features of the proposed association. The leading requirement is one
that cannot be too highly emphasized. How clearly soever the organizers
may have in their minds' eye the end in view, they must recognize the
fact that it cannot be attained in a day. In every branch of work which
is undertaken, there must be a single leader, and he must be the best
that the country, perhaps even the world, can produce. The required man
is not to be found without careful inquiry; in many branches he may be
unattainable for years. When such is the case, wait patiently till he
appears. Prudence requires that the fewest possible risks would be
taken, and that no leader should be chosen except one of tried
experience and world-wide reputation. Yet we should not leave wholly
out of sight the success of the Johns Hopkins University in selecting,
at its very foundation, young men who were to prove themselves the
leaders of the future. This experience may admit of being repeated, if
it be carefully borne in mind that young men of promise are to be
avoided and young men of performance only to be considered. The
performance need not be striking: ex pede Herculem may be possible; but
we must be sure of the soundness of our judgment before accepting our
Hercules. This requires a master. Clerk-Maxwell, who never left his
native island to visit our shores, is entitled to honor as a promoter
of American science for seeing the lion's paw in the early efforts of
Rowland, for which the latter was unable to find a medium of
publication in his own country. It must also be admitted that the task
is more serious now than it was then, because, from the constantly
increasing specialization of science, it has become difficult for a
specialist in one line to ascertain the soundness of work in another.
With all the risks that may be involved in the proceeding, it will be
quite possible to select an effective body of leaders, young and old,
with whom an institution can begin. The wants of these men will be of
the most varied kind. One needs scarcely more than a study and library;
another must have small pieces of apparatus which he can perhaps design
and make for himself. Another may need apparatus and appliances so
expensive that only an institution at least as wealthy as an ordinary
university would be able to supply them. The apparatus required by
others will be very largely human--assistants of every grade, from
university graduates of the highest standing down to routine drudges
and day-laborers. Workrooms there must be; but it is hardly probable
that buildings and laboratories of a highly specialized character will
be required at the outset. The best counsel will be necessary at every
step, and in this respect the institution must start from simple
beginnings and grow slowly. Leaders must be added one by one, each
being judged by those who have preceded him before becoming in his turn
a member of the body. As the body grows its members must be kept in
personal touch, talk together, pull together, and act together.
The writer submits these views to the great body of his fellow-citizens
interested in the promotion of American science with the feeling that,
though his conclusions may need amendment in details, they rest upon
facts of the past and present which have not received the consideration
which they merit. What he most strongly urges is that the whole subject
of the most efficient method of promoting research upon a higher plane
shall be considered with special reference to conditions in our own
country; and that the lessons taught by the history and progress of
scientific research in all countries shall be fully weighed and
discussed by those most interested in making this form of effort a more
important feature of our national life. When this is done, he will feel
that his purpose in inviting special consideration to his individual
views has been in great measure reached.
XII
CAN WE MAKE IT RAIN?
To the uncritical observer the possible achievements of invention and
discovery seem boundless. Half a century ago no idea could have
appeared more visionary than that of holding communication in a few
seconds of time with our fellows in Australia, or having a talk going
on viva voce between a man in Washington and another in Boston. The
actual attainment of these results has naturally given rise to the
belief that the word "impossible" has disappeared from our vocabulary.
To every demonstration that a result cannot be reached the answer is,
Did not one Lardner, some sixty years ago, demonstrate that a steamship
could not cross the Atlantic? If we say that for every actual discovery
there are a thousand visionary projects, we are told that, after all,
any given project may be the one out of the thousand.
In a certain way these hopeful anticipations are justified. We cannot
set any limit either to the discovery of new laws of nature or to the
ingenious combination of devices to attain results which now look
impossible. The science of to-day suggests a boundless field of
possibilities. It demonstrates that the heat which the sun radiates
upon the earth in a single day would suffice to drive all the
steamships now on the ocean and run all the machinery on the land for a
thousand years. The only difficulty is how to concentrate and utilize
this wasted energy. From the stand-point of exact science aerial
navigation is a very simple matter. We have only to find the proper
combination of such elements as weight, power, and mechanical force.
Whenever Mr. Maxim can make an engine strong and light enough, and
sails large, strong, and light enough, and devise the machinery
required to connect the sails and engine, he will fly. Science has
nothing but encouraging words for his project, so far as general
principles are concerned. Such being the case, I am not going to
maintain that we can never make it rain.
But I do maintain two propositions. If we are ever going to make it
rain, or produce any other result hitherto unattainable, we must employ
adequate means. And if any proposed means or agency is already familiar
to science, we may be able to decide beforehand whether it is adequate.
Let us grant that out of a thousand seemingly visionary projects one is
really sound. Must we try the entire thousand to find the one? By no
means. The chances are that nine hundred of them will involve no agency
that is not already fully understood, and may, therefore, be set aside
without even being tried. To this class belongs the project of
producing rain by sound. As I write, the daily journals are announcing
the brilliant success of experiments in this direction; yet I
unhesitatingly maintain that sound cannot make rain, and propose to
adduce all necessary proof of my thesis. The nature of sound is fully
understood, and so are the conditions under which the aqueous vapor in
the atmosphere may be condensed. Let us see how the case stands.
A room of average size, at ordinary temperature and under usual
conditions, contains about a quart of water in the form of invisible
vapor. The whole atmosphere is impregnated with vapor in about the same
proportion. We must, however, distinguish between this invisible vapor
and the clouds or other visible masses to which the same term is often
applied. The distinction may be very clearly seen by watching the steam
coming from the spout of a boiling kettle. Immediately at the spout the
escaping steam is transparent and invisible; an inch or two away a
white cloud is formed, which we commonly call steam, and which is seen
belching out to a distance of one or more feet, and perhaps filling a
considerable space around the kettle; at a still greater distance this
cloud gradually disappears. Properly speaking, the visible cloud is not
vapor or steam at all, but minute particles or drops of water in a
liquid state. The transparent vapor at the mouth of the kettle is the
true vapor of water, which is condensed into liquid drops by cooling;
but after being diffused through the air these drops evaporate and
again become true vapor. Clouds, then, are not formed of true vapor,
but consist of impalpable particles of liquid water floating or
suspended in the air.
But we all know that clouds do not always fall as rain. In order that
rain may fall the impalpable particles of water which form the cloud
must collect into sensible drops large enough to fall to the earth. Two
steps are therefore necessary to the formation of rain: the transparent
aqueous vapor in the air must be condensed into clouds, and the
material of the clouds must agglomerate into raindrops.
No physical fact is better established than that, under the conditions
which prevail in the atmosphere, the aqueous vapor of the air cannot be
condensed into clouds except by cooling. It is true that in our
laboratories it can be condensed by compression. But, for reasons which
I need not explain, condensation by compression cannot take place in
the air. The cooling which results in the formation of clouds and rain
may come in two ways. Rains which last for several hours or days are
generally produced by the intermixture of currents of air of different
temperatures. A current of cold air meeting a current of warm, moist
air in its course may condense a considerable portion of the moisture
into clouds and rain, and this condensation will go on as long as the
currents continue to meet. In a hot spring day a mass of air which has
been warmed by the sun, and moistened by evaporation near the surface
of the earth, may rise up and cool by expansion to near the
freezing-point. The resulting condensation of the moisture may then
produce a shower or thunder-squall. But the formation of clouds in a
clear sky without motion of the air or change in the temperature of the
vapor is simply impossible. We know by abundant experiments that a mass
of true aqueous vapor will never condense into clouds or drops so long
as its temperature and the pressure of the air upon it remain unchanged.
Now let us consider sound as an agent for changing the state of things
in the air. It is one of the commonest and simplest agencies in the
world, which we can experiment upon without difficulty. It is purely
mechanical in its action. When a bomb explodes, a certain quantity of
gas, say five or six cubic yards, is suddenly produced. It pushes aside
and compresses the surrounding air in all directions, and this motion
and compression are transmitted from one portion of the air to another.
The amount of motion diminishes as the square of the distance; a simple
calculation shows that at a quarter of a mile from the point of
explosion it would not be one ten-thousandth of an inch. The
condensation is only momentary; it may last the hundredth or the
thousandth of a second, according to the suddenness and violence of the
explosion; then elasticity restores the air to its original condition
and everything is just as it was before the explosion. A thousand
detonations can produce no more effect upon the air, or upon the watery
vapor in it, than a thousand rebounds of a small boy's rubber ball
would produce upon a stonewall. So far as the compression of the air
could produce even a momentary effect, it would be to prevent rather
than to cause condensation of its vapor, because it is productive of
heat, which produces evaporation, not condensation.
The popular notion that sound may produce rain is founded principally
upon the supposed fact that great battles have been followed by heavy
rains. This notion, I believe, is not confirmed by statistics; but,
whether it is or not, we can say with confidence that it was not the
sound of the cannon that produced the rain. That sound as a physical
factor is quite insignificant would be evident were it not for our
fallacious way of measuring it. The human ear is an instrument of
wonderful delicacy, and when its tympanum is agitated by a sound we
call it a "concussion" when, in fact, all that takes place is a sudden
motion back and forth of a tenth, a hundredth, or a thousandth of an
inch, accompanied by a slight momentary condensation. After these
motions are completed the air is exactly in the same condition as it
was before; it is neither hotter nor colder; no current has been
produced, no moisture added.
If the reader is not satisfied with this explanation, he can try a very
simple experiment which ought to be conclusive. If he will explode a
grain of dynamite, the concussion within a foot of the point of
explosion will be greater than that which can be produced by the most
powerful bomb at a distance of a quarter of a mile. In fact, if the
latter can condense vapor a quarter of a mile away, then anybody can
condense vapor in a room by slapping his hands. Let us, therefore, go
to work slapping our hands, and see how long we must continue before a
cloud begins to form.
What we have just said applies principally to the condensation of
invisible vapor. It may be asked whether, if clouds are already formed,
something may not be done to accelerate their condensation into
raindrops large enough to fall to the ground. This also may be the
subject of experiment. Let us stand in the steam escaping from a kettle
and slap our hands. We shall see whether the steam condenses into
drops. I am sure the experiment will be a failure; and no other
conclusion is possible than that the production of rain by sound or
explosions is out of the question.
It must, however, be added that the laws under which the impalpable
particles of water in clouds agglomerate into drops of rain are not yet
understood, and that opinions differ on this subject. Experiments to
decide the question are needed, and it is to be hoped that the Weather
Bureau will undertake them. For anything we know to the contrary, the
agglomeration may be facilitated by smoke in the air. If it be really
true that rains have been produced by great battles, we may say with
confidence that they were produced by the smoke from the burning powder
rising into the clouds and forming nuclei for the agglomeration into
drops, and not by the mere explosion. If this be the case, if it was
the smoke and not the sound that brought the rain, then by burning
gunpowder and dynamite we are acting much like Charles Lamb's Chinamen
who practised the burning of their houses for several centuries before
finding out that there was any cheaper way of securing the coveted
delicacy of roast pig.
But how, it may be asked, shall we deal with the fact that Mr.
Dyrenforth's recent explosions of bombs under a clear sky in Texas were
followed in a few hours, or a day or two, by rains in a region where
rain was almost unknown? I know too little about the fact, if such it
be, to do more than ask questions about it suggested by well-known
scientific truths. If there is any scientific result which we can
accept with confidence, it is that ten seconds after the sound of the
last bomb died away, silence resumed her sway. From that moment
everything in the air--humidity, temperature, pressure, and motion--was
exactly the same as if no bomb had been fired. Now, what went on during
the hours that elapsed between the sound of the last bomb and the
falling of the first drop of rain? Did the aqueous vapor already in the
surrounding air slowly condense into clouds and raindrops in defiance
of physical laws? If not, the hours must have been occupied by the
passage of a mass of thousands of cubic miles of warm, moist air coming
from some other region to which the sound could not have extended. Or
was Jupiter Pluvius awakened by the sound after two thousand years of
slumber, and did the laws of nature become silent at his command? When
we transcend what is scientifically possible, all suppositions are
admissible; and we leave the reader to take his choice between these
and any others he may choose to invent.
One word in justification of the confidence with which I have cited
established physical laws. It is very generally supposed that most
great advances in applied science are made by rejecting or disproving
the results reached by one's predecessors. Nothing could be farther
from the truth. As Huxley has truly said, the army of science has never
retreated from a position once gained. Men like Ohm and Maxwell have
reduced electricity to a mathematical science, and it is by accepting,
mastering, and applying the laws of electric currents which they
discovered and expounded that the electric light, electric railway, and
all other applications of electricity have been developed. It is by
applying and utilizing the laws of heat, force, and vapor laid down by
such men as Carnot and Regnault that we now cross the Atlantic in six
days. These same laws govern the condensation of vapor in the
atmosphere; and I say with confidence that if we ever do learn to make
it rain, it will be by accepting and applying them, and not by ignoring
or trying to repeal them.
How much the indisposition of our government to secure expert
scientific evidence may cost it is strikingly shown by a recent
example. It expended several million dollars on a tunnel and
water-works for the city of Washington, and then abandoned the whole
work. Had the project been submitted to a commission of geologists, the
fact that the rock-bed under the District of Columbia would not stand
the continued action of water would have been immediately reported, and
all the money expended would have been saved. The fact is that there is
very little to excite popular interest in the advance of exact science.
Investigators are generally quiet, unimpressive men, rather diffident,
and wholly wanting in the art of interesting the public in their work.
It is safe to say that neither Lavoisier, Galvani, Ohm, Regnault, nor
Maxwell could have gotten the smallest appropriation through Congress
to help make discoveries which are now the pride of our century. They
all dealt in facts and conclusions quite devoid of that grandeur which
renders so captivating the project of attacking the rains in their
aerial stronghold with dynamite bombs.
XIII
THE ASTRONOMICAL EPHEMERIS AND THE NAUTICAL ALMANAC
[Footnote: Read before the U S Naval Institute, January 10, 1879.]
Although the Nautical Almanacs of the world, at the present time, are
of comparatively recent origin, they have grown from small beginnings,
the tracing of which is not unlike that of the origin of species by the
naturalist of the present day. Notwithstanding its familiar name, it
has always been designed rather for astronomical than for nautical
purposes. Such a publication would have been of no use to the navigator
before he had instruments with which to measure the altitudes of the
heavenly bodies. The earlier navigators seldom ventured out of sight of
land, and during the night they are said to have steered by the
"Cynosure" or constellation of the Great Bear, a practice which has
brought the name of the constellation into our language of the present
day to designate an object on which all eyes are intently fixed. This
constellation was a little nearer the pole in former ages than at the
present time; still its distance was always so great that its use as a
mark of the northern point of the horizon does not inspire us with
great respect for the accuracy with which the ancient navigators sought
to shape their course.
The Nautical Almanac of the present day had its origin in the
Astronomical Ephemerides called forth by the needs of predictions of
celestial motions both on the part of the astronomer and the citizen.
So long as astrology had a firm hold on the minds of men, the positions
of the planets were looked to with great interest. The theories of
Ptolemy, although founded on a radically false system, nevertheless
sufficed to predict the position of the sun, moon, and planets, with
all the accuracy necessary for the purposes of the daily life of the
ancients or the sentences of their astrologers. Indeed, if his tables
were carried down to the present time, the positions of the heavenly
bodies would be so few degrees in error that their recognition would be
very easy. The times of most of the eclipses would be predicted within
a few hours, and the conjunctions of the planets within a few days.
Thus it was possible for the astronomers of the Middle Ages to prepare
for their own use, and that of the people, certain rude predictions
respecting the courses of the sun and moon and the aspect of the
heavens, which served the purpose of daily life and perhaps lessened
the confusion arising from their complicated calendars. In the signs of
the zodiac and the different effects which follow from the sun and moon
passing from sign to sign, still found in our farmers' almanacs, we
have the dying traces of these ancient ephemerides.
The great Kepler was obliged to print an astrological almanac in virtue
of his position as astronomer of the court of the King of Austria. But,
notwithstanding the popular belief that astronomy had its origin in
astrology, the astronomical writings of all ages seem to show that the
astronomers proper never had any belief in astrology. To Kepler himself
the necessity for preparing this almanac was a humiliation to which he
submitted only through the pressure of poverty. Subsequent ephemerides
were prepared with more practical objects. They gave the longitudes of
the planets, the position of the sun, the time of rising and setting,
the prediction of eclipses, etc.
They have, of course, gradually increased in accuracy as the tables of
the celestial motions were improved from time to time. At first they
were not regular, annual publications, issued by governments, as at the
present time, but the works of individual astronomers who issued their
ephemerides for several years in advance, at irregular intervals. One
man might issue one, two, or half a dozen such volumes, as a private
work, for the benefit of his fellows, and each might cover as many
years as he thought proper.
The first publication of this sort, which I have in my possession, is
the Ephemerides of Manfredi, of Bonn, computed for the years 1715 to
1725, in two volumes.
Of the regular annual ephemerides the earliest, so far as I am aware,
is the Connaissance des Temps or French Nautical Almanac. The first
issue was in the year 1679, by Picard, and it has been continued
without interruption to the present time. Its early numbers were, of
course, very small, and meagre in their details. They were issued by
the astronomers of the French Academy of Sciences, under the combined
auspices of the academy and the government. They included not merely
predictions from the tables, but also astronomical observations made at
the Paris Observatory or elsewhere. When the Bureau of Longitudes was
created in 1795, the preparation of the work was intrusted to it, and
has remained in its charge until the present time. As it is the oldest,
so, in respect at least to number of pages, it is the largest ephemeris
of the present time. The astronomical portion of the volume for 1879
fills more than seven hundred pages, while the table of geographical
positions, which has always been a feature of the work, contains nearly
one hundred pages more.
The first issue of the British Nautical Almanac was that for the year
1767 and appeared in 1766. It differs from the French Almanac in owing
its origin entirely to the needs of navigation. The British nation, as
the leading maritime power of the world, was naturally interested in
the discovery of a method by which the longitude could be found at sea.
As most of my hearers are probably aware, there was, for many years, a
standing offer by the British government, of ten thousand pounds for
the discovery of a practical and sufficiently accurate method of
attaining this object. If I am rightly informed, the requirement was
that a ship should be able to determine the Greenwich time within two
minutes, after being six months at sea. When the office of Astronomer
Royal was established in 1765, the duty of the incumbent was declared
to be "to apply himself with the most exact care and diligence to the
rectifying the Tables of the Motions of the Heavens, and the places of
the Fixed Stars in order to find out the so much desired Longitude at
Sea for the perfecting the Art of Navigation."