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work of the Russian empire, and which with perfect success sup-
plant the far more tedious and 'costly triangulation."*

In the wilds of Central Asia and Siberia, as in some portions
of our own territory, preliminary surveys baaed on observations
made with the pocKet chronometer and Pistor and Martin's pa-
tent sextant, may supply our present need of information ; but
eastward to the Ural and Caucasus, it has been found practicable
to transport the Repsold vertical circle and the Brauer's extra-
meridional transit. The methods of using these two instruments
are fully given in the two following publications :

Rep«oldoT Knig, Obronometri, Chronometretscheska Ezpedaitsir, 1859, goda.
P. Smyssloff, S. Peterbourg, 1868.

Die Zeitbestimmuog, yermittelst dei Tragbaren Darchgangs loatruments im Ver-
ticale des PolarstereSi yon W. Dollen^St. Petersburg, 1868.

A third memoir by Colonel Smyssloff (now Director of the
Observatory at Wilna),

Opoity dla sraTnajteljooi otsjenkaj raalaytschnech sposoboff ielegraphaj-tscheskoi
peredatschay vraymayne pray opredjelayoie rasnoste dolgote Poidkoyskoi ay Mo«-
koYskoi Obaeryatorie. P. Smyssloff, St. Petersboui^g, 1866,

gives the details of the latest and telegraphic determination of
the difierence of longitude between the observatories of Poul-
kova and Moscow. This determination was made previous to
the completion of the new portable transits by Brauer, and is
valuable on account of the comparison of the three methods of
communicating and observing the telegraphic signals.

The excellencies of the method given in the above quoted
memoir by Mr. Ddllen have during the past three years found
confirmation in the observations conducted by the military ofii-
cers studying with him. It merits a wide circulation in our own
land, which I hope to secure by a published translation with ap-
propriate tables ; questions of secondary importance seem to
nave prevented its exclusive adoption in the longitude determi-
nations needed for the arc of 68° 54' on the parallel of 62° north
latitude. The surprising reliability of the portable transits made
by Mr. Brauer, the mechanic of the Central Observatory, now
independently established in St. Petersburg, has shown tnem to
be adapted to the highest requirements of the present state of
• Otto StnxTe, Jahrasberidit, June 14, 1868.

Digitized by


C. Abhe on the Repsold Potiabk Circle. 211

geodesy, whilst the great saving of time when they are used in
the vertical of Polaris gives these instruments a remarkable su*
perioritv over the meridian transit, aflFording a fall confirmation
of the thesis propounded on page 13 of the above named memoir
by Mr. Dollen, " under all circumstances, the determination of time
for any given instant will be best made by mounting the porta-
ble transit, not in the plane of the meridian, but in the vertical of
the pole star." Mr. Brauer has intimated to me his intentioQ to
place his sixth transit on exhibition at the Paris Exposition. Nor
can I here refrain from expressing my conviction of the great
importance to the interests of our astronomy and surveying to
be attached to the establishment in this country of a mechanical
institute, which, under the charge of a person of the experience
of Brauer and the Bepsolds, shall be able to furnish us with
measuring instruments comparable with the objectives produced
by our opticians, and fitted to do the fine work yi which the as*
tronomer and geodesist are so much interested.

For the determination of latitude the same portable transit, by
being established in the plane of the prime vertical, yields ze-
nith distances whose accuracy is in general much greater than
that of the declinations of the stars observed, since these are in
general faint ones. The portable prime vertical transit loses
therefore somewhat of its importance, excepting for determin-
ations of latitude where the nighest accuracy is sought, and
when by the cooperation of fixed observatories, special simulta-
neous investigations into the dcQlinations of the stars observed
can be obtained.

In general, the use of the prime vertical transit restricts one
to the observation of a limited number of faint stars situated in
a narrow belt. The use of the Talcott zenith telescope demands
more accurate declinations of faint stars than are generally acces-
sible, and the increased size of the telescope as well as the time re-
quired for making a large number of observations on favorable
nights, constitute objections to the use of both those ingenious
methods in latitudes greater than 45^ (Poulkova is in latitude
60° N.), where the period favorable for field operations is com-
paratively short, ana distinguished by long twilight

The observations of azimuths or of zenith distances are adapt-
ed to the determination of time and latitude ; and if we adopt
the principle that a small number of accurate observations is
preferable to a larger number of less accurate ones, it becomes
necessary to restrict our attention to the three or four hundred
brighter stars whose present places are known with considerable
accuracy. The portable vertical circle offers itself to us as an
instrument equally applicable in all latitudes to the determina-
tion of latitude, and fit for the determination of time for secon-
dary stations between 70'' of latitude and the equator, if accu-
rately constructed as by Bepsold, and used so as to eliminate

Digitized by


SIS C. AVbe on the Beptold P&riabk Ctrck.

oonstaDt or systematic erroTS. By reason of the ease with wliieh
it is put in position, and the brightness of the stars observed, as
well as by the accuracy of its divided circles^ level and micro-
scopes,' there is no time lost nor money expended in building
stations, nor in waiting for nightfall, nor in tedious repetition of
observations. Some of the principles embodied in the Bepsold
construction of this instrument may be found introduced into
oth^r instruments previously constructed for Struve by these
artists, by Ertel, by Brauer, &c. ; but the first of those on the

Serfected pattern now adopted was constructed in 1851, from
esigns fumishedf by His Excellency, Otto Struve, the present
Director of the Central Observatory. This one belonged to the
topographical staff of the Imperial Military Academy, and was
d^tinea to be used in the surveys of the Caucasus; it could
therefore only be once used in the new revision of the latitudes
of the thirteen principal points of the Russian-Scandinavian arc;
the results for tnat one station, Kilpi Maki, 1862, afforded, how-
ever, a very satisfactory proof of the quality of the instrument
The consiclerable number of these instruments already made by
the Messrs. Bepsold, (and especially the fine one ordered for the
faydrographical staff, and into which were introduced a number of
minor improvements suggested by Mr. Brauer), have by their
continual use and their successive improvement, led to the belief
that the vertical circle has as yet but begun its course of useful-
ness, and will, with further improvements, eventually be entirely
depended on for doing the work that it is so admirably fitted to
accomplish, — and farther, that the principles carried out in its
construction, i. e., compactness, high magnifying powers, rever-
sibility, &c., have received authoritative confirmation as to their

The first of the memoirs of Colonel Smyssloff above quoted
gives a detailed description of the instruments used and the
work done in a chronometric expedition carried out by himself
in 1859, in the neighborhood of Poulkova, in which seventeen
points were accurately determined between the 18th of June and
the 81st of July. We shall here give a brief account of the verti-
cal circle used and of the plan of the expedition.

The aperture of the telescope used was 1^ inches with a focal
length of 20 inches — these dimensions, Specially the aperture,
have in later instruments been somewhat increased. The con-
ical tube holding the objective is 9\ inches long, being screwed
to the cube containing the prism of total reflection whose center
is 6 inches distant from the two Ys in which the pivots of the
axis rest, and 9^ inches distant from that end of the steel axis
that carries the two parallel wires midway, between which the
observed star is to be brought. The opposite end of the axis
being perforated admits light for the illumination of the fields

f See Are da Meridien. Inirod^ p. zxzriil.

Digitized by


C. Abbe on the Repwold Partabk Circle. 219

The bisection of a star by a single wire presents serioos disad-
vantages in attempting observations in strong twilight on faint
stars, and is not generally attempted. The wires are stretched
across the end of a cylindrical tube, whose independent connec*
tion with the axis isolates it as far as possible from the exterior
and protecting cylinder carrying the ocular. On either side of
the cube and clamped to it by outer plates are the two circles
having each 8 spokes and divided silver arcs of 11 inches diameter.

The supporting arms/whose extremities form the Y's, branch
from a conical column 6 inches high ; this is hollow, and within
is the vertical axis on which the reversion takes place from
circle and observer east to circle and observer west, or vice versa.
This vertical axis rests upon three horizontal legs through whose
extremities pass the foot screws with divided heads. The dis-
tance from tne foot screws to the center azis of the instrument
is about 7 inches; the whole height from the ground to objec-
tive when pointed to the zenith being two feet and two inches.
The weight of the instrument is probably about forty pounds.

A horizontal finding circle with two verniers and slow-motion
screw is attached to the vertical column just above the plane of
the horizontal legs. The vertical circle on the side of tne cube
opposite to the ocular is used as a finding circle and for giving
the slow vertical motion ; it is provided with two pointers at the
opposite ends of a horizontal bar which rests upon the horizontal
axis of revolution just within the pivot, and which is held in posi-
tion by a suspended vertical frame held hj an adjusting screw
six inches below the axis. A similar horizontal bar similarly
placed near the other pivot carries the level and the two reading
microscopes which are perpendicular to the plane of the .circle.

In observing, therefore, the eye being directed through the
telescope ocular, one has the microscopes on the left and right
in a horizontal line, distant from the eye some 5 or 6 inches,
whilst the level is directly in front, which convenient compact-
ness greatly fsbcilitates the observations.

The heads of the micrometer screws of the microscopes are
divided into 60 parts each representing 2" ; the level divisions
have the same value. The microscopes are about 6 inches long,
having single lenses of aperture 0*2 inches for their objectives,
and a magnifying power of 26-25 diameters, that of the telescope
being 60-65 diameters. In the present construction of the mi-
croscopes, following a suggestion of Mh Marth in his article <5n
the Greenwich Transit Circle, each micrometer screw is made to
carry two pairs of parallel wires, the centers of the pairs being
distant 1^ revolutions of the screw from each other. The image
of the divided limb, which is formed in the plane of the micro-
meter threads, is enlarged about S'5 times, corresponding there-
fore to a circle whose radius is the same as the local length of
the telescope objective.
▲m. Jouk. Sgi.— 8iooin> 8e*»i, Vol. XLIII, No. 19S.— March, 1867. '

38 . .

Digitized by V^OOQIC

%H C. AMe on the Repgold Portable Circle.

' By oomparing these dimeiisiona with those of the foar times
larger Ertel vertical circle of the Central Observatory, it is evi-
dent that the portable instrument, for which the actual probable
accidental error of a meridian ^nith distance resulting irom two
fK>inting8, one circle east and one circle west, is d:0''*6, has de-
rived a decided advantage from its small size and proportion-
ately higher magnifying power.

Recognizing the principle that in an astronomical measure-
ment the fewest possible assumptions must be made,r— and tbat
computed probable errors give a very unreliable or perhaps no
indication of the extent to which the constant or systematic
errors introduced by assumptions as to the condition of the in-
strument, &c., may have vitiated our results, — it is necessary not
only to examine thoroughly the instrument itself, but also in
using it to still farther reduce the influence of its imperfections.
Therefore a zenith distance is made to depend upon eight point-
ings of the telescope (or 4x8 pointings of the microscope micro-
meters), the four in one position of the circle being preceded
and succeeded by two in the opposite position ; the whole series
requiring from sixteen to twenty-four minutes for its complete
observation. A latitude or a time determination depends opon
a pair of stars observed on opposite sides of the zenith at the
same zenith distance; or upon sixteen pointings whose result is
sensibly free from any assumption as to the zenith pointy flexure
or refraction. /

The examination of the instrument used by Colonel Smyssloff
leads to the following results.

The error of bisecting the interval between the two wires of
either p^ir in the field of view of the microscope by a division
of the limb of the circle, the error arising from accidental errors
of the screw and the divisions of the screw head, and the error
of reading these divisions, combine to affect the mean of four
measurements with the microscopes, d:0"'17

The probable accidental error of a division of thb di'^

viaed circle, =h0"-46, affects the mean of four, rbO^'-ZS

The probable accidental error of a reading of the two

ends of the level bulb, ±:0"-12

The combination of these gives

\^(0"-l'7)2-+.(0"-23)a+(0"-12)2= ±0"-3 1 .

'The probable accidental error of pointing on a star may be
afterward investigated, — ^but if we assume that it equals an ap
parent visual angle ^)f 1', this will correspond to an arc of
d=0"-67. Whence

\^(0"-31)2-|-(0"-67)2 = i:0''-74.
A zenith distance depending on one pointing, circle right, and

Digitized by


C. Abbe an the Reptold Partmble Circle.


one, circle left, may therefore be expected to be affected with an
accidental error of

and for one depending on eight pointings we have a probable
accidental error, db0"*26. A latitude or lime determination de*
pending on two such zenith distances has accordingly the prob-
able accidental error of observation, dbO"*18.

The influences of refraction, clock correction, flexure, periodic
errors of division, still remain. The latter have not, to my
knowledge, as yet been specially investigated, — the circles are
divided with the same machine used in dividing the small cir*
cles investigated by Struve in Dorpat See his " Beschreibung
der Breite Gradmessung," and the '* Description de TObserva-
toire Central." The combined influence of all disturbing causes
can be investigated by a series of determinations of the latitude
of any known station, — the zenith point of the divided circle
being successively altered by arcs of 80"* or 46"*. Sixteen de^
terminations of the latftude of Poulkova afford an example oi;
this investigation which should be entered into by each observer.',
for his own instrument. Using the declinations given in the^.
British Nautical Almanac, there results the following series of -
values of the latitude of the station, which was the northeast
small dome on the grounds at Poulkova, and whose latitqde, by
reference to that of the Ertel vertical circle as deduced by Dr.
Peters, is +59° 46' 20"02. Each of the following values of <p^
results from one observation consisting of eight ]^ointing8 upon^
the respective stars.

Zenith point of the circle -Oo.

Sue Meridian Resultinf Meant

obaenred. sen. dist. latitude. Iiy pain.

« ^Un.MinoilB

oPUrs. Min.

a AurigiB
« Polaris

a Corona
^ Polaris


-14 68
+18 55

-31 41
+S2 85

-31 41
+33 35

5©0 4«'

Zenith point pf the circle r'WP^


20 -27)
19 73

20 ^11.


a Corone
a Corones

Meridian Rttultinff Meani
sen. disc latitude, by pairs.'

590 46*
-14058' 19-''-54)2^.gg
+15 22 19^20^*

-14 58 18-78{,ft4-|

+13 55 19 -241^*^

-31 41 20-81) *•

+82 85 19-78f'*'^

-81 41 19-18)

+82 85 19-54

, pUr».Min.«.p.-45 30

^aTauri +48 88

- pUr».Min.«.p.-45 80

''•aTauri +43 38

-74 23

+70 12

21 •<» I on .«» i« P Urs. Min. «. p. -45 80
19 -35 f*' *'r^- ATauri ■ +48 88

21 •441,, .4^14 PUrs. Min. 8. p.

jy aAurifl:8B8.p.


fl a Aurigae b. p. -74 23

^•aViiT^nla +70 12

21 -92
19 14
21 -46
18 -29



-45 80
+48 88

(JO .eqliK aPer8ci8.p. -70 52
-». ^^^aVirglnis +70 12



21 -48



iA aPersoi 8. p.

-70 52
+70 12

17 -82
21 -73



Mean of 8 pairs, 20 15

" 16 " +59o46'20''13

By reference to the £rtel cirde, 59 46 20 -02

Pilfierence, -10


Digitized by


IIS C. Abbe m tke RepsoU Portable Circle.

A.88aming the 16 valaes resulting from the 16 pairs to be free
from flexure, there results a probable error of latitude from
one pair = ^0"-85.

The difference of the latitudes resulting from the two stars of
each pair depends upon the flexure of the tube and the error in
the declinations, as well as upon any systematic error in the
refraction or the graduation, though tnis is probably insensible.
Assuming the latitude to be 69^ 46' 20"-00, we find the differ-
enoea from this to be represented by the formula

(A.) 4-y'168in(2-S0*-a);

applying this to each of the thirty^two observations, there resalta
a probable error of a latitude from two stars d:0"*84. From the
sixteen values of the flexures we derive a probable error result-
ing from the error in the ephemeris and the error of pointing
and reading; this is dbrO'^'Sl. And subtracting the latter source
of error, there results db0"'25 as the probable error of the decli-
nation in the British Nautical Almanac.

The investigation of flexure might also be made by means of
observations in the prime vertical, but here we probably have a
complicated combination of flexure and personal equation. Eight
determinations of time made by Colonel Smyssloff (each depend-
ing upon eight pointings on each of a pair of stars observed in
the prime vertical), compared with simultaneous observations
by Wagner at the Ertel transit gave

Wagner-Smyssloff = -0»'02 ±0»-0S ;
the probable error of a single determination resulting =±0«-09;
or, if we allow equal accuracy to each instrument, the probable
error of a clock correction given by the vertical circle =d=0«06.

A series of comparisons between Messrs. Smyssloff, Bolscheff
and Demetriefl^ in which each observed four of the eight point-
ings gave,

8.-D.= -0»098, S.-B.= - 0«-046, B.-D.:=+0«132 ;
and the probable error of a determination of time =5^=0**06,
which in the latitude 60^ corresponds to a vertical angle of

As in the determination of latitude so in that of time, a pair
of stars equally distant from the zenith is always observed, each
being pointed upon four times in each position of the circle, the
eight pointings requiring twenty minutes or less. The stars are
of course ob^rvea near the prime vertical

[To be ficodudcd.]

Digitized by


J. p. Cooke, Jr., on CryophyUUe. 8]7

Abt. XXYI. — On OryophyUite^ a new mineral species of the Mica
Family^ with some associated minerals in the granite of Bockport^
Massachusetts; by Josiah F. Cooe£, Jr.

In a paper published in a recent number of this Journal^ I
clescribea a new mineral species allied to Helvin, to which I
gave the name of Danalite. Associated with Danalite in the
granite ledges forming the extremity of Cape Ann, Massacbu*
setts, are two remarkable micas, one of which is the new species
to which on account of its easy fusibility and foliated struciara
I have given the name Cryophyllite.

Mineralogical Characters, — The mineralo^cal characters of cry-
ophyllite are as follows. Like other varieties of mica it crys-
tallizes in six-sided prisms, which are frequently of considerable
size, from one to two inches in length and of proportion<)t&diam-
eter. The basal cleavage is highly perfect, yielding thin flexible
and transparent laminie, which when examined with a polarizing
microscope give a biaxial image, the angle between the optical
axes varying from 65° to 60^ The angles 66°, 57° 80', and 60°,
were all measured on different specimens. The dispersion of the
axes, if any, is so slight that its character could not with certain-
ty be determined, the color of the mineral tending to obscure
any such effect. The perfect uniformity of the two systems of
rings both as to form and to color indicates that the mica belongs
to the trimetric system. Nevertheless, the angle between the
prismatic planes measured with an application goniometer 120°
as accurately as is possible with this instrument, and in one in-
stance the planes of an hexagonal pyramid terminating the
prism were distinctly seen. Considering, however, these crystals
as belonging to the trimetric system, in accordance with the gen*
erally received opinion of mineralogists as to crystals of the
mica family, all of which present essentially the same orystallo-
graphic characters, we must regard the six-sided prism of cryo*
phyllite as formed by the union of the planes / of the rhomibip
prism with the brachydiagonal basal planes u. The plane df
the optical axes coincides with the shorter diagonal of the riiomb
base, and the crystals are frequently much elongated in tilts di*
rection, so that the form of the cleavage face was as tifaown iii
the accompanying figure,
the line a b indicating the
position of the plane of.
the optical axes. Further- '
more, the crystals were fre-
quently twinned together
on the plane t f , and it was observed that in such cases the planes

• Vol zUi, No. 124, JqIj, 186«.

Digitized by


818 /. P. Cooke, Jr., on CrycphyUiie.

of cleavage of the two crystals were absolutely coincident, prov-
ing that the rhombic prisms are rectangular and not oblique, as
De Senormont has previously shown to be true of other crystals
of the mica family.

The color of cryophyllite in axial directions is dull emerald
green, not unlike glass colored with protoxyd of iron, and so
deep that the laminae are opaque unless quite thin, but like other
colored micas it is dichrous and appears brownish-red in the di-
rection of the lateral axes. The color of the streak is light gray
with a tint of green. The luster is brilliant on the cleavage face
inclining to resinous. The hardness is from 2 to 2*6 and tba
specific gravity 2*909.

Before the blowpipe cryophyllite very easily fuses with some
intumescence to a greyish enamel bead, and it even fuses in flakes
of considerable size in the flame of a candle, so that its fusibility
is from 1*5 to 2 of von Kobell's scale. It imparts to the flame
of a Bunsen's lamp a most brilliant lithia reaction, and by ex-
amining the colored flame with a spectroscope the presence of
potassium, sodium and rubidium may also be readily discovered.
The amount of sodium however must be exceedingly small as it
does not sensibly modify the lithia flame as seen by the naked
eye, and the same is true to a still greater degree of rubidium.
The presence of rubidium is best recognized by mixing the pul-
verized mineral with pure pulverized sulphate of lime, exposing
a small bead of this mixture supported by a loop of flne plati*
sum wire to the flame of a gas blowpipe and examining the
flame with a spectroscope. The characteristic double blue line
of rubidium is then seen very distinctly for a few moments^ bal
soon disappears. No trace of caesium could be discovered, either
by the mode of experimenting just described or by examining
the platinum salt obtained in the course of the analysis, by the
partial precipitation of the alkalies with chlorid of platinum.

Heated alone in a closed glass tube cryophyllite slightly
changes color, but gives no sublimate, although when heated in
the same with bisulphate of potash it gives a strong reaction of

Online LibraryJohn AlmonThe American journal of science and arts → online text (page 25 of 102)