From photograph taken by Professor E. E. Barnard, June 6, 1910, at the
Yerkes Observatory, Williams Bay, Wisconsin
]
Where is it now in its outward journey, at the present time of writing
(1925)? Science can answer the question as definitely as though it were
actually possessed of magic glasses, enabling it to follow the path of
the retreating comet, although it has long since passed beyond our range
of view. It is now approaching the orbit of the planet Neptune, crossing
it in 1933, and reaches its greatest distance outward from the sun in
1943, or 3,200 million miles. In 1964 it draws near to Neptune again,
and will be halfway between Neptune and Uranus in 1974, arriving at the
orbit of Saturn in 1984. Once more it will gladden the eyes of mortals
as it approaches the planet Jupiter, and draws near to pay its respects
to its mighty ruler, the sun.
At its return in 1758 the prediction erred on the side of thirty-two
days; at the return in 1835, by a margin of only two days; and in 1910,
by the amount of two and one-half days. Perchance, ere it makes its next
appearance in 1985,[10] the presence of another planet beyond Neptune
may have been detected, explaining the disturbing factor resulting in
that small discrepancy. The astronomers at that remote date (1984) may
succeed, therefore, in making a prediction so exact that the comet may
“swim into their ken” promptly to scheduled time. Few, if any, of the
present-time readers of this book (unless it falls into the hands of a
very youthful enthusiast) will be here to welcome the comet at its next
return, and even the youthful enthusiast may have the distressing
experience of the American astronomer Dr. Lewis Swift, who saw Halley’s
comet in 1835, and was able to welcome it at its return in 1910, but,
owing to failing eyesight, was unable to see it, much to his regret.
[Illustration:
The orbit of Halley’s Comet, which it passes over in 75 to 77 years,
showing where the comet is to be found now, and during its course
until its next return in 1985.
]
With regard to my first visit to the Yerkes Observatory, the following
facts regarding the great refractor may be of interest, as well as the
incident narrated to me by Miss Calvert while we were awaiting Professor
Barnard’s invitation to look for Halley’s comet, on that momentous
occasion. The story was deferred, in my account, to the final part of
this chapter, so as not to break the thread of the actual account of my
first view of the comet. Following the description of the telescope, the
story of a catastrophe which nearly ended its career is best told in
Professor Barnard’s own words, as quoted from the after-dinner speech,
in January, 1907, at Nashville, already referred to in this book.
“The tube of this instrument is about sixty-four feet long. In the
farther end of this tube is placed the great object glass, forty
inches clear in aperture. When one is looking overhead with this
giant telescope, he must be at a point some thirty feet or more
lower than when the tube is pointed toward the horizon. To avoid the
use of a high ladder to reach the observing end of the telescope in
its various positions, the floor of the dome itself is made into a
giant elevator, sixty-five feet in diameter. The rising and lowering
of this floor—which is done by electric motors—always keeps the
observer in a convenient and safe position with reference to the
eye-end. This floor is suspended by heavy steel cables which go over
wheels at the tops of four towers attached to the inside walls of
the dome. The floor is counterpoised by heavy iron weights at the
other ends of the cables.
“Within a little over a week after the completion of the instrument
and when we had seen through it only once or twice, the two south
cables pulled out of their sockets and the floor fell through fifty
feet to the ground and was destroyed. It was a terrible wreck. This
was on the morning of May 29, 1897, at 6.30 o’clock. Mr. Ellerman
and I had been working all night observing with the telescope. When
we quit at daylight we left the floor at its highest point for the
convenience of some workmen who were to be at work on the tube in
the morning. When the floor fell there was not a soul in the
building, and no one was injured. A couple of hours either way, and
death in all probability would have come to one or the other of us.
Only a few nights before this accident the president of the
University of Chicago and thirty or more trustees and prominent men
of the university had seen through the telescope, and the floor had
been up and down with them on it. If it had fallen then a heavy loss
of life would have been almost certain. A few days before that, Mr.
Clark, who made the great glass, had unpacked the forty-inch disks
on the floor at its highest point, and had put them in the cell
which he finally bolted to the end of the telescope. If the floor
had fallen then, the great lens would have been destroyed, with the
probability that no one would be able to make another, for Mr. Clark
died within a few days after he returned to Cambridge. It was
providential, then, that the floor fell when it did; for the fault
in the attachment of the cables made it certain that it must soon
have fallen.
“But this is not the end of the story. When the floor fell, it
lurched against the great iron pier of the telescope and must have
given it a violent blow. There was some fear that the great glass
might have been injured by the shock. It was nearly a hundred feet
up in the air and could not be reached to see if it was unharmed. By
climbing up on the dome (which is one hundred and ten feet high) and
looking down at the glass, it was seen to be apparently uninjured.
Still, the test could only be made by examining the stars through
it, which was not possible until the floor was replaced by a new
one. Four months were occupied in taking out the wreck and putting
in the new floor.
“There was great anxiety to see the sky through the glass, and the
first night available it was turned to the stars. To our
consternation, there was a great, long flare of light running
through every bright star we examined. This was so strong and
conspicuous that it would make the instrument utterly useless. It
looked as if the lens had been injured by the shock of the floor
against the pier. We examined it in all positions of the instrument,
but we could not get rid of the glaring defect. As I had used the
glass more than anyone else before the accident, my statement that
the defect did not then exist made the matter all the more serious.
It was with heavy hearts that we waited for day to again critically
examine the lens. The next day we all examined the great glass very
carefully, but could see nothing wrong with it. Then Professor Hale
noticed that just back of the glass in the tube was a thick mass of
spider webs stretched across the tube, all running in the same
direction. Upon comparing notes we found that the direction of the
spider webs coincided with that of the flare of light seen the night
before. It seemed that a spider had evidently got in the tube before
the object glass was put on by Clark, and had been unable to get
out; for there was no opening in the tube. During the time the tube
remained at rest, while the new floor was being put in, he had
climbed up to the great glass in the direction of the light; and
when he found his egress barred by the great window, he spun his
web, perhaps as a signal of distress, or maybe in the hope that some
unlucky fly might get in through the glass that he could not get out
of—anyway, with the result that he caused several astronomers the
most uneasy time of their lives. When these webs were swept out by
one of the astronomers climbing up in the tube with a feather
duster, it was found that night, when the stars were examined, that
the flare had vanished and the mighty glass was uninjured.”
CHAPTER SEVEN
ORIGIN OF COMETS AND METEORS
(THEORIES ADVANCED BY THE LATE RICHARD A. PROCTOR.)
Among the author’s most treasured possessions is a clipping from the
Cincinnati _Daily Gazette_ for February 18, 1874, containing a report of
a lecture given by her father, on “Comets and Meteors,” from which the
following is an extract:
“In this lecture on comets and meteors, I promised to give some
account of what is expelled from the sun when great explosions take
place. If I were to say that the comets were shot out from the sun
you might be startled, or if I asserted that they were also thrown
out of Jupiter and Saturn. But the evidence in connection therewith
is very curious. In the first place, we know that matter is shot out
from the sun, with a velocity so great as to be carried away from
him altogether and so would travel into space. That has only been
observed a few times, but the occurrence is probably very frequent.
The matter which was expelled, if it struck the earth at all, would
strike in the daytime. The side of the earth facing the sun will be
the illuminated side. The meteoric matter coming from the sun can
only strike the illuminated part, and this can only happen in the
daytime. You throw a stone at any object, and it must strike the
side of the object you aim at, that is turned toward you. Humboldt
affirmed that the largest number of meteoric masses had fallen in
the daytime. The larger aërolites have been examined and their
microscopic structure studied. Sorby of Sheffield, who examined some
of them, says they consist of a number of small globules and were
originally in a vaporous state before assuming their present
condition. Then came a chemical analysis by Professor Graham and
Chandler Roberts of London. They found in the iron of the meteoric
mass more hydrogen than iron in a natural condition. Professor
Graham said that in his opinion meteors certainly contained iron,
and that probably they had been expelled from one of the stars that
people space. He drew attention to the fact that stars contained
hydrogen in their atmosphere. These are some of the facts concerned
with the larger meteoric masses.
“How shall we account for those meteoric streams which travel close
to the path of Jupiter? All comets of short period have paths
closely approaching some of the large planets. The comet of 1680
went close to Jupiter, long before the explosive power of the sun
was noticed. I call them Jupiter’s family of comets. Sir John
Herschel said that it was very curious that they had that relation.
If we put forward the theory that Jupiter expelled these comets, we
have a very startling theory, but many of the theories which have
been propounded, some of the most important character and which have
been proved to be true, have been the most startling. It is said
that as Jupiter, Saturn, and Uranus go along their paths, they draw
in the comets which travel close to them, and capture them.
“I made a calculation about the November meteors to see how close
they must go to the path of Uranus in order to be captured, and
found that they must approach nearly as close as the nearest
satellite. Only those which came almost in contact with the planet
could be captured. Now, if they were shot out when Uranus was in a
sun-like condition, then it would be explained, whereas we find
great difficulty in imagining that a comet coming out of space would
be captured bodily by a planet like Uranus. Let us consider the
matter thus: if comets are expelled from a planet, they will be
carried along with the forward motion. If it could appear that some
of them went backward, then we would have no evidence of the theory
I have been advancing. If most of them travel forward, then we would
have some evidence for the theory. Now there is the curious fact
that among the comets of short period the whole of Jupiter’s family
travel forward. They do not travel in all directions of slope; all
have a very moderate slope to the paths of the planets. They do not
have the slope even of the asteroids. That is precisely what we
notice—that they travel very much with Jupiter. Taking the balance
between the two theories—that of expulsion and that of capture—it
seems to be in favor of the more startling one—that Jupiter has had
the power to expel these objects.”
It is interesting, in connection with this extract from the report of a
lecture given by my father some fifty years ago at present time of
writing (1925), to turn to a passage in the chapter on comets, by Dr. A.
C. D. Crommelin, in the _Splendour of the Heavens_, page 414, where he
refers as follows to the capture theory:
“The fact that the members of the Jupiter family (of comets) have
direct motion in all cases appears to give a fatal blow to the
capture theory. Practically as many comets would approach the planet
with retrograde motion as with direct; there is, indeed, the point
that those travelling in the same direction as the planet would
remain longer in its neighbourhood, and so have more time to be
perturbed, which would have some weight; but that out of some fifty
comets there is not a single retrograde one is too remarkable a fact
to pass over, and it clearly suggests that Jupiter played a
different part from that of a mere enslaver, and was concerned with
the origin of these bodies in a more intimate manner.
“Many of the considerations I have brought forward were stated by
Mr. R. A. Proctor some fifty years ago; they have therefore been
accessible to astronomers, who nevertheless have been, as a rule,
quite unaffected by them, so that it is time to state them afresh.
The consideration that the life of a short-period comet is limited
by the rapid wastage to which it is subject by the joint action of
the sun and Jupiter was not, I think, so fully realised, when
Proctor wrote as it is now. It serves further to invalidate the
capture theory, since it prevents our assigning to these bodies such
extended lives as that theory demands.”
According to my father’s theory, the giant planets are themselves the
parents of their comet-families, and he pictured their birth as having
occurred in a remote past, when the planets were more sun-like than they
are to-day. We have a great amount of evidence as to the energy of the
processes that are at work on Jupiter, as evidenced, for instance, by
the great Red Spot (though some have hinted at the possibility of its
being an early stage in the formation of a new satellite); Saturn,
Uranus, and Neptune also indicate vast upheavals, though distance in
their case hinders observation, and even on our own planet we have some
striking instances of the power of volcanic energy, as at the eruption
of Krakatoa in 1883. Sounds of the explosion were heard three thousand
miles away, and a huge volume of dust was blown to the highest regions
of the atmosphere, but we are entitled to expect much vaster convulsions
in Jupiter, which outweighs the earth three hundred times and is in a
much hotter state, judging by the deep envelope of vapours surrounding
it, and the rapid changes that are constantly taking place in its
appearance, on an enormous scale, as shown by the fine series of
photographs which have been obtained of the planet with the giant
telescopes.
Writing in his magazine, _Knowledge_, for January 1, 1887, page 64, my
father states:
“The theory of ejection was adopted as the only theory by which the
chemical, physical, and microscopic structure of meteorites of all
orders—from bolosiderites to asiderites—can be accounted for. They
were certainly once exposed to such conditions as exist only in the
interior of large orbs—suns or planets. And as certainly they have
somehow come forth from such interiors. The expulsive force shown by
observation to reside in the only sun-like body we can examine,
indicates the only way in which such expulsion can conceivably have
been effected. Hence, I infer (for my own part I feel assured of the
weight of evidence) that all orders of meteorites were expelled from
some orbs at some time when such orbs were in the sun-like stage.
Generalizing, I include in this theory all orders of meteors, and
find all their most characteristic peculiarities explained, and all
orders of meteor systems or comets, finding their several orders
thus and thus only explicable (if we include all suns now and in the
past, all planets in all solar systems, in their past sun-like
state, among the sources of meteors and comets). No other general
theory seems to me possible.”
Again, in an article in _Knowledge_ for April, 1887, page 135, my father
makes the following statement regarding his theory concerning comets and
meteors:
“All comets and meteors are sun-born. But it is not to our own sun,
nor to those other suns, the stars, that I attribute all comets and
meteor systems. Many millions have come doubtless from our sun
during the many millions of years he has been a sun, though few of
his cometic children are known to terrestrial astronomers. Millions
of millions have come from the many millions of suns in our galaxy
during the many millions of years of their sun-like existence. But
the giant planets were once suns,[11] and in their sun-like state,
which must have lasted millions of years, they must have ejected
their smaller comets and meteor systems which even now, after
millions of years, have paths passing near the orbits of their
parent orbs. Our earth and her fellow terrestrial planets had their
sun-like stage of life, too, and it must have been while the earth
was a sun that the meteors explained specially by Tschermak’s theory
were expelled.”
According to his theory, Tschermak, noting the resemblance of structure
between meteorites and volcanic products, suggests that meteors of all
orders (which would include meteor streams, and therefore comets) were
shot out from the earth in the days when she was young. But though this
is better than the other theories, in at least suggesting some sort of
an origin for comets and meteors, it will not account for comets which
do not approach within many millions of miles of the earth’s orbit,[12]
and a theory which fails for some among the comets cannot be the true
general theory for meteors either.
Mr. Sorby of Sheffield, the eminent mineralogist already referred to,
deduced from the microscopic structure of certain meteorites the
startling theory that they had once been inside the sun; for there is
evidence that their substance once existed in the form of globules of
molten metal, which aggregated with large masses, which in turn were
exposed to violent friction, indicating conflicting motions of very high
velocities.
“Where else,” wrote Sorby, in 1864, “could such conditions exist, except
first in the interior, and afterwards in the immediate neighborhood of
our sun!” But it is absolutely certain that the theory as thus suggested
cannot possibly be true, either as a general explanation of comets and
meteors, or even as an explanation of any known meteor system or comet,
unless, perhaps, a few of the comets whose orbits pass very near the sun
were sun-born, and subsequently disturbed by planetary attractions so as
not to return to their parent orb.
According to my father’s views on the subject:
“A flight of meteors shot out from the sun, as Sorby suggested,
might have velocity enough to get away from him forever, in which
case we should never see a trace of it again, even though we waited
for millions of years. If, however, it could not get away, then it
must return to its starting-place—that is, back to the sun’s
globe—unless, passing near enough to one of the giant planets, it
were so far disturbed as only to return by grazing past the sun’s
surface. (The comets of 1843, 1880, and 1882, which all traveled in
paths near the sun, almost grazing his surface, may well have been
parts of a single meteor-flight shot out from his interior millions
of years ago.)”
After the appearance of the new comet of 1887 in the southern skies, it
was found to be following along the same track as the comets of 1843,
1880, and 1882, thus confirming my father’s theory that these comets
were parts of one large comet, dissipated, doubtless, some millions of
years ago.
These comets were so bright when near the sun that they could be seen at
noon with the naked eye. As regards the heat experienced by the comet of
1843 when near the sun, Sir John Herschel remarked:
“Imagine a glare 25,000 times fiercer than that of an equatorial
sunshine at noonday. In such a heat there is no solid substance we
know of which would not run like water—boil—and be converted into
smoke or vapor.”
[Illustration: