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.
Of more special papers, some of which, however, were of general
and even popular interest, there were on the program 36,
distributed somewhat unequally among the sections into which
the academy is divided as follows: Mathematics, 0; Astronomy,
3; Physics and Engineering, 7; Chemistry, 1; Geology and
Paleontology, 6; Botany, 7; Zoology and Animal Morphology, 8;
Physiology and Pathology, 4; Anthropology and Psychology, 0. A
program covering all the sciences belongs in a sense to the
eighteenth rather than to the twentieth century; still there is
human as well as scientific interest in listening to those who
are leaders in the conduct of scientific work.
The academy was fortunate in meeting in the American Museum of
Natural History, where in addition to the scientific sessions
luncheon and an evening reception were provided. The museum has
assumed leadership both in exhibits for the public and in the
scientific research which it is accomplishing. The planning of
museum exhibits is itself a kind of research and in this
direction the American Museum, together with the National
Museum in Washington and the Field Museum in Chicago, now
surpasses any of the museums of the old world and in the course
of the next ten years will have no rivals there. It is
interesting that the city and an incorporated board of trustees
are able to cooperate in the support of the museum, as is also
the case with the Zoological Park and the Botanical Gardens
which the members of the academy visited in the course of the
meeting.
FREDERIC WARD PUTNAM
POWELL in Washington, Brinton in Philadelphia and Putnam in
Cambridge may be regarded as the founders of modern
anthropology in America. In the death of Putnam, at the age of
seventy-six years, we have lost the last of these leaders.
Putnam is often spoken of as the father of anthropological
museums because he, more than any other one person, contributed
to their development. He seems to have been a museum man by
birth, for at an early age we find him listed as curator of
ornithology in the Essex Institute of Salem, Mass. The Peabody
Museum of Archeology at Cambridge is largely his work, he
having entered the institution in 1875 and continued as its
head until his death. This institution is in many respects one
of the most typical anthropological museums in America. During
his college career Professor Putnam came under the influence of
Professor Louis Agassiz and was for several years an assistant
in the laboratory of that distinguished scientist. It seems
likely that this was the source of Professor Putnam's faith and
enthusiasm for the accumulation and preservation of concrete
data. As his interest in anthropology grew, he seems to have
sought to bring together in the Peabody Museum a collection of
scientific material that should have the same relation to the
new and developing science of anthropology as the collections
of Professor Agassiz's laboratory had to the science of
biology. Professor Putnam's great skill in developing the
Peabody Museum brought him into public notice and led to his
appointment as director of the anthropological section of the
World Columbian Exposition in Chicago The exhibit he prepared
made an unusual impression and it is said that largely to his
personal influence is due the interest of the late Marshall
Field in developing and providing for the museum which now
bears his name. After this achievement Professor Putnam was
invited by the American Museum of Natural History to organize
the department of anthropology which he proceeded to do upon
broad lines, giving it a status and impetus which is still
manifest. Later on he was invited to the University of
California to organize a department and a museum similar to the
one at Harvard and this also is now one of our leading
institutions. Thus it is clear that the history of American
anthropological museums is to a large extent the life history
of Professor Putnam.
The one new and important idea which Professor Putnam brought
into his museum work was that they should be in reality
institutions of research. Until that time they were chiefly
collections of curios brought together by purchase of
miscellaneous collections without regard to the scientific
problems involved. Professor Putnam's idea was that the museum
should go into the field and by systematic research and
investigation develop a definite problem, bringing to the
museum such illustrative and concrete data as should come to
hand in the prosecution of research. Professor Putnam also
played a large part in securing the recognition of anthropology
by universities and by his position at Harvard pointed the way
to mutual cooperation between museums and universities. He
possessed an unusual personality which enabled him to approach
and interest men of affairs so as to secure their financial
support for anthropological research and as a teacher he was
intensely interested in young men, offering them every possible
opportunity for advancement and never really losing personal
interest in them as long as he lived.
SCIENTIFIC ITEMS
WE record with regret the deaths of Brigadier-general George M.
Sternberg, retired, surgeon-general of the army, from 1893 to
1902, distinguished for his investigations of yellow fever and
other diseases; of Edward Lee Greene, associate in botany at
the Smithsonian Institution; of Wirt Tassin, formerly chief
chemist and assistant curator of the division of mineralogy, U.
S. National Museum; of Augustus Jay Du Bois, for thirty years
professor of civil engineering in the Sheffield Scientific
School, Yale University; of Sir Andrew Noble, F.R.S.,
distinguished for his scientific work on artillery and
explosives; of Edward A. Minchin, F.R.S., professor of
protozoology in the University of London, and of R. Assheton,
F.R.S., university lecturer in animal embryology at the
University of Cambridge.
THE Nobel prize for chemistry for 1914 has been awarded to
Professor Theodore William Richards, of Harvard University, for
his work on atomic weights. The prize for physics has been
awarded to Professor Max von Laue of Frankfort-on-Main, for his
work on the diffraction of rays in crystals.
PROFESSOR ADOLF VON BAEYER celebrated his eightieth birthday on
October 31. With the beginning of the present semester he
retired from the chair of chemistry at Munich in which he
succeeded von Liebig in 1875.--The Romanes lecture before the
University of Oxford will be delivered this year by Professor
E. B. Poulton, Hope professor of zoology in the university, on
December 7. The subject will be "Science and the Great War."
AT the recent meeting in Manchester, as we learn from Nature,
the general committee of the British Association unanimously
adopted the following resolution, which has been forwarded to
the Prime Minister, the Chancellor of the Exchequer and the
Presidents of the Board of Education and of Agriculture and
Fisheries: "That the British Association for the Advancement of
Science, believing that the higher education of the nation is
of supreme importance in the present crisis of our history,
trusts that his Majesty's government will, by continuing its
financial support, maintain the efficiency of teaching and
research in the universities and university colleges of the
United Kingdom."
COLUMBIA UNIVERSITY received by the will of Amos F. Eno the
residuary estate which may amount to several million dollars.
In addition, the General Society of Mechanics and Tradesmen
receives $1,800,000, and bequests of $250,000 each are made to
New York University, The American Museum of Natural History,
the Metropolitan Museum of Art and the New York Association for
improving the Condition of the Poor--Mr. James J. Hill has
presented $125,000 to Harvard University to be added to the
principal of the professorship in the Harvard graduate school
of business administration, which bears his name. The James J.
Hill professorship of transportation was founded by a gift of
$125,000, announced last commencement day, the donors including
John Pierpont Morgan, Thomas W. Lamont, Robert Bacon and Howard
Elliott.--The sum of about $400,000 has been subscribed in the
University of Michigan alumni campaign for $1,000,000 with
which to build and endow a home for the Michigan Union, as a
memorial to Dr. James B. Angell, president emeritus.