By W. F. DENNING, F.R.A.S.
The year 1781 was signalized by an astronomical discovery of great
importance, and one which marked the epoch as memorable in the annals
of science. A musician at Bath, William Herschel by name, who had been
constructing some excellent telescopes and making a systematic survey of
the heavens, observed an object on the night of March 13 of that year,
which ultimately proved to be a large planet revolving in an orbit
exterior to that of Saturn. The discovery was as unique as it was
significant. Only five planets, in addition to the Earth, had hitherto
been known; they were observed by the ancients, and by each succeeding
generation, but now a new light burst upon men. The genius of Herschel
had singled out from the host of stars which his telescope revealed
an object the true character of which had evaded human perception for
thousands of years!
[Illustration: FIG. 1.--APPROXIMATE PLACE OF URANUS AMONGST THE STARS AT
ITS DISCOVERY ON MARCH 13, 1781]
The centenary of this remarkable advance in knowledge naturally recalls
to mind the circumstances of the discovery, and makes us inquisitive to
know what new facts have been gleaned of Herschel's planet, now that
a hundred years have passed away, and we are enabled to look back and
review the vast amount of labor which has been accomplished in this wide
and attractive field of astronomical research. We may learn what new
features have been discerned of the new body, and what additional
discoveries in connection with other planets unknown in Herschel's day,
have been effected by aid of the powerful telescopes which have been
devoted to the work. We do not, however, intend dealing with the general
question of planetary discovery, for at a glance we are impressed with
its magnitude. While a century ago five planets only were known, we now
have some two hundred and thirty of these bodies, and the stream of
discovery flows on without abatement through each succeeding year. The
detection of Uranus seems, indeed, to have been the prelude to many
similar discoveries, and to have offered the incentive to greater
diligence and energy on the part of observers in various parts of the
world.
[Illustration: Fig. 2.--ORBITS OF THE URANIAN SATELLITES.]
Many great discoveries have resulted from accident; and the leading
facts attending that of Uranus prove that, in a large measure, the
result was brought about in a similar way. Herschel, as he unwearyingly
swept the heavens night after night, was in quest of sidereal
wonders--such as double stars and nebulae--and he happened to alight
upon the new planet in a purely chance way. He had no expectation of
finding such a remarkable object, and indeed, when he had found it,
wholly mistook its character. There could be no doubt that it was a body
wholly dissimilar to the fixed stars, and it was equally certain that it
could not be a nebula. It had a perceptible disk, for when it had first
come under the critical eye of its discoverer he had noticed immediately
that its appearance differed widely from the multitude of objects which
crossed the field of his telescope. He had been accustomed to see hosts
of stars pass in review, and their aspect was in one respect similar,
namely, they were invariably presented as points of light incapable of
being sensibly magnified, even with the highest powers. True, there was
a great variety of apparent brightness in these objects and a singular
diversity of configuration, but there was no exception to the invariable
feature referred to. The point of light was constant, and no striking
exception was anticipated until one night--March 13, 1781--Herschel
being intently engaged in the examination of some small stars in the
region of Gemini, brought an object under the range of, his telescope,
which his eye at once selected as one of anomalous character.
Applying a higher power, he noticed that it exhibited a planetary disk,
but his instrument failed to define it with sufficient distinctness, and
hence he became doubtful as to its real nature. The object was found to
be in motion, and subsequent observations led him to the assumption that
it must be a comet of rather exceptional type. This appeared to be the
best explanation of the strange body, for history contained many records
of curious comets, some of which were observed as nearly circular
patches of nebulous light, and probably of similar aspect to the object
then visible; and apart from this it must be remembered that the idea of
a large planet exterior to Saturn was a fact of such momentous import
that Herschel, with a due regard to that modesty which accompanies
true genius, refrained from attaching such an interpretation to his
observations. He was content to direct the notice of astronomers to it
as a phenomenon requiring close attention, and suggested that it might
be a comet in consequence of its motion and the faint and somewhat
ill-defined character of its appearance.
From the earliest ages five planets only were known, and the discovery
of another large planet beyond the sphere of Saturn must at once
revolutionize existing ideas as to the range of the solar system, and
immediately take rank as a scientific event of equal interest to the
discovery of the moons of Jupiter or the rings of Saturn, which each in
their day impressed men with new ideas of the celestial mechanism. But
the truth could not long be delayed. The new body being watched and its
orbit rigorously computed from a series of observed positions revealed
its true character, and Herschel was awarded the honor due to the author
of a discovery of such importance. His diligence and pertinacity alone
had enabled him to search out from among the multitude of stars thickly
strewn over the firmament this unknown and well-nigh invisible planet
which, during all the preceding years of the world's history, had eluded
human perception. Men had been all unconscious of its existence as it
had been slowly completing its circuits around the sun, obedient to the
same laws as the other planets of the solar system, and awaiting the
hour when the unfailing eve of Herschel should introduce it as the faint
and far-off planet girding our system within its expansive folds.
As soon as the existence of the new orb was confirmed and the fact
rendered indisputable, the question naturally arose whether it had ever
been seen in former years by the authors of star catalogues, who could
hardly have overlooked an object like this though its planetary nature
had manifestly escaped detection. It was just perceptible to the naked
eye, shining like a star of the sixth magnitude, and ought to have been
distinguished by those who had reviewed the heavens with the purpose
of determining and mapping the positions of the stars. Reference was,
therefore, made to the chief catalogues, when it was found at once that
the planet had been unquestionably observed by Tobias Mayer, Le Monnier,
Bradley, and Flamsteed. It was several times noted by these observers:
by Le Monnier no less than twelve times, and by Flamsteed on six
occasions; and it is remarkable that in every instance its true
character escaped detection. Neither its special appearance nor its
motion attracted attention, so that it was merely catalogued as an
ordinary fixed star. Thus Herschel was not anticipated in his discovery.
It remained for him, in 1781, to note its exceptional aspect, and to
specify it as an object requiring critical investigation. But the early
observations above alluded to served a useful purpose in testing the
accuracy of the computed orbit, for without waiting many years to
compare the theoretical and observed positions, astronomers had in these
old records a reliable series of points through which the previous
course of the planet could be traced.
The calculations showed that its mean distance from the sun was some
1,750,000,000 miles, and that a revolution was completed in about
eighty-four years. It was also found to be a very large planet, greatly
exceeding either Mercury, Venus, the Earth, or Mars, though considerably
inferior to either Jupiter or Saturn.
Here, then, was a discovery of the utmost importance, and one of the
most salient additions to our knowledge which the telescope had ever
achieved. The new planet was now definitely assigned its proper place in
the solar system, and was regarded as of equal significance with the
old planets. True, the new planet of Herschel could not be compared as
regards its visible aspect with the other previously known members of
our system, but it was nevertheless an object of equal weight. Its vast
distance alone rendered it faint. It formed one of the constituent parts
of the solar system, which, though separated by immense intervals of
space, are yet coherent by the far-reaching effects of gravitation.
There is, indeed, a bond of harmony between the series of planetary
orbits, which exhibit a marked degree of regularity in their successive
distances from the sun; and though they are not connected by any visible
links, they are firmly held together by unseen influences, and their
motions are subject to certain laws which have been revealed by
centuries of observation.
The question of suitably naming the new planet soon came to the fore.
Herschel himself proposed to designate it the "Georgium Sidus," in honor
of his patron, George III., just as Galileo had called the satellites
of Jupiter the "Medicean stars," after Cosmo de' Medici. But La Place
proposed that the planet should be named after its discoverer; and thus
it was frequently referred to as "Herschel," and sometimes as "The
Herschelian planet." Astronomers on the continent objected to this
system of personal nomenclature, and argued that the new body should
receive an appellative in accordance with those adopted for the old
planets, which had been selected from the heathen mythology. Several
names were suggested as suitable (on the basis of this principle), and
ultimately the one advanced by Bode received the most favor, and the
planet thereafter was called "Uranus."
The varying positions of the new body as observed on successive nights
were determined by comparisons with a group of six small stars, termed
by Herschel [Greek: alpha, beta, gamma, delta, epsilon] and afterwards
formed into a constellation under the designation of "Britannia," though
it does not appear that this little asterism is acknowledged as one of
our constellations. Its position is about midway between Taurus and
Gemini, and the following are the principal stars computed for 1881.0,
as given by Mr. Marth:
Star. Magnitude. Right Ascension. Declination.
h. m. s.
alpha 9.0 5 42 6.06 23° 35' 6.7" N.
eta 8.7 5 43 17.82 23 26' 7.2 N.
theta 8.8 5 44 0.99 23 53' 30.8 N.
epsilon 8.8 5 45 40.68 23 34' 46.8 N.
The stars are therefore merely telescopic, and are confined to a small
area of space, so that the propriety of adopting the group as a distinct
constellation is very questionable. Their positions close to Uranus at
the time of its discovery, and the fact that the planet's motion was
detected by means of comparisons with them, has given to these stars an
historical interest which in future years must often attract the student
to their reobservation. But it would be unwise, as forming a bad
precedent, to accept a group of stars of this inferior type as meriting
to rank among the old constellations, when we have numbers of richer
groups, situated on their confines, which first deserve such a
distinction. However special or unique the circumstances connected with
certain telescopic stars may be, and however necessary it may appear
to signalize them by a specific title, we are inclined to question the
adoption of such means as likely to exercise a wrong influence,
inasmuch as it may hereafter originate further innovations of a similar
character, and ultimate complications will be certain to arise.
Soon after the discovery of Uranus it was suspected that the planet
was encircled, like Saturn, by a luminous ring, but on subsequent
observation this was not confirmed, and no such appendage has ever been
revealed in the more perfected instruments of our own times. Indeed, if
Uranus displays a peculiarity of constitution in any way analogous to
the ring system of Saturn, it must be of the most minute character so as
to have thus evaded telescopic scrutiny during a hundred years.
The discovery soon attracted the notice of royalty, and the reigning
sovereign, George III., anxious to practically express his appreciation
of the valuable labors of Herschel, awarded him a pension of £200 a year
and furnished him with a residence at Slough, near Windsor, and the
means to erect a gigantic telescope with which he might be enabled
to continue his important researches. This instrument consisted of a
reflector on the "Front-view" construction, with a speculum 4 feet in
diameter and of 40 feet focal length. Upon its completion, Herschel
immediately began to observe the region of the new planet with the idea
of discovering any satellites which might belong to it, for analogy
suggested that it was surrounded by a numerous retinue of such bodies.
He was soon successful, for, on the night of January 11, 1787. he saw
two minute objects near the planet, which renewed observations revealed
to be satellites; and he detected two additional ones in 1790, and two
others in 1794, making six in all. But the observations were of extreme
difficulty. The path of the planet frequently passed near minute stars,
and it became hard to distinguish between them and the suspected
satellites. Herschel, however, considered he had obtained conclusive
evidence of the existence of six satellites with sidereal periods
ranging from 5d. 21h. 25m. to 107d. 16h. 39m., and his means of
observation being much superior to those possessed by any of his
contemporaries it was impossible to have corroborative testimony.
The matter was thus allowed to rest until the middle of the present
century, when Lassell, in the pure sky at Malta, endeavored to reobserve
the satellites with a two-foot reflector. This instrument was considered
superior to Herschel's telescope; and the atmosphere at this station
being decidedly more suitable for such delicate observations than
in England, it was removed there for the express purpose of dealing
successfully with objects of extreme difficulty. The results were very
important. Mr. Lassell became convinced that Uranus had only four
satellites, and that if any others existed they remained to be
discovered. Two of these were found to be identical with those seen by
Herschel in 1787, and now called Titania and Oberon. The other two,
Ariel and Umbriel, could not be identified with any of those alleged to
have been previously detected by Herschel, so that the inference was
that they were new bodies, and that the priority of discovery was due to
Mr. Lassell; whence it also followed that the older observations were
erroneous, and that in fact Herschel had been entirely mistaken with
regard to the four satellites he believed he had detected subsequently
to 1787.
In November, 1873, a fine twenty-six-inch object glass, by Alvan Clark,
was mounted at the U. S. Naval Observatory at Washington, and it was
soon employed upon the difficult task of solving the problem as to the
exact periods of the Uranian satellites. This was very satisfactorily
effected, and with distinct and conclusive favor to Mr. Lassell, whose
observations were fully corroborated. Only four satellites could be
distinguished by the American observers, and their periods, as computed
from a valuable series of measures, agreed with those previously derived
at Malta. In Appendix I. to the "Washington Observations" for 1873,
Prof. Newcomb gave a valuable summary of results--the first obtained, be
it noted, with that splendid instrument which soon afterward, in 1877,
revealed the satellites of Mars--which included the elements of the
satellites of Uranus as follows:
Mean Longitude.
Satellite. Epoch 1871. Radius of Period of
Dec. 31, W.M.T. Orbit. Revolution in days.
I. Ariel........ 21.83° 13.78" 2.52038
II. Umbriel..... 13.52 19.20 4.14418
III. Titania..... 229.93 31.48 7.70590
IV. Oberon...... 154.83 42.10 13.43327
Speaking of the comparative brightness of the satellites, Prof. Newcomb
says:
"The greater proximity of the inner satellites to the planet makes it
difficult to compare them photometrically with the outer ones, as actual
feebleness of light cannot be distinguished from difficulty of seeing
arising from the proximity of the planet. However, that Umbriel is
intrinsically fainter than Titania is evinced by the fact that, although
the least distance of the latter is somewhat less than the greatest
distance of the former, there is never any difficulty in seeing it in
that position. From their relative aspects in these respective positions
I judge Umbriel to be about half as bright as Titania. Ariel must be
brighter than Umbriel, because I have never seen the latter unless it
was farther from the planet than the former at its maximum distance....
I think I may say with considerable certainty that there is no satellite
within 2' of the planet, and outside of Oberon, having one-third the
brilliancy of the latter, and therefore that none of Sir William
Herschel's supposed outer satellites can have any real existence. The
distances of the four known satellites increase in so regular a way that
it can hardly be supposed that any others exist between them. Of what
may be inside of Ariel it is impossible to speak with certainty, since
in the state of atmosphere which prevails during our winter all the
satellites named disappear at 10" from the planet."
Prof. Newcomb mentions that no systematic search for new satellites
was undertaken because it must have interfered with the fullness and
accuracy of the micrometer measures of the old satellites, which
constituted the main purpose of the observations. Some faint objects
were occasionally glimpsed near the planet, and their relative places
determined, but they were never found to accompany Uranus. The fact,
therefore, that no additional satellites were discovered is not to
be regarded as a strong point in favor of the theory of their
non-existence, because the great power and excellence of the telescope
was expressly directed to the attainment of other ends; and moreover the
season in which the planet came to opposition was distinctly unfavorable
for the prosecution of a rigorous search for new satellites. There
can, however, be no doubt that the analogies of the planetary systems
interior to Uranus plainly suggest that this planet is attended by
several satellites which the power of our greatest telescopes has
hitherto failed to reveal; and that it is in this direction and that of
Neptune we may anticipate further discoveries in future years when the
conditions are more auspicious and the work is entered upon with special
energy, aided by instruments of even greater capacity than those which
have already so far conduced to our knowledge of the heavenly bodies.
Notwithstanding the extreme difficulty with which the Uranian satellites
are observed, the two brighter ones, Titania and Oberon, discovered by
William Herschel in 1787, have been occasionally detected in telescopes
of moderate power, and identified by means of an ephemeris which has
shown that the computed positions approximately agree with those
observed. During the last few years Mr. Marth has published ephemerides
of the satellites of both Saturn and Uranus, and many amateurs have to
acknowledge the valuable aid rendered by these tables, which supply a
ready means of identifying the satellites, and thus act as an incentive
to observers who are induced to pursue such work for the sake of the
interesting comparisons to be made afterward. In one exceptional
instance the two outer satellites of Uranus appear to have been glimpsed
with an object glass of only 43 inches aperture, and the facts are given
in detail in the "Monthly Notices of the R.A.S.," April 1876, pp. 294-6.
The observations were made in January, February, and March, 1876, by
Mr. J.W. Ward, of Belfast; and the positions of the satellites, as he
estimated them on several nights, are compared with those computed, the
two sets presenting tolerably good agreement. Indeed the corroborations
are such as to almost wholly negative any skepticism, though such
extraordinary feats should always be received with caution.
In this particular case the chances of being misled are manifold; even
Herschel himself fell into error in taking minute stars to be satellites
and actually calculating their periods; so that when we remember the
difficulties of the question our doubts are not altogether dispelled.
Extreme acuteness of vision will, in individual instances, lead to
success of abnormal character, and certainly in Mr. Ward's case the
remarkable accordances in the observed and calculated positions appear
to be conclusive evidence that he was not mistaken.
It will be readily inferred that the great distance and consequent
feebleness of Uranus must render any markings upon the disk of the
planet beyond the reach of our best telescopes; and indeed this appears
to have been a matter of common experience. Though the surface has been
often scanned for traces of spots, we seldom find mention that any have
been distinguished. Consequently the period of rotation has yet to be
determined. It is true that an approximate value was assigned by Mr.
T.H. Buffham from observations with a nine-inch reflector in 1870 and
1872. but the materials on which the computation was based were slender
and necessarily somewhat uncertain, so that his period of about twelve
hours stands greatly in need of confirmation. The bright spots and zones
seen on the disk in the years mentioned appear to have entirely eluded
other observers, though they are probably phenomena of permanent
character and within reach of instruments of moderate size. Mr. Buffham
[1] thus describes them:
[Footnote 1: "Monthly Notices K. A. S.," January, 1873.]
"1870, Jan. 25, 11h. to 12h. in clear and tolerably steady air; power
132 showed that the disk was not uniform. With powers 202 and 3.0, two
round, bright spots were perceived, not quite crossing the center but a
little nearer to the eastern side of the planet, the position angle of a
line passing through their centers being about 20° and 200--ellipticity
of Uranus seemed obvious, the major axis lying parallel to the line of
the spots.
"Jan. 27, 10h. to 10½h.; some fog, and definition not good, but the
appearance of the spots was almost exactly the same as on the 25th."
On March 19 glimpses were obtained of a light streak and two spots.
On April 1, 4, 6, and 8, a luminous zone was seen on the disk, and
in February and March, 1872, when observations were resumed, certain
regions were noted brighter than others, and underwent changes
indicating the rotation of the planet in a similar direction to that
derived from the results obtained in 1870. Mr. Buffham points out that,
if this is admitted, then the plane of the planet's equator is not
coincident with the plane of the orbits of the satellites. Nor need we
be surprised at this departure from the general rule, where such an
anomalous inclination exists. In singular confirmation of this is Mr.
Lassell's observation of 1862, Jan. 29, where he says: "I received an
impression which I am unable to render certain of an equatorial dark
belt, and of an ellipticity of form."
Some observations made in 1872-3 with the great six-foot reflector of
Lord Rosse may here be briefly referred to. A number of measures, both
of position and distance, of Oberon and Titania, were made, [1] and a
few of Umbriel and Ariel, but "the shortness of the time available (40
minutes) each night for the observation of the planet with the six-foot
instrument, the atmospheric disturbance, so often a source of annoyance
in using so large an aperture, and other unfavorable circumstances,
tended to affect the value of the observations, and to make the two
inner satellites rarely within detection."
[Footnote 1: "Monthly Notices R. A. S.," March, 1875.]
On Feb. 10, 1872, Lord Rosse notes that all four satellites were seen on
the same side of the planet. On Jan. 16, 1873, when definition was good,
no traces of any markings were seen. Diameter of Uranus = 5.29". Power
414 was usually employed, though at times the inner satellites could be
more satisfactorily seen with 625.
It may be mentioned as an interesting point that, some fifty years
after the first discovery of Uranus by Herschel, it was accidentally
rediscovered by his son, Sir John Herschel, who recognized it by
its disk, and had no idea as to the identity of the object until an
ephemeris was referred to. Sir John mentions the fact as follows, in a
letter to Admiral Smyth, written in 1830, August 8:
"I have just completed two twenty-foot reflectors, and have got some
interesting observations of the satellites of Uranus. The first sweep
I made with my new mirror I _re-discovered_ this planet by its _disk_,
having blundered upon it by the merest accident for 19 Capricorni."
In commenting upon the centenary of an important scientific discovery we
are naturally attracted to inquire what progress has been made in the
same field during the comparatively short interval of one hundred years
which has elapsed since it occurred. We have called it a short interval,
because it cannot be considered otherwise from an astronomical or
geological point of view, though, as far as human life is concerned,
it can only be regarded as a very lengthy period, including several
generations within its limits.
Since Herschel, in 1781, discovered Uranus, astronomy has progressed
with great rapidity, so that it would be impossible to enumerate in a
brief memoir the many additional discoveries which have resulted from
assiduous observation. A century ago only five planets were known
(excluding the Earth), now we are acquainted with about two hundred and
thirty of these bodies; and one of these, found in 1846, is a large
planet whose orbit lies exterior to that of Uranus. In fact, the state
of astronomical knowledge a century ago has undergone wonderful changes.
It has been rendered far more complete and comprehensive by the
diligence of its adherents and by the unwearying energy with which both
in theory and practice it has been pursued. A zone of small planets has
been discovered between Mars and Jupiter just where the analogies of the
planetary distances indicated the probable existence of a large planet.
The far-off Neptune was revealed in 1846 by a process of analytical
reasoning as unique as it was triumphant, and which proved how well
the theory of planetary perturbations was understood. The planet was
discovered by calculation, its position in the heavens assigned, and the
telescope was then employed merely as the instrument of its detection.
The number of satellites which a century ago numbered only ten has now
reached twenty, and the discovery in 1877 of two moons accompanying Mars
shows that the work is being continued with marked success.
In other departments we also find similar evidence of increasing
knowledge. The periodicity of the sun spots, the existence of systems of
binary stars, meteor showers, and their affinity with cometary orbits
may be mentioned as among the more important, while a host of new
comets, chiefly telescopic, have been detected. Large numbers of nebulæ
and double stars have been catalogued, and we have evidence every year
of the activity with which these several branches are being followed up.
In fine, it matters little to what particular department of astronomical
investigation we look for traces of advancement during the past hundred
years, for it is evident throughout them all, and sufficiently proves
that the interest formerly taken in the science has not only been well
sustained but has become more general and popular, and is extending its
attractive features to all classes of the community.
In Herschel's day large telescopes were rare. A man devoting himself to
the study of the heavenly bodies as a means of intellectual recreation
was considered a phenomenon, and indeed that appellation might be
fittingly applied to the few isolated individuals who really occupied
themselves in such work. How different is the case now that the pleasant
ways of science have called so many to her side and so far perfected her
means of research as to make them accessible to all who care to see and
investigate for themselves the unique and wonderful truths so easily
within reach! Large telescopes have become common enough, and there is
no lack of hands and eyes to utilize them, nor of understanding, ever
ready to appreciate, in sincerity and humbleness, those objects which
display in an eminent degree the all-wise conceptions of a great
Creator! It is, therefore, a most gratifying sign to notice this rapid
development of astronomy, and to see year by year the increasing number
of its advocates and the record of many new facts gleaned by vigorous
observation.
The character of recent discoveries distinctly intimates that, in future
years, some departments of the science will become very complicated,
owing to the necessity of dealing with a large number of minute bodies,
for the tendency of modern researches has been to reveal objects which
by their faintness had hitherto eluded detection. And when we consider
that these bodies are rapidly increasing year by year, the idea is
obviously suggested that, inasmuch as their numbers are comparatively
illimitable, and there is likely to be no immediate abatement in the
enthusiasm of observers, difficulties will arise in identifying them
apart and forming them into catalogues with their orbital elements
attached, so that the individual members may be redetected at any time.
In this connection we allude particularly to minor planets, to
telescopic comets, and to meteoric streams, which severally form a very
numerous group of bodies of which the known members are accumulating to
a great extent. As complications arise, some remedies must be applied to
their solution, and one probable effect will be that astronomers will be
induced each one to have a specialty or branch to which his energies are
mainly directed. The science will become so wide in its application and
so intricate in its details that it will become more than ever necessary
for observers to select or single out definite lines of investigation
and pursue them closely, for success is far more likely to attend such
exertions than those which are not devoted to any special end, but
employed rather in a general survey of phenomena.
We have already before us some excellent instances in which individual
energies have been aptly utilized in the prosecution of original work
in some specific branch of astronomy, and we are strongly disposed to
recommend such exclusive labors to those who have the means and the
desire to achieve something useful. Observers who find one subject
monotonous and then take up another for the sake of variation are not
likely to get far advanced in either. In the case of amateurs who use a
telescope merely for amusement, and indiscriminately apply it to nearly
every conspicuous object in the firmament without any particular purpose
other than to satisfy their curiosity, the matter is somewhat different,
and our remarks are not applicable to them. We refer more pointedly
to those who have a regard for the interests of the science and whose
enthusiasm enables them to work habitually and with some pertinacity.
History tells us that the Great Alexander wept when he found he had no
other worlds to conquer, and we fear that some astronomers will lament
that they have little prospect of discovering anything fresh in a sphere
to which our giant telescopes have been so often directed, but this is
founded on a palpable misconception. Certain objects, such as comets for
example, do not require great power, and the revelation of new meteor
showers is entirely a question for the naked eye. In fact, it may be
confidently asserted that observations undertaken with energy and
persistency will, if rightly directed, more than compensate for defects
of instrumental power.
It is true, however, that in certain quarters we must look to large
instruments alone for new discoveries. It would be useless searching for
an ultra-Neptunian planet, or for additional satellites to Uranus or
Neptune, or for the materials to determine the rotation periods of these
planets with a small telescope. Every observer will find objects suited
to the capacity of his instrument, and he may not only employ it
usefully but possibly make a discovery of nearly equal import with that
which rendered the name of Herschel famous a century ago.--_Popular
Science Review_.
* * * * *
THE VARYING SUSCEPTIBILITY OF PLANTS AND ANIMALS TO POISONS AND
DISEASES.
Much attention is being devoted to the causes which determine the
aptitude or immunity with animals for maladies. This is in a general
sense called medical geography, as a physician who has prescribed for
patients in various parts of the world, and belonging to different
races--the white, yellow, and black--has been able to note the
diversities in the same disease, and the contradictions in the remedies
employed.
The true social peril, hardly discovered before we became aware how
to conjure it, lies in those legions of animalcules or microbes that
surround us and in the middle of which we live. M. Pasteur has revealed
them to us as the factors in infectious diseases. Claude Bernard
has demonstrated the community which exists between animals and
vegetables--phenomena of movement, of sensibility, of production of
heat, of respiration, of digestion even, for there are the _Drosera_ and
kindred carnivorous plants. Iron cures chlorosis in vegetables as well
as in animals, and chloroform and ether render both insensible. There
resemblances are more striking still between animals. After Baudrimont,
insects are, in presence of alcohols, chloroform, and irrespirable
gases, similarly affected as man. Many maladies, too, are common to
man and several species of animals; and this organic identity is best
illustrated in the relationship between epidemics and epizootias,
cancer, asthma, phthisis, smallpox, rabies, glanders, charbon, etc.,
afflict alike man and many species of animals.
The differences between races are not less remarkable--odor and taste,
for example. According to anthropophagy, negroes are best, and white
people most detestable. Broca remarked, that, in the dissecting room,
the muscles of the negro putrefied less rapidly than those of whites. It
is perhaps to these anatomical differences that the diverse action of
the same poison, in the case of races or species, may be attributed. On
certain rodentia belladonna exercises no influence; morphine for a horse
is a violent stimulant; a snail remains insensible to digitalis; goats
eat tobacco with impunity; and in the Tarentin the inhabitants rear only
black sheep, because a plant abounds which is noxious for white sheep.
The nature of these conditions is a mystery for science. The _Solanæ_
tribe of plants furnish a principle which, as its name implies, produces
consolation or forgetfulness, by acting on the tissues of the brain
where resides the organ of thought; now, on the authority of Professor
Bouchardat, these opiates have the less of effect in proportion as the
animals possess the less of intelligence.
To the same anatomical peculiarities must be ascribed the choice that
disease makes in such or such a race. Glanders, for instance, so
virulent with the horse, the ass, and man, produce in the case of the
dog only a local accident; peripneumonia, so contagious among horned
cattle, is more benign in its action on Dutch than other breeds of
stock; the cattle plague that decimates so many farms is communicated by
cattle to each other from the slightest contact, while the closest and
most constant association is necessary to communicate the disease
to sheep, and even when they are affected its action is not severe.
Further, that plague only attacks ruminant animals--oxen, goats, sheep,
zebras, gazelles, etc. Ten years ago this plague broke out in the Jardin
d'Acclimatation; not a ruminant escaped, and also one animal not of that
class, a little tenant nearly related to the pig--the _peccari_.
Now, Dr. Condereau has demonstrated recently that the stomach of the pig
has a rudimentary organization recalling that of the ruminants. Clearly,
the stomach of the peccari, and perhaps that of the pig, present a
favorable medium for the parasitical microbe peculiar to the rinderpest.
In the potato disease, again, all the varieties are not affected with
the same degree of violence; it is more marked in its action on the
round yellows than the reds, and on the latter rather than the pink. But
the symptoms even of the same malady differ, the parasite's attacks on
the tissues being dissimilar. Oak galls are produced from the prickings
of insects; now around the same larva often four varieties of galls are
recognized. In the case of consumption in cattle, the disease marches
slowly; in that of pigs it takes the galloping form, as with man.
Each people or nation has its peculiar pathology and also its peculiar
cures. A negro can take a dose of tartar ten times more excessive than a
white; the same dose of brandy given to a black, a yellow, and a white,
will not produce on the three men either drunkenness at the same moment,
or intoxication at all. Mulattoes can sustain more drastic aperients
than other races; the negro does not suffer from yellow fever, but he
readily falls to phthisis; he will catch the cholera more quickly than a
white. Human races, where they may catch the same intermittent fever at
the identical moment and in the same swamp, will not the less display
different types of fever. Dr. Crevaux has shown that a certain insect
with the North American Indian is not the same as with the negro or the
maroon, and both differ from that peculiar to Europeans.
M. Pasteur's beautiful experiments have conclusively demonstrated that
fowls do not catch the _charbon_; now the vital warmth of birds is from
seven to nine degrees higher than in the case of mammiferous animals;
he imagined that if the fowl was cooled down by baths to the lower
temperature, it would be liable equally to become affected; he tried,
and the result proved he was correct.
The absence, then, of a certain temperature would be the reason why
birds are exempt. The microbes are the agents of infectious disease;
when these swarm in the blood of an individual they seem to leave there
something pernicious for parasites resembling themselves, or to bring
away with them something necessary to the life of their successors. A
glass of sugar and water, where leaven has already fermented and yielded
alcohol, is incapable of producing a second crop of leaven; similarly
the blood of an individual, once contaminated, becomes uninhabitable
afterward for like microbes. The individual has acquired immunity. Such
is the principle of vaccination.--_Paris Correspondent of the Kansas
City Review_.
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