| Day One: Tuesday Morning, August 25, 1835 | |
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Lately Made BY SIR JOHN HERSCHEL, L.L.D, F.R.S, &c. At The Cape of Good Hope. [From Supplement to the Edinburgh Journal of Science]
In this unusual addition to our Journal, we have the
happiness of making known to the British publick, and thence
to the whole civilized world, recent discoveries in
Astronomy which will build an imperishable monument to the
age in which we live, and confer upon the present generation
of the human race a proud distinction through all future
time. It has been poetically said, that the stars of heaven
are the hereditary regalia of man, as the intellectual
sovereign of the animal creation. He may now fold the
Zodiack around him with a loftier conscientiousness of his
mental supremacy.
It is impossible to contemplate any great Astronomical
discovery without feelings closely allied to a sensation of
awe, and nearly akin to those with which a departed spirit
may be supposed to discover the realities of a future state.
Bound by the irrevocable laws of nature to the globe on
which we live, creatures "close shut up in infinite
expanse," it seems like acquiring a fearful supernatural
power when any remote mysterious works of the Creator yield
tribute to our curiosity. It seems almost a presumptious
assumption of powers denied to us by divine will, when man,
in the pride and confidence of his skill, steps forth, far
beyond the apparently natural boundary of his privileges,
and demands the secrets and familiar fellowship of other
worlds.
We are assured that when the immortal philosopher to
whom mankind is indebted for the thrilling wonders now first
made known, had at length adjusted his new and stupendous
apparatus with the certainty of success, he solemnly paused
several hours before he commenced his observations, that he
might prepare his own mind for discoveries which he knew
would fill the minds of myriads of his fellow-men with
astonishment, and secure his name a bright, if not
transcendent conjunction with that of his venerable father
to all posterity.
And well he might pause! From the hour the first human
pair opened their eyes to the glories of the blue firmament
above them, there has been no accession to human knowledge
at all comparable in sublime interest to that which he has
been the honored agent in supplying; and we are taught to
believe that, when a work, already preparing for the press,
in which his discoveries are embodied in detail, shall be
laid before the public, they will be found of incomparable
importance to some of the grandest operations of civilized
life.
Well might he pause! He was about the become the sole
depository of wondrous secrets which had been hid from the
eyes of all men that had lived since the birth of time. He
was about to crown himself with a diadem of knowledge which
would give him a conscientious pre-eminence above every
individual of his species who then lives, or who had lived
in the generations that are passed away. He paused ere he
broke the seal of the casket which contained it.
To render our enthusiasm intelligible, we will state at
once, that by means of a telescope of vast dimensions and en
entirely new principle, the younger Herschel, at his
observatory in the Southern Hemisphere, has already made the
most extraordinary discoveries in every planet of our solar
system; has discovered planets in other solar systems; has
obtained a distinct view of objects in the moon, fully equal
to that which the naked eye commands of terrestrial objects
at the distance of a hundred yards; has affirmatively
settled the question whether this satellite be inhabited,
and by what order of things; has firmly established a new
theory of cometary phenomena; and has solved or corrected
nearly every leading problem of mathematical astronomy.
For our early and almost exclusive information
concerning these facts, we are indebted to the devoted
friendship of Dr. Andrew Grant, the pupil of the elder, and
for several years past the inseparable coadjutor of the
younger Herschel. The amanuensis of the latter at the Cape
of Good Hope, and the indefatigable superintendent of his
telescope during the whole period of its construction and
operation, Dr. Grant has been enabled to supply us with
intelligence equal, in general interest at least, to that
which Dr. Herschel himself has transmitted to the Royal
Society. Indeed our correspondent assures us that the
voluminous documents now before a committee of that
institution contain little more than details and
mathematical illustrations of the facts communicated to us
in his own ample correspondence.
For permission to indulge his friendship in
communicating this invaluable information to us, Dr. Grant
and ourselves are indebted to the magnanimity of Dr.
Herschel. who, far above all mercenary considerations, has
thus signally honored and rewarded his fellow-laborer in the
field of science. The engravings of lunar animals and other
objects, and of the phases of the several planets, are
accurate copies of drawings taken in the observatory by
Herbert Home, Esq., who accompanied the last powerful series
of reflectors from London to the Cape, and superintended
their erection; and he has thus recorded the proofs of their
triumphant success. The engravings of the belts of Jupiter
is a reduced copy of the imperial folio drawing by Dr.
Herschel himself, and contains the results of his latest
observation of that planet. The segment of the inner ring
of Saturn is from a large drawing by Dr. Grant.
We first avail ourselves of the documents which contain
a description and history of the instrument by which there
stupendous discoveries have been made. A knowledge of the
one is essential to the credibility of the other.
THE YOUNGER HERSCHEL'S TELESCOPE
It is well known that the great reflecting telescope of
the late elder Herschel, with an object-glass four feet in
diameter, and a tube forty feet in length, possesses a
magnifying power of more than six thousand times. But a
small portion of this power was ever advantageously applied
to the nearer astronomical objects; for the deficiency of
light from objects so highly magnified, rendered them less
distinct than when viewed with a power of a third or a
fourth of this extent. Accordingly the powers which he
generally applied when observing the moon or planets, and
with which he made his most interesting discoveries, ranged
from 220, 460, 750 and 900 times; although, when inspecting
the double and treble fixed stars, and the more distant
nebulae, he frequently applied the full capacity of his
instrument. The law of optics, that an object becomes dim
in proportion as it is magnified, seemed, from its
exemplification in this powerful telescope, to form an
insuperable boundary to further discoveries in our solar
system. Several years, however, prior to the death of this
venerable astronomer, he conceived it practicable to
construct an improved series of parabolic and spherical
reflectors, which, by uniting all the meritorious points in
the Gregorian and Newtonian instruments, with the highly
interesting achromatic discovery of Dolland, would, to a
great degree, remove the formidable obstruction. His plan
evinced the most profound research in optical science, and
the most dexterous ingenuity in mechanical contrivance; but
accumulating infirmities, and eventual death, prevented its
experimental application.
His son, the present Sir John Herschel, who had been
nursed and cradled in the observatory, and a practical
astronomer from his boyhood, was so fully convinced of the
value of the theory, that he determined upon testing it, at
whatever cost. Within two years of his father's death he
completed his new apparatus, and adapted it to the old
telescope with nearly perfect success. He found that the
magnifying power of 6,000 times, when applied to the moon,
which was the severest criterion that could be selected,
produced, under these new reflectors, a focal object of
exquisite distinctness, free from every achromatic
obscurity, and containing the highest degree of light which
the great speculum could collect from that luminary.
The enlargement of the angle of vision which was thus
acquired, is ascertained by dividing the moon's distance
from the observatory by the magnifying power of the
instrument; and the former being 240,000 miles, and the
latter 6,000 times, leaves a quotient of 40 miles as the
apparent distance of that planet from the eye of the
observer. Now it is well known that no terrestrial objects
can be seen at a greater distance than this, with the naked
eye, even from the most favorable elevations. The rotundity
of the earth prevents a more distant view than this with the
most acute natural vision, and from the highest eminences;
and, generally, objects seen at this distance are themselves
elevated on mountainous ridges. It is not pretended,
moreover, that this forty miles telescopic view of the moon
presented its objects with equal distinctness, though it did
in equal size to those of this earth, so remotely stationed.
The elder Herschel had nevertheless demonstrated, that
with a power of 1,000 times, he could discern objects in
this satellite of not more than 122 yards in diameter. If
therefore the full capability of the instrument had been
elicited by the new apparatus of reflectors constructed by
his son, it would follow, in mathematical ratio, that
objects could be discerned of not more than 22 yards in
diameter. Yet in either case they would be seen as mere
feeble, shapeless points, with no greater conspicuity than
they would exhibit upon earth to the unaided eye at the
distance of forty miles. But although the rotundity of the
earth presented no obstruction to a view of these
astronomical objects, we believe Sir John Herschel never
insisted that he had carried out these extreme powers of the
telescope in so full a ratio.
The deficiency of light, though greatly economized and
concentrated, still maintained some inverse proportion to
the magnitude of this planet, though magnificent and
sublime, enabled to confirm some discovered of former
observers, and to confute those of others. The existence of
volcanoes discovered by his father and by Schroeter of
Berlin, and the changes observed by the latter in the
volcano in the Mare Chrisium of Lucid Lake, were
corroborated and illustrated, as was also the prevalence of
far more extensive volcanic phenomena. The disproportionate
height attributed to the lunar mountains was corrected from
careful admeasurement; whilst the celebrated conical hills,
encircling valleys of vast diameter, and surrounding the
lofty central hills, were distinctly perceived. The
formation which Professor Frauenhofer uncharitably
conjectured to be lunar fortifications, he ascertained to be
a tubular buttress of a remarkably pyramidical mountain;
line which had been whimsically pronounced roads and canals,
he found to be keen ridges of singularly regular rows of
hills; and that which Schroeter imagined to be a great city
in the neighborhood of Marius, he determined to be a valley
of disjointed rocks scattered in fragments, which averaged
al least a thousand yards in diameter.
Thus the general geography of the planet, in its grand
outlines of cape, continent, mountain, ocean, and island,
was surveyed with greater particularity and accuracy than by
any previous observer; and the striking dissimilarity of
many of its local features to any existing on our own globe,
was clearly demonstrated. The best enlarged maps of that
luminary which have been published were constructed from
this survey; and neither the astronomer nor the public
ventured to hope for any greater accession to their
developments. The utmost power of the largest telescope in
the world had been exerted in a new and felicitous manner to
obtain them, and there was no reasonable expectation that a
larger one would ever be constructed, or that it could be
advantageously used if it were. A law of nature, and the
finitude of human skill, seemed united in inflexible
opposition to any further improvement in telescopic science,
as applicable to the known planets and satellites of the
solar system. For unless the sun could be prevailed upon to
extend a more liberal allowance of light to these bodies,
and they be induced to transfer it, for the generous
gratification of our curiosity, what adequate substitute
could be obtained? Telescopes do not create light, they
cannot even transmit unimpaired that which they receive.
That anything further could be derived from human skill in
the construction of instruments, the labors of his
illustrious predecessors, and his own, left the son of
Herschel no reason to hope. Huygens, Fontana, Gregory,
Newton, Hadley, Bird, Short, Dolland, Herschel, and many
others, all practical opticians, had resorted to every
material in any wise adapted to the composition either of
lenses or reflectors, and had exhausted every law of vision
which study had developed and demonstrated. In the
construction of his last amazing specula. Sir John Herschel
had selected the most approved amalgams that the advanced
stage of metallic chemistry had combined; and had watched
their growing brightness under the hands of the artificer
with more anxious hope than ever lover watched the eye of
his mistress; and he had nothing further to expect than they
had accomplished. He had the satisfaction to know that if
he could leap astride a cannon ball, and travel upon its
wings of fury for the respectable period of several millions
of years, he would not obtain a more enlarged view of the
distant stars than he could now possess in a few minutes of
time; and that it would require an ultra-railroad speed of
fifty miles and hour, for nearly the live-long year, to
secure him a more favorable inspection of the gentle
luminary of night.
The interesting question, however, whether this light
of the solemn forest, of the treeless desert, and of the
deep blue ocean as it rolls; whether this object of the
lonely turret, of the uplifted eye on the deserted
battle-field, and all of the pilgrims of love and hope, of
misery and despair, that have journeyed over the hills and
valleys of this earth, through all the eras of its unwritten
history to those of its present voluminous record; the
exciting question, whether this "observed" of all the sons
of men, from the days of Eden to those of Edinburgh, be
inhabited by beings like ourselves, of consciousness and
curiosity, was left for solution to the benevolent index of
natural analogy, or to the severe tradition that it is
tenanted only by the hoary solitaire whom the criminal code
of the nursery had banished thither for collecting fuel on
the Sabbath-day.
The limits of discovery in the planetary bodies, and in
this one especially, thus seemed to be immutably fixed; and
no expectation was elevated for a period of several years.
But, about three years ago, in the course of a
conversational discussion with Sir David Brewster upon the
merits of some ingenious suggestions by the latter, in his
article on optics in the Edinburgh Encyclopedia (p. 644),
for improvements in the Newtonian Reflectors, Sir John
Herschel adverted to the convenient simplicity of the old
astronomical telescopes that were without tubes, and the
object-glass of which, placed upon a high pole, three its
focal image to a distance of 150, and even 200 feet. Dr.
Brewster readily admitted that a tube was not necessary,
provided the focal image were conveyed into a dark
apartment, and there properly received by reflectors. Sir
John then said that, if his father's great telescope, the
tube alone of which, though former of the lightest suitable
materials, weighed 3,000 pounds, possessed an easy and
steady mobility with its heavy observatory attached, an
observatory moveable without the incumbrance of such a tube,
was obviously practical. This also was admitted, and the
conversation became directed to that all-invincible enemy.
The paucity of light in powerful magnifiers.
After a few moments silent thought, Sir John
diffidently inquired whether it would not be possible to
effect a transfusion of artificial light through the focal
object of vision! Sir David somewhat startled at the
originality of the idea, paused awhile, and then
hesitatingly referred to the refrangibility of rays, and the
angle of incidence. Sir John, grown more confident, adduced
the example of the Newtonian Reflector, in which the
refrangibility was corrected by the second speculum, and the
angle of incidence restored by the third. And," continued
he, "why cannot the illuminated microscope, say the
hydro-oxygen, be applied to render distinct, and, if
necessary, even to magnify the focal object?" Sir David
sprang from his chair in the ecstasy of conviction, and
leaping half-way to the ceiling, exclaimed, "Thou art the
man!" Each philosopher anticipated the other in
presenting the prompt illustration that if the rays of the
hydro-oxygen microscope, passed through a drop of water
containing the larvae of a gnat and other objects invisible
to the naked eye, rendered them not only keenly but firmly
magnified to dimensions of many feet; so could the same
artificial light, passed through the faintest focal object
of a telescope, both distinctify (to coin a new word for an
extraordinary occasion) and magnify its feeblest component
members. The only apparent desideratum was a recipient for
the focal image which should transfer it, without refranging
it, to the surface on which it was to be viewed under the
revivifying light of the microscopic reflectors. In the
various experiments made during the few following weeks, the
co-operative philosophers decided that a medium of the
purest plate glass (which it is said they obtained, by
consent, be it observed, from the shop window of Mons.
Desanges, the jeweller to his ex-majesty Charles X, in High
street) was the most eligible they could discover. It
answered perfectly with a telescope which magnified 100
times, and a microscope of about thrice that power.
Sir John Herschel then conceived the stupendous facric
of his present telescope. The power of his father's
instrument would still leave his distant from his favorite
planet nearly forty miles, and he resolved to attempt a
greater magnifier. Money, the wings of science as the
sinews of war, seemed the only requisite, and even the
acquisition of this, which is often more difficult than the
task of Sisyphus, he determined to achieve. Fully
sanctioned by the high optical authority of Sir David
Brewster, he laid his plan before the Royal Society, and
particularly directed it to the attention of His Royal
Highness the Duke of Sussex, the ever munificent patron of
science and the arts. It was immediately nd
enthusiastically approved by the committee chosen to
investigate it, and the chairman, who was the Royal
President, subscribed his name for a contribution of
œ10,000, with a promise that he would zealously submit the
proposed instrument as a fit object for the patronage of the
privy purse. He did so without delay, and his Majesty, on
being informed that the estimated cost was œ70,000, naively
inquired if the costly instrument would conduce to any
improvement in navigation? On being informed that it
undoubtedly would, the sailor King promised a carte blanche
for the amount which might be required.
Sir John Herschel had submitted his plans and
calculations in adaptation to an object-glass of twenty-four
feet in diameter: just six times the size of his venerable
father's. For casting this ponderous mass, he selected the
large glass-house of Messrs. Hartly and Grant, (the brother
of our invaluable friend Dr. Grant) at Dumbarton. The
material chosen was an amalgamation of two parts of the best
crown with one of flint glass, the use of which, in separate
lenses, constituted the great achromatic discovery of
Dolland. It had been found, however, by accurate
experiments, that the amalgam would as completely triumph
over every impediment, both from refrangibility and
discoloration, as the separate lenses. Five furnaces of the
metal, carefully collected from productions of the
manufactory, in both the kinds of glass, and known to be
respectively of nearly perfect homogenous quality, were
united, by one grand conductor, to the mould; and on the
third of January, 1833, the first cast was effected. After
cooling eight days, the mould was opened,a nd the glass
found to be greatly flawed within eighteen inches of the
centre. Nothwithstanding this failure, a new glass was more
carefully cast on the 27th of the same month, which upon
being opened during the first week of February, was found to
be immaculately perfect, with the exception of two slight
flaws so near the line of its circumference that they would
be covered by the copper ring in which it was designed to be
enclosed.
The weight of this ponderous lens was 14,826 lbs. or
nearly seven tons after being polished; and its estimated
magnifying power 42,000 times. It was therefore presumed ot
be capable of representing objects in our lunar satellite of
little more than eighteen inches in diameter, providing its
focal image of them could be rendered distinct by the
transfusion of article light. It was not, however, upon the
mere illuminating power of the hydro-oxygen microscope, as
applied to the focal pictures of this lens, that the younger
Herschel depended for the realization of his ambitious
theories and hopes. He calculated largely upon the almost
unlimited applicability of this instrument as a second
magnifier, which would supersede the use, and infinitely
transcend the powers of the highest magnifiers in reflecting
telescopes.
So sanguinely indeed did he calculate upon the
advantages of this splendid alliance, that he expressed
confidence in his ultimate ability to study even the
entomology of the moon, in case she contained insects upon
her surface. Having witnessed the completion of this great
lens, and its safe transportation to the metropolis, his
next care was the construction of a suitable microscope, and
of the mechanical frame-work for the horizontal and vertical
action of the whole. His plans in every branch of his
undertaking having been intensely studied, even to their
minutest details, were easily nd rapidly executed. He
awaited only the appointed period at which he was to convey
his magnificent apparatus to its destination.
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