Evening star., 1901-08-24
cTo be continued.)
ENCKE'S COMET.
Named for the Astronomer Who Dis
covered Its PeriOdicity.

Named for the Astronomer Liz
covered Its PeriOdfcfty.
From the Philadelphia Times.
The comet which has been named after
Johann Franz Encke, who discovered Its
periodicity in 1919 is expected to put in an
appearance about the middle of September
this year. A comet had been seen at in
tervals for some fifty years prior to the
date above mentioned, so that when Encke
computed the orbit of that of 1919 and
compared it with the prior appearances he
was able to state that they were all the
same comet and to predict to a nicely that
1t would again be visible in 1922, but that
on account Of its position In the heavens
and planetary perturbations 1t would only
| be seen in the southern hemisphere 1t
was, therefore, watched for by astronomers
| living in that part of the world and was re-
ported by Rumker from Paramatta In New
South Wales in the month of June.
Its next return was predicted for lS2o,
| and sure enough it was sighted by Nalz
| from Nismes in that year. On the 18th OF
| October, 1928, 1t was seen by Struve at
| Dorpat in Russia and remained in view to
| the European observatories until December
| %. Upon this occasion star OF the efeV-
| enth magnitude was mistaken for Its nu-
| cleus until the error was discovered The
| brightness of the star was, however, in no
| way diminished by the intervention of the
| comet. 1t was also noticed at the time that
| it's brightness increased, and this was at
| tributed to greater condensation of the
| nebulous matter as 1t moved away from the
| sun. In 1882 it returned again, but was IN
| favorably located for observation, but was
| seen by Harding at Gottingen on August
| q, by Henderson at the Cape Of Good Hope
| and in Buenos Ayres.
| Encke figured that it's period Of revolu-
| tion was regularly losing about two and
] one-half hours at each return to perihelion.
He thought this was due to the retarding
action of the medium through which 1t
| moved, and the theory appeared to be con-
firmed by it's reappearances in 1912, 1S4S,
| 1852 1850 1858 1862 and up to 1868, but
| upon it's return on this last date Its &C
/ celeration had fallen to one-half what had
| been until then it's constant value, and this
! change has proved permanent, which tends
! to Danish the idea of resisting medium.
The comet was observed upon its return
! to perhelion in 1895 and 1898, and 1t is ex-
pected it will be again seen in 1901. It is
generally only visible through telescope,
! but under very favorable conditions can be
seen by the unaided eye. 1t is described
| as being of an irregular form, showing no
well-defined nucleus; it exhibits but few
| Jets and envelopes and has a tail, which
| when visible is only about degree or two
| in length. 1t also appears to contract as
| tance of 130, 600, 900 miles from the sun it
| seems to have diameter of 100000 miles,
| while when 1T is near perihelion, say 3d.
600 600 miles, It's diameter is only 1900 or
1900 miles. Mr.. John Herschel thinks
this difference is more optical than actual;
that when near the sun a part Of the COM
etary matter becomes invisible on account
| of its being, SO to speak, evaporated by the
increased heat