Overview

Lesson Procedure

65-75 minutes of class time across 5 phases.

1. Warm-Up10 minutes
2. Direct Instruction20 minutes
3. Guided Practice15 minutes
4. Independent Practice15-20 minutes
5. Closure5-10 minutes

1. Warm-Up10 minutes

   If you have a kettle, boil it at the front of the room (teacher only, away from students) and let students look at the gap between the spout and the plume. Then show the sentence below.

   Warm-Up Prompt

   "Rewrite this sentence so that a ten-year-old could understand it, without making it false: 'The visible plume above a boiling kettle is not water vapor, which is an invisible gas, but a cloud of liquid droplets that condense as the vapor cools in the room air.'"

   Collect three or four versions and test each one twice: is it simpler, and is it still true? "The steam you see is water vapor" is simpler but false. "The white stuff is tiny drops of water that form when the invisible gas from the kettle cools" passes both tests. Tell students that RST.11-12.2 asks for exactly this, and that a physicist made the same point about a locomotive in 1872.

2. Direct Instruction20 minutes

   Part 1: Where simplification goes wrong. A paraphrase restates one idea in new words; a summary restates the central idea and the key points of a whole passage. Both must be simpler than the original and still accurate. The table lists the ways simplification breaks accuracy.

   Simplification traps in science paraphrase

   Trap	What goes wrong	Check
   Dropping a cause	"Air cools as it rises" loses why	Does the paraphrase still say what causes what?
   Dropping a condition	"Clouds vanish" loses when and how fast	Are the if, when and depends-on words still there?
   Changing a comparison	"faster in dry air" becomes "only in dry air"	Are more, less, faster and slower kept as comparisons?
   Changing a quantity or limit	"59 inches" becomes "a lot" or "about 50"	Are numbers and units kept, or rounded honestly?
   Reading an analogy literally	"water-dust" read as dry dust	Is the comparison marked as a comparison?
   Blending in later science	adding a modern fact as if the author said it	Is every claim in the paraphrase in the text?

   Part 2: Model with Tyndall. Tyndall has just traced a river back to the rain that feeds it, and asks where rain comes from. Read paragraphs 6-9 aloud. After each example, ask the class the two questions from the Warm-Up: simpler? still true?

   6. But we cannot end here. Whence comes the rain which forms the mountain streams? Observation enables you to answer the question. Rain does not come from a clear sky. It comes from clouds. But what are clouds? Is there nothing you are acquainted with which they resemble? You discover at once a likeness between them and the condensed steam of a locomotive. At every puff of the engine a cloud is projected into the air. Watch the cloud sharply: you notice that it first forms at a little distance from the top of the funnel. Give close attention and you will sometimes see a perfectly clear space between the funnel and the cloud. Through that clear space the thing which makes the cloud must pass. What, then, is this thing which at one moment is transparent and invisible, and at the next moment visible as a dense opaque cloud?

   7. It is the steam or vapour of water from the boiler. Within the boiler this steam is transparent and invisible; but to keep it in this invisible state a heat would be required as great as that within the boiler. When the vapour mingles with the cold air above the hot funnel it ceases to be vapour. Every bit of steam shrinks when chilled, to a much more minute particle of water. The liquid particles thus produced form a kind of water-dust of exceeding fineness, which floats in the air, and is called a cloud.

   8. Watch the cloud-banner from the funnel of a running locomotive; you see it growing gradually less dense. It finally melts away altogether, and if you continue your observations you will not fail to notice that the speed of its disappearance depends upon the character of the day. In humid weather the cloud hangs long and lazily in the air; in dry weather it is rapidly licked up. What has become of it? It has been reconverted into true invisible vapour.

   9. The drier the air, and the hotter the air, the greater is the amount of cloud which can be thus dissolved in it. When the cloud first forms, its quantity is far greater than the air is able to maintain in an invisible state. But as the cloud mixes gradually with a larger mass of air it is more and more dissolved, and finally passes altogether from the condition of a finely-divided liquid into that of transparent vapour or gas.

   • Central conclusion

     What conclusion do paragraphs 6-9 reach about clouds?

     Result: A cloud is not vapour but condensed vapour: "Every bit of steam shrinks when chilled, to a much more minute particle of water," and the particles form "a kind of water-dust of exceeding fineness, which floats in the air, and is called a cloud." The cloud disappears when it is "reconverted into true invisible vapour," which happens faster in drier and hotter air. One sentence: a cloud is invisible water vapour that has cooled into tiny floating drops of liquid, and it vanishes again as those drops evaporate into the surrounding air.

   • Paraphrase: simpler and accurate

     Paraphrase paragraph 7 for a general reader.

     Result: Inside the boiler, steam is an invisible gas. When it meets cold air, it condenses into countless tiny drops of liquid water, and those floating drops are the cloud. The paraphrase keeps the two states (invisible gas, visible liquid) and the cause (cold air), which are the parts a shorter version such as "the cloud is steam" gets wrong.

   • Keeping a comparison and two conditions

     Paraphrase: "The drier the air, and the hotter the air, the greater is the amount of cloud which can be thus dissolved in it."

     Result: Accurate: the drier and the warmer the air, the more of the cloud it can turn back into invisible vapour. Inaccurate: "hot air dissolves clouds." That version drops "drier," and it turns a comparison ("the greater") into a flat rule. Tyndall's italics mark the two conditions, so a paraphrase must keep both.

   • Paraphrasing the text, not correcting it

     Tyndall says the cloud is "dissolved" in the air, and the air can "maintain" only so much of it "in an invisible state." Should a paraphrase say that air holds water like a sponge?

     Result: A paraphrase reports what Tyndall says: "when the cloud first forms, there is more of it than the air can keep invisible; as it mixes with more air, it turns back into vapour." It should not add a sponge image he does not use. If a student knows the modern account (the teacher note in Closure), it goes in a separate sentence labeled as today's view, never inside the paraphrase.

3. Guided Practice15 minutes

   Pairs read Tyndall's account of tropical rain. First they find the sentence Tyndall himself marks as his key point (he introduces it with "It is this"). Then they paraphrase paragraphs 72-74 as a chain of four plain-language steps, and compare their chain with Diagram 1 and their key sentence with Diagram 2. Circulate and ask of each step: what causes it?

   70. But long before the air and vapour from the equator reach the poles, precipitation occurs. Wherever a humid warm wind mixes with a cold dry one, rain falls. Indeed the heaviest rains occur at those places where the sun is vertically overhead. We must enquire a little more closely into their origin.

   71. Fill a bladder about two-thirds full of air at the sea level, and take it to the summit of Mont Blanc. As you ascend, the bladder becomes more and more distended; at the top of the mountain it is fully distended, and has evidently to bear a pressure from within. Returning to the sea level you find that the tightness disappears, the bladder finally appearing as flaccid as at first.

   72. The reason is plain. At the sea level the air within the bladder has to bear the pressure of the whole atmosphere, being thereby squeezed into a comparatively small volume. In ascending the mountain, you leave more and more of the atmosphere behind; the pressure becomes less and less, and by its expansive force the air within the bladder swells as the outside pressure is diminished. At the top of the mountain the expansion is quite sufficient to render the bladder tight, the pressure within being then actually greater than the pressure without. By means of an air-pump we can show the expansion of a balloon partly filled with air, when the external pressure has been in part removed.

   73. But why do I dwell upon this? Simply to make plain to you that the unconfined air, heated at the earth's surface, and ascending by its lightness, must expand more and more the higher it rises in the atmosphere.

   74. And now I have to introduce to you a new fact, towards the statement of which I have been working for some time. It is this: The ascending air is chilled by its expansion. Indeed this chilling is one source of the coldness of the higher atmospheric regions. And now fix your eye upon those mixed currents of air and aqueous vapour which rise from the warm tropical ocean. They start with plenty of heat to preserve the vapour as vapour; but as they rise they come into regions already chilled, and they are still further chilled by their own expansion. The consequence might be foreseen. The load of vapour is in great part precipitated, dense clouds are formed, their particles coalesce to rain-drops, which descend daily in gushes so profuse that the word "torrential" is used to express the copiousness of the rainfall. I could show you this chilling by expansion, and also the consequent precipitation of clouds.

   75. Thus long before the air from the equator reaches the poles its vapour is in great part removed from it, having redescended to the earth as rain. Still a good quantity of the vapour is carried forward, which yields hail, rain, and snow in northern and southern lands.

   Debrief with one question: In paragraph 74, the rising currents "come into regions already chilled, and they are still further chilled by their own expansion." Why must a paraphrase keep "still further"? Students should see that Tyndall names two sources of cold (the cold air high up, and the expansion itself) and that a paraphrase with only one of them has changed his explanation.

   For Activity 3 (Help-Page Rewrite). The manual page below was written for this page, modeled on the notes that come with a household humidity monitor. It explains the same physics as Tyndall's paragraph 9 in modern terms.

   Display. The monitor shows three readings: temperature (°C), relative humidity (RH, %) and dew point (°C). The readings update every 10 seconds.

   Relative humidity. RH compares the water vapor in the air with the most water vapor that can be present at the same temperature before it begins to condense. At 100% RH the air is saturated. Because that maximum rises steeply with temperature, the same amount of vapor gives a lower RH in warm air than in cool air. Air at 20 °C and 50% RH that is warmed to 25 °C, with no vapor added or removed, reads about 37% RH.

   Dew point. The dew point is the temperature to which the air would have to be cooled, with no change in its water vapor, for the RH to reach 100%. Below it, dew or fog forms. Unlike RH, the dew point does not change when the room is heated or cooled, as long as no vapor is added or removed. It is therefore the better reading for comparing how much moisture two rooms contain. Air at 20 °C and 50% RH has a dew point of about 9 °C.

   Condensation warning. The droplet symbol appears when the dew point is within 2 °C of the room temperature. Windows and cold-water pipes are often colder than the room air, so water may condense on them even when the display shows less than 100% RH.

   Accuracy. RH: ±3% between 20% and 80% RH, ±5% outside that range. Temperature: ±0.5 °C. After moving the monitor to another room, wait 30 minutes before reading it.

4. Independent Practice15-20 minutes

   Students read Tyndall's section on "mountain condensers" and answer quiz questions 1-20 on their own with the passage open. The questions cite Tyndall's own paragraph numbers (81-84). Place names: Magillicuddy's Reeks are the highest mountains in Ireland, in County Kerry in the southwest; Cahirciveen is a town on the Kerry coast; Portarlington is a town in the Irish midlands; Lombardy is the plain of northern Italy, south of the Alps.

   81. To complete our view of the process of atmospheric precipitation we must take into account the action of mountains. Imagine a south-west wind blowing across the Atlantic towards Ireland. In its passage it charges itself with aqueous vapour. In the south of Ireland it encounters the mountains of Kerry: the highest of these is Magillicuddy's Reeks, near Killarney. Now the lowest stratum of this Atlantic wind is that which is most fully charged with vapour. When it encounters the base of the Kerry mountains it is tilted up and flows bodily over them. Its load of vapour is therefore carried to a height, it expands on reaching the height, it is chilled in consequence of the expansion, and comes down in copious showers of rain. From this, in fact, arises the luxuriant vegetation of Killarney; to this, indeed, the lakes owe their water supply. The cold crests of the mountains also aid in the work of condensation.

   82. Note the consequence. There is a town called Cahirciveen to the south-west of Magillicuddy's Reeks, at which observations of the rainfall have been made, and a good distance farther to the north-east, right in the course of the south-west wind, there is another town, called Portarlington, at which observations of rainfall have also been made. But before the wind reaches the latter station it has passed over the mountains of Kerry and left a great portion of its moisture behind it. What is the result? At Cahirciveen, as shown by Dr. Lloyd, the rainfall amounts to 59 inches in a year, while at Portarlington it is only 21 inches.

   83. Again, you may sometimes descend from the Alps when the fall of rain and snow is heavy and incessant, into Italy, and find the sky over the plains of Lombardy blue and cloudless, the wind at the same time blowing over the plain towards the Alps. Below the wind is hot enough to keep its vapour in a perfectly transparent state; but it meets the mountains, is tilted up, expanded, and chilled. The cold of the higher summits also helps the chill. The consequence is that the vapour is precipitated as rain or snow, thus producing bad weather upon the heights, while the plains below, flooded with the same air, enjoy the aspect of the unclouded summer sun. Clouds blowing from the Alps are also sometimes dissolved over the plains of Lombardy.

   84. In connection with the formation of clouds by mountains, one particularly instructive effect may be here noticed. You frequently see a streamer of cloud many hundred yards in length drawn out from an Alpine peak. Its steadiness appears perfect, though a strong wind may be blowing at the same time over the mountain head. Why is the cloud not blown away? It is blown away; its permanence is only apparent. At one end it is incessantly dissolved, at the other end it is incessantly renewed: supply and consumption being thus equalized, the cloud appears as changeless as the mountain to which it seems to cling. When the red sun of the evening shines upon these cloud-streamers they resemble vast torches with their flames blown through the air.

5. Closure5-10 minutes

   Exit ticket: "Write Tyndall's key sentence from paragraph 74 in your own words, in 15 words or fewer. Then write one tempting paraphrase that is simpler but false, and name the trap it falls into." Read a few of the false versions aloud; they make good warm-ups for the next class.

   Teacher note on the 1872 science. Tyndall's central explanations still hold: clouds are condensed droplets, and rising air cools because it expands (today called adiabatic cooling). Four details have changed; discuss them after the quiz and homework, and keep them out of students' paraphrases of the text. (1) Paragraph 9 describes cloud "dissolved" in air that can "maintain" only so much vapour. Today the limit is described as depending on temperature, not on the air holding water; the practical rule (drier and warmer air evaporates a cloud faster) is right, and the manual page (T5) states it in modern terms. (2) Paragraph 70 says rain falls "wherever a humid warm wind mixes with a cold dry one." Mixing alone makes fog or light cloud at most; heavy rain needs air to be lifted and cooled, as paragraph 74 explains. (3) The rainfall figures in the quiz passage come from nineteenth-century records; modern averages for the Irish midlands are higher, roughly 30-40 inches a year, but the southwest coast still receives far more, so the contrast Tyndall describes is real. (4) The homework passage describes one great loop of air from the equator to the poles; see the note below.

   Teacher note on the language. The passages keep Tyndall's British spelling ("vapour") and terms: "aqueous vapour" is water vapour, and "precipitated" means condensed out of the air as cloud, rain or snow. "Bishop Heber" is Reginald Heber, whose 1819 hymn begins "From Greenland's icy mountains." The passages contain no offensive language.

   Homework passage. The homework uses the passage below. The "[...]" marks two paragraphs left out, about an older mistake concerning glaciers. Today's picture of the circulation is more complex than Tyndall's single loop: air rising at the equator flows toward the poles high up but sinks at about 30 degrees of latitude and returns toward the equator near the surface as the trade winds, and the middle and polar latitudes have circulations of their own. Students paraphrase what Tyndall says; Problem 4 asks for one separate "Today" sentence.

   56. The sun, you know, is never exactly overhead in England. But at the equator, and within certain limits north and south of it, the sun at certain periods of the year is directly overhead at noon. These limits are called the Tropics of Cancer and of Capricorn. Upon the belt comprised between these two circles the sun's rays fall with their mightiest power; for here they shoot directly downward, and heat both earth and sea more than when they strike slantingly.

   57. When the vertical sunbeams strike the land they heat it, and the air in contact with the hot soil becomes heated in turn. But when heated the air expands, and when it expands it becomes lighter. This lighter air rises, like wood plunged into water, through the heavier air overhead.

   58. When the sunbeams fall upon the sea the water is warmed, though not so much as the land. The warmed water expands, becomes thereby lighter, and therefore continues to float upon the top. This upper layer of water warms to some extent the air in contact with it, but it also sends up a quantity of aqueous vapour, which being far lighter than air, helps the latter to rise. Thus both from the land and from the sea we have ascending currents established by the action of the sun.

   59. When they reach a certain elevation in the atmosphere, these currents divide and flow, part towards the north and part towards the south; while from the north and the south a flow of heavier and colder air sets in to supply the place of the ascending warm air.

   60. Incessant circulation is thus established in the atmosphere. The equatorial air and vapour flow above towards the north and south poles, while the polar air flows below towards the equator. The two currents of air thus established are called the upper and the lower trade winds.

   61. But before the air returns from the poles great changes have occurred. For the air as it quitted the equatorial regions was laden with aqueous vapour, which could not subsist in the cold polar regions. It is there precipitated, falling sometimes as rain, or more commonly as snow. The land near the pole is covered with this snow, which gives birth to vast glaciers in a manner hereafter to be explained.

   [...]

   64. In the process of ordinary distillation, the liquid to be distilled is heated and converted into vapour in one vessel, and chilled and reconverted into liquid in another. What has just been stated renders it plain that the earth and its atmosphere constitute a vast distilling apparatus in which the equatorial ocean plays the part of the boiler, and the chill regions of the poles the part of the condenser. In this process of distillation heat plays quite as necessary a part as cold, and before Bishop Heber could speak of "Greenland's icy mountains," the equatorial ocean had to be warmed by the sun. We shall have more to say upon this question afterwards.

Differentiation Strategies

Assessment Guidance

1. Question 1 of 20 · Multiple Choice

   According to paragraph 81, which part of the south-west wind from the Atlantic is "most fully charged with vapour"?

   AThe highest layer of the wind BThe part that has already crossed the Kerry mountains CThe lowest layer of the wind, nearest the sea DAll layers carry the same amount

2. Question 2 of 20 · Multiple Choice

   Which is the best plain-language paraphrase of "it is tilted up and flows bodily over them"?

   AIt is pushed up the slopes and over the top as a whole BIt pushes against the mountains until they tilt over CIt flows around the sides of the mountains instead DIt stops at the foot of the mountains and turns back toward the sea

3. Question 3 of 20 · Multiple Choice

   In paragraph 81, what does "In its passage it charges itself with aqueous vapour" mean?

   AAs it blows, the vapour gives it an electric charge BAs it crosses the Kerry mountains, it drops its vapour as rain CIt picks up vapour only after it reaches the coast of Ireland DWhile crossing the ocean, it takes up a load of water vapour

4. Question 4 of 20 · Multiple Choice

   Paragraph 81 ends: "The cold crests of the mountains also aid in the work of condensation." What does "also" tell a reader who is summarizing?

   AThat the cold crests are the only real cause of the rain in Kerry BThat the crests are a second, lesser cause beside expansion CThat the cold crests stop the vapour from condensing at all DThat Tyndall doubts his own explanation by expansion

5. Question 5 of 20 · Multiple Choice

   "From this, in fact, arises the luxuriant vegetation of Killarney; to this, indeed, the lakes owe their water supply." What does "this" refer to both times?

   AThe heavy rain the lifted wind drops on the mountains BThe Atlantic Ocean itself, which flows into the lakes CThe melting of mountain glaciers in Kerry DThe luxuriant vegetation of Killarney

6. Question 6 of 20 · Multiple Choice

   By how many inches a year did the rainfall at Cahirciveen exceed the rainfall at Portarlington?

   A80 inches BAbout 2.8 inches C38 inches D21 inches

7. Question 7 of 20 · Multiple Choice

   Portarlington's rainfall is closest to what fraction of Cahirciveen's?

   AAbout two-thirds BAbout one-half CAbout three times as much DAbout one-third

8. Question 8 of 20 · Multiple Choice

   In paragraph 82, what does "the latter station" refer to?

   ACahirciveen BPortarlington CMagillicuddy's Reeks DKillarney

9. Question 9 of 20 · Multiple Choice

   What job does the question "What is the result?" do in paragraph 82?

   AIt introduces the figures that confirm the consequence he predicted BIt shows that Tyndall does not know what the result will be CIt asks readers to go out and measure the rainfall themselves DIt moves the lecture on to a new subject, the weather of the Alps above Italy

10. Question 10 of 20 · Multiple Choice

    In the situation described in paragraph 83, which way is the wind blowing?

    ADown from the Alps onto the plain BAlong the line of the Alps, from east to west CThere is no wind; the air over Lombardy is still DOver the plain towards the Alps

11. Question 11 of 20 · Multiple Choice

    According to paragraph 83, why is the sky over the plains of Lombardy clear while rain and snow fall on the heights?

    AThe plains receive no wind at all, so no cloud can reach them from the sea BThe air over the plains is a different body of air from the air that reaches the mountains CWarm air low down keeps its vapour invisible; lifted and chilled, it condenses DThe high mountains block the sunshine from reaching the heights, so they stay cold

12. Question 12 of 20 · Multiple Choice

    Which is the best paraphrase of "Clouds blowing from the Alps are also sometimes dissolved over the plains of Lombardy"?

    AClouds from the Alps sometimes fall as rain once they drift out over the plains BClouds drifting out over the plains sometimes turn back into invisible vapour CThe plains sometimes send their own clouds up into the high Alps DClouds from the Alps always bring heavy storms down onto Lombardy

13. Question 13 of 20 · Multiple Choice

    Paragraph 81 begins: "To complete our view of the process of atmospheric precipitation we must take into account the action of mountains." What does this sentence tell the reader about the section?

    AThat mountains are the only cause of rain anywhere on earth BThat the section will disprove Tyndall's earlier account of rain CThat the section is mainly about the scenery of Ireland and of the Alps DThat the section adds mountains to the account of rain already given

14. Question 14 of 20 · Multiple Choice

    Which detail could a simpler summary of paragraphs 81-84 leave out without losing any of Tyndall's explanation?

    AThat the rising air expands BThat the wind is carrying vapour CThat places beyond the mountains receive less rain DThat the rainfall figures were shown by Dr. Lloyd

15. Question 15 of 20 · Short Answer

    Paraphrase paragraph 81's explanation of why Killarney is so rainy, in two or three sentences a general reader could follow. Keep every cause, in order.

    Show model answer

16. Question 16 of 20 · Short Answer

    Paraphrase paragraph 84's explanation of the cloud streamer for a ten-year-old. Then explain what is wrong with the simpler version "the cloud is stuck to the mountain."

    Show model answer

17. Question 17 of 20 · Short Answer

    Paragraphs 81 and 83 describe the same process in two places. What does the Lombardy example in paragraph 83 add to Tyndall's central idea that the Kerry example does not? Quote one phrase from paragraph 83.

    Show model answer

18. Question 18 of 20 · Short Answer

    Convert the two rainfall figures in paragraph 82 to centimeters (1 inch = 2.54 cm), rounded to the nearest centimeter. Then write one plain sentence that a newspaper could print, comparing the two towns accurately.

    Show model answer

19. Question 19 of 20 · Short Answer

    Write a summary of paragraphs 81-84 in 80-100 words for a general reader. It must be simpler than Tyndall's text, still accurate to it, and must state his central idea.

    Show model answer

20. Question 20 of 20 · Short Answer

    A classmate paraphrases paragraph 82 as "Portarlington is drier because it is farther from the sea." Is this an accurate paraphrase of Tyndall? Explain with a quotation, and rewrite it so that it is simple and accurate.

    Show model answer

These standards connect to RST.11-12.2: prerequisites to review first, parallel standards at the same level, and next steps that build on it.

Standard text: Common Core State Standards for English Language Arts & Literacy. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.