William F. Denning.

Telescopic Work for Starlight Evenings online

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of peculiar definition, such as oval or triangular star disks, have
been occasionally recorded, but we must content ourselves with a bare
reference to these phenomena. With regard to the general question it
may, however, be added that the character of the seeing often varies at
very short intervals in this climate. In the course of a night’s work
the definition will sometimes fluctuate in a most remarkable manner. An
observer who comes to the telescope and finds it impossible to obtain
satisfactory images should not entirely relinquish work at the first
trial. After an interval he should again test its performance, for
it frequently happens that a night ushered in by turbulent vapours,
improves greatly at a later period, and in the morning part becomes so
fine that it is worthy to be included in the select 100 hours assigned
by Sir W. Herschel as the annual limit. Those who reside in towns
will usually get the best definition after midnight, because there
is less interference then from smoke and heated vapours. It would
greatly conduce to our knowledge of atmospheric vagaries as affecting
definition, if observers, especially those employing large aperture,
preserved records as to the quality of the seeing, also direction of
wind and readings of the barometer and thermometer.

_Vision._—There are perhaps differences quite as considerable in
powers of vision as in quality of definition. It is not meant by
this that the same person is subject to great individual variations,
though some people are certainly liable to fluctuations, according to
state of health and other conditions. Some eyes, as already stated,
are less effective in defining planetary markings than in detecting
minute stars or faint satellites of distant planets. Of course the
natural capacity is greatly enhanced by constant practice, for the
human eye has proved itself competent to attain a surprising degree of
excellence by habitual training. Frequent efforts, if not overpressed
so as to unduly strain the optic nerves, are found to intensify rather
than weaken the powers of sight. Thus a distinguishing trait among
astronomers has been their keenness of vision, which, in many cases,
they have retained to an advanced age. It is true Dr. Kitchiner said
his “eye at the age of forty-seven became as much impaired by the
extreme exertion it had been put to in the prosecution of telescope
trials, as an eye which has been employed only in ordinary occupations
usually is at sixty years of age!—to cultivate a little acquaintance
with the particular and comparative powers of telescopes requires many
extremely eye-teasing experiments.” But the Doctor’s opinion is not
generally confirmed by other testimony, the fact being that the eye is
usually strengthened by special service of this character. To unduly
tax or press its powers must result in injury; but it is well known
that the capacities of our sight and other senses are enhanced by
their healthy exercise, and that comparative disuse is a great source
of declining efficiency. Before the observer may hope to excel as a
telescopist it is clear that a certain degree of training is requisite.
Many men exhibit very keen sight under ordinary circumstances, but
when they come to the telescope are hopelessly beaten by a man who has
a practised eye. On several occasions the writer was much impressed
with evidences of extraordinary sight in certain individuals, but upon
being tested at the telescope they were found very deficient, both as
regards planetary detail and faint satellites. Objects which were quite
conspicuous to an experienced eye were totally invisible to them. I
believe it is a good plan for habitual observers to employ method in
exercising their sight. In my own case I invariably use the right eye
on the markings of planets and the left on minute stars and satellites.
Practice has given each eye a superiority over the other in the special
work to which it has been devoted, and I fancy the practice might be
more generally followed with success.

It is an advantage to keep both eyes open when in the act of observing,
especially when surrounding objects are perfectly dark and there is no
distracting light from neighbouring windows or lamps. The slight effort
required to keep the disengaged eye closed interferes with the action
of the other, and though this is but trivial, critical work is not
efficiently performed under such conditions. Whenever light interferes
the observer may exclude it by a shade so arranged as to afford
complete protection to the unoccupied eye.

If faint objects are to be examined the observer should remain in a
dark situation for some little time previously, so that the pupil
of the eye may be dilated to the utmost extent and in a state most
suitable for such work. After coming from a brilliantly lit apartment,
or after viewing the Moon or a conspicuous planet, the eye is totally
unfit to receive impressions from a difficult object, such as a minute
star or faint nebula or comet; some time must be allowed to elapse
so that the eye may recover its sensitiveness. As a rule amateurs
will find it best to confine their attention to one class of objects
only on the same evening, for if the Moon is first examined and then
immediately afterwards the telescope is directed upon double stars
and nebulæ, the latter objects are little likely to be seen with good
effect. If faint objects generally are persistently studied night after
night and the observer refrains from solar and lunar work, his eye
will acquire greater sensitiveness and he will readily pick up minute
forms which are utterly beyond the reach of a man who indiscriminately
employs his eye and telescope upon bright and faint objects.

_Records._—With regard to records, every observer should make a note
of what he sees, and at the earliest possible instant after the
observation has been effected. If the duty is relegated to a subsequent
occasion it is either not done at all or done very imperfectly. The
most salient features of whatever is observed should be jotted down in
systematic form, so as to permit of ready reference afterwards. It is
useful to preserve these records in a paged book, with an index, so
that the matter can be regularly posted up. The negligence of certain
observers in this respect has resulted in the total loss of valuable
observations. Even if the details appear to possess no significance,
they should be faithfully registered in a convenient, legible form,
because many facts deemed of no moment at the time may become of
considerable importance. The observer should never refrain from such
descriptions because he attributes little value to them. Some men keep
voluminous diaries in which there is scarcely anything worth record;
but this is going to the other extreme. All that is wanted is a concise
and brief statement of facts. Some persons have omitted references to
features or objects observed because they could not understand them,
and rather distrusted the evidence of their eyes; but these are the
very experiences which require careful record and reinvestigation.

_Drawing._—Few observers are good draughtsmen; but it is astonishing
how seldom we meet with real endeavours to excel in this respect. Every
amateur should practise drawing, however indifferent his efforts may
be. Delineations, even if roughly executed, are often more effective
than whole pages of description. Pictorial representations form the
leading attraction of astronomical literature, and are capable of
rendering it more interesting to the popular mind than any other
influence. They induce a more apt conception of what celestial objects
are really like than any amount of verbal matter can possibly do.
For this reason it becomes the obvious duty of every observer to
cultivate sketching and drawing, at least in a rudimentary way. He will
frequently find it essential to illustrate his descriptions, so as
to ensure their ready comprehension. In fact, a thoroughly efficient
observer must of necessity become a draughtsman. It should, however,
be his invariable aim to depict just what he sees and in precisely
the form in which it impresses his eye. Mere pictorial embellishments
must be disregarded, and he should be careful not to include doubtful
features, possibly existing in the imagination alone, unless he intends
them simply for his own guidance in future investigations. If he sees
but little, and it is faithfully delineated, it will be of more real
value than a most elaborate drawing in which the eye and imagination
have each played a part. It is an undoubted fact that some of the most
striking illustrations in astronomical handbooks are disfigured by
features either wrongly depicted or having no existence whatever. There
is very great need for caution in representing such markings only as
are distinctly and unmistakably visible. In all cases where the object
is new or doubtful the observer should await duplicate observations
before announcing it. It is better that new features should evade
discovery than that delusive representations should be handed down to
posterity. As regards selenographical drawings I would refer the reader
to what Mr. Eiger advises on p. 21 and 22 of volume v. of the ‘Journal
of the Liverpool Astronomical Society.’ My own plan in sketching at
the telescope is to first roughly delineate the features bit by bit
as I successively glimpse them, assuring myself, as I proceed, as to
general correctness in outline and position; then, on completion, I go
indoors to a better light and make copies while the details are still
freshly impressed on the mind. To soften details a small piece of
blotting-paper must be wrapped round the pointed end of the pencil, and
the parts requiring to be smoothed gently touched or rubbed until the
desired effect is attained. This simple method, properly applied, will
enable delicate markings to be faithfully reproduced, and it certainly
adds in no small degree to the merit of a drawing.

_Friendly Indulgences._—Every man whose astronomical predilections
are known, and who has a telescope of any size, is pestered with
applications from friends and others who wish to view some of the
wonders of the heavens. Of course it is the duty of all of us to
encourage a laudable interest in the science, especially when evinced
by neighbours or acquaintances; but the utility of an observer
constituting himself a showman, and sacrificing many valuable hours
which might be spent in useful observations, may be seriously
questioned. The weather is so bad in this country that we can ill
spare an hour from our scanty store. Is it therefore desirable to
satisfy the idle curiosity of people who have no deep-seated regard for
astronomy, and will certainly never exhibit their professed interest
in a substantial manner? Assuredly not. The time of our observers is
altogether too valuable to be employed in this fashion. Yet it is an
undisputed fact that some self-denying amateurs are unwearying in their
efforts to accommodate their friends in the respect alluded to. My own
impression is that, except in special cases, the observer will best
consult the interests of astronomy, as well as his own convenience and
pleasure, by declining the character of showman; for depend upon it
a person who appreciates the science in the right fashion will find
ways and means to procure a telescope and gratify his tastes to the
fullest capacity. Some years ago I took considerable trouble on several
evenings in showing a variety of objects to a clerical friend, who
expressed an intention to buy a telescope and devote his leisure to the
science. I spent many hours in explanations &c.; but some weeks later
my pupil informed me his expenses were so heavy that he really could
not afford to purchase instruments. Yet I found soon after that he
afforded £30 in a useless embellishment of the front of his residence,
and it so disgusted me that I resolved to waste no more precious time
in a similar way.

_Open-Air Observing._—Night air is generally thought to be pernicious
to health; but the longevity of astronomers is certainly opposed to
this idea. Those observers who are unusually susceptible to affections
of the respiratory organs must of course exercise extreme care, and
will hardly be wise in pursuing astronomical work out of doors on
keen, wintry nights. But others, less liable to climatic influences,
may conduct operations with impunity and safety during the most severe
weather. Precautions should always be taken to maintain a convenient
degree of warmth; and, for the rest, the observer’s enthusiasm
must sustain him. A “wadded dressing-gown” has been mentioned as
an effective protection from cold. I have found that a long, thick
overcoat, substantially lined with flannel, and under this a stout
cardigan jacket, will resist the inroads of cold for a long time. On
very trying nights a rug may also be thrown over the shoulders and
strapped round the body. During intense frosts, however, the cold will
penetrate (as I have found while engaged in prolonged watches for
shooting-stars) through almost any covering. As soon as the observer
becomes uncomfortably chilly he should go indoors and thoroughly warm
his things before a fire. He may then return fortified to his work and
pursue it for another period before the frost again makes its presence
disagreeably felt. On windy nights a knitted woollen helmet to cover
the head, and reaching to the shoulders, is an excellent protection;
but an observer had better not wear it more often than is imperative,
or it becomes a necessity on ordinary nights. It is a great mistake to
suppose that “a glass of something hot” before going into the night air
is a good preventive to catching cold. It acts rather in the contrary
way. The reaction after the system has been unduly heated only renders
the observer more sensitive, and the inhalation of cold air is then
very liable to induce affections of the throat.

A telescope permanently erected in the open, and exposed to all
weathers, must soon lose its smart and bright appearance, but it need
lose none of its efficiency, which is of far more importance; for it is
intended for service, not for show. The instrument should be kept well
painted and oiled. I find vaseline an excellent application for the
screws and parts controlling the motions, as it is not congelative like
common oils. The observer, before a night’s work and before darkness
sets in, will do well to examine his instrument and see that it is in
the best condition to facilitate work. Whole tribes of insects take up
their habitation in the base or framework, and even in the telescope
itself if they can effect a lodgment; and I have sometimes had to
sweep away a perfect labyrinth of spiders’ webs from the interior of
the main tube. On one occasion I could not see anything through the
finder, try how I would. I afterwards discovered that a mason-wasp
(_Odynerus murarius_) had adopted the vacuity in front of the eye-lens
as a suitable site for her nest; and here she had formed her cells,
deposited her eggs, and enclosed the caterpillars necessary for the
support of the young when hatched. On another night I came hurriedly to
the telescope to observe Jupiter with my single-lens eyepiece, power
252, but could make nothing out of it but a confused glare, subject
to sudden extinctions and other extraordinary vagaries. I supposed
that the branches of a tree, waving in the wind, must be interposed
in the line of sight, but soon saw this could not possibly be the
explanation. Looking again into the eyepiece, I caught a momentary
glimpse of what I interpreted for the legs of an insect magnified
into gigantic proportions and very distinct on the bright background
formed by Jupiter much out of focus. On detaching the eyepiece and
carrying it indoors to a light, an innocent-looking sample of the
common earwig crawled out of it. The gyrations of the insect in its
endeavours to find a place of egress from its confinement had clearly
caused the effects alluded to. Telescopic observers are thus liable to
become microscopic observers before they are conscious of the fact,
and perhaps also in opposition to their intention. Other experiences
might be narrated, especially as regards nocturnal observing in country
or suburban districts, where the “serious student of the skies” may,
like myself, find diversion to his protracted vigils by the occasional
capture of a too-inquisitive hedgehog or some other marauding quadruped.

[Illustration: Fig. 19.

The Author’s Telescope: a 10-inch With-Browning Reflector.]

_Method._—Nearly all the most successful observers have been men of
method. The work they took in hand has been followed persistently and
with certain definite ends in view. They recognized that there should
be a purpose in every observation. Some amateurs take an incredible
amount of pains to look up an object for the simple satisfaction
of seeing it. But seeing an object is not observing it. The mere
view counts for nothing from a scientific standpoint, though it may
doubtless afford some satisfaction to the person obtaining it. A
practical astronomer, with his own credit at stake and the interests of
the science at heart, will require something more. In observing a comet
he will either fix its position by careful measurement with reference
to stars near, or critically examine its physical peculiarities, or
perhaps both. In securing these data he will have accomplished useful
work, which may quite possibly have an enduring value. In other
branches of observation his aim will be similar, namely to acquire new
materials with regard to place or to physical phenomena, according
to the nature of the research upon which he happens to be engaged.
Such results as he gathers are neatly tabulated in a form convenient
for after comparisons. There have been instances, we know, where
sheer carelessness has resulted in the loss of important discoveries.
Lalande must have found Neptune (and mathematical astronomy would
have been robbed of its greatest triumph) half a century before it was
identified in Galle’s telescope, but his want of care enabled it to
elude him just when he was hovering on the very verge of its discovery.
Numerous other instances might be mentioned. Failure may either arise
from imperfect or inaccurate records, from a want of discrimination,
from neglect in tracing an apparent discordance to its true source,
or from hesitation. I may be pardoned for mentioning a case within
my own experience. On July 11, 1881, just before daylight, I stood
contemplating Auriga, and the idea occurred to me to sweep the region
with my comet eyepiece, but I hesitated, thinking the prospect not
sufficiently inviting. Three nights later Schæberle at Ann Arbor,
U.S.A., discovered a bright telescopic comet in Auriga! Before sunrise
on October 4 of the same year I had been observing Jupiter, and again
hesitated as to the utility of comet-seeking, but, remembering the
little episode in my past experience, I instantly set to work, and
at almost the first sweep alighted upon a suspicious object which
afterwards proved itself a comet of short period. These facts teach one
to value his opportunities. They cannot be lightly neglected, coming
as they do all too rarely. The observer should never hesitate. He must
endeavour to at least effect a little whenever an occasion offers;
for it is just that little which may yield a marked success—greater,
perhaps, than months of arduous labour may achieve at another time.

_Perseverance._—Persistency in observation, apart from the value
derived from cumulative results, increases the powers of an observer
to a considerable degree. This is especially the case when the same
objects are subjected to repeated scrutiny. A first view, though it
may seem perfectly satisfactory in its conditions and results, does
not represent what the observer is capable of doing with renewed
effort. Let us suppose that a lunar object with complicated detail
is to be thoroughly surveyed. The observer delineates at the first
view everything that appears to be visible. But a subsequent effort
reveals other features which eluded him before, and many additional
details are gradually reached during later observations. Ultimately
the observer finds that his first drawing is scarcely more than a mere
outline of the formation as he sees it at his latest efforts. Details
which he regarded as difficult at first have become comparatively
conspicuous, and a number of delicate structures have been exhibited
which were quite beyond his reach at the outset. The eye has become
familiarized with the object, and its powers fairly brought out by
training and experience. This training is very serviceable, but
is seldom appreciated in the degree of its influence. Many a tyro
has abandoned a projected series of observations on finding that
his initiatory view falls wofully short of published drawings or
descriptions. He considers himself hopelessly distanced, and regards
it as impossible to attain—much less excel—the results achieved by
his predecessors. He does not realize that their work is the issue
of years of close application, and that it represents the collective
outcome of many successive nights. I need hardly say that it is a
great mistake to anticipate failure in this way. No telescopic work
has been done in the past that will not be done better in the future.
No observer can rate his capacity until he has rigorously tested it by
experience. The eye must become accustomed to an object before it is
able to do itself justice. Those who have been sedulously engaged in a
certain research will, as a rule, see far more than others who are but
just entering upon it—not from a natural superiority of vision, but
because of the aptitude and power acquired by practice. No matter how
meagre an observer’s primary attempts may be, he should by no means
relax his efforts, but rather feel that his want of success must be
remedied by experience. It is a common fault with observers that they
leave too much to their instruments, and rely upon them for the results
which really depend entirely upon their personal endeavours. A skilled
workman will do good work with indifferent tools; for after all it is
the character of the man that is evident in his results, and not so
much the resources which art places in his hands.

Much also depends upon the feelings by which the amateur is actuated
when he commences work. A few enter into it with a degree of energy
and determination that knows no wearying and will accept no defeat.
Others display a half-hearted enthusiasm, and are constantly doubting
either their personal ability or their instrumental means. Many
others, again, when the circumstances appear a little against them
regard failure as inevitable. It need hardly be said, however, that
every difficulty may be surmounted by perseverance, and that a man’s
enthusiasm is often the measure of his success, and success is rarely
denied to him whose heart is in his work.

_Definition in Towns._—The astronomical journals contain some
interesting references to the definition of telescopes in large towns.
Of course the purer the air the better for observational purposes.
But observers who reside in populous districts need not despair of
doing really useful work. The vapours hanging over a large city are
by no means so objectional as is commonly supposed. When they are
circulating rapidly across the observer’s field of view they will
prove very troublesome at times; but in a comparatively tranquil
state of the air definition is excellent. I have frequently found
planetary markings very sharp and steady through the smoke and fog of
Bristol. The interposing vapours have the effect of moderating the
bright images and improving their quality. When there is a driving
wind, and these heated vapours from the city are rolling rapidly past,
objects at once appear in a state of ebullition, and the work of
observation may as well be postponed. Smoke from neighbouring chimneys
is utterly ruinous to definition: a bright star is transformed into a
seething, cometary mass, and the planets undergo contortions of the
most astonishing character. Large instruments being more susceptible
to such influences—and, indeed, to atmospherical vagaries of all
kinds—are chiefly affected by the drawbacks we have alluded to; but
there are many opportunities when their powers may be fully utilized.
In sweeping for faint comets, or in other work (such as the observation
of nebulæ) where a dark sky is the first essential, a town station



Online LibraryWilliam F. DenningTelescopic Work for Starlight Evenings → online text (page 7 of 32)