HASTINGS COLLEGE FACULTY LECTURES:
“THE ATMOSPHERE AND RADIO WAVES”
The Structure of the Atmosphere and the Transmission of
During recent years we have heard and read much about the various flights into the upper air made by stratospheric balloons. Closely allied with this interest is the continual discussion of how radio waves are transmitted over long distances, why there is such a variety of effects upon these waves when climatic changes occur, and why there have been variations between day and night radio transmissions. The net result of these matters is to give everyone an increased interest in the atmosphere as a whole.
From ancient times people have been interested in the skies and have wondered at the stars. Out of these processes of thought they eventually developed the science of astronomy. Little did these ancient peoples realize how much of importance, and interest, lay between the earth and the distant bodies that so intensely fascinated them. Some may have speculated, as we do today, as to just how far up into space the atmosphere goes and what there is in the atmosphere at the top.
However, no very serious attempts at studying of the air were made until men began to make a practical study in the effort to learn enough about the air to foretell weather conditions. Later came the radio, and the problems connected with the transmission of its waves led to further study of the air, though on a somewhat different line of attack, than that followed by the weather observers and forecasters.
Probably the first really scientific question raised – and answered – about the atmosphere was regarding its composition: “Just what is the air made of?” And the next was, “How much is there of it?” The early chemists succeeded in showing that the air is made up of two main gases – nitrogen and oxygen, and that the air is made up of about 1/5 oxygen and 4/5 nitrogen.
The answer as to how much there is of the air came through the invention of the barometer by Galileo Galilei and the use of it, as extended by his pupil, Evangelista Torricelli in 1643. They found that we are living in a great sea of air whose pressure is greatest in its deepest parts, which are at sea level, and that the pressure grows less as one ascends up the mountains. This fact showed that the air has weight, and since the weight of the air makes a load of about 15 lbs. per square inch over the surface of the earth, it is possible to calculate the total weight of the air surrounding the earth.
It turns out that the air alone makes up about one millionth of the weight of the world. The weight of the air on the ground is so considerable that geologists sometimes consider that sudden changes in air pressure may be responsible for the beginning of earthquakes, by either suddenly increasing or decreasing the total load over a given area of land. At the rate of 15 lbs. per square inch the load on a square yard of surface is 8.3 tons, and when the barometer changes as much as it commonly does between stormy and fair weather, the difference in pressure indicated is at least a quarter of a ton per square yard. When this is considered, it is evident that the change in total load over a large section of the country would be enormous.
The air is compressed about the earth in a thin film when its thickness is compared with the radius of the earth, and is held in place by the earth’s strong gravitational pull. The air molecules are traveling about with velocities of approximately ¼ mile per second and the speed increases with an increase in temperature. Since the earth and the air are floating through space in a nearly perfect vacuum, it is evident that this strong gravitational pull is necessary to prevent the air from leaving us, never to return! Such a disaster as this has happened to the smaller celestial bodies, such as the moon, whose gravitational pull is so small that not only the air but also all the water vapor has escaped from its surface – probably taken by the earth. We may, then, picture in our minds, the world as a ball to which is clinging a small layer of gas which presses against it with a weight of 15 lbs. per square inch. Since the air is a gas and is very compressible, the weight of the upper air compresses the air at the surface of the earth so that it is much more dense than the higher air and, since the density decreases continually with the height, it is impossible to locate where the boundary exists between the last vestige of air and the surrounding vacuum.
Due to the above-mentioned compression of the air, most of it is very near the surface; half of the air is closer than 3.5 miles to the surface of the earth. If all the air were compressed to the same density as it is at the surface, the whole layer would be about 5 miles thick. Since the radius of the earth is 4,000 miles, it is evident that this gaseous covering is really only a thin film.
There have been many studies made with a view to finding the approximate upper bounds of the air by both observation and by calculations. There are three main methods for making observations on this problem:
1. Observations on meteors.
2. Measurements of the duration of twilight.
Observations on the aurora
It is known that
the flash of meteors is caused by the heat generated by the friction of the
rapidly moving particles from space, when they strike the atmosphere. The speed
of these particles varies from about 7 to 18 miles per second and, therefore, a
rather rare quantity of air may offer considerable resistance to its motion.
The method of observation is simple: two observers are stationed at a known
distance apart, and both record the position in the sky where a meteor is seen.
The angular elevation above the level is measured by each observer and then,
with the distance between them known, it is easy to compute the height of the
meteor. The height found for the atmosphere by this method varies from 90-120
The second method, depending on observations on the duration of twilight, gives only about 40 miles as the height of the air surface. This method is subject to many errors, however. Its use depends upon the diffusion of the sun’s light by the air molecules themselves, and the scattering by dust particles carried in the air. Of course, the deeper the air, the longer season of twilight would be found, but so many other variable conditions enter into the effect of the air in scattering the sun light down from the upper air levels that no really definite measurements can be made.
The method of observations upon auroral displays, gives an average of about 300 miles as the height of the atmosphere. The aurora is caused by electrically charged particles from the sun penetrating the earth’s magnetic field and causing a discharge in the rarefied gases of the upper air, in much the same manner that electric current makes the gas in the now familiar neo signs glow – that is, any gas under low pressure will give out light when treated with electricity of the proper voltage. The colors of the light seen in the neon tubes depends upon the kind of gas present, and therefore, the color of the light seen in the auroral displays, tells something about the kind of gas there is up there and the position of the lights, as noted by two observers set at a known distance apart, gives the means of computing the actual distance above ground level.
There is a great variation in the reports of the observed heights of these phenomena. A certain sea captain reported that he observed an auroral display near the coast of Norway, in which the light streamers came between him and the cliffs on the shore. This indicates that rarefied air is not essential to auroral displays, though such an occurrence as the above is very rare.
In my own experience, I once took observations on a particularly bright red cloud high in the northeast and compared its position, as it appeared to me, with the position as it appeared to a friend in Wisconsin. By taking the distances as measured on a map and estimating the angles of the elevation as closely as we could we obtained 400 miles as about the average results of measurements on the heights of these displays. Our observation was reported in the same article that the report of the observation by the sea captain was announced – so the great variation in individual reports has been recognized. All of this means that there are many variable conditions present in the air and that these determine the position of the auroral phenomena more definitely than does the degree of refraction of the air itself.
In the meantime, work has been done in investigating the air from observations made in airplanes, free balloons, and by sounding balloons. Airplanes have ascended to a little more than eight miles; free balloons up to thirteen miles, and sounding balloons have, in at least one case, reached a height of twenty-two miles, though there is very little chance of any balloons reaching above nineteen miles. A sounding balloon is sent up alone, carrying automatically recording instruments, investigating the possibility that the air is made up of several more or less definitely determined layers.
The layer all about us and extending up to about 8 miles above us is called the “troposphere.” In this layer, occur all the common forms of clouds with which we are familiar. There are strong winds possible at all heights of this layer and there are also great rising, and descending air currents, due to the unequal heating of the earth and of the air in contact with its surface. The ascending and descending currents cause variations in our barometric readings. If the air is ascending, the barometer will indicate a reduced pressure on the earth; while if it is descending, there will be increased pressure on the earth. Ascending currents carry warm moist air up into the cooler layers of the air where the vapor is condensed into clouds – forming the cumulus clouds, or what are commonly known as the “thunder heads.” These clouds usually occur at heights of from ¾ mile to 1 mile. The rapid expansion of the air, as it rises from an area of high pressure to one of low pressure, also accounts for the further cooling – and often the water is frozen – forming hail storms. The rising column is often set into a rapidly whirling motion and thus into a tornado.
The average rain cloud is about 1 mile above the earth, and the highest is about 2.5 miles high.
Lightning originates in the region of the troposphere about 1.5 miles up in the air. It seems that everything of immediate concern to us (rain, wind, clouds, etc.) takes place within that very limited portion of the air near the surface of the earth. Recent studies indicate, however, that our weather may be made far above us, or even very far away toward the polar regions. It will require much more study on the theory of total air-mass movements, excluding surface winds and local effects, to determine whether this is the solution of the puzzling problem of weather making.
At 2.5 to 2 ¾ miles above the earth air becomes so rare that oxygen must be supplied for comfort, if not for safety, to the explorer in the air; but airplane flights are common up to three miles with the use of gas masks. This altitude still lacks two miles of equaling that of the peak of Mt. Everest, which stands nearly 5.5 miles high. At about 2.5 miles a small bunch cloud called the “alto-cumulus,” is common; and at heights near that of Mt. Everest, thin clouds which form in layers called the “cirrostratus clouds,” are found (the latter are probably of fine ice crystals, for the temperature here is about forty degrees below zero Fahrenheit).
Another important and interesting property of the troposphere is its electrical behavior. There is often a high difference in potential between the earth and the upper layers of the air; in fact so much difference that there have been serious efforts to use this potential electrical energy for doing useful work.
The Bureau of Terrestrial Magnetism in Washington has done much research work in the study of this phase of the air. Last spring one of our Hastings College students tried out a few of such instruments as are available here to see whether any peculiar electrical phenomena accompany our dust storms. His observations were sufficient to show that sudden increase in the wind velocity made equally sudden changes in the electrical condition of the air; and he also found that the charge on the earth is not always the same – that is, it might be positive at one time and negative at another. At any rate, there is a continual exchange of electricity between the earth and the upper air; and it is estimated that the total current running from the earth into the air is about 3,000,000 amperes.
At the top of the
troposphere is a relatively thin region called the “Tropopause,” which is merely
a transition layer from the troposphere into the stratosphere. This layer is
from seven to eight miles high in the temperate zones, much higher at the
equator and lower at the poles. It also varies somewhat with the time of the
year and also with the time of the day.
The existence of
the stratosphere was unknown until 1902, when the French meteorologist, de Port
discovered it by means of a sounding balloon. One of these balloons has reached
a height of twenty-two miles, far up into the stratosphere. The stratosphere as
a layer is about sixteen miles thick. The astonishing fact about the
stratosphere is that temperatures no longer decrease with increasing height, as
they do near the earth. There are great variations in temperature at different
places at the same level, but there is no variation vertically above a given
point. There are winds known as the “upper trade winds” in the stratosphere
which blow East over the tropical regions and West of the higher latitudes (they
are found in the lower part of the stratosphere). In the upper portion of the
stratosphere there is a region of little wind velocity. The temperature
throughout the stratosphere is about 67º below zero Fahrenheit, though the
results by Captains Stevens and Anderson give the later value of 74º below zero,
which existed fourteen miles above the plains of South Dakota. Within this cold
region is found a peculiar kind of cloud called “nacreous,” or “mother of
pearl,” because of its iridescence. Some authorities believe that these clouds
contain droplets of water, despite the low temperature. They occur twelve to
eighteen miles above the earth. From 1902 to 1923 it was assumed that the
steady temperature condition within the stratosphere continued indefinitely to
the top of the atmosphere. However, at that time two English observers,
Lindemann and Dobson, determined by observations on meteors that there is a
layer above the stratosphere where there are temperatures as high as at the
earth’s surface. This layer begins at about twenty-two miles height and extends
to between thirty-five and forty miles high. The spectroscope tells us that
there is considerable ozone in the upper air, though there is scarcely any in
the air itself, and that the concentration is greatest in this region. There
the temperatures may be as much as 110º above zero Fahrenheit, the reason being
is that the ozone absorbs nearly all of the ultra violet light from the sun and
that the energy so absorbed is turned into heat. That is to say, the upper air
is not transparent to ultra violet light. This layer is called the
We all know that the sun’s light passes through the air about us without warming it perceptibly; this means that the air is practically transparent to all this light. The same remark applies to any transparent object – for example, the windowpanes are scarcely warmed by the light passing through them, but the light will warm our hands when allowed to fall on them to be absorbed. There are many wavelengths of light given off by the sun which never reach the earth because the atmosphere does not transmit them. The wavelengths of light are measured in Angstrom units, which are equal to about one four-billionth of an inch. The shortest waves which we can see are about 4000 Angstrom units long and the longest are about 8,000. The shorter the waves of light, the more readily they are absorbed in the air, so that the shortest wave-length that reaches the earth is about 3000 Angstrom units long, and all the shorter waves are stopped by the ozone layer where the light energy is turned into heat. The existence of the ozone layer is well established because it is the most probable gas to be present under the conditions; and also spectroscopic observations support the theory. So far this sphere has been reached only by sounding balloons.
A very novel
experimental method has been used to prove that there is a layer of warmer air
in the upper atmosphere. This experiment made use of the fact that sound
travels faster in warm air than in cold air; hence, if sound travels at an angle
into a warm layer from a cold layer the sound wave will be bent and, if it is at
a sufficiently great angle, the sound may be reflected from the layer and travel
once again back into the cold region. Sensitive sound detectors, which are also
not only to measure the intensity of sound but also to tell the direction from
which it comes, are used. Heavy explosions are set off at predetermined times,
and observers located at various distant posts are ready to observe the
intensity and direction of the sound waves which reach them. From these
observations it is found that there actually seems to be such a layer at about
the height predicted. The layer acts like a window does in reflecting sound and
thus creating an echo.
Just above the ozonosphere is another layer of air in which there are vertical ascending and descending currents of the air. Here again the temperatures decrease with the increasing height. This layer is reached where the heat liberated is just equal to the heat received, and there is once again a condition of equilibrium maintained. Since this layer is much like the troposphere, it has been called the “Alto-Troposphere.” It extends from about forty to approximately fifty-six miles above the earth; the temperature at the top of this layer is about 270º below zero Fahrenheit.
In the alto-troposphere layer are found the highest observable clouds – clouds so high that the sun shines on them even after it is dark on the surface of the earth; these are called “Noctilucent clouds,” because they shine at night. They are thought to be composed of fine particles of dust that have been thrown up by the force of volcanic eruptions or else dust from meteors or other cosmic sources. One such eruption was that of Mt. Krakatoa, which blew dust so high into the air that unusual clouds were in evidence for more than three years afterwards, and dust from the explosion was found on the snows of the Arctic regions. Simultaneous photographs of the noctilucent clouds, taken by observers stationed at known distances apart, show that the clouds shine at heights of more than forty miles above the earth. (Doctor Humphreys, of the U.S. Weather Bureau, says that the presence of these clouds foretells the existence of strong rising and falling currents of air in this region.) At fifty-six miles, this layer ends, for here the heat lost is just equal to the heat gained from below and temperatures once again become steady. At this point increasing height does not result in decreased temperature. This is the beginning of the alto-stratosphere.
The alto-stratosphere is really the most interesting of all the upper regions of the atmosphere and it possesses properties which are of great importance in our present day affairs. In this layer are found the major displays of the aurora. However, the most important feature of this layer is that the very rarefied gases present are strongly ionized – that is, the region here conducts electricity.
Perhaps an explanation of what is meant by “ionization” is in order at this point. It is known that all matter is made up of atoms and molecules, which are in turn, made up of positively, and negatively charged particles called “protons” and “electrons” respectively. In the atoms and molecules of ordinary materials the number of protons and electrons are equal in each case, so that we say the atom or molecule is “neutral,” for they contain as much of the negative electricity as of the positive charge. It is possible, however, for some of the electrons to be removed from the atoms, thus leaving an excess of protons; in this case the atom or molecule is left positively charged. Also, under some circumstances, atoms may gain electrons and become negatively charged. In either case, we say the atom has become an “ion” or has become “ionized.”
Atoms in the ionized condition are much different in their behavior from that of the neutral atom, for now they are strongly affected by the presence of an electrical influence that may approach them and, if the electrical influence (or field) is of a variable or vibrating nature, the ions may vibrate in tune with the electrical fields. Such a vibrating electrical influence is a “radio wave” and it is evident, therefore, that we may expect this ionized layer to have some unusual effects on radio waves that come into this region. It is possible that electrons may be entirely freed from the atoms with which they are normally associated. Such free electrons will also respond readily to a changing electrical influence and vibrate in harmony with it. Electrons in the free state are present in the common radio tube and are responsible for carrying the current which operates the receiver.
There are three main means by which atoms may become ionized: (1) by high temperatures; (2) by a strong electrical field; or (3) by the effect of wavelengths of lights of proper frequency to remove the electrons. The chief ionizing influence present in the alto-stratosphere is the ultra-violet light present in the sun light. These wave lengths are very short and therefore of such high frequency that they carry a great deal of energy. When they strike the atoms or molecules of air, many of them receive so much energy that one or more electrons are released. This ionization process takes place with different intensities in different regions of the alto-stratosphere; these regions are known as “Ionospheres” and designated by letters or other symbols. There are at present, four such layers recognized and labeled “E,” “M,” “F1,” and “F2” layers, in order of their ascending height: the E-layer extends from about fifty six miles to eighty miles above the earth; while the M-layer reaches above this to about 230 miles. There is undoubtedly more air above this and it is also bound to be ionized, but no definite division into layers has yet been made for it.
The feature of
the ionospheres that makes them of such interest to us at present is the way
they affect radio waves. Radio waves are much the same as light waves, except
that they are of much greater wave-length; and just as light will be bent in
passing through a lens or prism where the speed is different from that of the
air, so are these radio waves bent when they pass from the lower layers of the
air into the ionized layers where they travel more freely than in the lower
un-ionized layers. The effect of these layers, then, is to make the waves bend
downward so that they seem to be reflected back to the earth from out in space.
The importance of this reflecting effect to us in our reception of radio
messages is great. If it were not for this layer, most of the energy sent out
from a radio transmitter would pass on out into space never to return to us; and
we would have to be near enough to a station that the waves could reach us
directly across the country from the antenna. Under such a circumstance the
most powerful stations would have only a very limited area in which they could
be heard. The Ionospheres, however, transforms the world into a monstrous radio
“whispering gallery,” for they act just like the ceiling in a large auditorium
which reflects sound so that whispers can he heard for great distances. In
cases where messages are heard for thousands of miles, it is thought that the
waves reflect from the sky to earth, back to the sky, and so forth for many
times before reaching the receiving antennae. This reflection makes it possible
for radio signals to be sent over high mountain ranges without loss in
The reason that Short Wave Radio signals can travel so much farther than the ordinary broadcast waves is that these short waves penetrate far higher into the ionized layers and hence can be reflected farther than the longer waves which reflect from the lower layers. During the day when the sun is shining in, the air is ionized down to lower levels and the international broadcasters use shorter waves during this time in order to penetrate to the higher levels. At night, however, the ionized layers are higher and longer waves may be used; nineteen meters to twenty-five meters are common wavelengths to be used for day signals while thirty-one meters to forty-nine meters are used at night. This variation in the wave-lengths used by stations often confuses people in tuning for their programs; and it is necessary to have a schedule of their operating programs in order to keep accurate account of where to tune for the desired station. Many scientific magazines will send a list of the more than 100 short-wave broadcasting stations upon receipt of a stamp.
As man continues his study of the air it is likely that many more facts of practical importance will be learned but such talk is great and the higher the studies are carried the more difficult they become; with modern means of study at the disposal of scientific men it is to be expected that ultimately the whole mystery of the atmosphere will be solved.
(Note: The above is all that can be covered in one hour’s time. The following material was in readiness to be presented but was omitted due to lack of time).
The story of the discovery of the Ionospheres and experiments concerning them really began some time ago, for it was then that the first hint of the existence of such a thing as radio waves was given. In 1873 the English physicist, Maxwell, presented to the world his electro-magnetic theory of light in which he showed that light really is an electro-magnetic wave and predicted that there should be waves such as we now know as “radio waves.” In 1888, the German physicist, Hertz, discovered a method of producing and detecting, the waves predicted by Maxwell only five years before.
Following Hertz’s discovery, Marconi began work on radiotelegraphy and by 1901 his work had proceeded to the point where he was able to send signals across the Atlantic from England to the United States.
Immediately after these long distance transmissions were announced, the great English physicist, Lord Raleigh, raised the question of why it is that the waves will follow around the bulge of the earth and not be dissipated immediately out into space, with only a relatively small local area being able to detect the waves which follow out near the ground about the station, called the “ground wave.”
Another English physicist and electrical engineer had also thought of this question and as early as 1900 this man, Heaviside, had suggested that there might be an upper layer of ionized air in the atmosphere capable of reflecting the waves back down to the earth, or of conducting them to distant places. He compared it to a “ceiling” which had reflecting properties somewhat like that of some large auditoria in which whispers can be heard for great distances. He noted that this layer must be above the clouds, for they did not seem to have such an effect. He also recognized that there must be a difference in the layer by day than by night and figured that the layers lie at lower levels during the day than at night.
In 1902 Marconi discovered the difference between day and night signaling, while on a voyage from England to New York. He found little difference between day and night signals up to a distance of 500 miles. Day signals were heard at a distance of 700 miles, but were unreadable at 800 miles, while the night signals were readable at 2,000 miles. Since the day signals were received at 700 miles, where the receiving ship is sixty miles below the level of the sending station, there was strong evidence in favor of believing in some sort of reflection from the sky. If it was a case of reflection it meant that the highest the wave got above the ground was thirty miles – and this was then considered to be the height of the supposed layer.
Beginning in 1909 the U.S. Navy carried our a series of experiments under the direction of L.W. Austin over long distances between various of the battle cruisers and the great Fessenden Station at Brant Rock. They tested on two different wave-lengths, 3,750 meters and 1,000 meters, to see whether this made any difference in the reception. They also tried to find out whether or not the air absorbs any of the radio waves. Some of the torpedo boats were equipped with small antennae and experimented with short waves. Out of this experimentation was derived the Austin daylight formula for ocean transmission. They were not able to work out anything mathematically useful for night conditions, but the daylight formula was useable.
It was about this time that amateur radiotelegraphy became popular and the investigators gathered reports from the amateurs from every location in the world. By 1915, they had accumulated enough experimental data to get some reasonable start on the mathematical theory of radio transmission.
By 1919, the English radio engineer, G.N. Watson, had developed a mathematical theory, which showed that the reflecting layer theory as proposed by Heaviside, and now called “The Kennelly-Heaviside Layer,” was a sufficient explanation for the various vagaries of radio transmission.
In 1924, another radio engineer, Larmoor, investigated the bending of light waves around a small model of the earth, so made that its size was of the same proportion to light waves as the earth is to the radio waves being used in their study. He showed that there was little of a “creeping” effect of the ordinary light about the sphere. He supported the theory that there was an ionized layer in the upper air and suggested ionization. As far back as 1912 another engineer, Eccles, had suggested that there might be several layers of ionized air and that these might bend the radio waves gradually rather than reflecting them, as was suggested by Heaviside.
In 1925, another great advance was made – this time by the English radio engineer, Appleton. He constructed an instrument, which was not only capable of measuring the intensity of the waves but also of telling the direction from which the waves came to the receiver. He sought to answer: (1) the old question of why long distance reception is possible at all, and (2) why the signals vary so greatly in both intensity and direction, particularly at night and more especially on winter nights. He worked from within short distances from the signal station out to distances of several hundred miles. He claimed to have obtained the first direct experimental proof of the existence of the Heaviside layer. He found that fading, particularly in short waves, is due to interference of two or more waves arriving at the receiver by coming over two different paths – one of them longer that the other – so that they arrive out of step. This difference in path might be due to a part of the waves coming directly across country to the receiver while the other part went up into the air, thus being reflected from the Heaviside layer so that it might have had to travel several hundred miles farther in getting to the receiver. This would account for the fading well enough. However, it is also possible for the waves to interfere by one part’s coming in from the side after being “slowed up” by some inhomogeniety of the earth – such as ore beds.
Therefore a second set of tests was made to ascertain whether there were any waves coming from the side of where they actually seemed to come in from the upper air. Appleton was able to show definitely that the waves were actually coming down from above at an angle of sixty to seventy degrees with the ground. He also thought of the possibility that waves may reflect from the sky layer and then reflect again from the earth back to the sky and then down again, thus making a double reflection, before the wave finally reached the receiver. At about 100 miles above the earth the effect of the ground wave and the sky wave was about equal. For this reason at that distance at night, there is a great deal of inference. At greater distances the signal is almost entirely due to the reflected ray from the sky and thus is stronger at night than by day. Since there is no reason to believe the direct wave to be different at night from day, it appears that any observed variations are the result of reflection.
The Reflection Theory vs. the Refraction
There has been, all through the years of the investigations of this layer, a question as to whether the radio waves were reflected as light from a polished surface or whether they traveled into the layer and bent out again like light passing through a prismatic piece of glass. There are many facts in support of the belief that the waves do not reflect but that they refract; that is, bend by transmission just like the sound waves did as they were used in locating the ozonosphere as described in the earlier pages of this report.
The sun ionizes the air to some extent in the layers near the earth, so that the waves begin to bend before they ever reach the region of high ionization, (that is, the Heaviside layer proper). Once the waves reach this highly ionized layer, the free electrons, with their long free path, are able to carry the electric oscillations for long distances without any appreciable loss of energy. One of the greatest of the present-day radio engineers, E.O. Hulburt, says that the straight reflection theory is untenable in the light of our present experimental knowledge. Pictures of radio waves taken with the oscillograph give unmistakable evidence of the fact of “reflection,” while theoretical considerations, based upon our knowledge of the action of electrons in electric fields, apparently clinch the proposition that the so-called reflection is really a case of refraction.
It is evident, from the above discussion that much remains to be learned about the atmosphere. The recent interest in cosmic rays is the phase which may have a bearing upon what is going on in the upper layers of the air. Also, the matter of weather forecasting by a study of air mass movements, rather than on a basis of surface study provides another matter for further study.
The average person is often skeptical about the value of such studies as those described above and asks, “What are their uses?” The radio works just as well whether or not we have the right explanation of how the waves get through the great distances. There is no particular value to be derived from the great ionized layer above us. “Why spend time and money upon studying it or any other thing so far removed from us?” The answer can be given in general terms: it has been said that “Man is the interpreter of nature; science is the right interpretation.” All of our great body of scientific knowledge is the result of attempts by man to interpret nature and to satisfy his own curiosity regarding things that come under his observation. From that standpoint, it is sufficient to indicate in answer to the above question that, “since we do not know about this particular trick of nature we must find it out. The serious scientist must not be interested in anything but results – and that is, after all, the true measure of whether something is practical or not.
The great English physicist, Lord Kelvin, once said, “When you can measure what you are talking abut and express it in numbers you know something about it, but until you can do that your knowledge is of a meager and unsatisfactory kind, and you have not yet progressed to the stage of science.” In other words, if your state of understanding is not quantitative, it is not scientific.