rollo1 and told him that1 if he tried the experiment again1 he must light the small end1 and it would make a flame not so big as a pea4 ,rollo explained to ,jonas what ,miss ,mary had said1 and they resolved on attempting the experiment again that evening4 ,and they did so4 ,dorothy stood by watching the process1 as she had done the evening before1 but ,rollo did not assert so confidently and positively what the result would be4 ,he had learned moderation by the experience of the night before4 ,when all was ready1 ,jonas lighted the end of the slender roll in the lamp1 and plunged it carefully into the tumbler4 ,it went out immediately4 ,there6 said ,rollo1 clapping his hands1 it goes out4 ,why1 it is only because the wind blew it out4 ,no1 ,dorothy1 said ,rollo1 there isn't any wind in the tumbler4 ,yes1 replied ,dorothy1 when you push it down1 it makes a little wind1 just enough to blow it out4 ,get another tumbler1 said ,jonas1 and let us see4 ,so ,dorothy brought another tumbler1 and ,jonas put the burning end of the paper down into it1 with about as rapid a motion as that with which he had put it before into the tumbler he had at first4 ,the paper continued to burn4 ,there1 said he to ,dorothy1 when ,i put it down into common air1 it burns on the same as ever2 so it can't be that the wind puts it out4 ,jonas repeated the experiment a number of times2 the effect was always the same4 ,whenever he put it into the tumbler of common air1 it burned on without any change2 but whenever he put it into the choke damp1 it immediately went out4 ,even ,dorothy was satisfied that there was a difference in the kind of air contained in the two tumblers4 ,that evening1 when ,rollo gave his mother a full account of their attempts1--describing particularly their failure at first1 and their subsequent successes1--his mother seemed much interested4 ,when he had finished1 she said1-- ,well1 ,rollo1 ,i don't see but that you have learned two lessons in philosophy4 ,two lessons8 said ,rollo4 ,yes1 replied his mother4 ,the first is1 that fire will not burn in choke damp2 and the second is1 that it requires nice attention and care to verify philosophical truths by experiment4 ,yes1 said ,rollo1 we missed the first time1 just because we had too big a paper4 ,,questions4 ,why did ,jonas suppose that the stump would not burn8 ,what was ,rollo's first mode of setting it on fire8 ,how did it succeed8 ,what did ,jonas do with his axe1 when he came8 ,what was the object of this8 ,what did he say was necessary to make fires burn8 ,what did ,rollo at first think was the reason why the bark went out when held over the fire8 ,what did he next think was the reason8 ,how did ,jonas say that different kinds of airs were prepared8 ,in what places did he say that choke damp was naturally produced8 ,how did they attempt to prepare some of this gas8 ,did they succeed in preparing it8 ,did they succeed in their experiment at first8 ,what was the cause of the failure8 ,,chapter ,x4 ,,gravitation4 ,one evening1 after tea1 when ,rollo was a pretty big boy1 he came and began to climb up into his father's lap4 ,when he had climbed up1 he took his place astride of his father's knee1 as if he were riding a horse4 ,his little brother ,nathan came up and stood near1 wanting to get up too1 only there was not room4 ,his cousin ,james was there1 that evening1 on a visit4 ,he sat upon a cricket before the fire1 and his mother was at the table doing some sort of work4 ,o dear me6 said ,rollo's father1 imitating the tone in which ,rollo sometimes uttered that exclamation4 ,what1 sir8 said ,rollo4 ,why1 ,i should like very well to hold you in my lap1 said his father1 if it was not for the great mighty earth1 down below us4 ,how8 said ,rollo4 ,he did not know what his father meant4 ,why1 when you are upon my knee1 the earth1 the ponderous earth1 pulls you down hard and heavy upon it4 ,so saying1 he put his hands upon ,rollo's shoulders1 and crowded them down1 by way of showing him how the earth acted upon him4 ,it pulls1 he continued1 with a strong and steady pull1 all the time2 and so makes you a very heavy weight4 ,is that what makes weight8 said ,rollo4 ,yes1 said his father4 ,so1 if ,i had a monstrous stone to move1 and if ,i thought the earth would listen to me1 and let go its hold1 ,i might make a speech to it thus3-- ',o earth1 thou vast and ponderous ball1 please to relax thy hold1 for a few minutes1 upon this stone1 and leave it free to move2 and then ,rollo can tie a string to it1 and move it easily along to the place where ,i want it to lie2 then thou mayst seize it again with thy mighty attraction1 and hold it down as firmly as thou wilt4' ,o father6 exclaimed ,rollo2 ,nathan and ,james laughed1 and ,rollo's mother looked up from her work to listen to this strange apostrophe4 ,it would seem1 continued his father1 in a pompous tone1 as if still addressing the earth--it would seem1 most mighty planet1 a very easy thing for thee to release this single stone1 for a few minutes1 from the grasp with which thou holdest all things down upon thy surface4 ,and by it ,i shall gain much1 while thou wilt lose nothing2 for1 if thou wilt not willingly give up the stone1 ,i must get three or four yoke of strong oxen1 and1 by main force1 pull it away4 ,is that what makes everything heavy8 said ,rollo4 ,yes1 said his father1 answering now in his natural tone2 the attraction of the earth is what makes everything heavy1 and holds it down4 ,and could we move a monstrous great stone1 said ,rollo1 as light as a feather8 ,no1 said his father1 it would not move along quick and light1 like a feather4 ,you could not move it quick4 ,suppose1 for instance1 you had two boats1 floating upon the water1 of the same size2 one made very light indeed1 of something very thin1 like paper1 and empty2 and the other made of wood1 and loaded with iron as heavily as it would bear4 ,now1 they would both be supported upon the water1 so that their weight would be neutralized2 and yet they would move very differently4 ,you could push the light one about easily1 anywhere1 but the heavy one would move very slowly4 ,you would not have to push very hard upon it1 but you would have to push for some time1 to set it in motion2 and then it would be hard to stop it4 ,this is called its inertia4 ,yes1 said ,rollo1 it would go harder against the bank4 ,the reason is1 continued his father1 that the heavy boat contains a great many more particles of matter than the light one1 and they have all got to be put in motion4 ,so it requires greater effort1 or the same effort must be continued a longer time4 ,for instance1 if we suppose that the light boat has one million of particles of matter1 the heavy one would have1 perhaps1 twenty millions4 ,of course the effect of the pushing has to be divided among twenty times as many particles1 and of course will only carry them one twentieth part as far2 so that the bodies that are now large and heavy1 would only move slowly1 though they would move easily1 if the attraction of the earth were to cease4 ,there is another way to illustrate it1 he continued4 ,suppose there was a large mass of lead1 as big as a load of hay1 hanging by a chain2 and also a great puff of feathers1 or a balloon of the same size1 hanging in the same way4 ,now1 if they were both suspended freely1 they would both move easily1 for their weight would be supported by the chain2 but the heavy one would move very slowly4 ,nathan could move it1 but he could only move it slowly and a little way4 ,i should not think that he could move it but very little1 said ,rollo4 ,no1 he could not2 because you see that1 in that way of suspending anything1 the moment that it begins to move1 it begins to swing off and to rise2 so that it cannot be moved at all without being lifted a little4 ,and the more it is moved1 the higher it is lifted1 so that it would take a great force to move it far away from the centre1 where it was hanging4 ,but we can hang it in a way to avoid that difficulty4 ,how1 sir8 said ,rollo4 ,rollo seemed to be very much interested in this conversation4 ,he had dismounted from his father's knee1 and stood by his side1 listening eagerly4 ,his mother1 too1 was paying close attention4 ,as for ,nathan1 he sat still2 though it is not by any means certain that he understood it very well4 ,let us suppose1 said his father1 that the mass of lead1 as big as a load of hay1 is fastened to one end of a stick of timber4 ,that would not be strong enough to hold it1 said ,rollo4 ,well1 then1 to a beam of iron1 as large as a stick of timber1 rejoined his father4 ,o1 said ,james1 you could not get such a big bar of iron4 ,no1 replied his father1 only an imaginary one2 and that will be just as good as any4 ,now1 suppose the great mass of lead is fastened to one end of this bar1 and another one1 just like it1 to the other end1 to balance it4 ,now1 suppose that the lower end of the great chain is secured around the middle of the iron beam1 and the upper end to be fastened to some strong support up in the air4 ,now1 we can move the mass of lead without having to lift it at all2 for1 if we push against it1 and make it move1 it will move round and round1 without rising at all1 as it did before1 when it was hung up directly by the chain4 ,rollo's father then went on to explain to them that1 in such a case as this1 the weight of the two masses of lead would not prevent their moving easily1 for they would exactly balance each other4 ,a little child would be able to move them2 but still they would move exceedingly slow at first1 and it would be hard to stop them1 when they were in motion4 ,so1 he said1 if the earth should cease to attract and draw down any great1 heavy body1 like a large stone1 for example1 the smallest child could lift it1 though it would come up slowly1 just as a very heavy body would move1 if it was suspended by a string1 or was afloat upon the water4 ,and so1 said ,rollo1 if the earth should not attract us1 could we push ourselves right up off from the ground8 ,yes1 said his father1 most undoubtedly4 ,what1 and go about anywhere in the air8 ,certainly4 ,rollo began to laugh aloud at this idea1 and looked very much interested and pleased4 ,o1 then ,i wish there was no gravitation1 said ,rollo2 ,i do1 really4 ,but1 then1 continued his father1 if you should get up into the air1 you could not get down again4 ,why not8 said ,nathan1 beginning to look a little concerned4 ,unless1 said his father1 you had something above you1 to push against1 so as to push yourselves down4 ,you would be just like a boy in a boat1 off from the shore1 and without any paddle or pole4 ,he could not get back again4 ,we might tie a rope to something1 said ,james1 before we went up1 and so pull ourselves down4 ,yes1 that you might do4 ,and could not we flap our hands1 like a bird1 and so fly a little8 ,perhaps you could1 said his father4 ,here the children all began to flap their hands1 like young birds trying to fly2 and ,rollo said again1 he wished1 with all his heart1 there was no gravitation2 for then1 said he1 we should have strength enough to fly4 ,that would lead to serious consequences1 said his father4 ,what consequences8 said ,james4 ,much more serious than you would suppose4 ,tell us what they would be1 uncle1 said ,james4 ,o1 ,i know1 said ,rollo2 you could not stand up straight without gravitation4 ,o1 we could1 couldn't we1 father8 said ,nathan4 ,what makes you think1 ,rollo1 said his father1 without replying to ,james's question--what makes you think that we could not stand up straight without gravitation8 ,why1 you see1 said ,rollo4--,here he paused1 and looked confused1 and did not know what to say4 ,he had an indistinct recollection of having read something about it in some book2 but he could not tell what4 ,i don't see what should prevent any body's standing up straight1 if the attraction of the earth should cease2 in fact1 if it made any difference1 it would be rather easier to stand up straight4 ,here ,rollo looked rather foolish1 but he did not reply4 ,the truth is1 like almost all other children1 who take an interest in reading1 he was sometimes a little vain of his knowledge2 and in this case1 instead of listening attentively1 and endeavoring to learn something new from his father's explanations1 he seems to have thought it a good plan for him to help him elucidate the subject to ,james and ,nathan4 ,he exchanged the character of learner for teacher too soon4 ,well1 uncle1 said ,james1 what would be the consequence if gravitation should cease8 ,why1 in the first place1 said ,rollo's father1 all the streams in the world would stop running4 ,the streams6 said ,rollo1 astonished4 ,yes1 said his father1 every river1 brook1 and rill4 ,the reason why the streams flow is1 that the earth attracts the water from the mountains and hills1 down into the valleys and towards the sea4 ,well1 sir1 what else8 said ,rollo4 ,why1 there would never be any more rain4 ,no more rain6 exclaimed all the children4 ,no1 he replied4 ,the drops of rain fall only because the earth draws them down by its attraction2 and1 of course1 if this attraction should cease1 they would remain where they are4 ,the children were musing a minute upon these strange effects1 when ,rollo asked if anything else would happen4 ,why1 yes1 said his father1 worse disasters than these2 but ,i do not know whether you would understand them1 if ,i should explain them4 ,o1 try1 said ,rollo2 ,i think we shall understand4 ,well1 let me think1 said his father4 ,you have noticed how a chaise wheel1 on a muddy road1 in a wet day1 holds the mud upon it1 until when it is going very swiftly down a hill1 and then the mud flies off in all directions4 ,yes1 sir1 said all the children4 ,and if the mud did not stick to the wheel pretty tight1 it would be thrown off at all times1 even when the wheel was going slow4 ,you understand this4 ,yes1 sir4 ,well1 now1 this whole earth1 you all know1 is whirling around through space1 and moving on also around the sun4 ,and all the loose things upon the surface would be thrown off at once1 if they were not held to it by a strong attraction4 ,if this attraction were to cease suddenly1--whisk6--away we should all go in an instant--rocks1 houses1 men1 animals1 all in confusion4 ,o father6 exclaimed ,rollo2 where should we go to1--off into the air8 ,not exactly into the air1 for the air would all fly off1 and be dissipated too2 we should fly off into the sky somewhere1 some in one direction1 and some in another4 ,you'd be a thousand miles off from the earth1 almost before you would know it4 ,would it kill us1 father8 said ,nathan4 ,yes1 said his father4 ,i don't know that there would be any shock that would hurt us1 but we should have no air to breathe1 and it would be dark and dismal4 ,dark8 said ,rollo4 ,there would be the sun4 ,yes1 said his father1 there would be the sun2 and the sun would look bright enough when you looked directly towards it1 but there would be no general light about you1 unless there was air4 ,the children all paused to reflect upon the strange results which their father had told them would ensue from a suspension of the earth's attractive force4 ,rollo began to think that he had been too hasty in his wish that there was no gravitation4 ,but1 father1 said he1 the houses would not go off1 certainly2--only the loose things would go4 ,very well2 houses are loose4 ,o father6 they are fastened down4 ,how are they fastened down8 asked his father4 ,o1 they are nailed--and1 ,not nailed to the ground1 certainly1 said his father4 ,no1 said ,rollo1 laughing2 but then they are built with great stones and mortar4 ,yes1 but there is no mortar under the lowest stones4 ,the foundations are simply laid upon the ground4 ,well1 rejoined ,rollo1 ,i thought they were fastened somehow or other4 ,no1 said his father2 they dig the cellar1 and only just lay the foundations upon the ground1 without any fastening4 ,the earth holds them in place4 ,well1 father1 said ,rollo1 that is what ,i meant1 when ,i said we could not stand up straight4 ,i meant the houses4 ,i read in a book that houses would be blown away1 if the gravitation did not hold them down4 ,here ,rollo's father had a hearty laugh2 and he told ,rollo that he thought that was rather wide shooting4 ,rollo wanted to know what he was laughing at2 and ,nathan asked him what he meant by wide shooting4 ,why1 said he1 ,rollo1 you undertook to explain to us1 from your stores of knowledge1 what the effects of a suspension of gravitation would be2 and1 in attempting to tell that houses would be in danger of being blown away1 you came no nearer than to tell us that boys could not stand up straight2 and that is what ,i call pretty wide shooting4 ,so saying1 he rose from his seat1 and walked away1 appearing to be very much amused4 ,james laughed too1 and even ,rollo could not help smiling at the ridiculous figure which his display of his learning made4 ,as for ,nathan1 he continued to look grave2 and said he did not see that it was any shooting at all4 ,after a short pause1 ,rollo's mother said1 ,so you see1 children1 the cause of all the pressure1 both of air and of water1 and all the effects produced by them1 are the results of their gravitation towards the earth4 ,yes1 said ,rollo1 ,i believe ,i understand it now4 ,after this1 ,rollo took ,james and ,nathan out into the yard1 to see if some beans had come up1 which he had been planting in a sunny corner of the garden the day before4 ,,questions4 ,what was ,mr4 ,holiday's apostrophe to the earth8 ,what is the cause of weight8 ,why did the boys wish that there was no gravitation8 ,what was the first evil consequence which their father said would ensue1 if there was no gravitation8 ,what was the second evil consequence8 ,what did their mother say after the conversation with their father was closed8 ,,chapter ,,xi4 ,,air ,,in ,,motion4 ,rollo's dam1 which he had made when he was studying the philosophy of water1 and which was at first undermined by the pressure of the water1 was afterwards carried away by its momentum4 ,rollo learned1 at that time1 that water moving rapidly had a great momentum2 and about this time he had an opportunity of learning that air1 when in motion1 had a momentum too1 capable of producing very powerful effects4 ,the circumstances of the case were as follows3-- ,one morning1 towards the latter part of ,march1 ,jonas1 being out in the barn1 observed some indications that the roof wanted repairs4 ,it had been strained and weakened by the heavy snows in the winter4 ,he reported the fact to ,rollo's father1 who said that he might go1 the next day1 and get the carpenter to come and repair it4 ,the carpenter lived ten miles distant1 near the shore of a long pond4 ,when ,rollo heard of this proposed expedition1 he wanted to go too2 and his father gave him permission4 ,jonas was going in the wagon4 ,he told ,rollo1 the evening before1 that he meant to set out at six o'clock4 ,but suppose it looks like a storm1 said ,rollo4 ,then there will be more need of going1 said ,jonas2 for if the equinoctial storm comes on before the roof is strengthened1 it may get carried away4 ,what is the equinoctial storm8 said ,rollo4 ,o1 it is a great storm1 which comes generally about this time of year4 ,i shouldn't wonder if it should come on to-morrow4 ,but it may not come for a week2 and so ,i hope we shall have time to get the roof mended first4 ,does it look like a storm to-night8 said ,rollo4 ,no1 not much1 replied ,jonas4 ,it is a little hazy in the south-west4 ,however1 if it looks like a storm in the morning1 you need not go1 unless you choose2 though ,i shall4 ,i wish you'd wait till the storm is over1 said ,rollo4 ,no1 said ,jonas1 ,i had rather go in the storm than not4 ,why8 said ,rollo4 ,because1 said ,jonas1 ,i like to be out in storms4 ,sometimes it is very grand4 ,the next morning1 when ,rollo awoke1 he found that it was light1 but not yet sunrise4 ,he arose1 and looked out of the window to see if it was pleasant4 ,the sky was somewhat overcast1 but there was a little blue to be seen1 and ,rollo thought that it would be pleasant4 ,he heard a noise in the barn-yard1 and1 looking in that direction1 he saw ,jonas just leading the horse out of the stable4 ,so he dressed himself soon1 and went down4 ,when he got ready1 he went down into the yard1 and found that ,jonas had got the horse harnessed1 and everything prepared4 ,there was a little bag of oats in the back part of the wagon1 and also a tin pail1 with a cover1 which contained a luncheon4 ,jonas fastened the horse to a post1 and said1-- ,now1 ,rollo1 we'll go in and get some breakfast4 ,i thought that luncheon was for breakfast1 said ,rollo4 ,no1 said ,jonas1 that is for dinner4 ,shall we be gone all the day8 said ,rollo4 ,we may be gone till after dinner1 said ,jonas1 and so ,i thought ,i would be sure4 ,the two boys went into the house1 and there they found that ,dorothy had got some breakfast ready for them upon the kitchen table4 ,after eating their breakfast1 they got into the wagon1 and set out4 ,jonas first put in a large umbrella4 ,just as they were driving out of the yard1 the first beams of the morning sun shone in under the branches of a great tree in the yard1 and brightened up the tips of the horses' ears and the boys' faces4 ,at the same time1 a rude gust of wind came around the corners of the house1 and slammed to the gate of the front yard4 ,it's going to be pleasant1 said ,rollo2 the sun is coming out4 ,i'm not very sure of that1 said ,jonas2 the wind is rising4 ,we start just at sunrise1 said ,rollo4 ,yes1 replied ,jonas1 the sun always rises at six o'clock at this time of the year4 ,the boys rode along for about three hours1 before they came to the carpenter's4 ,they were obliged to travel very slow1 for the roads were not good4 ,it is true that the snow was all gone1 and the frost was nearly out of the ground2 but there were many deep ruts1 and in some places it was muddy4 ,the sun went into a cloud soon after they set out1 and it continued overcast all the morning4 ,there was some wind too1 but1 as it was behind them1 and as the road lay through woods and among sheltered hills1 they did not observe it much4 ,jonas said that there was a storm coming on1 but he thought it was coming slowly4 ,they arrived at length at the pond4 ,there was a little village there1 upon the shore of the pond4 ,the reason why there happened to be a village there1 was this3 ,a stream of water1 which came down from among the mountains1 emptied into the pond here1 and1 very near where it emptied1 it fell over a ledge of rocks1 making a waterfall1 where the people had built some mills4 ,now1 where there are mills1 there must generally be a blacksmith's shop1 to mend the iron work when it gets broken1 and to repair tools4 ,there is often a tavern1 also1 for the people who come to the mills2 and then there is generally a store or two2 for wherever people have to come together1 for any business1 there is a good place to open a store1 to sell them what they want to buy4 ,thus there was a little village about these mills1 which was generally called the ,mill village4 ,jonas inquired where the carpenter lived1 and then drove directly to his house4 ,he found that he was not at home4 ,he had gone across the pond1 to mend a bridge1 which had been in part carried away by the floods made when the snow went off4 ,rollo sat in the wagon in the yard by the side of the carpenter's house1 while ,jonas stood at the door1 making inquiries and getting this information4 ,if you want to see him very much1 said the carpenter's wife1 ,i presume you can get a boat down in the village1 and go across the pond4 ,how far is he from the other side of the pond8 ,o1 close by the upper landing1 said she2 not a quarter of a mile from the shore1 right up the road4 ,jonas thanked the woman for her information1 and got into the wagon4 ,let us get a boat and go over1 ,jonas1 said ,rollo1 as they were turning the wagon round4 ,i should1 said ,jonas1 if there was not such a threatening of a storm4 ,it does not blow much1 said ,rollo4 ,no1 said ,jonas1 not much now1 but the wind may rise before we get back4 ,however1 we'll go and see if we can get a boat4 ,after some inquiry1 they found a boat1 at a little distance out of the village1 in a sort of cove1 where there was a fine1 sandy beach4 ,the boat was of very good size1 and it had in it two oars and a paddle4 ,jonas looked out upon the water1 and up to the sky1 and he listened to hear the moaning of the wind upon the tops of the trees4 ,he wanted very much to persevere in his effort to find the carpenter2 but then1 on the other hand1 he was not sure that it was quite safe to take ,rollo out upon the water at such a time4 ,he sat upon a log upon the shore a few minutes1 and seemed lost in thought4 ,illustration3 ,and very soon they were gliding smoothly along out of the cove4--,page #afg4 ,at last he said1-- ,well1 ,rollo1 ,i believe we'll go4 ,the worst that will happen will be1 that you may get frightened a little4 ,we can't get hurt4 ,why can't we get hurt8 said ,rollo4 ,why1 even if it comes on to blow hard1 it will probably be a steady gale1 and ,i can run before it1 if ,i can't do anything else4 ,and there can't be much of a sea in this pond4 ,rollo did not know what ,jonas meant by much of a sea in the pond2 but1 as ,jonas immediately went to work taking the horse out of the wagon1 ,rollo did not ask any questions4 ,the boys unharnessed the horse1 for ,jonas said he would stand easier out of harness1 and they might be gone more than an hour4 ,they fastened him then to a tree1 and poured the oats down before him upon the ground4 ,then ,jonas helped ,rollo into the boat1 and put in the tin pail containing their luncheon1 and also the umbrella2 though he said he did not think it would rain before they got back4 ,then he shoved off the boat1 and jumped in himself2 and very soon they were gliding smoothly along out of the cove4 ,rollo wanted to row2 and so ,jonas let him take one oar1 while he himself sat in the stern with the paddle4 ,rollo soon learned the proper motion1 so that his efforts assisted considerably in propelling the boat4 ,they found1 when they were out at a little distance upon the water1 that the wind blew much harder than ,rollo had expected4 ,jonas1 said he1 the wind blows more here than it did upon the shore4 ,no1 said ,jonas1 only we feel it more here than when we were under the lee of the land4 ,what do you mean by the lee of the land8 said ,rollo4 ,i mean the shelter of it1 replied ,jonas4 ,whenever a ship at sea is sheltered by anything1 they say the ship is under its lee4 ,the boys went on1 ,rollo rowing1 and ,jonas paddling behind1 until at length ,rollo got tired4 ,jonas then told him to spread the umbrella1 and hold it up for a sail4 ,rollo did so4 ,the wind was blowing pretty nearly in the direction in which they were going1 and1 by its impulse upon the umbrella1 it caused it to pull very hard4 ,rollo rested the middle of the handle of the umbrella upon his shoulder1 holding the crook in his hand1 turning it in such a position as to present the open part of the umbrella fairly to the wind4 ,jonas continued to paddle1 and so they went on very prosperously until they had got two thirds across the pond1 when ,jonas ordered ,rollo to take in sail4 ,why1 said ,rollo1 we have not got across yet4 ,no1 replied ,jonas1 but the wind is taking us out of our course4 ,rollo drew down the umbrella1 and looked around4 ,they were still at a considerable distance from the shore4 ,jonas extended his paddle out into the water as far as he could reach1 and then drew it in towards him with several quick and strong strokes1 as if he were endeavoring to pull the stern of the boat1 in which he was sitting1 round4 ,what are you doing so for8 said ,rollo4 ,i am trying to bring her up into the wind1 replied ,jonas4 ,what is that for8 asked ,rollo4 ,why1 we've drifted to leeward1 said ,jonas1 and ,i must bring her up2 for we want to land around behind that point on the starboard bow4 ,rollo did not understand ,jonas's technical language very well4 ,he particularly did not know what ,jonas meant by bringing her up1 for it seemed to him that the pond was perfectly level1 so that there was no up or down either way4 ,he did not know that1 in sea language1 against the wind was always up1 and with the wind1 down4 ,jonas found it hard to bring the boat up into the wind4 ,the waves had begun to be pretty large1 and they beat against the bows of the boat1 and some of the water dashed over upon ,rollo4 ,the wind blew quite heavily1 too2 and now that they had changed their direction so as to bring the wind upon their side1 it embarrassed1 if it did not absolutely retard their progress4 ,some drops of rain also began to fall4 ,however1 by hard and persevering exertion1 ,jonas at length succeeded in urging the boat forward until he began to draw nigh to the point of land2 and soon afterwards they came under the shelter of it1 where the water was smooth1 and the air comparatively still4 ,here ,rollo put in his oar again1 and they passed along close under a high shore1 for some distance1 until they came to the landing4 ,here they fastened the boat1 and then began to walk along up the road4 ,the road lay through the woods1 and among hills1 so that it was sheltered2 and the only indications of the wind which the boys noticed1 was a distant roaring sound among the forests4 ,they came at length to the bridge1 where they found several workmen busily engaged in laying abutments of stone1 but the carpenter himself was not there4 ,the men told ,jonas that he had gone about half a mile away1 on a by-road1 to select and cut some timber to be used in the construction of the bridge4 ,how long will he be gone8 asked ,jonas4 ,he will be gone two or three hours1 said a man with a stone hammer in his hand4 ,what shall we do now8 asked ,rollo1 addressing ,jonas1 after a short pause4 ,keep on until we find him1 replied ,jonas4 ,but you may stay here and see them build the bridge1 while ,i go after the carpenter4 ,accordingly ,jonas went on1 leaving ,rollo seated upon a bank watching the work4 ,in about three quarters of an hour1 he returned2 and then he and ,rollo went back to the boat4 ,the wind had all this time continued to increase1 though they were so much sheltered1 that they did not notice it much4 ,jonas1 however1 observed that some light1 scudding clouds were flying across the sky1 very low1 being apparently far beneath the other clouds4 ,when they reached the boat1 ,rollo proposed that they should stop and eat some luncheon2 but ,jonas said that he should eat his with a better appetite on the other side of the pond4 ,so he hastened ,rollo into the boat1 and1 talking his station in the stern1 he began to ply his paddle with all his force1 running the boat along under the shelter of the high shore4 ,there isn't much wind1 ,jonas1 said ,rollo4 ,we can tell better when we come round the point1 replied ,jonas4 ,rollo observed that ,jonas looked a little anxious1 and he also seemed to be exerting himself so much in the long1 steady strokes of his paddle1 that it appeared to be rather an interruption to him to hear and answer questions4 ,rollo therefore did not talk4 ,he found1 however1 as he drew near the point1 that the waves were running by it1 with great speed and force1 down the pond4 ,as the boat shot out from the shelter of the point into this place of exposure1 the storm struck them suddenly1 with a blast which swept the bows of the boat at once round out of her course1 and dashed the spray from the waves all over ,rollo's face and shoulders4 ,it was with great difficulty that ,jonas could bring the boat to the wind again4 ,he succeeded1 however1 at length1 and they went on1 for some time1 pitching and tossing1 through the waves1--the wind pressing so hard upon the boat that it was very difficult for ,jonas to make any headway4 ,the wind had changed its direction1 so that it blew now almost exactly across their course2 and it required great exertion for ,jonas to prevent being blown away down the pond1 out of his track altogether4 ,in the mean time1 the wind rather increased than diminished2 and the water dashed in so much over the bows that ,rollo had to dip it up with the cover of the tin pail1 and pour it out over the side of the boat into the pond again4 ,they were going on in this way1 both toiling very laboriously1 when suddenly they began to hear a sound like distant thunder1 somewhat louder than the ordinary roaring of the wind4 ,they both looked towards the shore in the direction from which the sound came4 ,on the declivity of a range of hills covered with forests they saw an unusual commotion among the trees4 ,the tops were bowed down with great force2 the branches were broken off1 and ,jonas thought that he could see fragments of them flying in the air2 and presently1 farther down1 he observed several tall pines bending over1 and then sinking down till they disappeared4 ,what is it8 said ,rollo4 ,a squall1 said ,jonas1--and coming down directly upon us4 ,what shall we do8 asked ,rollo4 ,put the boat before the wind1 replied ,jonas1 and let her run3 we must go where the squall carries us4 ,jonas immediately began to pull the stern of the boat around with his paddle1 so as to turn the head of it away from the quarter which the wind was blowing from2 and then the wind drove the boat along very rapidly over the waves1 which curled and foamed on each side1 driving onward with great fury4 ,when they looked around behind them1 they saw that the pond1 which was of a very dark color1 though spotted with the white tips of the waves all over its surface1 was almost black for a large space in the direction from which the squall was coming4 ,it advanced with great rapidity1 and at last struck the boat with a noise like thunder4 ,the froth and foam flew over the surface of the water like tufts of cotton1 and the boat seemed to fly along the water with almost as much speed as they2 and the roaring of the winds and waves was so loud that ,rollo had great difficulty in making ,jonas hear what he had to say4 ,after a few minutes1 the violence of the wind somewhat abated2 but it still blew a steady and furious gale1 so that ,jonas had to keep his boat directly before it4 ,thus they were driven on1 wherever the wind chose to carry them1 for more than half an hour4 ,then they began to draw near the land1 far1 however1 very far from the place where they had intended to go4 ,rollo observed that ,jonas was looking out very eagerly towards the shore1 and he asked him what he was looking for4 ,why1 here we are1 said ,jonas1 on a lee shore1 and ,i am looking out for a place to land4 ,rollo looked1 and saw that the waves were tumbling with great violence upon the rocks and gravelly beaches which lined the shore1 and he was afraid that the boat would get dashed to pieces upon them4 ,jonas1 however1 observed a large tree1 which originally stood upon the bank1 but which had fallen over1 and now lay with its top partly submerged4 ,he thought that this might afford him some shelter1 and so he made great exertions to guide the boat so as to bring it in to the shore around behind this tree4 ,by means of great efforts he succeeded2 and so he and ,rollo both escaped safe to land4 ,the boys did not get home until late that night1 for they were thrown upon the shore nearly two miles from the ,mill village1 and of course they had that distance to walk4 ,jonas was detained a little there1 too1 in making arrangements to send a boy for the boat after the storm had subsided4 ,when they got home1 ,rollo's father said that he was sorry for their fatigues and exposures1 but he was very glad that ,jonas had persevered and found the carpenter2 for the high wind had blown down the back chimney and broken the roof over the kitchen1 and it was very necessary to have it repaired immediately4 ,,questions4 ,what is momentum8 ,has air momentum1 when it is in motion1 as well as water8 ,at what time in the spring of the year does the sun rise at six o'clock8 ,what did ,rollo think was the prospect in respect to the weather8 ,what did ,jonas think8 ,what is meant by being under the lee of a shore8 ,what is a squall8 ,what indications did ,jonas observe of the approach of the squall8 ,what course did he pursue in order to avoid the danger of it8 ,,chapter ,,xii4 ,,air ,,at ,,rest4 ,a few days after the adventure described in the preceding chapter1 ,rollo heard his father proposing to his mother that they should take a walk the next morning before breakfast4 ,rollo wanted to go too4 ,his father said that they should be very glad to have his company2 and he promised to wake him in season4 ,rollo felt rather sleepy1 when his father called him the next morning2 but he jumped up and dressed himself1 and was ready first of all4 ,it was a cool1 but a very pleasant morning4 ,the sun was just coming up4 ,the ground in the path before the door was frozen a little1 and the air seemed very still4 ,when ,rollo's mother came out to the door1 she said1-- ,well1 husband1 which way shall we go8 ,up on the rocks1 said ,rollo2 let's go up on the rocks1 mother4 ,it will be beautiful there this morning4 ,well1 replied his mother2 we'll go up on the rocks4 ,the place which ,rollo called the rocks1 was the summit of a rocky hill1 which had a grassy slope upon one side1 by which they could ascend1 and a precipice of ragged rocks upon the other4 ,there was a very pleasant prospect from the top of the rocks4 ,as they walked along1 ,rollo said that it was very different weather that still morning1 from what it was the day that he and ,jonas were out upon the pond4 ,yes1 said his father1 you had an opportunity to see the effects of air in motion then4 ,and now air at rest1 replied ,rollo4 ,pretty nearly1 said his father4 ,yes1 sir1 entirely1 said ,rollo2 there is no wind at all1 this morning3 hold up your hand1 and you can feel4 ,so ,rollo stopped a moment upon the grass1 and held up his hand to see whether there was any wind4 ,i know there is not any wind that you can perceive in that way1 said his father4 ,how can we perceive it1 then8 said ,rollo4 ,i'll tell you1 replied his father1 when we get to the top of the hill4 ,they reached the top of the hill soon after this1 and sat down upon a smooth stone4 ,there was a very wide prospect spread out before them1--fields1 forests1 hamlets1 streams1--and here and there1 scattered over the landscape1 a little patch of snow4 ,the sun was just up1 and the whole scene was very bright and beautiful4 ,now1 father1 said ,rollo1 tell me how you know that there is any wind at all4 ,i did not say that there was any wind4 ,i said motion of the air4 ,why1 father1 replied ,rollo1 ,i thought that wind was motion of the air4 ,so it is1 said his father2 but all motion of the air is not wind4 ,wind is a current of air1 that is1 a progressive motion2--and in fact1 there is1 this morning1 a slight current from the westward4 ,how can you tell1 father8 asked ,rollo4 ,by the smokes from the chimneys2 don't you see that they all lean a little from the west towards the east8 ,not but a little1 father2--and there's one1 from that red house1 which goes up exactly straight4 ,yes1 said his father1 there is one2 but1 in general1 the columns of smoke lean2 which is proof that there is a gentle current of air to the eastward4 ,westward1 you said1 father1 rejoined ,rollo4 ,yes1 from the westward1 but to the eastward4 ,that is what is called a progressive motion1 continued ,rollo's father2 that is1 the whole body of air makes progress2 it advances from west to east4 ,but there is another kind of motion1 called a vibratory motion4 ,what kind of a motion is that1 father8 asked ,rollo4 ,it is a very hard kind to describe1 at any rate1 said his father4 ,it is a kind of quivering1 which begins in one place and spreads in every direction4 ,don't you hear a kind of a thumping sound8 ,yes1 said ,rollo1 a great way off2 what is it8 ,look over across the pond there1 said his father2 don't you see that man cutting wood8 ,yes1 said ,rollo2 that's what makes the noise4--,no1 father1 he continued1 after a moment's pause1 that's not it4 ,look1 father1 and you'll see that the thumping sound comes when his axe is lifted up4 ,they all looked1 and found that it was as ,rollo had said4 ,the strokes of the axe kept time1 pretty well1 with the sound of blows1 which they heard1 only the sounds did not correspond with the descent of the axe4 ,when the axe appeared to strike the wood1 they did not hear any sound1 but they did hear one every time the axe was lifted up4 ,so1 you see1 said ,rollo1 it is not that man that we hear4 ,there must be some other man cutting wood4 ,we will wait a minute1 said his father1 until he gets the log cut off1 and then he will stop cutting2 and we will see whether we cease to hear the sound4 ,so they sat still1 and watched the man for a minute4 ,presently he stopped cutting1--and1 to ,rollo's great surprise1 the sound stopped too4 ,that's strange1 said ,rollo4 ,in a moment more1 the man had rolled the log over1 and commenced cutting upon the other side2 and in an instant after he began to cut1 ,rollo began to hear the sound of strokes again4 ,yes1 said ,rollo1 it must be his cutting that we hear2 but it is very strange that he makes a noise when he lifts up his axe1 and no noise when it goes down4 ,i'll tell you how it is1 said his father4 ,he makes the noise when his axe goes down2 but1 then1 it takes some little time for the sound to get here2 and by the time the sound gets here1 his axe is up4 ,o1 said ,rollo1 is that it8 ,yes1 replied his father1 that is it4 ,rollo watched the motion of the axe several minutes longer in silence1 and then his attention was attracted by the singing of a bird upon a tree in his father's garden1 at a short distance below him4 ,pretty soon1 however1 his mother said that it was time for her to return2 and they all1 accordingly1 arose from their seats1 and rambled along together a short distance upon the brow of the hill1 but towards home4 ,then the sound moves along through the air1 said ,rollo1 from the man to us4 ,yes1 said his father2 that is1 there is a vibratory motion of the air1--a kind of quivering1--which begins where the man is1 and spreads all around in every direction1 until it reaches us4 ,but there is no progressive motion2 that is1 none of the air itself1 where the man is at work1 leaves him1 and comes to us4 ,but1 husband1 said ,rollo's mother1 ,i don't see how anything can come from where the man is1 to us1 unless it is the air itself4 ,it is rather hard to understand1 said his father4 ,but ,i can make an experiment with a string1 when we get home1 that will show you something about it4 ,they rambled about among the rocks for a short time longer1 and then they descended by a steep and crooked path1 in a different place from where they had ascended4 ,when they had got nearly home1 ,rollo said that he would run forward and get his father's ball of twine and bring it out2 and so have it all ready for the experiment4 ,accordingly1 when ,rollo's father and mother arrived at the front door1 they found ,rollo ready there with a small ball of twine in his hand1 about as large as an apple4 ,now1 ,rollo1 said his father1 you may take hold of the end of the twine1 and walk along out into the street1 while ,i hold the ball1 and let the string unwind4 ,rollo did so4 ,he drew out a long piece of twine1 as long as the whole front of the house1 and then he stopped to ask his father if that was enough4 ,no1 said his father2 walk along4 ,so ,rollo walked on for some distance farther1 until1 at last1 the ball was entirely unwound4 ,rollo had one end of it1 and was standing at some distance down the road1 while his father1 with the other end1 stood at the gate of the front yard4 ,the middle of the string hung down pretty near to the ground4 ,draw tight1 ,rollo1 said his father4 ,so ,rollo pulled a little harder1 and by that means drew the line straighter4 ,now1 said his father1 walk along slowly4 ,so ,rollo walked along1 drawing the end of the line with him4 ,his father followed with the other end4 ,thus they advanced several steps along the side of the road4 ,there1 said his father4 ,stop4 ,that1 you see1 was a progressive motion4 ,yes1 sir1 replied ,rollo4 ,the whole string advanced along the road1 added his father4 ,it made progress1 and so it was a progressive motion4 ,now1 fasten your end of the string1 ,rollo1 to that tree directly behind you4 ,rollo looked behind him1 and saw that he was standing near a small maple-tree1 which had been planted1 a few years before1 by the side of the road4 ,tie it right around the stem of the tree1 said his father1 about as high as your shoulder4 ,rollo fastened the string as his father had directed4 ,then his father fastened his end1 in the same way1 to another tree1 which was growing near where he was standing4 ,now1 said he1 there can be no more progressive motion1 but there can be a vibratory one4 ,take hold of the string near where it is fastened to the tree4 ,rollo took hold of it1 as his father had directed1 and then his father told him to shut his eyes4 ,when his eyes were shut1 so that he could not see1 his father said that he was going to strike the string1 at his end of it1 with his pencil-case1 and he asked ,rollo to observe whether he could feel any motion4 ,rollo held very still1 while his father struck the string2 and immediately afterwards he called out1 ,yes1 sir4 ,then his father struck the string again1 several times1 and every time ,rollo could feel a distinct vibratory or quivering motion1 which was transmitted very rapidly through the string1 from one end to the other2 although1 as the string was fastened by both ends to the trees1 it was evident that there could be no progressive motion4 ,rollo's mother had been standing all this time at the step of the door1 watching the progress of the experiment2 and1 when she saw the expression of satisfaction upon ,rollo's countenance1 while he was standing1 with his eyes shut1 holding the end of the string1 she wanted to come and take hold of it herself1 so as to see what sort of a sensation the vibratory motion of the string produced4 ,so she came out through the gate1 and asked ,mr4 ,holiday to wait a moment while she went to where ,rollo was standing1 and took hold of the string4 ,but he said that it would not be necessary for her to go there1 as she could take hold of his end of the line just as well1 and let ,rollo strike the other end4 ,they accordingly performed the experiment in that way1 and ,rollo's mother could feel the vibrations very distinctly4 ,one thing you must observe1 said ,mr4 ,holiday2 and that is1 that the vibrations pass along from one end of the line to the other very quick indeed4 ,we feel them at one end almost at the same instant that the other end is struck4 ,exactly at the same instant1 sir1 said ,rollo4 ,no1 replied his father1 not exactly at the same instant1 though it is very nearly the same4 ,i did not see any difference1 said ,rollo4 ,no1 replied his father1 you cannot perceive any difference in so short a string1 but if we had a string1 or a wire1 a mile long1 ,i presume that we should find that it would require a sensible period of time to transmit the vibrations from one end to the other4 ,what do you mean by a sensible period of time1 father8 asked ,rollo4 ,why1 a length of time that you could perceive1 said his father2 just as it was with the man cutting wood4 ,we could see that some time elapsed between the striking of the blow1 and our hearing the sound4 ,yes1 said ,rollo1 just as long as it took him to lift up his axe4 ,that is not certain1 replied his father1 because the sound that we heard might have belonged to a blow made before4 ,that is1 it might be that1 when he had struck one blow1 he had time to raise his axe and strike another1 and then raise his axe again1 before the sound of the first blow came to us4 ,yes1 sir1 said ,rollo1 ,i understand4 ,mr4 ,holiday then told ,rollo that he might unfasten the string from the trees1 and wind it up again into a ball1 and bring it in4 ,then he and ,rollo's mother went into the house1 to see if breakfast was not almost ready4 ,that morning1 after they were all seated at the breakfast table1 ,rollo said to his father that he did not exactly understand what sort of a motion the vibratory motion of the air was1 after all4 ,no1 said his father1 ,i suppose you do not4 ,and1 in fact1 ,i do not understand it very perfectly myself4 ,i only know that the philosophers say1 that1 when a man strikes a blow with an axe upon a log of wood1 it produces a little quivering motion of the air1 which spreads all around1 darting off in every direction very swiftly4 ,if a boy strikes a tin pail with a drum-stick1 it makes another kind of quivering or vibration1 which is different from that which is made by the axe2 but ,i don't know precisely how it differs4 ,so1 when the air is full of sounds1 on a still morning1 it is full of these little vibrations1 like a string which trembles from end to end1 though its ends are fastened so that it cannot move away4 ,then the air is never at rest1 said ,rollo's mother4 ,no2 certainly not1 when any sound is to be heard2 and it is never perfectly silent4 ,there is one thing very extraordinary1 said ,mrs4 ,holiday4 ,what is it8 asked ,rollo's father4 ,why1 that1 when a great many sounds are made at the same time1 she replied1--as1 for example1 when we are upon the top of a hill1 on a still morning1 and hear a great many separate sounds1 as a man cutting wood1 birds singing1 a bell ringing1 and perhaps a man shouting to his oxen1--all those tremblings or vibrations1 being in the air together1 do not interfere with one another4 ,yes1 said ,mr4 ,holiday1 it is very extraordinary indeed4 ,they do not seem to interfere at all4 ,when there are too many sounds1 or if there is a wind with them1 they do interfere2 but1 in a calm morning1 like this1 when the air is at rest1 you can hear a great many distant sounds very distinctly4 ,yes1 said ,rollo1 and ,i mean to go up to the top of the rocks again after breakfast1 and listen4 ,,questions4 ,what time of the year was it when ,rollo took this walk8 ,how did ,rollo satisfy himself that there was no wind at all8 ,how did his father prove that there was a little wind8 ,is all motion of the air wind8 ,what two kinds of motion are mentioned8 ,what sound did they hear8 ,what made ,rollo think the sound was not made by the man whom they saw cutting wood8 ,how did his father explain this phenomenon8 ,what experiment did they try with the string8 ,were the vibrations transmitted slowly or rapidly through the string8 ,did ,rollo think that he understood perfectly the nature of the vibrations8 ,what extraordinary circumstance did ,rollo's mother mention at the breakfast table8