STARTING ON THE VOYAGE TO THE WEST
"If I remember correctly, you stated some time ago, Professor, that the
barometer indicated the pressure of the atmosphere, and in that way it
was useful in letting us know what the weather would be. Before we sail,
would it not be well to make one of them? If we had possession of one of
the articles, we might not have been caught in the storm the first time
we took out No. 3."
"That is a good suggestion. I intended to propose that, because with the
barometer and the compass we shall be equipped with two of the most
useful instruments needed."
"I cannot comprehend how the air pressure has anything to do with the
weather. Is the air pressure really greater at one time than at
another?"
"Heated air ascends, does it not?"
"Yes; I can understand that."
"As it ascends it is, therefore, lighter at that point than normally. On
the other hand, moist air is heavier than dry air. These two conditions
would be indicated by the barometric column, would they not?"
"I presume they would; but when the air is moisture laden we don't need
a barometer to tell it is going to rain. We know it and feel it. What I
particularly wanted to know was how the barometer by its actions would
indicate it ahead for any length of time."
"The barometer does not indicate with any degree of accuracy on land;
but on sea it has a much better application. The instrument shows the
present pressure of the atmosphere, and its variations correspond to
atmospherical changes which have already taken place, the effects of
which may follow their cause at a greater or less interval."
"Then how could it be ascertained from the instrument when there would
be a storm or rain?"
"After a continuance of dry weather, if the barometer begins to fall
slowly and steadily, rain will certainly ensue; but if the fine weather
has been of long duration, and the mercury may fall for two or three
days before any perceptible change takes place; the more time elapses
before the rain comes, the longer the wet weather is likely to last."
"Then what indicates dry weather?"
"If, after a great deal of wet weather, with the barometer below its
mean height, the mercury begins to rise steadily and slowly, fine
weather will come, though two or three wet days may first elapse; and
the fine weather will be more permanent in proportion to the length of
time that passes before the perceptible change takes place."
"Is this the case at all times of the year?"
"The seasons affect the barometer, it is true. A sudden fall of the
barometer in the autumn or in the spring indicates wind; in the summer
or in hot weather it prognosticates a thunderstorm; in winter, after
frost, a sudden fall of the mercury shows a change of wind or a thaw
with rain; but in a continued frost a rise of mercury indicates
approaching snow."
"It seems, then, that a man must be pretty well versed in the weather to
be able to read the signs."
"That is a correct observation. The instrument in the hands of one who
has had experience with its use is absolutely necessary; it is not a
very satisfying device for those who do not take the time or trouble to
read all the signs, and note all the indications."
As detailed in a preceding chapter, the hardened steel rod for the
compass was brought out for the purpose of securing it in a little case,
so that it might be utilized to give them the true north.
It was a difficult task to find a means of suspending it, for the reason
that they had no tools which would make fine and carefully pivoted
balances, but eventually this was done, and they were gratified to see
the little rod or bar swing around and point north and south.
The work of arranging suitable closets for the various provisions and
providing a miniature kitchen was the next thing in order. This occupied
several days. Instead of taking the bedding in their house, it was
decided that new mattresses should be made up from the barley, of which
there was quite a quantity on hand.
One of the receptacles taken from the cave was a copper jar, which held
five gallons of water. A top was made for this which could be sealed up,
to hold a reserve supply of water. In addition two other vessels were
also provided for the regular supply, and also fitted with covers, so
that they had about ten gallons, an amount which was considered
sufficient.
The matter of fuel was a more difficult one to solve, unless they
intended to prepare most of the food before starting; but George
insisted that the small stove should be put aboard, and about fifty
pounds of the coal stowed away.
"How long do you think we should provision for?" was George's inquiry,
as they were carrying the various things aboard.
Harry had no ideas on the subject, but the Professor ventured the
opinion that at least two weeks' supply should be arranged for.
This conclusion rather startled the boys, who had not expected more than
a few days' trip, and when they questioned him about his reasons for
making the statement, he said: "Did you ever hear of the old lady who
attended a special meeting of prayer for rain? She came with an
umbrella, and the people laughed and chided her. The minister reproved
them, saying: 'She, at least, has faith, which you have not.' We are
going for two purposes: one is to learn something about the island we
are on, and the other to rescue our companions if they can be found. We
couldn't rescue them and let them starve."
Those words impressed them as nothing theretofore had, that the
Professor believed they were really going to find their former
shipmates, and that they would have stirring times before them.
Nothing so stimulates the actions of men, or boys, as the prospect of
adventure. Their trip had a double meaning, and it is not venturing too
much to say that their feelings were most tense during the entire period
in which they were engaged at the task of fitting out the little ship.
At last the day was set for the departure. The cattle could take care of
themselves. A tablet was prepared to be put up on their dwelling,
stating who were the owners of the habitation, their present
destination, and briefly relating the knowledge they possessed of the
inhabitants of the island, a statement of the direction they had taken,
and the kind of boat to which they trusted their destiny, and when they
expected to return.
A copy of this was then carried to the pole on Observation Hill, and
nailed to the mast, to replace the small tablet which had hitherto
filled that place. They were to launch the boat for the start on the
morrow.
That night a storm blew up from the west, as most of the winds had
previously blown from that quarter during the past month. The storm was
severe during the entire night, and abated somewhat in the forenoon, but
it again increased in fury before noon and continued with more or less
vigor all that day and during the night.
"I am afraid this storm will prevent us from starting for several days,
on account of its widespread character. The sea for hundreds of miles
has been subject to this monsoon, and we would have a very rough time
until the sea quiets down."
The delay was a bitter thing for the boys. Expectation had run high.
Anticipation doesn't mildly or easily brook waiting. They did not know
what to do, or how to pass the time in the interim. It was such a new
and trying condition for them.
The Professor noticed how they chafed under the restraint, but
apparently took no heed of it. However, he encouraged them in every
effort they made to divert themselves and to occupy their minds during
the waiting period.
During one of these spells which come on all more or less during such
trying hours, George could not hold in any longer, but broke out
impatiently: "What is the use of waiting any longer? The storm may keep
up for a week."
"Then do you think we had better venture a start under these
conditions?"
George thought a while. He appreciated the risk. Harry, too, was anxious
and nervous, and expressed a willingness to take the risk.
"Let me put another side to the question," said the Professor. "We are
perfectly safe here. You take no risks by remaining. You have in the
cave treasure that will make you millionaires. You cannot afford to take
any risks. If we knew something of the conditions on the island, and had
a certain knowledge that our comrades were in danger, the considerations
I have named should not deter us from starting. But with all these
things in the dark, and with the monsoons likely to break out again at
any time, the question is whether we can afford to risk the safety of
the enterprise because of impatience at delay."
"Yes," answered Harry. "I have thought of these things, and I feel that
the Professor's advice should be followed."
The boys were particularly surprised that he should refer to the money
in the cave as a reason why they should consider their actions in the
matter. It was so unlike him to refer to any sordid considerations as a
reason for not performing a great duty.
"I would also remind you that one of the greatest boons ever given to
the great investigators of the world came through delays. Time is a
wonderful reasoner. It is also a great modifier of events. Darwin was
prevented for twenty years in promulgating his great thesis; some of the
most marvelous inventions took years to bring out and develop into such
a state as to make them acceptable to the world. Delays, patiently
borne, make strong men. The impetuous think they represent wasted
opportunities. Davy Crockett enunciated one of the greatest principles
of human action when he said, 'Be sure you are right, then go ahead.' It
was only another way of advising against recklessness or impatience in
any enterprise."
Thus three days passed, and not without misgivings, the signal was given
for the start. Angel accompanied them, and with a new flag which the
days of leisure had given them an opportunity to prepare, the little
craft sailed down the waters of Cataract, in a shining sun, bound for a
haven which might mean rest, or to a shore which might offer no welcome
to them. The wind was coming mildly from the north, and when they had
cleared the shore line and were beyond the influence of the swells,
their course was directed to the west. Several miles beyond was a point
which projected out to sea; they could see this plainly from Observation
Hill, and during the last long trip inland they reached the sea beyond
this cape.
The shore line beyond was absolutely unknown to them, but it extended to
the west as far as they could see, and when night set in the faint mist
prevented them from judging how much farther it ran in that direction.
Without proper instruments at sea, distance is always a difficult matter
to judge, and the boys were constantly venturing guesses as to the
distance traveled. The start was made shortly after nine o'clock, and it
was now past six in the evening.
"How far do you think we have gone during the day?" was George's
question.
The Professor made a mental calculation before replying. "If we have
traveled at the same speed during the entire course that we made during
the first three miles to the cape, we have gone about thirty miles."
"Do you know it is three miles to the cape?"
"Yes, it is approximately that distance. I measured it by triangulation
some time ago, using our house and Observation Hill as the base line."
The boys had neglected to take this precaution.
"What was your object in doing that?"
"So that we might have some means to observe the speed our boat could
make. If we knew the speed of the wind, we might be able to calculate
our distance."
"But the wind has been coming from the north and we are sailing due
west. Would not the difference in the speed of the wind make a
difference in the speed of the boat?"
"It was for that reason I stated if our rate of travel was the same we
would have made that distance. The wind has been variable at different
points along the coast, so that our average may have been four miles per
hour."
"At what speed has the wind been during the day; I mean the average
speed?"
"Less than eight miles an hour?"
"If the wind had been coming from the east we could have made much
better time, and we might then have been near the mouth of the West
River," was Harry's conclusion.
"Why do you think we should have made better time?" asked the Professor.
"Because we should then have been going with the wind."
"You are entirely wrong in your assumption. Sailing ships travel faster
when tacking than when sailing with the wind."
The boys looked at the Professor in astonishment.
"It does not seem possible," replied George, "that any movement of the
wind pushing sidewise could be more effective than a pressure straight
ahead. Can you explain the reason for the statement?"
"When the wind blows straight against a sail, certain eddies are
produced which cause a convolute stream around its edges. These currents
are counter to the forward movement of the vessel. Assuming that this
normal pressure of the wind is 1,000 pounds, it is estimated that fully
half is lost in effectiveness. On the other hand, if the ship is moving
forward at right angles to the direction of the wind, and the sail is
set at forty-five degrees, that is what is called a tack; while it has
only about six-sevenths the surface that it had when going with the
wind, the sail is constantly going into new wind and, therefore, the
pressure is a constant one and most efficiently applied to the surface."
"Do you mean by this that if I hold up a sail so that the wind blows
flat against it, the pressure will not be as great as if I held it at an
angle?"
[Illustration: _Fig. 21. Fig. 22. ILLUSTRATING WIND PRESSURE_]
"No; I had reference to a moving object. I can better explain the
phenomenon by illustrating the two conditions: In the drawing (Fig. 21),
let A represent a sail with 100 square feet of surface. The darts (1)
represent the wind blowing dead against it. This is called the normal
position. You will see the darts representing the direction of the
movement of the wind. Now look at the next sketch (Fig. 22). Here the
sail (B) is put at an angle of forty-five degrees from the direction of
the wind. The sail is still the same size vertically, but it is somewhat
smaller horizontally across the line (C), this diminution in size being
about one-seventh of the entire area. The darts (D) in both cases
represent the movement of the boat, and the darts (2) in the last sketch
show the wind striking the sail at an angle."
"In the first sketch the darts (1) strike the sail normally, as you say,
in what way do the darts (2) in the next figure strike the sail?"
"At an angle of incidence. If you will notice the behavior of the wind
in the first view it will be seen that the wind curves around the edges
of the sail, and strikes against the back of it, and thus produces the
retarding effect I referred to. On the other hand, by examining the
second sketch, the darts (2) plainly show their course across the sail
diverted from their straight source, and behind the bulging sail the air
does not press against the sail, but tries to continue in a straight
line. As a result a partial vacuum is formed along the region designated
by E, and this produces a most effective pull, since the sail constantly
tries to move forward and fill this vacuum. Is this made clear to you?"
"I can plainly see now what the action of the air is, but does the air
push just as hard against each square foot when it is at an angle as
when it is blowing against it straight?"
"That is a good observation, and one that might ordinarily be
overlooked. No, it does not, but the difference can be readily
calculated."
"Then supposing the sail to be 10 feet square, and the wind is blowing
against it straight, as in the first sketch, at the rate of twenty miles
an hour; what pressure would there be against the entire sail?"
"At that speed of wind the pressure on each square foot of surface is 2
pounds, and this multiplied by 100 equals 200 pounds."
"When it is at forty-five degrees, what is the pressure on each square
foot?"
"This is determined in the following manner: Square the speed of the
wind, which means multiplying 20 by 20, and this produces the square,
400. In mathematics, as in many of the sciences, a constant is employed.
A constant is a figure which never varies. In this case the constant is
designated by the decimal .005. That means 5/1000th, or reduced to its
lowest denomination, 1/200th. If, now, we divide 400 by 1/200, the
result will be 2 pounds. This figure thus represents the pressure of air
on each square foot of surface, which, multiplied by the sail area, 100
square feet, makes 200 pounds."
"If that is the push when it is normal, what will it be at 45 degrees?"
"Each angle of incidence has its own figure, or coefficient, or for your
better understanding, value, and the value at 45 degrees is .666. So
that by multiplying 200 by this value, we get a total pressure of 133.2
pounds."
"These figures are used a great deal in flying machines; are they not?"
"Yes; and that is a subject which we might pursue, but there are some
things right ahead that may for the present interest us more."
Through the haze which had now settled down, a faint outline of land was
made out in the distance. The course was altered to the northeast, and
after a quarter-hour sail, land was again espied ahead, so that to avoid
the shore the course was taken due north. This was evidence that the
land projected northwardly, and the Professor suggested that the effort
should be made to chart as accurately as possible the shore line. This
could be done mentally.
"I had forgotten to take any note," said Harry. "What is the proper
thing to observe in making these calculations?"
"Two things must always be uppermost in the mind of the explorer on the
sea: First the time, and second the speed. Time can always be accurately
determined, but the question of speed can come by experience only. A
good sailor can very accurately determine speed by an examination of the
passing water, where the sea is comparatively calm. I have known where
the distances have been thus estimated within a hundred feet in each
mile in a ten-mile course, and where the speeds were varied along the
route. Then, a good observer must have the gift of direction. If he has
sailed one hour at a certain speed in a given direction his mental chart
may be of the greatest service to him. In our case it would be
invaluable. It is a quality well worth our effort to acquire."