New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1884-05-12
THE SUN AND HIS SATELLITES.
CURRENT SCIENCE NOTES BY RICHARD A.
PROCTOR.
KEw. EngIand, ApriI ~.

Uranus. green; and Neptune blue. The arrange
,oent is singular though of course there nothing
really significant in the correspondence between the
distances of these eve planets from the sun and the
tints of the solar spectrum; nor does Mr.. Ma1weh
Hall who notices the relation suggest that there
any physical significance in it.
But il is worthy of notice that in the case OF four
ont Of the Eve planets Just mentioned, the observed
color is probably due to the inherent hght oil tne
plauet Mars of course is planet belonging 10 the
same family "a the earth. All the features OF thS
miniature world suggest that he is planet having
continents and seas and an atmosphere OF moderate
density-hazy and cloud-laden at times ana o'o'
certain regions but still not preventing us from 3D.
serving his real surface. 1t is otherwise WIN
Jupiter and Saturn, aud probably also with uranus
and Neptune Apart from number OF considera-
tions in the case Of the two frst-name6planets Whch
nrove practically to demonstraton) That THESE
nlopets are really very much smaller than the
olobes we measure as theirs and are grt round by
cloud-laden envelopes many thousands of miles IN
depth probably not atmospheric ut all IN the sense
in which our air is an atmospheric envelopel' IL Is
only necessary to consider the lustre OF the lour
outer planets to see that they are in condition very
different from that Of our earth. the moon, Mars
Venus OF Mercury. If we take the planet Mars as
showing us how much light is rejected from
rlauet in the same condition as the earth, then we
much light Us we should were he in that condition;
from Saturn. about twice rs much; from Uranus
ucarlv three times as much and from Neptune
nearly twice as much. If instead of Mars we had
taken the moon. we should have judged the bright
ness of the -four outer planets to exceed IN yet
greater degree that due to mere reflection 1or MARS
gives half as much light again tthe proportion Oh
tanned by Z0ner was 2,672 to 1856 as he would
If his surface were like the moons; but then the
L. p1nrt n
confirmation OF the view that part of the light OF
the outer planets is inherent, we note that on eel
tain occasions satellite of Jupiter has appeared as
dark as its own shadow, seen beside it on the same
znno of the giant planets surface In such cases II
is clear that from the region in shadow whence no
reflected light came, as much light OF some sort
issued as was reflected from the surface OF the
satellite which corresponds with the theory that
one-half of Jupiters light at least is Inherent the
other half that which is reflected from the planet
snrfooe. Again Dr. Henry Draper found with the
spectroscOpe that the light from the great Orange
red spot Oh Jupiter was in great part inherent We
may therefore believe that tie inherent part OF
Jnpiter's light is orange-tlnted The inherent night
of Saturn is in like manner probably yellow that OF
Irrauus preeuish that of Neptune blue. For, moth
inc that is known about the planets suggests as
probable OF even possible the theory that their sur
faces are tinted with these colors as rock substances
Of different kinds are tinted. The visible surfaces
of Jupiter and Saturn are certainly not solid and II
would be utterly unlikely that those OF then fellow
giants Uranus and Neptune would be So while the
evidence derived from the superior lu5tre OF these
outer planets that s the excess of their lusre over
that due to reflection from rock substances enables
lie at once to reject the idea that these bodies owe
their color 10 the light which their surfaces reflect
We may them say that there is reason for sup
nosnr that could il be viewed from great dis
lance BY an eye keen enough to see tue giant
planets and so situated that only a small portion OF
their reflected light could be discerncd, the solar
system would appear as a quintupe star, the chleI
orb being white, the Others (vety much fainter OF
coursc being in the order of their distance from
their primary. orange. yellow. green ana Diue'
Moreover from what know Of the coioIs OF the
double and multiple staIs, we are justified in us
pecting that the cOoTs of Jupiter, saturn, Uranus
and Neptune are due to the absOrptive action OF the
vanorous masses which surround them and indeed
entirely hide their real surfaces from view.
This suggests that il would be interesting 10 OBJ
serve very carefully the spectrum OF the whoie
breadth of Jupiter's disc taking both polar ana
equatorial diameter TO note whether there IS any
marked difference between the spectra Of the edge
and of the middle of the disc. There should he, II
We remember that the light from the middle OF the
disc comes through very much smaller range "l
clopd-strewn space than the light from near the
edge of the disc similar observation might be
made on Saturn and perhaps on Uranus; but at
present Neptune would probably be too d!ihcuIt an
object for this sort of spoctrOscopic work.
Mr. Maxwell Hall notes also that the brightness
of Neptune varies in such way as 10 Suggest that
the period of the planets rotation may De de-
tern,incd by observations of the change of NcPunes
brightness even though no telescope yet made can
he expected TO show definite features on his face.
IIaII IA make ont with cons der
able probability q period of III. Dom. Only OF
conrse all such computations open 10 the Oh &C.
tIon that if at givenSntervals planet shows dark
and light alternately. 1t does not necessarily follow
that there have been complete rotations al such ~
teryals If there were two dark regions on opposite
sides OF the planet then each hall rotation WOuld
produce the observed change of brightness. I'D
other words we remain IN doubt lOt tne Pi f I
whether Mr. Maxwell Halls observations OF NeP-
time should be regarded as suggesting IN Dom. or
18Th som. for the planets rotation period;
similar difficulty led to an erroneous deterlnlha
ton of the rotation period of Mars III CassnlS time
Two opposite faces of Mars. seen with telescopes oi
moderate power, look very similar, so that certain
astronomers at Bologna We're disPoset 10 as2en 20
Mars a rotation period of little over twelve hours
The warmth with which the elder Casslnl oDur-
gated those astronomers OF BOLOGNA was amusing
enonoh when the small intrinsic importance OF Their
error IS considered. May Heaven coniound HIM Tor
his theory Of irregular verbs saiH q co'IDi" 'i
QIammarau of another Greek scholar CasSlhI
seemed in like manner to think that only torture
and Imprisonment would fully meet the case OF the
careless BOOgnese observers.
Nv the wav | should be glad to receive from
American observers Of Mars any mICiOhetfcal
measures which may have been made Of tie passage
of tie well-known Kaiser Sea across the centre 81
the disc of Mars during the last few months, or II
the cape to which Mr. Nathaniel Green has gyen
ile name Cape Proctor-the point from which Beer
and Nadler measured Marian long tuaes-has been
automatically observed in central passage that
would do equally well From observations made
last month. but not automatically, combined WIN
The series extending over some 300 years which
had already employed. get the same result as be-
fore OH 37m. 22.73s.; nor Is II likely That even
The most exact observations at this end OF the long
neriod will do much to correct this estimate, since
hr Hooke's observation IN lGCO cannot be relied