The New York herald. [volume] (New York [N.Y.]) 1840-1920, 1875-03-05

remains to inquire how the knowledge now hsa
can be augmented through the approaching
eclipse observations
THE PREPARATIONS FOR OBSERVING
the April eclipse hardly yet mature; but.
without such unfortunate weather as was ex.
perienced in 1870 the SIAM expedition will De
likely 10 secure the best Photographic records
ever yet obtained. Strange to say. the prospective
credit OF the April work, whatever IL may be, Will
belong not TO the Europeans. but to the King OF
siam, who has taken the initiative in inviting
astronomers TO his domiDIons and providing for
their entertainment while there. on the 9th Of
last October His Siamese Majesty, through his
private secretary, Bhashakarawangse, extended
this courtesy to the Royal Astronomical and Royal
Societies and TO any astronomers they might ac-
credit TO him, Tor the purpose OF ut izing tins
coming opportunity. Other letters to other sOcie.
ties and to friendly governments have, we believe,
been addressed The English government has ap-
prOpriated about 5000 TO deiray the expenses OF
its own eclipse expedition and to provide the
suitable apparatus so as 10 secure the fruit which
has been SO long ripenng and Is now ready "a
drop into the hands OF science. The time inter
vening before the eclipse comes or Ia short; but
the Nicobar and Siam stations can be reached by
fast steamers from Calcutta or Gale connecting
with the Mediterranean steamships navigating
via the Suez Canal.
The siderostats to be employed by the English
have been constructed by Messrs- Cook & Sons, OF
York, who, It Ia said have improved upon the
original model OF the inventor. The arrange
ments are no doubt already perfected, and the
expeditonary parties on their way to Calcutta
The French government Will be represented BY
an expedition under control OF NJ. Jansen, the
we'll known astronomer, whose probable desti.
nation Is Hue. In very recent letter to the
French Academy OF Sciences, Mr. LocKyer, OF
England, writes that the English observations, In
the Nicobar Islands aud Slam. will be directed
mainly ito the spectra Of the chromosphere ana
the coronal atmosphere, with the principal view
to determine the chemical constitution OF the LAT.
ter" The same line OF inquiry will PROBABLY 10
followed by the French observers.
The latest European intelligence from those ins
terested in the eclipse observations states that
DR.. Vogel, the well known Berlin astronomer, will
join the outgoing astronomers at Suez and DR..
Jansen at Singapore. the Italians are also to b
represented by Professor Tachini. who IS already
In Calcutta ready to move to the eclipse stations.
The British expedition sailed from Southampton
on the 18th OF February, In the Peninsular and
Oriental Company's steamer Surat for Gale ana
| Singapore. 1t Is, we understand, o matter Of
regret to American astronomers that. Congress-
having made no provision for the United States 70
take part in tho eclipse expeditions no organized
party can be despatched hence IN time for the I'M
portanr event. But the fullest preparations and
instrumental equipments have gone forth with tho
European scientists, and all the circumstances
are suspicious.
But, among all tho circumstances which lend
importance and give promise OF success never
before attained, to the forthcoming eclipse oo.
servations, the proposed application OF the new
instrument.
THE sIDERosrAr.
1t has been well and beautifully remarked thaa
the barometer 'has brought In sight new coun-
try, and has enriched science. not only with new
facts. but new principles." Tho same eulogum
may aptiy serve to characterize the destined
utility Of the siderostat Grand as the resultu
have been, which have been developed BY the use
Of spectrum photography. the latter application II
OF very limited value unless combined with such
an instrument Is the siderostat which Is doubt
less, to ef,eot greas revolution IN astronomical
observation. The coming eclipse 10 to be the oh.
jet Of Its novel and special attack, and the proc
pect Is very exhilaratng to astronomers
The siderostas was devised to enable the Oh.
server to escape the Inconvenience and often the
impossibilty OF changing his position to follow the
eyepece OF his telescope, when turned upon the
moving sun or star. With the best telescope
mountings ana arrangements which have hereto
fore been employed the observer is put frequently
in the most uncomfortable positions, and his work
nervous handling OF his glasses at the exciting
and critical moment Of the eclipse. The ingenoul
scientist Foucaut. the perfecrer OF tho siderossa
aimed to give the equatorial the power OF making
the entire heavens pass before the observer with
out his having to disturb himself to dlspace the
instrument The slderostat, as arranged by him.
is, therefore. telescope fixed horizontally in an
inyarlable position, before which plane mirror
brings SUCCESSFULLY the various points Of the SKY.
rtssd hv
three screws, with two levels and q regulating
azimuth movement. The plano mirror Is carried
by q horizontal axis on the top OF two vertical
supports, which revolve round q centre. the move
ment being perfectly erected by small wheels "a
the loot OF The supports. BY the employment, OF .
CL0CKwoRK MOVEMENT,
the isochronous regulator Of Foucault. placed ~
the foot Of the instrument. communicates to the
plane mirror motion sensiby equa to the di-
urnal motion, SO that tho heavenly bodies main
tain invariable positions In the neld Of the hort.
zontal telescope, in front OF the apparatus
directed toward the mirror. This clock uovo'
ment, which has been applied to equatorlals. II
perfectly regular, and won for its inventor the
grand prize in the mechanical arts at the Uni
vcrsal Exhibition OF 1867. The apparatus givea
perfect steadiness in experiments for measuring
tho position OF spectrum lines and OF the displaco-
ment Of the lines BY means Of large nxed spec.
troscopes. Its adaptability has been tested DUR
ing the recent Photographic experiments In
connection with the transit of Venus, and with
the greatest ease It combines with tho observing
telescope the apparatus necessary Tor the
work of celestial photography Tor photometr1a
researches. The complete instrument. telescope
and sIderostat, placed in the plane Of the mert
dian, may also be regarded O meridian instru-
ment 10 that 1t IL, perhaps, the most powerful
weapon OF modern astronomy; and, when desredt
spectroscopes and Photographic apparatus csn "
attached to the eye-piece Of the telescope, of q
size even larger than the telescope itself
The instr mental advantages with which asu.oM