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The Popular Science Monthly Volume LXXXVI July to September, 1915

U >> Unkown >> The Popular Science Monthly Volume LXXXVI July to September, 1915




[3] The earliest name for this richly colored variety is Limax
coccineus Gistel, but it is not Limax coccineus Martyn, 1784;
so the next name, lamarckii, prevails.



One could see that there had once been considerable
excavations, but the good layers were now deeply covered by
talus, and could only be exposed after much digging. It was
about thirty years since the pits had been worked. Dr.
Bacmeister found for us a strong country youth, Max Deschle,
who dug under our direction all next day in the quarry near the
house. The rock is not so easy to work as that at Florissant,
and it does not split so well into slabs, but we readily found
a number of fossils. Most numerous were the plants; leaves of
cinnamon (Cinnamomurn polymorphum), soapberry (Sapindus
falcifolius), maple (Acer trilobatum), grass (Poacites loevis)
and reeds (Phragmites oeningensis), with twigs of the conifer
Glyptostrobus europoeus. We obtained a single seed of the very
characteristic Podogonium knorrii. Certain molluscs were
abundant; Planorbis declivis, Lymnoea pachygaster, Pisidium
priscum, with occasional fragments of the mussel Anodonta
lavateri. Ostracods, Cypris faba, were also found. The best
find, however, was a well-preserved fish, the lepidocottus
brevis (Agassiz), showing in the region of the stomach its last
meal, of Planorbis declivis. This greatly interested Max, who
during the rest of the day chanted, as he swung the pick,
"Fischlein, Fischlein, komme!"--but no other Fischlein was
apparently within hearing distance. Not a single insect was
obtained, except that on the talus at one of the other quarries
I picked up a poorly preserved beetle, apparently the Nitidula
melanaria of Heer.

We left Wangen on the morning of August 6, and proceeded up the
Rhine to Schaffhausen and Basle. At Basle we found a certain
number of Oeningen (Wangen) fossils in the museum.

Comparing Wangen with Florissant, it appears that the Colorado
locality is more extensive, more easily worked, and provides
many more well-preserved fossils. On the other hand, Wangen has
proved far richer in vertebrates and crustacea, and on the
whole gives us a better idea of the fauna as it must have
existed. Florissant far exceeds Wangen in the number of
described species, but this is only because it has so many more
insects. Each locality furnishes us with extraordinarily rich
materials, enabling us to picture the life of Miocene times.
Each, by comparison, throws light on the other, and while the
period represented is not sufficiently remote to show much
evidence of progressive evolution, it is hard to exaggerate the
value of the facts for students of geographical distribution.
Much light may also be thrown on the relative stability of
specific characters.

Work on the Florissant fauna is going forward, though not so
fast as one could wish. It is very much to be hoped that the
Wangen quarries will receive attention before many years have
passed. Labor is comparatively cheap in Germany, and with a
force of a dozen men it would not take long to open up the
quarries and get at the best beds. It is really extraordinary
that no one has seen and taken advantage of the opportunities
presented. Probably no obstacles of any consequence would be
put in the way; at least the owner of the quarries came by when
we were digging, and expressed only his good will. With new
researches in the field, combined with studies of the rich
materials awaiting examination at Zurich and elsewhere, no
doubt the knowledge we possess of the European Miocene fauna
could be very greatly increased, to the advantage of all
students of Tertiary life.



THE THEORY AND PRACTISE OF FROST FIGHTING[1]

[1] Some of the instruments used were obtained through a grant
from the Elizabeth Thompson Science Fund.

BY ALEXANDER McADIE

BOTCH PROFESSOR OF METEOROLOGY, HARVARD UNIVERSITY

ONLY in recent years have aerologists given much attention to
the slow-moving currents of the lower strata of the atmosphere.
These differ greatly from the whirls and cataracts of both low
and high levels which we familiarly know as the winds. The
upper and larger air streams play a part in the formation of
frost, and we do not underestimate their function; but
primarily it is a slow surface flow, almost a creeping of the
air near the ground, which controls the temperature and is
all-important in frost formation. So important is it that the
first law of frost fighting may be expressed as follows:

Where air is in motion and where there is good circulation,
frost is not so likely to occur as where the air is stagnant.

In other words frost in the ordinary meaning of the word is a
problem IN LOCAL AIR DRAINAGE. It is true that there are times
when with thorough ventilation and mixing of the air strata the
temperature will fall rapidly and damage from frost result; but
such conditions are perhaps more fittingly described as cold
waves or freezes, as distinguished from frosts. Thus, in
California during the first week of January, 1913, when there
was much air movement, the citrus fruit crop was damaged to the
extent of $20,000,000. The condition is generally referred to
as a frost, but it was quite different from the usual frost
conditions in that section. It is, however, interesting to note
that improved frost-fighting devices were used with much
success and the total savings aggregated about $25,000,000. The
orange growers also had the benefit of accurate forecasts and
expert advice and were thus able to provide fuel and labor in
advance. Passing over at present the larger disturbances, we
shall consider only the frosts of still nights. And it should
not be forgotten that the accumulated losses of these frosts
may equal the losses of the individual freezes, for the latter
occur at long intervals, while the quiet frosts of the early
fall and the late spring are recurrent, destroying flowers,
fruits and tender vegetation in many sections, year after year.

Air may flow in any direction, but attention has been centered
more upon the flow in a horizontal than in a vertical
direction. Thus none of the wind instruments used at Weather
Bureau stations gives any record of the up and down movement of
the air. In frosts of the usual type this vertical displacement
is all-important. True, there may be brought into the district,
by horizontal displacement, large masses of cold air and the
temperature thus materially lowered; but the marked INVERSION
of temperature occurs only when these horizontal currents or
winds are lulled. On windy nights, as is well known, there is
less likelihood of frost than on quiet nights, because of the
thorough mixing of the air vertically. There is then no
tendency for stratification and the formation of levels of
different temperature, followed by low surface temperature.

In general, the temperature falls as one rises in the air; but,
at times of frost, it is found that the higher levels are
warmer than the lower ones. The coldest stratum is found about
ten centimeters (four inches) above the ground; while at a
distance of ten meters temperatures are as much as five degrees
higher than at the ground.

It may be well to refer for a moment to the variations in
temperature known as inversions. In the accompanying diagram
it will be seen that the temperature falls with elevation, and
starting from the ground on a day when the temperature is near
the freezing point, 273 degrees A., one finds at a height of
seven thousand meters a fall of about forty degrees. It is not
easy to represent on a single diagram the variation in detail
and therefore we have divided the air column into three parts,
the scales being as one to a hundred.

The right-hand diagram shows the gradual rise in temperature
for a height of one meter and the peculiar inversion that
occurs a few centimeters above the ground. Unfortunately it is
in this layer where detailed temperature observations are most
needed that our instruments are least satisfactory. Ordinary
thermometers can not be relied on for such small differences
and the exploration of this stratum by self-recording
instruments is difficult. In the middle diagram is shown the
temperature gradient at times of frost, from the ground to a
height of one hundred meters. It will be seen that at a height
of fifty meters the temperature may be ten degrees higher; and
in general the rise continues with elevation. A good
illustration of a valley inversion is given by the chart of May
20, in which continuous records for three levels, 18, 64 and
196 meters above sea level, are given. At such times fruit or
flowers on hillsides escape damage from frost while in all the
depressions and low level places the injury may be marked.
These differences in temperature are not at all unusual and may
be anticipated on clear, still nights during spring, fall and
winter. Clouds or a moderate wind will prevent such an
inversion. We shall refer again to this in speaking of the
cranberry bogs of the Cape Cod district and the frost warnings
issued from Blue Hill Observatory.

The great inversion in the atmosphere, however, is that which
we have indicated as occurring at the height of nine thousand
meters. Above this, the temperature ceases to fall and we enter
what has been called the stratosphere or isothermal region. For
convenience we will call this upper change the MAJOR inversion
and the lower one near the ground the MINOR inversion. In some
ways we know more about the former than the latter. Strictly
speaking, the minor inversion is the chief factor in
determining local climate since it controls night and early
morning temperatures and in large measure the early or late
blooming of flowers and ripening of fruits.

Ordinarily cold air falls to the ground; but not always, for
under certain conditions cold, heavy air may actually rise,
displacing warm, lighter air. But such conditions can be
explained and there is no contradiction of the fundamental law
that if acted on only by gravity, cold air, being denser, will
settle to the ground and warm air, being lighter, will rise.
And there must be a certain relation between the height of the
level from which the cold air falls and the level to which the
warm air rises. In other words, we have to apply the laws of
falling bodies since a given mass of air, although invisible,
is matter and as subject to gravity as a cannon ball.

One of Galileo's most ingenious experiments consisted in
swinging a pendulum and then by means of a nail driven in
various positions intercepting the swing. He found that the bob
always rose to the same level whatever circuit it was forced to
take. But Galileo did not know what every schoolboy to-day
knows, that air exerts pressure and is subject to physical
processes like other matter, else he would certainly have given
to the world a delicate air pendulum; and devised experiments
on the movement of air that would have opened men's eyes to the
fascinating flow and counter-flow of the air, even on a
seemingly still night, one favorable for the formation of
frost.

The problem of the moving air mass, however, is more
complicated than it looks. For with the air is mixed a quantity
of water vapor. In a strict sense they are independent
variables, and the view set forth in most text-books that air
has a certain capacity for water vapor is misleading. We seldom
meet with pure, dry air. A cubic meter of such a gas mixture
would weigh 1,247 grams, at a temperature of 283 degrees A. (50
degrees F.). If chilled ten degrees, that is, to the freezing
point of water, it would weigh 46 grams more. So that by
cooling, air becomes denser and heavier. A cubic meter of a
mixture of air and water vapor at saturation, at the first
temperature above mentioned weighs only 1,242 grams, or five
grams less, and if this were cooled ten degrees the mixture
would weigh three grams less than the same volume of pure dry
air. We see that in each case the mixture of air and water
vapor weighs less than the air by itself. One would think that
by adding water vapor which, while light, still has weight, the
total weight would be the sum of both. It really is so,
notwithstanding the above figures, and the explanation of the
puzzle is that there was an increase in pressure with
expansion, so that the volume of the air and saturated vapor
was greater than one cubic meter. Since then a cubic meter of
air and saturated vapor weighs less than a cubic meter of dry
air at freezing temperature, speaking generally, we may expect
moist air to rise and dry air to fall. Consequently, if in
addition to falling temperature there is also a drying of the
air, we shall have an accelerated settling or falling of cold
dry air to the ground, which of course favors the formation of
frost. The water vapor plays also another role besides that of
varying the weight per unit volume. The heat received by the
ground consists of waves of a certain wavelength; but the heat
re-radiated by the ground consists of waves of longer
wave-length, and these so-called long waves (12 thousandths of
a millimeter) are readily absorbed by water vapor. Thus water
vapor acts like a blanket and holds the heat, preventing loss
of heat by radiation to space. Further on we shall speak of the
high specific heat of both water and water vapor as compared
with air and show the bearing of this in frost fighting; but at
present we may from what precedes formulate the second law of
frost fighting as follows: "Frost is more likely to occur where
the air is dry than where it is moist." It is also true that a
dusty atmosphere is less favorable for frost than a dust-free
atmosphere. Thus we may generalize and say that whatever favors
clear, still, dry air favors frost. The theory of successful
frost fighting then is to interfere with or prevent these
processes which as we have seen facilitate cooling close to the
ground. In what way can this best be done?

The most natural way would be by conserving the earth's heat,
which could be accomplished by covering plants with cloth,
straw, newspaper, or perhaps better still, modern weather-proof
sheeting, or in still another way by a cover of moistened dense
smoke, generally called a smudge. A second method would be by
means of direct application of heat; and this is accomplished
in orange groves by means of improved orchard heaters. Large
fires waste heat and are neither economical nor effective. A
third method would be based upon a mixing of the air strata,
thus getting the benefit of the warmer higher levels. Fourth,
advantage might be taken of some agency such as water or water
vapor, having a high specific heat. Finally, if the crop is of
a certain character such as the cranberry, it will be found
advisable to use sand, to drain and clean, here again making
use of the specific heat of some intermediary. And,
furthermore, any one of these methods may be combined with some
other method.

Regarding the first method, that of covers, it may be said that
the practice goes back to the early husbandmen; but only in the
last few years has the true function of the cover been properly
interpreted and we are still far from obtaining maximum
efficiency. Nor is there yet a suitable, scientific cover
available. Any medium that interferes with loss of heat through
free radiation before and after sunset is a cover. The best
type of cover is a cloud; and clouds, whether high or low, are
good frost protectors. On cloudy nights there is little
likelihood of frost; and when we can bring about the formation
of a layer of condensed water vapor we can practically
eliminate frost. We have mentioned above the fact that the
earth radiates the heat it has received not in the same but in
longer wave-lengths perhaps three times as long. These are
easily trapped and held by the vapor of water. Furthermore, the
rate of radiation is a function of the absolute temperature and
so the rapidity of loss depends somewhat upon the heat
received. Therefore the cover should be used as early in the
afternoon as possible, that is just before sunset. Aside from
the water cover or vapor cover there are cheap cloth screens,
fiber screens and in some places lath screens.

The second method, that of direct heating, has met with much
success in the orange groves of California and elsewhere.
Modern heating and covering methods date from experiments begun
in 1895. A number of basic patents granted to the writer in
this connection have been dedicated to the public. At the
present time there are on the market some twenty forms of
heaters, which have been described with more or less detail in
farm journals and official publications. It is not necessary to
refer to them further here. The fuel originally used was wood,
straw and coal, but these are now supplanted by crude oil or
distillate. It has also been seriously proposed to use electric
heaters; also to use gas in the groves. With modern orchard
heaters properly installed and handled, there is no difficulty
in raising the temperature of even comparatively large tracts
five degrees and maintaining a temperature above freezing, thus
preventing refrigeration of plant tissue.

The third method, that of utilizing the heat of higher levels
by mixing, has not yet been commercially developed; but the
methods of applying water, either in the spraying of trees or
the running of ditches or the flooding of bogs, together with
methods of sanding, cleaning; and draining, have all been
proved helpful. Methods available and most effective in one
section may not necessarily be effective in another section or
with different crop requirements. Certain devices most
effective in the groves of California may not answer in Florida
or Louisiana because of entirely different weather conditions.
In the Gulf coast states where water is available it may be
advantageously used to hold back ripening and retard
development until after the cold waves of middle and late
February have passed, whereas in the west coast sections
conditions are very different, water having a definite value
and the critical periods coming in late December or early
January.

In what precedes stress has been laid chiefly upon the fall of
temperature and the congelation of the water vapor. There is,
however, another important matter connected with injury to
plant tissue, and that is the rise in temperature AFTER the
frost. A too rapid defrosting may do considerable damage where
no damage was originally done by the low temperature. It is in
this connection that water may be used to great advantage.
Water, water-vapor and ice have, compared with other
substances, remarkably high specific heats. If the specific
heat under constant pressure of water be taken as unity, that
of ice is 0.49; of water-vapor 0.45 and of air 0.24. Or in a
general way we may say that water has four times the capacity
for heat that air has. Therefore it is apparent that water will
serve excellently to prevent rapid change in temperature. This
is important at sunrise and shortly after when some portion of
the chilled plant tissue may be exposed to a warming sufficient
to raise the temperature of the exposed portion ten degrees in
an hour. The latent heat of fusion of ice is 79.6 calories and
the latent heat of vaporization of water is nearly 600 calories
(a gram calorie is the amount of heat that will raise the
temperature of a gram of pure water one degree) or in exact
terms from 273 degrees A. to 274 degrees A. Therefore in the
process of changing from solid to liquid to vapor, as from ice
to water to vapor, there is a large amount of heat required.
The latent heat serves to prevent fall in temperature and also
serves to retard a too rapid rise. This does not mean, as is
generally assumed, that the air will be warmed, but it does
mean a retardation of temperature change. And it is essential
that the restoration of the tissues and juices to their normal
state be accomplished gradually, neither too rapidly nor yet
too slowly.

There is probably an optimum temperature for thawing or
defrosting frozen fruits and flowers. Finally the temperature
records as ordinarily obtained need careful interpretation. It
may be that the freezing point of liquids under pressure in the
plant cells or exposed to the air through the stomata is not
the same as in the free air. It is unfortunate too that in most
places data showing temperatures of soil, plant and air are of
doubtful character. A word of warning may be given against the
too ready acceptance of Weather Bureau records made in cities
and on the roofs of buildings. Garden and field conditions vary
greatly from these. It is further advisable to obtain a
continuous record of the temperature of evaporation such as is
shown by the records herewith. The two temperature curves made
simultaneously and easily read at any moment enable the
gardener or orchardist to forecast the probable minimum
temperature of the ensuing ten or twelve hours. But not always,
and some study is necessary. A slight increase in cloudiness or
a slight shift in wind direction will prevent the fall in
temperature which otherwise seemed probable. With a persistent
inversion of temperature there is sometimes an increasing
absolute humidity.

SUMMARY

The problem is many sided and we must consider the motion of
the air vertically as well as horizontally. Air gains and loses
heat chiefly by convection, and any gain or loss by conduction
may be neglected. The plant gains heat by convection, radiation
and perhaps by conduction of an internal rather than surface
character. The ground gains and loses heat chiefly by
radiation. But the whole process is complicated and may not
even be uniform. Frosts generally are preceded by a loss of
heat from the lower air strata, due to convection and a
horizontal translation of the air. Then follows an equally
rapid and great loss of heat by free radiation. There are minor
changes such as the setting free of heat in condensation and
the utilization in evaporation, but these latent heats are of
less importance than the actual transference of the air and
vapor and the removal of the latter as an absorber and retainer
of heat.

Frosts are recurrent phenomena reasonably certain to occur
within given dates, and, as pointed out above, the cumulative
losses are considerable. Methods of protection to be
serviceable must be available for more than one occasion, for
there is no profit in saving a crop on one night and losing it
on the succeeding night. But the effort is worth while.
Consider that the horticulturist regularly risks the labor of
many months on the temperatures of a few hours. An efficient
frost fighting device is in a way the entering wedge for
solving problems of climate control. One may not take a crop
indoors, it is true, but there is no valid reason, in the light
of what has been already accomplished, why at critical periods
which may be anticipated, the needed volume of surface air may
not be sufficiently warmed; and the losses which have
heretofore been considered inevitable be prevented.



THE PROGRESS OF SCIENCE

THE NEW YORK MEETING OF THE NATIONAL ACADEMY OF SCIENCES

THE National Academy of Sciences held its annual autumn meeting
during the third week of November in the American Museum of
Natural History. The central situation of New York City and its
scientific attractions led to a large meeting and an excellent
program There were present over sixty members, nearly one half
of a membership widely scattered over the country. When the
academy was established in 1863 as the adviser of the
government in scientific questions, the membership was limited
to fifty which was subsequently increased to 100, under which
it was kept until recently. The present distribution of the 141
members among different institutions in which there are more
than two is: Harvard, 19; Yale, 15; Chicago, 13; Johns Hopkins,
12; Columbia, 11; U. S. Geological Survey, 8; Carnegie
Institution, 5; California, Rockefeller Institute, Smithsonian,
4; Clark, Wisconsin, Cornell, Stanford, 3.

The scientific program of the meeting began with a lecture by
Professor Michael I. Pupin, of Columbia University, who
described the work on aerial transmission of speech of which no
authentic account has hitherto been made public. To Professor
Pupin we owe the discovery through mathematical analysis and
experimental work of the telephone relays which recently made
speech by wire between New York City and San Francisco
possible, and we now have an authoritative account of speaking
across the land and sea a quarter way round the earth. One
session of the academy was devoted to four papers of general
interest. Professor Herbert S. Jennings, of the Johns Hopkins
University, described experiments showing evolution in
progress, and Professor John M. Coulter, of the University of
Chicago, discussed the causes of evolution in plants Professor
B. B. Boltwood made a report on the life of radium which may he
regarded as a study of inorganic evolution. Professor Theodore
Richards, of Harvard University, spoke of the investigations
recently conducted in the Wolcott Gibbs Memorial Laboratory.
These are in continuation of the work accomplished by Professor
Richards in the determination of atomic weights, which led to
the award to him of a Nobel prize, the third to be given for
scientific work done in this country, the two previous awards
having been to Professor Michelson, of the University of
Chicago, in physics, and Dr. Carrel, of the Rockefeller
Institute, in physiology.

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