GIFT or

Professor C. L. Cory

ENGINEERING L1DRARY

X

T HE 0 El A

MOTVS CORPORVM

COELESTIVM

IN

SECTIONIBVS CONICIS SOLEM AMBIENTIVM

A V C T O R E

CAROLO FRIDERICO GAVSS.

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THEORY

OF THE

MOTION OF THE HEAVENLY BODIES MOVING ABOUT
THE SUN IN CONIC SECTIONS:

A TRANSLATION OF

GAUSS'S "THEORIA MOTUS."

WITH AN APPENDIX.

BT

CHARLES HENRY DAVIS,

COMMANDEB UNITED STATES NAVY, SUPERINTENDENT OF THE AMERICAN EPHEMERIS AND NAUTICAL ALMANAC.

BOSTON:
LITTLE, BROWN AND COMPANY.

1857.

*\ "K^esaK C.L C0_ Ac
ENGINEERING LIBRARY

Published under the Authority of the Navy Department by the Nautical Almanac and

Smithsonian Institution.

«« -*^'j •««*•' * ' *

J « « I * . r* " * "* rf

.:;•*: .>;*," ti -•.'••- •-•

TRANSLATOR'S PREFACE.

Ix 1852, a pamphlet, entitled The Computation of an Orbit from Three Complete
Observations, was published, under the authority of the Navy Department, for the use
of the American Ephemeris and Nautical Almanac, the object of which was to excerpt
from various parts of GAUSS'S Theoria Motus, and to arrange in proper order the numer
ous details which combine to form this complicated problem. To these were added an
Appendix containing the results of Professor EXCKE'S investigations, Ueber den Avsnah-
mefall einer doppelten Bahnbestimmung aus denselben drei geocentrischen Oertern (Ab-
handlungen de.r Akademie der Wisse.nschaften zu Berlin, 1848), and also Professor PEIRCE'S
Graphic Delineations of the Curves showing geometrically the roots of GAUSS'S Equa
tion IV. Article 141.

After this pamphlet was completed, the opinion was expressed by scientific friends
that a complete translation of the Theoria Motus should be undertaken, not only to meet
the wants of the American Ephemeris, but those also of Astronomers generally, to whom
this work (now become very rare and costly) is a standard and permanent authority.
This undertaking has been particularly encouraged by the Smithsonian Institution,
which has signified its high estimate of the importance of the work, by contributing to
its publication. And by the authority of Hon. J. C. DOBBIN, Secretary of the Navy, this
Translation is printed by the joint contributions of the Nautical Almanac and the Smith
sonian Institution.

The notation of GAUSS has been strictly adhered to throughout, and the translation
has been made as nearly literal as possible. No pains have been spared to secure typo
graphical accuracy. All the errata that have been noticed in ZACH'S Monatliche Corre-

spondenz, the Berliner Astronomisches Jahrbuch, and the Astronomische Nachrichten, have

(v)

842502

vi TRANSLATOR'S PREFACE.

been corrected, and in addition to these a considerable number, a list of which will be
found in GOULD'S Astronomical Journal, that were discovered by Professor CHADVENET
of the United States Naval Academy, who has examined the formulas of the body of
the work with great care, not only by comparison with the original, but by independent
verification. The proof-sheets have also been carefully read by Professor . PHILLIPS, of
Clmpel Hill, North Carolina, and by Mr. RUNKLE and Professor WINLOCK of the Nautical
Almanac office.

The Appendix contains the results of the investigations of Professor ENCKE and
Professor PEIRCE, from the Appendix of the pamphlet above referred to, and other mat
ters which, it is hoped, will be found interesting and useful to the practical computer,
among which are several valuable tables : A Table for the Motion in a Parabola from
LEVERRIER'S Annales de L' Observatoire Imperial de Paris, BESSEL'S and POSSELT'S
Tables for Ellipses and Hyperbolas closely resembling the Parabola, and a convenient
Table by Professor HUBBARD for facilitating the use of GAUSS'S formulas for Ellipses and
Hyperbolas of which the eccentricities are nearly equal to unity. And in the form of
notes on their appropriate articles, useful formulas by BESSEL, NICOLAI, EXCKE, GAUSS,
and PEIRCE, and a summary of the formulas for computing the orbit of a Comet,
with the accompanying Table, from OLHERS'S Abhandlung ue.ber die le.ichteste und be-
quemste Methods die Bahn eines Cometen zu berechnen. Weimar, 1847.

17

CON T E N T S .

PAH
PREFACE 1X

FIKST BOOK.

GENERAL RELATIONS BETWEEN THE QUANTITIES BY WHICH THE MOTIONS
OF HEAVENLY BODIES ABOUT THE SUN ARE DEFINED.

FIRST SECTION. — Relations pertaining simply to position in the Orbit
SECOND SECTION. — Relations pertaining simply to Position in Space .

THIRD SECTION. — Relations between Several Places in Orbit 100

FOURTH SECTION. — Relations between Several Places in Space ..... 153

SECOND BOOK.

INVESTIGATION OF THE ORBITS OF HEAVENLY BODIES FROM GEOCENTRIC

OBSERVATIONS.

FIRST SECTION. — Determination of an Orbit from Three Complete Observations . .161

SECOND SECTION. — Determination of an Orbit from Four Observations, of which Two only

are Complete

THIRD SECTION. — Determination of an Orbit satisfying as nearly as possible any number of

Observations whatever .......••••

FOURTH SECTION. — On the Determination of Orbits, taking into account the Perturbations . 274

APPENDIX • 279

TABLES 329

(vii)

OAHBKIDG E :
P1IKTID BT itLIN AND FABNHAM

PREFACE.

AFTER the laws of planetary motion were discovered, the genius of KEPLER
was not without resources for deriving from observations the elements of mo
tion of individual planets. TYCHO BRAKE, by whom practical astronomy had
been carried to a degree of perfection before unknown, had observed all the
planets through a long series of years with the greatest care, and with so
much perseverance, that there remained to KEPLER, the most worthy inheritor
of such a repository, the trouble only of selecting what might seem suited
to any special purpose. The mean motions of the planets already deter
mined with great precision by means of very ancient observations diminished
riot a little this labor.

Astronomers who, subsequently to KEPLER, endeavored to determine still
more accurately the orbits of the planets with the aid of more recent or
better observations, enjoyed the same or even greater facilities. For the
problem was no longer to deduce elements wholly unknown, but only
slightly to correct those already known, and to define them within narrower
limits.

The principle of universal gravitation discovered by the illustrious NEWTON

b (ix)

£, PREFACE.

opened a field entirely new, and showed that all the heavenly bodies, at
least those the motions of which are regulated by the attraction of the sun,
must necessarily, conform to the same laws, with a slight modification only,
by which KEPLER had found the five planets to be governed. KEPLER, rely
ing upon the evidence of observations, had announced that the orbit of every
planet is an ellipse, in which the areas are described uniformly about the
sun occupying one focus of the ellipse, and in such a manner that in differ
ent ellipses the times of revolution are in the sesquialteral ratio of the semi-
axes-major. On the other hand, NEWTON, starting from the principle of
universal gravitation, demonstrated d, priori that all bodies controlled by the
attractive force of the sun must move in conic sections, of which the planets
present one form to us, namely, ellipses, while the remaining forms, parabo
las and hyperbolas, must be regarded as being equally possible, provided
there may be bodies encountering the force of the sun with the requisite
velocity ; that the sun must always occupy one focus of the conic section ;
that the areas which the same body describes in different times about the
sun are proportional to those times; and finally, that the areas described
about the sun by different bodies, in equal times, are in the subduplicate
ratio of the semiparameters of the orbits: the latter of these laws, identical
in elliptic motion with the last law of KEPLER, extends to the parabolic and
hyperbolic motion, to which KEPLER'S law cannot be applied, because the rev
olutions are wanting. The clue was now discovered by following which it
became possible to enter the hitherto inaccessible labyrinth of the motions of
the comets. And this was so successful that the single hypothesis, that their
orbits were parabolas, sufficed to explain the motions of all the comets which
had been accurately observed. Thus the system of universal gravitation had

PREFACE. Xi

paved the way to new and most brilliant triumphs in analysis; and the
comets, up to that time wholly unmanageable, or soon breaking from the
restraints to which they seemed to be subjected, having now submitted to
control, and being transformed from enemies to guests, moved on in the
paths marked out by the calculus, scrupulously conforming to the same eter
nal laws that govern the planets.

In determining the parabolic orbits of comets from observation, difficul
ties arose far greater than in determining the elliptic orbits of planets, and
principally from this source, that comets, seen for a brief interval, did not
afford a choice of observations particularly suited to a given object : but the
geometer was compelled to employ those which happened to be furnished
him, so that it became necessary to make use of special methods seldom
applied in planetary calculations. The great NEWTON himself, the first geome
ter of his age, did not disguise the difficulty of the problem: as might have
been expected, he came out of this contest also the victor. Since the time
of NEWTON, many geometers have labored zealously on the same problem,
with various success, of course, but still in such a manner as to leave but
little to be desired at the present time.

The truth, however, is not to be overlooked that in this problem the
difficulty is very fortunately lessened by the knowledge of one element of
the conic section, since the major-axis is put equal to infinity by the very
assumption of the parabolic orbit. For, all parabolas, if position is neg
lected, differ among themselves only by the greater or less distance of the
vertex from the focus; while conic sections, generally considered, admit of
infinitely greater variety. There existed, in point of fact, no sufficient reason
why it should be taken for granted that the paths of comets are exactly

PREFACE.

parabolic: on the contrary, it must be regarded as in the highest degree
improbable that nature should ever have favored such an hypothesis. Since,
nevertheless, it was known, that the phenomena of a heavenly body moving
in an ellipse or hyperbola, the major-axis of which is very great relatively to
the parameter, differs very little near the perihelion from the motion in a
parabola of which the vertex is at the same distance from the focus; and
that this difference becomes the more inconsiderable the greater the ratio of
the axis to the parameter : and since, moreover, experience had shown that
between the observed motion and the motion computed in the parabolic
orbit, there remained differences scarcely ever greater than those which might
safely be attributed to errors of observation (errors quite considerable in
most cases) : astronomers have thought proper to retain the parabola, and
very properly, because there are no means whatever of ascertaining satis
factorily what, if any, are the differences from a parabola. We must except
the celebrated comet of HALLEY, which, describing a very elongated ellipse and
frequently observed at its return to the perihelion, revealed to us its periodic
time ; but then the major-axis being thus known, the computation of the re
maining elements is to be considered as hardly more difficult than the determi
nation of the parabolic orbit. And we must not omit to mention that astrono
mers, in the case of some other comets observed for a somewhat longer time,
have attempted to determine the deviation from a parabola. However, all
the methods either proposed or used for this object, rest upon the assumption
that the variation from a parabola is inconsiderable, and hence in the trials
referred to, the parabola itself, previously computed, furnished an approximate
idea of the several elements (except the major-axis, or the time of revolu
tion depending on it), to be corrected by only slight changes. Besides, it

PREFACE. Xlll

must be acknowledged, that the whole of these trials hardly served in any
case to settle any thing with certainty, if, perhaps, the comet of the year
1770 is excepted.

As soon as it was ascertained that the motion of the new planet, discov
ered in 1781, could not be reconciled with the parabolic hypothesis, astrono
mers undertook to adapt a circular orbit to it, which is a matter of simple
and very easy calculation. By a happy accident the orbit of this planet had
but a small eccentricity, in consequence of which the elements resulting from
the circular hypothesis sufficed at least for an approximation on which could
be based the determination of the elliptic elements. There was a concur
rence of several other very favorable circumstances. For, the slow motion of
the planet, and the very small inclination of the orbit to the plane of the
ecliptic, not only rendered the calculations much more simple, and allowed
the use of special methods not suited to other cases; but they removed the
apprehension, lest the planet, lost in the rays of the sun, should subsequently
elude the search of observers, (an apprehension which some astronomers might
have felt, especially if its light had been less brilliant) ; so that the more
accurate determination of the orbit might be safely deferred, until a selection
could be made from observations more frequent and more remote, such as
seemed best fitted for the end in view.

Thus, in every case in which it was necessary to deduce the orbits of
heavenly bodies from observations, there existed advantages not to be de
spised, suggesting, or at any rate permitting, the application of special
methods ; of which advantages the chief one was, that by means of hypo
thetical assumptions an approximate knowledge of some elements could be

PREFACE.

obtained before the computation of the elliptic elements was commenced.
Notwithstanding this, it seems somewhat strange that the general problem,—

To determine the orbit of a heavenly body, iviihmd, any hypothetical assumption,
from observations not embracing a great period of time, and not allowing a selection
ti.ith a view to the application of special methods, was almost wholly neglected up
to the beginning of the present century; or, at least, not treated by any one
in a manner worthy of its importance ; since it assuredly commended itself
to mathematicians by its difficulty and elegance, even if its great utility in
practice were not apparent. An opinion had universally prevailed that a
complete determination from observations embracing a short interval of time
was impossible, — an ill-founded opinion, — for it is now clearly shown that
the orbit of a heavenly body may be determined quite nearly from good
observations embracing only a few days ; and this without any hypothetical
assumption.

Some ideas occurred to me in the month of September of the year 1801,
engaged at the time on a very different subject, which seemed to point to
the solution of the great problem of which I have spoken. Under such cir
cumstances we not unfrequently, for fear of being too much led away by
an attractive investigation, suffer the associations of ideas, which, more atten
tively considered, might have proved most fruitful in results, to be lost from
neglect. And the same fate might have befallen these conceptions, had they
not happily occurred at the most propitious moment for their preservation
and encouragement that could have been selected. For just about this time
the report of the new planet, discovered on the first day of January of that
year with the telescope at Palermo, was the subject of universal conversation;

PREFACE. XV

and soon afterwards the observations made by that distinguished astronomer
PIAZZI from the above date to the eleventh of February were published. No
where in the annals of astronomy do we meet with so great an opportunity,
and a greater one could hardly be imagined, for showing most strikingly, the
value of this problem, than in this crisis and urgent necessity, when all hope
of discovering in the heavens this planetary atom, among innumerable small
stars after the lapse of nearly a year, rested solely upon a sufficiently ap
proximate knowledge of its orbit to be based upon these very few observa
tions. Could I ever have found a more seasonable opportunity to test the
practical value of my conceptions, than now in employing them for the de
termination of the orbit of the planet Ceres, which during these forty-one
days had described a geocentric arc of only three degrees, and after the
lapse of a year must be looked for in a region of the heavens very remote
from that in which it was last seen ? This first application of the method
was made in the month of October, 1801, and the first clear night, when
the planet was sought for* as directed by the numbers deduced from it, re
stored the fugitive to observation. Three other new planets, subsequently
discovered, furnished new opportunities for examining and verifying the effi
ciency and generality of the method.

Several astronomers wished me to publish the methods employed in these
calculations immediately after the second discovery of Ceres ; but many
things — other occupations, the desire of treating the subject more fully at
some subsequent period, and, especially, the hope that a further prosecution
of this investigation would raise various parts of the solution to a greater

•By de ZACH, December 7, 1801.

2

xvj PREFACE.

degree of generality, simplicity, and elegance, — prevented my complying at
the time with these friendly solicitations. I was not disappointed in this ex
pectation, and have no cause to regret the delay. For, the methods first
employed have undergone so many and such great changes, that scarcely
any trace of resemblance remains between the method in which the orbit of
Ceres was first computed, and the form given in this work. Although it
would be foreign to my purpose, to narrate in detail all the steps by
which these investigations have been gradually perfected, still, in several
instances, particularly when the problem was one of more importance than
usual, I have thought that the earlier methods ought not to be wholly sup
pressed. But in this work, besides the solutions of the principal problems,
I have given many things which, during the long time I have been en
gaged upon the motions of the heavenly bodies in conic sections, struck
me as worthy of attention, either on account of their analytical elegance,
or more especially on account of their practical utility. But in every case
I have devoted greater care both to the subjects and methods which are
peculiar to myself, touching lightly and so far only as the connection seemed
to require, on those previously known.

The whole work is divided into two parts. In the First Book are de
veloped the relations between the quantities on which the motion of the
heavenly bodies about the sun, according to the laws of KEPLER, depends ;
the two first sections comprise those relations in which one place only is
considered, and the third and fourth sections those in which the relations
between several places are considered. The two latter contain an explanation
of the common methods, and also, and more particularly, of other methods,
greatly preferable to them in practice if I am not mistaken, by means of

PREFACE. XVli

which we pass from the known elements to the phenomena; the former treat
of many most important problems which prepare the way to inverse pro
cesses. Since these very phenomena result from a certain artificial and intri
cate complication of the elements, the nature of this texture must be thor
oughly examined before we can undertake with hope of success to disentangle
the threads and to resolve the fabric into its constituent parts. Accordingly,
in the First Book, the means and appliances are provided, by means of which,
in the second, this difficult task is accomplished ; the chief part of the labor,
therefore, consists in this, that these means should be properly collected to
gether, should be suitably arranged, and directed to the proposed end.

The more important problems are, for the most part, illustrated by appro
priate examples, taken, wherever it was possible, from actual observations.
In this way not only is the efficacy of the methods more fully established
and their use more clearly shown, but also, care, I hope, has been taken that
inexperienced computers should not be deterred from the study of these sub
jects, which undoubtedly constitute the richest and most attractive part of
theoretical astronomy.

GOTTINGEN, March 28, 1809.

FIRST BOOK.

GENERAL RELATIONS BETWEEN THOSE QUANTITIES BY WHICH THE
MOTIONS OF HEAVENLY BODIES ABOUT THE SUN ARE DEFINED.

FIEST SECTION.

RELATIONS PERTAINING SIMPLY TO POSITION IN THE ORBIT.

1.

IN this work we shall consider the motions of the heavenly bodies so far only
as they are controlled by the attractive force of the sun. All the secondary
planets are therefore excluded from our plan, the perturbations which the
primary planets exert upon each other are excluded, as is also all motion of
rotation. We regard the moving bodies themselves as mathematical p6ints, and
we assume that all motions are performed in obedience to the following laws,
which are to be received as the basis of all discussion in this work.

I. The motion of every heavenly body takes place in the same fixed
plane in which the centre of the sun is situated.

II. The path described by a body is a conic section having its focus in the
centre of the sun.

III. The motion in this path is such that the areas of the spaces described
about the sun in different intervals of time are proportional to those intervals.
Accordingly, if the times and spaces are expressed in numbers, any space what
ever divided by the time in which it is described gives a constant quotient.

1

2 RELATIONS PERTAINING SIMPLY [BOOK I.

IV. For different bodies moving about the sun, the squares of these quotients
are in the compound ratio of the parameters of their orbits, and of the sum of the
"•> jhjiftfgs of the sun and the moving bodies.

, Denoting, therefore, the parameter of the orbit in which the body moves by
J %p, the' mass of this body by p (the mass of the sun being put = = 1), the area it

describes about the sun in the time t by kg, then ^wff+Tj! wil1 be a constant
for all heavenly bodies. Since then it is of no importance which body we use
for determining this number, we will derive it from the motion of the earth, the
mean distance of which from the sun we shall adopt for the unit of distance ; the
mean solar day will always be our unit of time. Denoting, moreover, by n the
ratio of the circumference of the circle to the diameter, the area of the entire
ellipse described by the earth will evidently be n <Jp, which must therefore be
put — %y, if by t is understood the sidereal year; whence, our constant becomes

In order to ascertain the numerical value of this constant, here-
~

after to be denoted by k, we will put, according to the latest determination, the

sidereal year or /= 365.2563835, the mass of the earth, or ^ = 354710 =
0.0000028192, whence results

Iog2jt ........ 0.7981798684

Compl. log t ...... 7.4374021852

Compl. log. \/ (!+!"*) • • • 9.9999993878

log k ......... 8.2355814414

k= 0.01720209895.

2.

The laws above stated differ from those discovered by our own KEPLER
in no other respect than this, that they are given in a form applicable to all kinds
of conic sections, and that the action of the moving body on the sun, on which
depends the factor y/(l-j-(U-), is taken into account. If we regard these laws as
phenomena derived from innumerable and indubitable observations, geometry
shows what action ought in consequence to be exerted upon bodies moving about

SECT. 1.] TO POSITION IN THE ORBIT. 3

the sun, in order that these phenomena may be continually produced. In this
way it is found that the action of the sun upon the bodies moving about it is
exerted just as if an attractive force, the intensity of which is reciprocally
proportional to the square of the distance, should urge the bodies towards the
centre of the sun. If now, on the other hand, we set out with the assumption of
such an attractive force, the phenomena are deduced from it as necessary
consequences. It is sufficient here merely to have recited these laws, the con
nection of which with the principle of gravitation it will be the less necessary to
dwell upon in this place, since several authors subsequently to the eminent
NEWTON have treated this subject, and among them the illustrious LA PLACE, in
that most perfect work the Mecanique Celeste, in such a manner as to leave
nothing further to be desired.

3.

Inquiries into the motions of the heavenly bodies, so far as they take place in
conic sections, by no means demand a complete theory of this class of curves ;
but a single general equation rather, on which all others can be based, will answer
our purpose. And it appears to be particularly advantageous to select that one
to which, while investigating the curve described according to the law of attrac
tion, we are conducted as a characteristic equation. If we determine any place
of a body in its orbit by the distances x, y, from two right lines drawn in the
plane of the orbit intersecting each other at right angles in the centre of the
sun, that is, in one of the foci of the curve, and further, if we denote the distance
of the body from the sun by r (always positive), we shall have between r, x,y,
the linear equation r-\-ax-\-(iy = y, m which a, ft, y represent constant quan
tities, y being from the nature of the case always positive. By changing the
position of the right lines to which x,y, are referred, this position being essentially
arbitrary, provided only the lines continue to intersect each other at right angles,
the form of the equation and also the value of y will not be changed, but the
values of a and ft will vary, and it is plain that the position may be so determined
that ft shall become = 0, and a, at least, not negative. In this way by putting for
«, y, respectively e. p, our equation takes the form r-\-ex=p. The right line to

4 RELATIONS PERTAINING SIMPLY BoOK I.

which the distances y are referred in this case, is called the line of apsides, p is the
semi-parameter, e the eccentricity; finally the conic section is distinguished by the
name of ellipse, parabola, or hyperbola, according as e is less than unity, equal to
unity, or greater than unity.

It is readily perceived that the position of the line of apsides would be
fully determined by the conditions mentioned, with the exception of the single
case where both a and /? were = 0; in which case r is always =j», whatever the
right lines to which x, y, are referred. Accordingly, since we have e = 0, the
curve (which will be a circle) is according to our definition to be assigned to
the class of ellipses, but it has this peculiarity, that the position of the apsides
remains wholly arbitrary, if indeed we choose to extend that idea to such a case.

4.

Instead of the distance x let us introduce the angle v, contained between the
line of apsides and a straight line drawn from the sun to the place of the body
(the radius vector}, and this angle may commence at that part of the line of apsides
at which the distances x are positive, and may be supposed to increase in the
direction of the motion of the body. In this way we have x = r cos v, and thus
our formula becomes r— , from which immediately result the following

1 -(- e cos v ' '

conclusions : —

I. For v = 0, the value of the radius vector r becomes a minimum, that is,
= j-4^j : this point is called the perihelion.

II. For opposite values of v, there are corresponding equal values of r ; con
sequently the line of apsides divides the conic section into two equal parts.

III. In the ellipse, v increases continuously from v = 0, until it attains its
maximum value, -~, in aphelion, corresponding to v = 180°; after aphelion, it
decreases in the same manner as it had increased, until it reaches the perihelion,
corresponding to v — 360°. That portion of the line of apsides terminated at one
extremity by the perihelion and at the other by the aphelion is called the major

SECT. 1.] TO POSITION IN THE ORBIT. 5

axis ; hence the semi-axis major, called also the mean distance, =. ^ — ; the dis
tance of the middle point of the axis (the centre of the ellipse) from the focus will
be ej^ =ea, denoting by a the semi-axis major.

IV. On the other hand, the aphelion in its proper sense is wanting in the
parabola, but r is increased indefinitely as v approaches -(- 180°, or — 180°. For
v = + 180° the value of r becomes infinite, which shows that the curve is not cut
by the line of apsides at a point opposite the perihelion. Wherefore, we cannot,
with strict propriety of language, speak of the major axis or of the centre of the
curve ; but by an extension of the formulas found in the ellipse, according to the
established usage of analysis, an infinite value is assigned to the major axis, and
the centre of the curve is placed at an infinite distance from the focus.

V. In the hyperbola, lastly, v is confined within still narrower limits, in fact
between v = — (180° — if), and v = -{-(180° — if), denoting by if the angle of

which the cosine =-. For whilst v approaches these limits, r increases to

infinity ; if, in fact, one of these two limits should be taken for v, the value of r
would result infinite, which shows that the hyperbola is not cut at all by a right
line inclined to the line of apsides above or below by an angle 180° — if. For
the values thus excluded, that is to say, from 180° — if to 180° -(-if, our formula
assigns to r a negative value. The right line inclined by such an angle to the
line of apsides does not indeed cut the hyperbola, but if produced reversely,
meets the other branch of the hyperbola, which, as is known, is wholly sepa
rated from the first branch and is convex towards that focus, in which the sun is
situated. But in our investigation, which, as we have already said, rests upon the
assumption that r is taken positive, we shall pay no regard to that other branch
of the hyperbola in which no heavenly body could move, except one on which
the sun should, according to the same laws, exert not an attractive but a repulsive
force. Accordingly, the aphelion does not exist, properly speaking, in the hyper
bola also ; that point of the reverse branch which lies in the line of apsides,

and which corresponds to the values z> = 180°, r== — j~i> might be consid
ered as analogous to the aphelion. If now, we choose after the manner of the

6 RELATIONS PERTAINING SIMPLY [BOOK I.

ellipse to call the value of the expression ^~ — , even here where it becomes
negative, the semi-axis major of the hyperbola, then this quantity indicates
the distance of the point just mentioned from the perihelion, and at the
same time the position opposite to that which occurs in the ellipse. In the
same way ep-, that is, the distance from the focus to the middle point between
these two points (the centre of the hyperbola), here obtains a negative value on
account of its opposite direction.

5.

We call the angle v • the true anomaly of the moving body, which, in the
parabola is confined within the limits — 180° and -(-180°, in the hyperbola
between — (180° - - 1/>) and -)- (180° — y> ), but which in the ellipse runs through
the whole circle in periods constantly renewed. Hitherto, the greater number of
astronomers have been accustomed to count the true anomaly in the ellipse not
from the perihelion but from the aphelion, contrary to the analogy of the parabola
and hyperbola, where, as the aphelion is wanting, it is necessary to begin from the
perihelion : we have the less hesitation in restoring the analogy among all classes
of conic sections, that the most recent French astronomers have by their example
led the way.

It is frequently expedient to change a little the form of the expression

— : the following forms will be especially observed : —
1 -|- e cos v ' J

r — P _ — P

1 -)- e — 2e sin2 ^v 1 — e-\-2e cos2 ^ v

- P

Accordingly, we have in the parabola

-_ P .
~2cos2lt>'

in the hyperbola the following expression is particularly convenient,

CT. 1.1 TO POSITION IN THE ORBIT.

6.

Let us proceed now to the comparison of the motion with the time. Putting,
as in Art. 1, the space described about the sun in the time t=$g, the mass of the
moving body = jit, that of the sun being taken = 1, we h&v&ff
The differential of the space = krrdv, from which there results
=frr&v, this integral being so taken that it will vanish for t = 0. This integra
tion must be treated differently for different kinds of conic sections, on which
account, we shall now consider each kind separately, beginning with the ELLIPSE.

Since r is determined from v by means of a fraction, the denominator of which
consists of two terms, we will remove this inconvenience by the introduction of a
new quantity in the place of v. For this purpose we will put tan £ v ^ T — =

i -\-e

tan % E, by which the last formula for r in the preceding article gives

=

n r\

^ r=r- (

Moreover we have ^ = y^, and consequently dv = f

hence

rrd(, '==_££_.(l

and integrating,

— e sin ^) ^Constant.

(1 — e ey

Accordingly, if we place the beginning of the time at the perihelion passage, where
v = 0, E= 0, and thus constant = 0, we shall have, by reason of l^_ee = <*,

In this equation the auxiliary angle E, which is called the eccentric anomaly,
must be expressed in parts of the radius. This angle, however, may be retained

in degrees, etc., if e sin E and **V(H-f*) are aiso expressed in the same manner ;

or
these quantities will be expressed in seconds of arc if they are multiplied by the

8 RELATIONS PERTAINING SIMPLY [BOOK I.

number 206264.81. We can dispense with the multiplication by the last quan
tity, if we employ directly the quantity k expressed in seconds, and thus put,
instead of the value before given, k = 3548".18761, of which the logarithm =

3.5500065746. The quantity - a expressed in this manner is called the

a?
mean anomaly, which therefore increases in the ratio of the time, and indeed every

day by the increment 7~ , called the mean daily motion. We shall denote

a*

the mean anomaly by M.

7.

Thus, then, at the perihelion, the true anomaly, the eccentric anomaly, and the
mean anomaly are = 0 ; after that, the true anomaly increasing, the eccentric
and mean are augmented also, but in such a way that the eccentric continues to
be less than the true, and the mean less than the eccentric up to the aphelion,
where all three become at the same time = 180°; but from this point to
the perihelion, the eccentric is alwa}rs greater than the true, and the mean
greater than the eccentric, until in the perihelion all three become = 360°, or,
which amounts to the same thing,- all are again = 0. And, in general, it is
evident that if the eccentric E and the mean M answer to the true anomaly v,
then the eccentric 360° --E and the mean 360° — M correspond to the true
360° — v. The difference between the true and mean anomalies, v — M, is called
the equation of the centre, which, consequently, is positive from the perihelion
to the aphelion, is negative from the aphelion to the perihelion, and at the
perihelion and aphelion vanishes. Since, therefore, v and M run through an
entire circle from 0 to 360° in the same time, the time of a single revolution,
which is also called the periodic time, is obtained, expressed in days, by dividing

360° by the mean daily motion -^ p^, from which it is apparent, that for dif-

a

ferent bodies revolving about the sun, the squares of the periodic times are pro
portional to the cubes of the mean distances, so far as the masses of the bodies,
or rather the inequality of their masses, can be neglected.

SECT. 1.] TO POSITION IN THE ORBIT. 9

8.

Let us now collect together those relations between the anomalies and the
radius vector which deserve particular attention, the derivation of which will
present no difficulties to any one moderately skilled in trigonometrical analysis.
Greater elegance is attained in most of these formulas by introducing in the
place of e the angle the sine of which = e. This angle being denoted by <p, we
have

_ ee) — cosy, y/(l + e) = cos (45° — i 9) y/2,

— e) = 2 cos£y, \/(l-\-e) — y/(l — e) = 2 sin i <p.

The following are the principal relations between a, p, r, e, (f, v, E, M.
I. p — a cos2 y
II. r = TJf—

i -\-e cos w

III. r = a(l — ecosE)

j-y „ cos v -j- e cos ^J — e

1 -[- e cos w ' 1 — e cos ^?

V. siniJir=\/ HI — cos^") =sin^i/r

• e cos v

ini^^VHl — cos J?) =sinif YT

V 1 -\-ecos

P

VL cosi^= v/i (1 -j-

= sm

e cos »

VII. tan iJ?= tan i» tan (45°—

VIII. sin.E'^:

r sm v cos qo r sin u

p a cos qj

IX. r cos 0 = a (cos E — e) = 2 a cos ( * E + } 9 + 45°) cos ( £ j£ — i 9 -- 45°)

X. sin i (y — ^/) = sin J y sin v J - = sin J y sin _£" t/ £

XI. sin i(y-(-^')^cos^9sin^i -=r cos
XII. M=E—

10 KELATIOXS PERTAINING SIMPLY [BOOK I.

9.

If a perpendicular let fall from any point whatever of the ellipse upon the
line of apsides is extended in the opposite direction until it meets the circle
described with the radius a about the centre of the ellipse, then the inclination to
the line of apsides of that radius which corresponds to the point of intersection
(understood in the same way as above, in the case of the true anomaly), will
be equal to the eccentric anomaly, as is inferred without difficulty from equation
IX. of the preceding article. Further, it is evident that r sin v is the distance of
any point of the ellipse from the line of apsides, which, since by equation VIII. it
= a cosy sin E, will be greatest for E= 90°, that is in the centre of the ellipse.

This grecitest distance, which =acos(p = - — = \jap, is called the semi-axis minor.
In the focus of the ellipse, that is for v = 90°, this distance is evidently =p, or
equal the semi-parameter.

10.

The equations of article 8 comprise all that is requisite for the computation
of the eccentric and mean anomalies from the true, or of the eccentric and true
from the mean. Formula VII. is commonly employed for deriving the eccentric
from the true ; nevertheless it is for the most part preferable to make use of
equation X. for this purpose, especially when the eccentricity is not too great, in
which case E can be computed with greater accuracy by means of X. than of
VII. Moreover, if X. is employed, the logarithm of sine E required in XII. is
had immediately by means of VIII. : if VII. were used, it would be neces
sary to take it out from the tables; if, therefore, this logarithm is also taken
from the tables in the latter method, a proof is at once obtained that the calcula
tion has been correctly made. Tests and proofs of this sort are always to be
highly valued, and therefore it will be an object of constant attention with us to
provide for them in all the methods delivered in this work, where indeed it can
be conveniently done. We annex an example completely calculated as a more
perfect illustration.

SECT. 1.] TO POSITION IN THE ORBIT. 11

Given v = 310° 55' 29'/.64, c; = 14° 12' 1".87, log r = 0.3307640 ; p, a, E, M,
are required.

log sin (f . . ' . . 9.3897262
log cosy .... 9.8162877

9.2060139 whence e cos v = 0.1606993

log (1 + e cost') . . 0.0647197
logr 0.3307640

logp 0.3954837

log cos2 tp .... 9.9730448

log a 0.4224389

log sin z; .... 9.8782740 n*
logi/jj .... 0.0323598.5

9.8459141.5»
log sin £ 9 ... 9.0920395

logsmi(w — E) . 8.9379536.5M, hence J(» — E} = — 4°58'22".94;

v — -£" = — 9° 56' 45".88 ; ^= 320° 52' 15".52.
Further, we have

Calculation of log sin E by formula VIII.

loge . . . . 9.3897262 r

i oncocx o Koi^on log- sin y .... 9.8135543re

log 206264.8 . 5.3144251 ° p

log e in seconds 4.70415T3 log cosy 9.9865224

logsin.E'. . . 9.8000767« logsin.E' ..... 9.8000767«

4.5042280 n, hence e sin E in seconds = 31932".14 = 8° 52'
12*14 ; and M= 329° 44' 27".66.

The computation of E by formula VII. would be as follows : —

i» = 155°27'44".82 log tan iv .... 9.6594579w

45° — iy = 37°53'59".065 log tan (45° — iy) . 9.8912427

log tan IE . . . . 9.55070067
whence $E= 160°26'7".76, and E= 320° 52' 15". 52, as above.

* The letter n affixed to a logarithm signifies that the number corresponding to it is negative.

12 RELATIONS PERTAINING SIMPLY [BOOK I.

11.

The inverse problem, celebrated under the title of Kepler's problem, that of
finding the true anomaly and the radius vector from the mean anomaly, is much
more frequently used. Astronomers are in the habit of putting the equation of
the centre in the form of an infinite series proceeding according to the sines of the
angles M, 2M, BM, etc., each one of the coefficients of these sines being a series
extending to infinity according to the powers of the eccentricity. We have con
sidered it the less necessary to dwell upon this formula for the equation of the
centre, which several authors have developed, because, in our opinion, it is by
no means so well suited to practical use, especially should the eccentricity not be
very small, as the indirect method, which, therefore, we will explain somewhat
more at length in that form which appears to us most convenient.

Equation XII, E = M-\- esmfi, which is to be referred to the class of tran
scendental equations, and admits of no solution by means of direct and complete
methods, must be solved by trial, beginning with any approximate value ofJE, which
is corrected by suitable methods repeated often enough to satisfy the preceding
equation, that is, either with all the accuracy the tables of sines admit, or at least
with sufficient accuracy for the end in view. If now, these corrections are intro
duced, not at random, but according to a safe and established rule, there is scarcely
any essential distinction between such an indirect method and the solution by
series, except that in the former the first value of the unknown quantity is in a
measure arbitrary, which is rather to be considered an advantage since a value
suitably chosen allows the corrections to be made with remarkable rapidity. Let
us suppose t to be an approximate value of E, and x expressed in seconds the cor
rection to be added to it, of such a value as will satisfy our equation .£"= t -j- x.
Let e sin e, in seconds, be computed by logarithms, and when this is done, let the
change of the log sin e for the change of 1" in e itself be taken from the tables ;
and also the variation of log e sin e for the change of a unit in the number e sin e ;
let these changes, without regard to signs, be respectively A., p, in which it is
hardly necessary to remark that both logarithms are presumed to contain an
equal number of decimals. Now, if e approaches so near the correct value of E

SECT. 1.] TO POSITION IN THE ORBIT. 13

that the changes of the logarithm of the sine from e to E -j- x, and the changes of
the logarithm of the number from e sin e to e sin (e -|- x\ can be regarded as
uniform, we may evidently put

e sin (e -f- x) = e sin e + -— ,

the upper sign belonging to the first and fourth quadrants, and the lower to the
second and third. Whence, since

£-\-z = M-\- e sin (e -\- x), we have x =. -^*y (M-\- e sin c — e),
and the correct value of 2?, or

e -j- x = M -j- c sin£ + ^ry (M-\- esms — E),

the signs being determined by the above-mentioned condition.

Finally, it is readily perceived that we have, without regard to the signs,
/x : X — 1 : e cos e, and therefore always p > 1, whence we infer that in the first and
last quadrant M-\- e sin e lies between £ and f, -\- x, and in the second and third,
e-\-x between t and M-\- e sin e, which rule dispenses with paying attention to the
signs. If the assumed value e differs too much from the truth to render the fore
going considerations admissible, at least a much more suitable value will be found
by this method, with which the same operation can be repeated, once, or several
times if it should appear necessary. It is very apparent, that if the difference
of the first value £ from the truth is regarded as a quantity of the first order, the
error of the new value would be referred to the second order, and if the operation
were further repeated, it would be reduced to the fourth order, the eighth order,
etc. Moreover, the less the eccentricity, the more rapidly will the successive
corrections converge.

12.

The approximate value of E, with which to begin the calculation, will, in most
cases, be obvious enough, particularly where the problem is to be solved for
several values of M of which some have been already found. In the absence
of other helps, it is at least evident that E must fall between M and M± e, (the
eccentricity e being expressed in seconds, and the upper sign being used in the

]4 RELATIONS PERTAINING SIMPLY [BoOK I.

first and second quadrants, the lower in the third and fourth), wherefore, either
M, or its value increased or diminished by any estimate whatever, can be taken
for the first value of E. It is hardly necessary to observe, that the first calcu
lation, when it is commenced with a value having no pretension to accuracy, does
not require to be strictly exact, and that the smaller tables * are abundantly suffi
cient. Moreover, for the sake of convenience, the values selected for e should be
such that their sines can be taken from the tables without interpolation ; as, for
example, values to minutes or exact tens of seconds, according as the tables
used proceed by differences of minutes or tens of seconds. Every one will be
able to determine without assistance the modifications these precepts undergo if
the angles are expressed according to the new decimal division.

13.

Example. — Let the eccentricity be the same as in article 10. M=332°28'
54".77. There the log e in seconds is 4.7041513, therefore e = 50600'' = 14° 3' 20".
Now since E here must be less than M, let us in the first calculation put e — 326°,
then we have by the smaller tables

log sin « 9.7475GW, Change for V ... 19, whence A = 0.32.

log c in seconds . . 4.70415

4.45171«;

hence esiner -28295"= 7°51'35". Change of logarithm for a unit of the table which is here

Jtf-L. e gin £ . 324 3720 equal to 10 seconds ... 16; whence/* =1.6.

differing from £ .... 1 22 40 = 4960". Hence,

fl 39

~ X 4960" = 1240" = 20' 40".

l.zo

Wherefore, the corrected value of ^becomes 324°37'20" — 20'40"= 324°16'40",
with which we repeat the calculation, making use of larger tables.

log sine .... 9.766305Sw I = 29.25

loge 4.7041513

4.4704571 n fi = U7

* S'ich as those which the ill istrious LALANDE furnished.

SECT. 1.] TO POSITION IN THE ORBIT. 15

e sin e =_ 29543".18 = — 8°12'23".18
Jf+esine .... 324 16 31 .59
differing from e . . . 8 .41.

1 90 95

This difference being multiplied by -^ri = n775 Sives 2"09> whence, finally, the
corrected value of E — 324°16'31".59 — 2".09 = 324°16'29".50, which is exact
within 0".01.

14.

The equations of article 8 furnish several methods for deriving the true
anomaly and the radius vector from the eccentric anomaly, the best of which we
will explain.

I. By the common method v is determined by equation VII, and afterwards
r by equation II. ; the example of the preceding article treated in this way
is as follows, retaining for p the value given in article 10.

i^=16208/14".75 log e ..... 9.3897262

log tan IE. . . . 9.5082198w log cos v .... 9.8496597

log tan (45°— $9) . 9.8912427 9.2393859

•log tan 40 .... 9.6169771w ecosv =0.1735345

i0 = 157°30'41".50 logp ..... 0.3954837

123.00 log (1 + ecosv) . . 0.0694959

logr ..... 0.3259878.

II. The following method is shorter if several places are to be computed,
for which the constant logarithms of the quantities y/a(l -4- e), y/ a(l — e) should
be computed once for all. By equations V. and VI. we have

sin £ v y/ r = sin £ E y/ a (1-4-e)
cos i v \J r = cos J E y/«(l — e)

from which J v and log y/ r are easily determined. It is true in general that if we
have P sin Q = A, P cos Q = B, Q is obtained by means of the formula tan

-A. A 7?

Q = -j,, and then P by this, P = ^—^, or by P = — =. : it is preferable to use
ft' sin Q' J cos Q

16

RELATIONS PERTAINING SIMPLY

[BOOK I.

the former when sin Q is greater than cos Q ; the latter when cos Q is greater than
sin Q. Commonly, the problems in which equations of this kind occur (such as
present themselves most frequently in this work), involve the condition that P
should be a positive quantity ; in this case, the doubt whether Q should be taken
between 0 and 180°, or between 180° and 360°, is at once removed. But if such
a condition does not exist, this decision is left to our judgment.
We have in our example e = 0.2453162.

9.4867632 log cos IE . . . 9.9785434ra

0.2588593

logvX+7) .
Hence

log sin i v \Jr .

logcosi»v'r •

log cos \v . .

0.1501020.

9.7456225 1 whence, log tan %v — 9.6169771 »
0.1286454 n] %v = 157°30'4r/.50

9.9656515?* e>=315 123.00

log y/r .... 0.1629939
logr ..... 0.3259878

III. To these methods we add a third which is almost equally easy and expe
ditious, and is much to be preferred to the former if the greatest accuracy should
be required. Thus, ris first determined by means of equation III, and after that,
v by X. Below is our example treated in this manner.

loge ..... 9.3897262
logcos^ . . . 9.9094637

ecosE =

9.2991899
0.1991544

log(l —

0.4224389
9.9035488

0.3259877

log sin E .... 9.7663366«
log \j(l — ecosE) . 9.9517744

9.8145622»
log sin £9 . . . . 9.0920395

log sin } (v — E} . . 8.9066017w
l(» — E) =— 4°37'33".24
v — E =—9 15 6.48
»=316 123.02

Formula VIII., or XI, is very convenient for verifying the calculation, par
ticularly if v and r have been determined by the third method. Thus ;

SECT. 1.] TO POSITION IN THE ORBIT. 17

log - sin E . . .
log cos y . . . .

9.8627878w
9.9865224

log sin 1
log cos I

ty; ... 9.8145622w
y . . . . 9.9966567

log sin y ....

9.8493102«
9.8493102w

log sin i

9.8112189w
(v-\-E}. 9.8112189w

15.

Since, as we have seen, the mean anomaly M is completely determined by
means of v and y, in the same manner as v by 3/ and y, it is evident, that if all
these quantities are regarded as variable together, an equation of condition ought
to exist between their differential variations, the investigation of which will not
be superfluous. By differentiating first, equation VII., article 8, we obtain

dE dv d9>

sm-E sinf cos<p'

by differentiating likewise equation XII.-, it becomes

dM=(l — ecosE)AE — sin E cos y d y.
If we eliminate d^from these differential equations we have

r sin E (1 — e cos E) ,

smt>

or by substituting for sin E, 1 — e cos E, their values from equations VIII., III.,

j iir rr j r (r -4- p) sm v -,

dM= - — dv -- v ~^% — dcp,

a a cos <p a a cos cp

or lastly, if we express both coefficients by means of v and <p only,
*M= n 1°SS(P v dv-(2 + e™v} Sin^°s2qi dy .

(1 -(- e cos vy (1 -j- e cos »)*

Inversely, if we consider v as a function of the quantities M, (p, the equation has
this form :• —

cos <p

or by introducing E instead of v

^ (2 — e cos E— e e) sin Ed y.

"s

18 RELATIONS PERTAINING SIMPLY [BOOK I.

The radius vector r is not fully determined by v and (f, or by Jf and 9, but
depends, besides these, upon p or «; its differential, therefore, will consist of three
parts. By differentiating equation II. of article 8, we obtain

d r d p . e sin v -, cos m cos v ,

— = —-4-- -dfl — =-r-2- -dm.

r /> ' 1 -)- e cos v 1 -[- e cos v 7

By putting here

Ap da 0 , ,

— - = -- U tan (f d q>

p a

(which follows from the differentiation of equation I.), and expressing, in con
formity with the preceding article, d v by means of d M and d y, we have, after
making the proper reductions,

dr da , a , -, -,. a ,

— == -- 1 — tan (p sin vd M -- cosy cos v dtp,

dr = - da -f- a tan y sinvd M — a cosy coswdy.

Finally, these formulas, as well as those which we developed in the preceding
article, rest upon the supposition that v, (f, and M, or rather d v, d (p, and d M,
are expressed in parts of the radius. If, therefore, we choose to express the vari
ations of the angles v, (p, and M, in seconds, we must either divide those parts of
the formulas which contain d v, d 9, or d M, by 206264.8, or multiply those which
contain dr, dp, da, by the same number. Consequently, the formulas of the pre
ceding article, which in this respect are homogeneous, will require no change.

17.

It will be satisfactory to add a few words concerning the investigation of the
greatest equation of the centre. In the first place, it is evident in itself that the dif
ference between the eccentric and mean anomaly is a maximum for E= 90°,
where it becomes = e (expressed in degrees, etc.) ; the radius vector at this point
= a, whence v = 90° -j- <jp, and thus the whole equation of the centre = (p -(- e,

SECT. 1.] TO POSITION IN THE ORBIT. 19

which, nevertheless, is not a maximum here, since the difference between v and
E may still increase beyond 9. This last difference becomes a maximum for
d (f — E ) = 0 or for d v = d E, where the eccentricity is clearly to .be regarded
as constant. With this assumption, since in general

dv AE

sinu ~ sin.fi'

it is evident that we should have sin v = sin E at that point where the difference
between v and E is a maximum ; whence we have by equations VIII., III.,

r = a cosy, e cosE = 1 — cos 9, or cos E = -(- tan J 9.
In like manner cos v = — tan £ 9 is found, for which reason it will follow * that

v = 90° -{- arc sin tan $ 9, E = 90° — arc sin tan i 9 ;
hence again

sin E — V (1 — tan2 } 9) = *

cos £ qp '
so that the whole equation of the centre at this point becomes

2 arc sin tan i 9 -|- 2 sin i 9 y' cos 9,

the second term being expressed in degrees, etc. At that point, finally, where
the whole equation of the centre is a maximum, we must have d v = d M, and
so according to article 15, r =. a \J 0039 ; hence we have

POSI>- 1— cos*? . E._l — V/cosg)_ 1 — cos go tan £9

l^Uo t/ - • OLIO _L/ — - 7^ j 7 -^ - i j I .

e e e (1 -\- y cos <f) l-|-vcos<p

by which formula E can be determined with the greatest accuracy. E being
found, we shall have, by equations X., XII.,

equation of the centre = 2 arc sin !1!L2_2_!1 ' _|_ e sm Jgr.

y'cosgj

We do not delay here for an expression of the greatest equation of the centre by
means of a series proceeding according to the powers of the eccentricities, which
several authors have given. As an example, we annex a view of the three
maxima which we have been considering, for Juno, of which the eccentricity,
according to the latest elements, is assumed = 0.2554996.

* It is not necessary to consider those maxima which lie between the aphelion and perihelion,
because they evidently differ in the signs only from those which are situated between the perihelion and
aphelion.

20

RELATIONS PERTAINING SIMPLY

[BOOK I.

Maximum.

E

E—M

v—E

v—M

E—M
v—E
v — M

90° 0' 0"
82 32 9
86 14 40

14°38'20".57
14 30 54 .01
14 36 27 .39

14°48'11".48
14 55 41 .79
14 53 49 .57

29° 26' 32".05
29 26 35 .80
29 30 16 .96

18.

In the PARABOLA, the eccentric anomaly, the mean anomaly, and the mean
motion, become = 0 ; here therefore these ideas cannot aid in the comparison of
the motion with the time. In the parabola, however, there is no necessity for an
auxiliary angle in integrating r r d v ; for we have

and thus,

frrdv = i pp (tan $ v -j- £ tan3 if)-)- Constant.

If the time is supposed to commence with the perihelion passage, the Constant
= 0 ; therefore we have

by means of which formula, t may be derived from v, and v from t, when p and
jit are known. In the parabolic elements it is usual, instead of p, to make use of
the radius vector at the perihelion, which is | p, and to neglect entirely the mass
[>. It will scarcely ever be possible to determine the mass of a body, the orbit of
which is computed as a parabola ; and indeed all comets appear, according to the
best and most recent observations, to have so little density and mass, that the
latter can be considered insensible and be safely neglected.

19.

The solution of the problem, from the true anomaly to find the time, and, in
a still greater degree, the solution of the inverse problem, can be greatly abbrevi
ated by means of an auxiliary table, such as is found in many astronomical works.

SECT. 1.] TO POSITION IN THE ORBIT. 21

But the Barkerian is by far the most convenient, and is also annexed to the
admirable work of the celebrated OLBERS, (Abhandlung uber die leichtcste und
bequemste Methodc die Bahn eines Cometen zu lerechnen: Weimar, 1797.) It contains,
under the title of the mean motion, the value of the expression 75 tan i v -\- 25
tan3 i v, for all true anomalies for every five minutes from 0 to 180°. If
therefore the time corresponding to the true anomaly v is required, it will be

necessary to divide the mean motion, taken from the table with the arguments,

150 k
by — 5-, which quantity is called the mean daily motion; if on the contrary the

P*

true anomaly is to be computed from the time, the latter expressed in days will

be multiplied by - — , in order to get the mean motion, with which the correspond-

P*
ing anomaly may be taken from the table. It is further evident that the same

mean motion and time taken negatively correspond to the negative value of the v ;
the same table therefore answers equally for negative and positive anomalies. If
in the place of jo,we prefer to use the perihelion distance bp = q, the mean daily

motion is expressed by — ~ — - — -, in which the constant factor ^y/ 2812.5 =

9b
0.912279061, and its logarithm is 9.9601277069. The anomaly v being found,

the radius vector will be determined by means of the formula already given,

20.

By the differentiation of the equation

tan i v -\- I tan8 %v =
if all the quantities v, t, p, are regarded as variable, we have

Stk

rr

22 RELATIONS PERTAINING SIMPLY [BoOK I.

If the variations of the anomaly v are wanted in seconds, both parts also of
dv must be expressed in this manner, that is, it is necessary to take for Jc the value
3548".1S8 given in article 6. If, moreover, $p = q is introduced instead of p, the
formula will have the following form :

, <qj.
dz>z=-*— idt --- c

rr

in which are to be used the constant logarithms

log * \l 2 = 3.7005215724, log 3 k \/ } = 3.8766128315.
Moreover the differentiation of the equation

P

T ^^z

2cos2^-t»
furnishes

— = —-(- tan i v d v.

r p

or by expressing dv by means of d^ and dp,

d .
•*

\p
By substituting for t its value in v, the coefficient of dp is changed into

1 3»tan2iw ptan^if 1 /i t i . 9 1 ,-21 1-21 9 1 \

•* _. m___ f — I JL. [ _ JL T'lll* * 41 - O O1V|* -Jf •)) -Jt O1T~l •» 11 TOYl* *• 'Jt I

— •"-— • -. — — -. • — — — I ff "T" 2 ttlll 5 V — ~ -()- bill j V 9 bill 3 V tclll 9 V I •

p irr 4rr r \

but the coefficient of d^ becomes - — . From this there results

r\IP

, . ks\n v , ,

d r = £ cos t> d jt? -| — T — d r,

or if we introduce q for p

d-, ,
r::= cos pd-

The constant logarithm to be used here is log£ \j J = 8.0850664436.

21.

In the HYPERBOLA,9 and E would become imaginary quantities, to avoid
which, other auxiliary quantities must be introduced in the place of them. We
have already designated by y> the angle of which the cosine =-, and we have
found the radius vector

SECT. 1.] TO POSITION IN THE ORBIT. 23

r==

' 2 e cos •£ (v — ifj) cos £ (v -f- i/>) "

For # = 0, the factors cos $ (v — tp), and cos £ (y -)- y), in the denominator of this
fraction become equal, the second vanishes for the greatest positive value of v,
and the first for the greatest negative value. Putting, therefore,

cos ^ (v -(- if>) ~

we shall have u = 1 in perihelion ; it will increase to infinity as v approaches its
limit 180° — i//; on the other hand it will decrease indefinitely as v is supposed
to return to its other limit — (180° — 1/>) ; so that reciprocal values of u, or, what
amounts to the same thing, values whose logarithms are complementary, corre
spond to opposite values of v.

This quotient u is very conveniently used in the hyperbola as an auxiliary
quantity ; the angle, the tangent of which is

/e — 1

can be made to render the same service with almost equal elegance ; and in order
to preserve the analogy with the ellipse, we will denote this angle by I F. In
this way the following relations between the quantities v, r, u, F are easily brought
together, in which we put a = — b, so that b becomes a positive quantity.

I. l=.p cotan2 y
H. r = p - = _ pcoay _

1 -}- e cos v 2 cos J (v — y) cos £ (v -\- 1/>)

HI.

_t ,45
-

•y 1 _ i / I 1 -. _ 1 -)- cos if> cos v _ e -f- cos v

cosl'~ i u' 2 cos ^ (v — 1/>) cos^ (v-\-\f>) l-f-ecos»*

By subtracting 1 from both sides of equation V. we get,
VI. smJ, = ™

24 RELATIONS PERTAINING SIMPLY [BOOK. 1.

In the same manner, by adding 1 to both sides, it becomes

vii.

By dividing VI. by VII. we should reproduce III. : the multiplication produces
VIII. r sin v =pcoian y tan F= I tani/> tan F

= i jo cotan y (u -- ) = i b tan y (u -- ) .
From the combination of the equations II. V. are easily derived
IX. rcosv=b(e — -j,) = tb(2

u —

22.

By the differentiation of the formula IV. (regarding y as a constant quantity)
we get

du , / , , . , x\ T rtanil;

— = i (tan 3 (v -4-w) — tan * (v — r
M \ » i > ^~

hence,

dpr ,
n\ — J. f\ ni

or by substituting for r the value taken from X.

MM' u

Afterwards by integrating in such a manner that the integral may vanish at the
perihelion, it becomes

(}e(u — ) — \ogu}=

The logarithm here is the hyperbolic; if we wish to use the logarithm from
Brigg's system, or in general from the system of which the modulus = \, and

SECT. 1.] TO POSITION IN THE ORBIT. 25

the mass \i (which we can assume to be indeterminable for a body moving in an
hyperbola) is neglected, the equation assumes the following form : —

).kt

VT

XL — -- — ,

or by introducing F,

I e tan F— log tan (45° + $ F] = — .

6'

Supposing Brigg's logarithms to be used, we have

log X = 9.6377843113, log 1 7c = 7.8733657527 ;

but a little greater precision can be attained by the immediate application of the
hyperbolic logarithms. The hyperbolic logarithms of the tangents are found in
several collections of tables, in those, for example, which SCHULZE edited, and still
more extensively in the Magnus Canon Triangular. Logurtthmicus of BENJAMIN URSIN,
Cologne, 1624, in which they proceed by tens of seconds.

Finally, formula XI. shows that opposite values of t correspond to reciprocal
values of u, or opposite values of F and v, on which account equal parts of the
hyperbola, at equal distances from the perihelion on both sides, are described in
equal times.

23.

If we should wish to make use of the auxiliary quantity u for finding the
time from the true anomaly, its value is most conveniently determined by means
of equation IV. ; afterwards, formula II. gives directly, without a new calculation,

p by means of r, or r by means of p. Having found u, formula XI. will give the

ikt
quantity —=-, which is analogous to the mean anomaly in the ellipse and will be

5*
denoted by N, from which will follow the elapsed time after the perihelion transit.

Since the first term of N, that is Ji!^I 2 may, by means of formula VIII. be

made — 4-4 — - , the double computation of this quantity will answer for testing
its accuracy, or, if preferred, JV can be expressed without u, as follows : —

XII. ^V =

cos » —

- ___

2 cos ^ (v -f- u>) cos i (v — w) ° cos £ (v

4

26

RELATIONS PERTAINING SIMPLY

[BOOK I.

Example. — Let e = 1.2618820, or V = 37° 35' 0", v = 18° 51' 0", log r =
0.0333585. Then the computation for u, p, I, N, t, is as follows : —

log cos * (v — y) . . 9.99417061

log cos i (t> + y) • . 9.9450577)

logr 0.0333585

log'2e 0.4020488

log;? 0.3746356

log cotan2

0.2274244

log* 0.6020600

logj 9.4312985

log sin v 9.5093258

logX 9.6377843

Compl. log sin i/> . . 0.2147309

8.7931395
0.0621069
0.0491129

First term of N=
log u =

N = 0.0129940

logJLA ...... 7.8733658)

f log b 0.9030900)

hence, log u

uu =

0.0491129
1.1197289

1.2537928

The other calculation.

log(Mtt--l) . . . 9.4044793

Compl. log u . . . 9.9508871

log I 9.6377843

logje 9.7999888

8.7931395

\N 8.1137429

Difference .... 6.9702758

log* 1.1434671

t= 13.91448

24.

If it has been decided to carry out the calculation with hyperbolic logarithms,
it is best to employ the auxiliary quantity F, which will be determined by equa
tion III., and thence N by XI. ; the semi-parameter will be computed from the
radius vector, or inversely the latter from the former by formula VIII. ; the
second part of N can, if desired, be obtained in two ways, namely, by means of the
formula hyp. log tan (45°'-f- J F}, and by this, hyp. log cos $ (v — if) — hyp. log
cos 1 (v -(- if ). Moreover it is apparent that here where X = 1 the quantity N

SECT. 1.]

TO POSITION IN THE ORBIT.

27

will come out greater in the ratio 1 : X, than if Brigg's logarithms were used.
Our example treated according to this method is as follows : —

log tan 4 y .... 9.5318179
log tan 4 v . 9.2201009

log tan 4 F

8.7519188

log e . . . . • . . . 0.1010188
log tan I7 9.0543366

9.1553554

etznF= 0.14300638

hyp. log tan (45° + 4 F}= 0.11308666

N= 0.02991972

log& ...... 8.2355814)

| log b 0.9030900 /

417=3°13'58".12

C. hyp. log cos 4 (v — 1/>) = 0.01342266
C. hyp. log cos 4 (v + Y) = 0.12650930

Difference

= 0.11308664

log^V 8.4759575

Difference 7.3324914

logl 1.1434661

t= 13.91445

25.

For the solution of the inverse problem, that of determining the true anomaly
and the radius vector from the time, the auxiliary quantity u or F must be first
derived from N= "kk b ^t by means of equation XI. The solution of this tran
scendental equation will be performed by trial, and can be shortened by devices
analogous to those we have described in article 11. But we suffer these to pass
without further explanation ; for it does not seem worth while to elaborate as
carefully the precepts for the hyperbolic motion, very rarely perhaps to be exhib
ited in celestial space, as for the elliptic motion, and besides, all cases that can
possibly occur may be solved by another method to be given below. After
wards F or u will be found, thence v by formula III., and subsequently r will be
determined either by II. or VIII. ; v and r are still more conveniently obtained
by means of formulas VI. and VII. ; some one of the remaining formulas can be
called into use at pleasure, for verifying the calculation.

28

RELATIONS PERTAINING SIMPLY

[BoOK I.

26.

Example. — Retaining for e and I the same values as in the preceding example,
let t = 65.41236 : v and r are required. Using Briggs's logarithms we have

log* 1.8156598

log 31*$-$ .... 6.9702758

log N 8.7859356, whence N= 0.06108514. From this it is

seen that the equation N— X e tan F — log tan (45° -j- £ F) is satisfied by
F= 25°24'27".66, whence we have, by formula III,

log tan 4 F . . . . 9.3530120
log tan 4 y . . . . 9.5318179

and thus 4 v = 33° 31'29".S9, and v =

log tan lv .... 9.8211941,
67° 2' 59".7S. Hence, there follows,

£**«.»(. + ,.) • 0.2137476

C. log cos 4 (v — w) . 0.0145197 J

logfi. . ... . . 9.9725868

log r . 0.2008541.

***•»(«•+**)

0.1992280

27.

If equation IV. is differentiated, considering u, v, y, as variable at the same
time, there results,

d_M _ ^ sin ift d v -|- sin v d y _ r tan \f> , . r sin v •,

U ~ ~ 2 COS |(j) - I/)) COS ^ (v -j- «;) ~ ~^ V T" ) T *

By differentiating in like manner equation XL, the relation between the
differential variations of the quantities u, y, JV, becomes,

or

COS2 1/1

SECT. 1.] TO POSITION IN THE ORBIT. 29

Hence, by eliminating d u by means of the preceding equation we obtain

djST rr -, . /-, . r\ r sin v -,

-r- = TTT d v 4- ( 1 -\ — I?— — d w ,

X. ootanifi \ p/OOOBIfi

or

dani , ,T /b . b \ sin v tan T/I
V = — T--dJV — (- -

'

r ' p / cosii>
JJtaniOj ,, /-. . «\sint- ,

= — Y— - d iv — ( 1 4- - ) - - d w ,

t.rr \ r/smty

28.

By differentiating equation X., all the quantities r, b, e, u, being regarded as
variables, by substituting

dsnil/ -,
e = — f- dw,

cos

and eliminating dz« with the help of the equation between dJV, d««, dif, given in
the preceding article, there results,

r , , , l>bt>,(uu — 1) , ,r . b ( , 1. . , 1\ • ) n

^i;d6-] — —day -4- 5- —j- < (M + -) smw — (u -- ) sin v } aw.

b 2iur I 2cos-i \ ' u' v u' i

The coefficient of d N is transformed, by means of equation VIII., into , ~ : but

J I sm i/) '

the coefficient of d y, by substituting from equation IV.,

u (sin y — siny) = sin (y — v}, - (sin if -(- sin y) = sin (i// -f- f ),
is changed into

5 sin i/; cos v __ p cos u ^
cos2 1// sin i/> '

so that we have

6 ' ?. sin i/;

So far, moreover, as N is considered a function of b and t, we have

which value being substituted, we shall have d r, and also d v in the preceding
article, expressed by means of d t, d b, d t//. Finally, we have here to repeat our

30

RELATIONS PERTAINING SIMPLY

[BoOK 1.

previous injunction, that, if the variations of the angles v and y are conceived to
be expressed, not in parts of the radius, but in seconds, either all the terms con
taining d v, d y>, must be divided by 206264.8, or all the remaining terms must be
multiplied by this number.

29.

Since the auxiliary quantities (f, E, M, employed in the ellipse obtain
imaginary values in the hyperbola, it will not be out of place to investigate their
connection with the real quantities of which we have made use : we add therefore
the principal relations, in which we denote by i the imaginary quantity y/ — 1.

l

sin cp = e = -

COS lp

tan (45°— } 9) =

= * tan

tan (p -- | cotan (45° — i 9) — i tan (45° — i 9) = -- :

cos f/3 = i tan y

(f = 90° -f- f log (siii 9 + 1 cos 9) = 90° — » log tan (45°

tan i E= i tan i F = *>fll)

«+l

i

= I cotan

tan

:= — z cotan F,

or

or

cotan E= % cotan J^ —

r-.

SWJ! '

-\-l

2 M

or

«'-£'=: log (cos E -f- * sin E] = log -,
J? = Hog w =: i log (45° -f-

The logarithms in these formulas are hyperbolic.

SECT. 1.] TO POSITION IN THE ORBIT. 31

30.

Since none of the numbers which we take out from logarithmic and trigo
nometrical tables admit of absolute precision, but are all to a certain extent
approximate only, the results of all calculations performed by the aid of these
numbers can only be approximately true. In most cases, indeed, the common
tables, which are exact to the seventh place of decimals, that is, never deviate
from the truth either in excess or defect beyond half of an unit in the seventh
figure, furnish more than the requisite accuracy, so that the unavoidable errors
are evidently of no consequence : nevertheless it may happen, that in special
cases the effect of the errors of the tables is so augmented that we may be
obliged to reject a method, otherwise the best, and substitute another in its place.
Cases of this kind can occur in those computations which we have just explained;
on which account, it will not be foreign to our purpose to introduce here some
inquiries concerning the degree of precision allowed in these computations by
the common tables. Although this is not the place for a thorough examination
of this subject, which is of the greatest importance to the practical computer, yet
we will conduct the investigation sufficiently far for our own object, from which
point it may be further perfected and extended to other operations by any one
requiring it.

31.

Any logarithm, sine, tangent, etc. whatever, (or, in general, any irrational
quantity whatever taken from the tables,) is liable to an error which may amount
to a half unit in the last figure : we will designate this limit of error by to, which
therefore is in the common tables = 0.00000005. If now, the logarithm, etc.,
cannot be taken directly from the tables, but must be obtained by means of inter
polation, this error may be slightly increased from two causes. In the first place, it is
usual to take for the proportional part, when (regarding the last figure as unity) it
is not an integer, the next greatest or least integer ; and in this way, it is easily
perceived, this error may be increased to just within twice its actual amount. But

32 RELATIONS PERTAINING SIMPLY [BOOK I.

we shall pay no attention to this augmentation of the error, since there is no
objection to our affixing one more than another decimal figure to the propor
tional part, and it is very evident that, if the proportional part is exact, the inter
polated logarithm is not liable to a greater error than the logarithms given
directly in the tables, so far indeed as we are authorized to consider the changes
in the latter as uniform. Thence arises another increase of the error, that this
last assumption is not rigorously true ; but this also we pretermit, because the
effect of the second .and higher differences (especially where the superior tables
computed by TAYLOR are used for trigonometrical functions) is evidently of no
importance, and may readily be taken into account, if it should happen to turn
out a little too great. In all cases, therefore, we will put the maximum unavoid
able error of the tables =co, assuming that the argument (that is, the number the
logarithm of which, or the angle the sine etc. of which, is sought) is given with
strict accuracy. But if the argument itself is only approximately known, and
the variation a/ of the logarithm, etc. (which may be defined by the method of
differentials) is supposed to correspond .to the greatest error to which it is liable,
then the maximum error of the logarithm, computed by means of the tables, can
amount to m -\- a/.

Inversely, if the argument corresponding to a given logarithm is computed
by the help of the tables, the greatest error is equal to that change in the argu
ment which corresponds to the variation to in the logarithm, if the latter is cor
rectly given, or to that which corresponds to the variation w -j- w' in the loga
rithm, if the logarithm can be erroneous to the extent of w'. It will hardly be
necessary to remark that w and a/ must be affected by the same sign.

If several quantities, correct within certain limits only, are added together,
the greatest error of the sum will be equal to the sum of the greatest individual
errors affected by the same sign ; wherefore, in the subtraction also of quantities
approximately correct, the greatest error of the difference will be equal to the
sum of the greatest individual errors. In the multiplication or division of a
quantity not strictly correct, the maximum error is increased or diminished in the
same ratio as the quantity itself.

SECT. 1.] TO POSITION IN THE ORBIT. 33

32.

Let us proceed now to the application of these principles to the most useful
of the operations above explained.

I. If (f and E are supposed to be exactly given in using the formula VII.,
article 8, for computing the true anomaly from the eccentric anomaly in the
elliptic motion, then in log tan (45° — £ (f) and log tan i E, the error w may be
committed, and thus in the difference = log tan i v, the error 2w; therefore the
greatest error in the determination of the angle £ v will be

3 at di v 3 w sin v

d log tan I v 2 1

I. denoting the modulus of the logarithms used in this calculation. The error,
therefore, to which the true anomaly v is liable, expressed in seconds, becomes

^Ap 206265 = 0".0712 sin v,

if Brigg's logarithms to seven places of decimals are employed, so that we may
be assured of the value of v within 0".07 ; if smaller tables to five places only, are
used, the error may amount to 7". 12.

II. If e cos E is computed by means of logarithms, an error may be committed
to the extent of

3 ta e cos E

~T '

therefore the quantity

1 — e cos E. or - ,

a *

will be liable to the same error. In computing, accordingly, the logarithm of this
quantity, the error may amount to (1 -)- <?) w> denoting by d the quantity

3 e cos E
1 — ecosJS

taken positively : the possible error in log r goes up to the same limit, log a being
assumed to be correctly given. If the eccentricity is small, the quantity d is
always confined within narrow limits; but when e differs but little from 1,
1 — e cos E remains very small as long as E is small ; consequently, 8 may

5

34 RELATIONS PERTAINING SIMPLY [BOOK I.

increase to an amount not to be neglected : for this reason formula III., article 8,
is less suitable in tbis case. Tbe quantity d may be expressed thus also,

3 (a — r) __ 3 e (cos v-\-e) •

r l — ee '

which formula shows still more clearly when the error (1 -\- d) to may be neglected.

III. In the use of formula X., article 8, for the computation of the true from

the mean anomaly, the logt/- is liable to the error (£ -|- Jd) w, and so the log

sin | (f sin E \ I - to that of (f -f- \ 8*} to ; hence the greatest possible error in the
determination of the angles v — E or v is

or expressed in seconds, if seven places of decimals are employed,

(0".166 -f 0".024 tf) tan l(v — E).

When the eccentricity is not great, S and tan i (v — E) will be small quantities,
on account of which, this method admits of greater accuracy than that which
we have considered in I. : the latter, on the other hand, will be preferable
when the eccentricity is very great and approaches nearly to unity, where 8 and
tan J (v — JE) may acquire very considerable values. It will always be easy to
decide, by means of our formulas, which of the two methods is to be preferred.

IV. In the determination of the mean anomaly from the eccentric by means
of formula XII., article 8, the error of the quantity e sin E, computed by the help
of logarithms, and therefore of the anomaly itself, M, may amount to

~T '

which limit of error is to be multiplied by 206265" if wanted expressed in
seconds. Hence it is readily inferred, that in the inverse problem where E is to
be determined from M by trial, E may be erroneous by the quantity

£ . ™. 206265"=^-^. 206265",

X. (1 M lr

even if the equation E — e sin E= M should be satisfied with all the accuracy
which the tables admit.

SECT. 1.]

TO POSITION IN THE ORBIT.

35

The true anomaly therefore computed from the mean may be incorrect in
two ways, if we consider the mean as given accurately; first, on account of the
error committed in the computation of v from E, which, as we have seen, is of
slight importance ; second, because the value of the eccentric anomaly itself may
be erroneous. The effect of the latter cause will be expressed by the product of

the error committed in E into ^, which product becomes

206265" =

^r. 206265" =

lr

if seven places of decimals are used. This error, always small for small values of
e, may become very large when e differs but little from unity, as is shown by the
following table, which exhibits the maximum value of the preceding expression
for certain values of e.

t

maximum error.

e

maximum error.

e

maximum error.

0.90

0".42

0.94

0".73

0.98

2".28

0.91

0.48

0.95

0.89

0.99

4.59

0.92

0 .54

0.96

1 .12

0.999

46 .23

0.93

0.62

0.97

1 .50

V. In the hyperbolic motion, if v is determined by means of formula III.,
article 21, from F and ift accurately known, the error may amount to

p. 206265";
but if it is computed by means of the formula

u and y being known precisely, the limit of the error will be one third greater,

that is,

4 to sin v

for seven places.

VI. If the quantity

206265" = 0".09 sin v

nt

$

is computed by means of formula XL, article 22, with the aid of Briggs's logo-

36 RELATIONS PERTAINING SIMPLY [BoOK I.

rithms, assuming e and u or e and F to be known exactly, the first part will be
liable to the error

5 (uu — l)e<o

if it has been computed in the form

or to the error

3(«M-fl).

if computed in the form

A. G it •"-" ~ •
2 u'

or to the error 3 e (a tan F if computed in the form X e tan F, provided we neglect
the error committed in log X or log i k. In the first case the error can be
expressed also by Sew tan F, in the second by -— »» whence it is apparent that
the error is the least of all in the third case, but will be greater in the first or
second, according as u or - ]> 2 or < 2, or according as + _F>- 36° 52' or < 36° 52'.

But, in any case, the second part of N will be liable to the error w.

VII. On the other hand, it is evident that if u or F is derived from JV by
trial, u would be liable to the error

( w + 5 e o» tan F) -r^=,

or to

, . Beta •. du

according as the first term in the value of .ZV is used separated into factors, or into
terms ; F, however, is liable to the error

dF

(w + 3 e at

The upper signs serve after perihelion, the lower before perihelion. Now if
•^ is substituted here for -r-^ or for — ^, the effect of this error appears in
the determination of v, which therefore will be

SECT. 1.]

TO POSITION IN THE ORBIT.

37

5 5 tan i/> (1 + 3 e tan .F ) w bbtsmip(l -\-3 e secF)ia

if the auxiliary quantity u has been employed ; on the other hand, if F has been
used, this effect becomes,

b b tan i/; (1 + 3 e tan F) to __ to I (1 -)- e cos «)2 , 3 e sin t>(l -j- e cos t> ) )

~ ^ \ tansif> tan2!^ '

If the error is to be expressed in seconds, it is necessary to apply the factor
206265". It is evident that this error can only be considerable when t/; is a small
angle, or e a little greater than 1. The following are the greatest values of this
third expression, for certain values of e, if seven places of decimals are employed:

<

maximum error.

1.3

0".34

1.2

0 .54

1.1

1 .31

1.05

3 .03

1.01

34.41

1.001

1064 .65

To this error arising from the erroneous value of F or u it is necessary to
apply the error determined in V. in order to have the total uncertainty of v.

VIII. If the equation XL, article 22, is solved by the use of hyperbolic loga
rithms, F being employed as an auxiliary quantity, the effect of the possible
error in this operation in the determination of v, is found by similar reasoning
to be,

(1 -f- e cos vf ot' , 3 e sin v (1 -(- e cos v) w
8 > tan2 1>

tan8

i tan2 1/>

where by cu' we denote the greatest uncertainty in the tables of hyperbolic loga
rithms. The second part of this expression is identical with the second part of
the expression given in VII. ; but the first part in the latter is less than the first
in the former, in the ratio X w' : CD, that is, in the ratio 1 : 23, if it be admissible
to assume that the table of Ursin is everywhere exact to eight figures, or

•to' = 0.000000005.

RELATIONS PERTAINING SIMPLY [BoOE I.

33.

The methods above treated, both for the determination of the true anomaly
from the time and for the determination of the time from the true anomaly,* do
not admit of all the precision that might be required in those conic sections of
which the eccentricity differs but little from unity, that is, in ellipses and hyper
bolas which approach very near to the parabola ; indeed, unavoidable errors,
increasing as the orbit tends to resemble the parabola, may at length exceed all
limits. Larger tables, constructed to more than seven figures would undoubtedly
diminish this uncertainty, but they would not remove it, nor would they prevent
its surpassing all limits as soon as the orbit approached too near the parabola.
Moreover, the methods given above become in this case very troublesome, since a
part of them require the use of indirect trials frequently repeated, of which
the tediousness is even greater if we work with the larger tables. It certainly,
therefore, will not be superfluous, to furnish a peculiar method by means of
which the uncertainty in this case may be avoided, and sufficient precision may
be obtained with the help of the common tables.

34.

The common method, by which it is usual to remedy these inconveniences,
rests upon the following principles. In the ellipse or hyperbola of which e is the
eccentricity, p the semi-parameter, and therefore the perihelion distance

let the true anomaly v correspond to the time t after the perihelion; in the
parabola of which the semi-parameter = 2 q, or the perihelion distance = q, let
the true anomaly w correspond to the same time, supposing in each case the
mass \i to be either neglected or equal. It is evident that we then have

33 MM

* Since the time contains the factor a- or i*. the greater the values of a = — £— , or J= ? .

1 — ee e* — 1

the more the error in M or JVwill be increased.

SECT. 1.] TO POSITION IN THE ORBIT. 39

r pp&v f r iqqAw , , „

J (T^Iecosw)2' J (1 + cosw)2 — \P:\^2>

the integrals commencing from v = 0 and w = 0, or

r (i+e)^i« _ r 2dw

J (l+ecost>)V2~J (l+cosic)2

Denoting - - by a, tan I v by 6, the former integral is found to be
1 -\-e

-j- H3 ( 1 — 2 a ) — |$5 ( 2 a — 3a«)-)-^(57(3aa^4«3) — etc.) ,

the latter, tan i w -j- ^tan3 £ «c. From this equation it is easy to determine to
by a and v, and also y by a and w by means of infinite series : instead of a may
be introduced, if preferred,

Since evidently for a = 0, or 8 •=. 0, we have f = w, these series will have the
following form : —

iv = v -+- d v' + (Tdy" + d3/" -f- etc.

» = w + d ^ + ^ d w" + d^e/" -f etc.

where v', v", v'", etc. will be functions of v, and «/, «/', ?yw, functions of zp. When
d is a very small quantity, these series converge rapidly, and few terms suffice for
the determination of w from v, or of v from w. t is derived from w, or w from t,
by the method we have explained above for the parabolic motion.

35.

Our BESSEL has developed the analytical expressions of the three first coeffi
cients of the second series w', ^v", w'", and at the same time has added a table con
structed with a single argument w for the numerical values of the two first w'
and w", (Von Zach Momtliche Correspondent, vol. XII, p. 197). A table for the
first coefficient w', computed by SIMPSON, was already in existence, and was
annexed to the work of the illustrious OLBERS above commended. By the use
of this method, with the help of BESSEL'S table, it is possible in most cases to
determine the true anomaly from the time with sufficient precision; what remains
to be desired is reduced to nearly the following particulars: —

•40 RELATIONS PERTAINING SIMPLY [BoOK I.

I. In the inverse problem, the determination of the time, that is, from the
true anomaly, it is requisite to have recourse to a somewhat indirect method, and
to derive w from v by trial. In order to meet this inconvenience, the first series
should be treated in the same manner as the second : and since it may be readily
perceived that — v' is the same function of v as ?// of iv, so that the table for w'
might answer for v' the sign only being changed, nothing more is required than
a table for v", by which either problem may be solved with equal precision.

Sometimes, undoubtedly, cases may occur, where the eccentricity differs but
little from unity, such that the general methods above explained may not appear
to afford sufficient precision, not enough at least, to allow the effect of the third
and higher powers of d in the peculiar method just sketched out, to be safely
neglected. Cases of this kind are possible in the hyperbolic motion especially, in
which, whether the former methods are chosen or the latter one, an error of
several seconds is inevitable, if the common tables, constructed to seven places of
figures only, are employed. Although, in truth, such cases rarely occur in prac
tice, something might appear to be wanting if it were not possible in all cases to
determine the true anomaly within 0".l, or at least 0".2, without consulting the
larger tables, which would require a reference to books of the rarer sort. We
hope, therefore, that it will not seem wholly superfluous to proceed to the exposi
tion of a peculiar method, which we have long had in use, and which will also
commend itself on this account, that it is not limited to eccentricities differing but
little from unity, but in this respect admits of general application.

36.

Before we proceed to explain this method, it will be proper to observe that
the uncertainty of the general methods given above, in orbits approaching the
form of the parabola, ceases of itself, when E or F increase to considerable mag
nitude, which indeed can take place only in large distances from the sun. To
show which, we give to

3»*a_nnvf 206265",

the greatest possible error in the ellipse, which we find in article 32, IV., the
following form,

SECT. 1.]

TO POSITION IN THE ORBIT.

41

^"Ml-TcosV)'""- 206265";

from which is evident of itself that the error is always circumscribed within
narrow limits when E acquires considerable value, or when cos E recedes further
from unity, however great the eccentricity may be. This will appear still more
distinctly from the following table, in which we have computed the greatest
numerical value of that formula for certain given values of E, for seven decimal
places.

E= 10° maximum error = 3".04

20 0 .76

30 0 .34

40 0 .19

50 0 .12

60 0 .08

The same thing takes place in the hyperbola, as is immediately apparent, if the
expression obtained in article 32, VII., is put into this form,

w cos F (cos F-\- 3 e sin F) y' (e e — 1)

The following table exhibits the greatest values of this expression for certain
given values of F.

F

a

maximum error.

10°

1.192

0.839

8".66

20

1.428

0.700

1 .38

30

1.732

0.577

0.47

40

2.144

0.466

0 .22

50

2.747

0.364

0.11

60

3.732

0.268

0 .06

70

5.671

0.176

0.02

When, therefore, E or F exceeds 40° or 50° (which nevertheless does not easily
occur in orbits differing but little from the parabola, because heavenly bodies
moving in such orbits at such great distances from the sun are for the most part
withdrawn from our sight) there will be no reason for forsaking the general
method. For the rest, in such a case even the series which we treated in article

6

42 RELATIONS PERTAINING SIMPLY [BOOK I.

34 might converge too slowly ; and therefore it is by no means to be regarded
as a defect of the method about to be explained, that it is specially adapted
to those cases in which E or F has not yet increased beyond moderate values.

*

37.

Let us resume in the elliptic motion the equation between the eccentric
anomaly and the time,

where we suppose E to be expressed in parts of the radius. Henceforth, we
shall leave out the factor- \/ ( 1 -j-/u>) ; if a case should occur where it is worth
while to take it into account, the symbol t would not express the time itself after
perihelion, but this time multiplied by y/(l -j-fi). We designate in future by q the
perihelion distance, and in the place of E and sin E, we introduce the quantities

E—smE, and E— -^ (E— sin E) = ^E+^ sin E:

the careful reader will readily perceive from what follows, our reason for selecting
particularly these expressions. In this way our equation assumes the following
form : —

As long as E is regarded as a quantity of the first order,

& E+ TV sin E= E — J0- E3 + ^ E* — etc.
will be a quantity of the first order, while

E-smE=\E* — ^E6 + -sfaE'' — etc.,

will be a quantity of the third order. Putting, therefore,

6(ff— sinJ?) _.. &E+^smE _ „
--

will be a quantity of the second order, and

^==l + dW^4 — etc.

will differ from unity by a quantity of the fourth order. But hence our equation
becomes

SECT. 1.]

TO POSITION IN THE ORBIT.

43

[1]

By means of the common trigonometrical tables, TBff E -\- -^ sin E may be com
puted with sufficient accuracy, but not E — sin E when E is a small angle; in this
way therefore it would not be possible to determine correctly enough the quan
tities A and B. A remedy for this difficulty would be furnished by an appro
priate table, from which we could take out with the argument E, either B or the
logarithm of B • the means necessary to the construction of such a table will
readily present themselves to any one even moderately versed in analysis. By
the aid of the equation

20 B

\j A can be determined, and hence t by formula [1] with all desirable precision.

The following is a specimen of such a table, which will show the slow increase
of log B ; it would be superfluous to take the trouble to extend this table, for
further on we are about to describe tables of a much more convenient form.

E

log B

E

logB

E

log B

0°

0.0000000

25°

0.0000168

50°

0.0002675

5

00

30

0349

55

3910

10

04

35

0645

60

5526

15

22

40

1099

20

69

45

1758

38.

It will not be useless to illustrate by an example what has been given in the
preceding article. Let the proposed true anomaly = 100°, the eccentricity
= 0.96764567, log q = 9.7656500. The following is the calculation for E, B,
A, and t : —

log tan * v 0.0761865

,1 — e

9.1079927

log tan

9.1841792, whence } E= 8° 41' 19*32, and U =

44 RELATIONS PERTAINING SIMPLY [BOOK I.

17° 22' 38".G4. To this value of E corresponds log B = 0.0000040 ; next is found
in parts of the radius,^ = 0.3032928, sin E= 0.2986643, whence -2\ E-\- ^ sin E
= 0.1514150, the logarithm of which = 9.1801689, and so log A* = 9.1801649.
Thence is derived, by means of formula [1] of the preceding article,

2'4589614 log— - • • 3-7601038

log A* ..... 9.1801649 log^l1 ........ 7.5404947

log 43.56386= . . 1.6391263 log 19.98014= ..... 1.3005985.
19.98014

63.54400 = *.

If the same example is treated according to the common method, e sin E in
seconds is found = 59610".79 = 16°33'30".79, whence the mean anomaly =
49' 7".85 = 2947'^ 85. And hence from

log &(— -)*= 1.6664302

is derived t = 63.54410. The difference, which is here only i^t^nr part of a day,
might, by the errors concurring, easily come out three or four times greater.
It is further evident, that with the help of such a table for log B even the inverse
problem can be solved with all accuracy, E being determined by repeated trials,
so that the value of t calculated from it may agree with the proposed value.
But this operation would be very troublesome : on account of which, we will now
show how an auxiliary table may be much more conveniently arranged, indefinite
trials be altogether avoided, and the whole calculation reduced to a numerical
operation in the highest degree neat and expeditious, which seems to leave
nothing to be desired.

-

39.

It is obvious that almost one half the labor which those trials would require,
could be saved, if there were a table so arranged that log B could be immedi
ately taken out with the argument A. Three operations would then remain ;
the first indirect, namely, the determination of A so as to satisfy the equation

SECT. 1.] TO POSITION IN THE ORBIT. 45

[1], article 37 ; the second, the determination of E from A and B, which rna'y be
done directly, either by means of the equation

or by this,

sin E=

the third, the determination of v from E by means of equation VII., article 8.
The first operation, we will bring to an easy calculation free from vague trials ;
the second and third, we will really abridge into one, by inserting a new quantity
C in our table by which means we shall have no need of E, and at the same
time we shall obtain an elegant and convenient formula for the radius vector.
Each of these subjects we will follow out in its proper order.

First, we will change" the form of equation [1] so that the Barkerian table
may be used in the solution of it. For this purpose we will put

5 — 5e

j

:

from which comes

ITK A OCA •?

7 5 tan i?f 4- 2 5 tan %ws=

denoting by a the constant

If therefore B should be known, w could be immediately taken from the Barkerian
table containing the true anomaly to which a'nswers the mean motion -^ ; A will
be deduced from w by means of the formula

A = fi tan2 i iv,
denoting the constant

5 — 5 e , ,,

r+^ by^-

Now, although B may be finally known from A by means of our auxiliary table,
nevertheless it can be foreseen, owing to its diifering so little from unity, that if
the divisor B were wholly neglected from the beginning, w and A would be
affected with a slight error only. Therefore, we will first determine roughly w
and A, putting 2? = 1 ; with the approximate value of A, we will find B in our

46 RELATIONS PERTAINING SIMPLY [BOOK I.

auxiliary table, with which we will repeat more exactly the same calculation ;
most frequently, precisely the same value of B that had been found from the
approximate value of A will correspond to the value of A thus corrected, so that a
second repetition of the operation would be superfluous, those cases excepted in
which the value of E may have been very considerable.

Finally, it is hardly necessary to observe that, if the approximate value of B
should iri any other way whatever be known from the beginning, (which may
always occur, when of several places to be computed, not very distant from each
other, some few are already obtained,) it is better to make use of this at once in
the first approximation : in this manner the expert computer will very often not
have occasion for even a single repetition. We have arrived at this most rapid
approximation from the fact that B differs from unity, only by a difference of the
fourth order, and is multiplied by a very small numerical coefficient, which advan
tage, as will now be perceived, was secured by the introduction of the quantities
E — sin E, ^E-\- TV sin E, in the place of E and sin E.

40.

Since, for the third operation, that is, the determination of the true anomaly,
the angle E is not required, but the tan J E only, or rather the log tan i E, that
operation could be conveniently joined with the second, provided our table sup
plied directly the logarithm of the quantity

which differs from unity by a quantity of the second order. "We have preferred,
however, to arrange our table in a somewhat different manner, by which, not-
withstanding the small extension, we have obtained a much more convenient
interpolation. By writing, for the sake of brevity, T instead of the tan2 i E, the
value of A, given in article 37,

is easily changed to

. __ T— g r'-f-f Ts— y T4 4-jf T5 — etc.
-

SECT. 1.] TO POSITION IN THE ORBIT. 47

in which the law of progression is obvious. Hence is deduced, by the inversion
of the series,

7 = 1 — -M + jHJH. Th A3 + ^nh ^ + T^Wiln, # + etc. ;
Putting, therefore,

C will be a quantity of the fourth order, which being included in our table, we
can pass directly to v from A by means of the formula,

i±f _ - ____ —

denoting by y the constant

i + 5«

In this way we gain at the same time a very convenient computation for the
radius vector. It becomes, in fact, (article 8, VI.),

Nothing now remains but to reduce the inverse problem also, that is, the
determination of the time from the true anomaly, to a more expeditious form of
computation : for this purpose we have added to our table a new column for T.
T, therefore, will be computed first from v by means of the formula

then A and log.B are taken from our table with the argument T, or, (which is
more accurate, and even more convenient also), 0 and log B, and hence A by
the formula

finally t is derived' from A and B by formula [1], article 37. If it is desired to
call into use the Barkerian table here also, which however in this inverse problem

48 RELATIONS PERTAINING SIMPLY [BOOK 1.

has less effect in facilitating the calculation, it is not necessary to pay any regard
to A, but we have at once

tan } w — tan lv

and hence the time t, by multiplying the mean motion corresponding to the true

73

anomaly, w, in the Barkerian table, by — .

42.

We have constructed with sufficient fulness a table, such as we have just
described, and have added it to this work, (Table I.). Only the first part pertains
to the ellipse ; we will explain, further on, the other part, which includes the
hyperbolic motion. The argument of the table, which is the quantity A, proceeds
by single thousandths from 0 to 0.300 ; the log B and C follow, which quantities
it must be understood are given in ten millionths, or to seven places of decimals,
the ciphers preceding the significant figures being suppressed ; lastly, the fourth
column gives the quantity T computed first to five, then to six figures, which
degree of accuracy is quite sufficient, since this column is only needed to get the
values of log B and C corresponding to the argument T, whenever t is to be
determined from v by the precept of the preceding article. As the inverse prob
lem which is much more frequently employed, that is, the determination of v and
r from t, is solved altogether without the help of T, we have preferred the quan
tity A for the argument of our table rather than T, which would otherwise have
been an almost equally suitable argument, and would even have facilitated a little
the construction of the table. It will not be unnecessary to mention, that all the
numbers of the table have been calculated from the beginning to ten places, and
that, therefore, the seven places of figures which we give can be safely relied upon;
but we cannot dwell here upon the analytical methods used for this work, by a
full explanation of which we should be too much diverted from our plan.
Finally, the extent of the table is abundantly sufficient for all cases in which it
is advantageous to pursue the method just explained, since beyond the limit
A ==0.3, to which answers T= 0.392374, or ^=64° 7', we may, as has been
shown before, conveniently dispense with artificial methods.

SECT. 1.] TO POSITION IN THE ORBIT. 41)

43.

We add, for the better illustration of the preceding investigations, an example
of the complete calculation for the true anomaly and radius vector from the time,
for which purpose we will resume the numbers in article 38. We put then e =
0.9674567, log q= 9.7656500, t = 63.54400, whence, we first derive the constants
log a = 0.03052357, log ft = 8.2217364, log y = 0.0028755.

Hence we have log a t = 2.1083102, to which corresponds in Barker's table
the approximate value of w— 99° 6' whence is obtained A= 0.022926, and from
our table log B = 0.0000040. Hence, the correct argument with which Barker's

table must be entered, becomes log ^5 = 2.1083062, to which answers w = 99° 6'
13".14 ; after this, the subsequent calculation is as follows : —

log tan2 km . . . 0.1385934 log tan i w ...... 0.0692967

log/J ..... 8.2217364 logy ........ 0.0028755

..... 8.3603298 * Comp. log(l— 1 4 + 0) . 0.0040143

A= ..... 0.02292608 log tan i » ...... 0.0761865

hence log B in the same manner as before ; $ v= ..... 50° 0' 0"

C— . 0.0000242 v= ..... 10000

l — ±A-{-C= . 0.9816833 log q ........ 9.7656500

4+0= . 1.0046094 2. Comp. log cos *t> . . .- 0.3838650

log(l— 1 4+0). . . . 9.9919714

C.log(l+|4 + 0). . . 9.9980028

logr ........ 0.1394892

If the factor B had been wholly neglected in this calculation, the true anomaly
would have come out affected with a very slight error (in excess) of 0".l only.

*

! ... 44. ' ,

It will be in our power to despatch the hyperbolic motion the more briefly,
because it is to be treated in a manner precisely analogous to that which we
have thus far expounded for the elliptic motion.

7

50 RELATIONS PERTAINING SIMPLY [BOOK I.

We present the equation between the time t and the auxiliary quantity u in .
the following form : —

in which the logarithms are hyperbolic, and

2V(«~

is a quantity of the first order,

J(«— 5

a quantity of the third order, when log u may be considered as a small quantity
of the first order. Putting, therefore,

i) + ^log«

n .1 A ~ — •"'

^

A will be a quantity of the second order, but B will differ from unity by a differ
ence of the fourth order. Our equation will then assume the following form : —

..... [2]

which is entirely analogous to equation [1] of article 37. Putting moreover,

T will be a quantity of the second order, and by the method of infinite series
will be found

Wherefore, putting

C will be a quantity of the fourth order, and

A —

Finally, for the radius vector, there readily follows from equation VII., article 21,

? _

(1 — T)co^iv ~~ (l-Tpl-j- C)cos*$v'

SECT. 1.] TO POSITION IN THE ORBIT. 51

45.

The latter part of the table annexed to this work belongs, as we have remarked
above, to the hyperbolic motion, and gives for the argument A (common to both
parts of the table), the logarithm of B and the quantity 0 to seven places of
decimals, (the preceding ciphers being omitted), and the quantity T to five and
afterwards to six figures. The latter part is extended in the same manner as
the former to ^1=0.300, corresponding to which is T= 0.241207, u= 2.930,
or = 0.341, jF— + 52°19'; to extend it further would have been superfluous,
(article 36).

The following is the arrangement of the calculation, not only for the determi
nation of the time from the true anomaly, but for the determination of the true
anomaly from the time. In the former problem, T will be got by means of the
formula

-

e-\-\

with T our table will give log B and 0, whence will follow

finally t is then found from the formula [2] of the preceding article. In the last
problem, will first be computed, the logarithms of the constants

/5

- y r_pre-

A will then be determined from t exactly in the same manner as in the elliptic
motion, so that in fact the true anomaly w may correspond in Barker's table to
the mean motion -^,and that we may have

A = (l tan2 % w ;
the approximate value of A will be of course first obtained, the factor B being

52

RELATIONS PERTAINING SIMPLY

[BOOK I.

either neglected, or, if the means are at hand, being estimated ; our table will
then furnish the approximate value of B, with which the work will be repeated ;
the new value of B resulting in this manner will scarcely ever suffer sensible cor
rection, and thus a second repetition of the calculation will not be necessary. C
will be taken from the table with the corrected value of A, which being done we
shall have,

From this it is evident, that no difference can be perceived between the formulas
for elliptic and hyperbolic motions, provided that we consider /3, A, and T, in the
hyperbolic motion as negative quantities.

46.

It will not be unprofitable to elucidate the hyperbolic motion also by some
examples, for which purpose we will resume the numbers in articles 23, 26.

I. The data are e = 1.2618820, log q = 0.0201657, v = 18° 51' 0" : t is
required. We have

2 log tan i v .

. . . 8.4402018

losT . . .

. . 7.5038375

loo- —

90036357

log (1+67).

. . 0.0000002

&e + l

C. log (1 — 4

T) . 0.0011099

JQOT J^

Y o03S3To

d

loir -A

. . 7.5049476

r— . .

. . . 0.00319034

°

loo;.g —

. . . 00000001

C — . .

. . . 00000005

locr "

2 ^fifU44 Ino- 2

5(l + 9e)/ y \

2QCM OKQO

O £ »/ (Q i \ '

loo; A2 .

. 8.7524738 log .4

15 k \e — \)

t

.oo'tOQoa

62574214

log 13.77584= .

. 1.1391182 loeO.

138605— . .

. . . 91417796

0.13861

13.91445 = *.

II. e and q remaining as before, there is given t = 65.41236 ; v and r are
required. We find the logarithms of the constants,

SECT. 1.]

TO POSITION IN THE ORBIT.

53

log « = 9.9758345
log 0 = 9.0251649
log 7 = 9.9807646.

Next we have log a t = 1.7914943, whence by Barker's table the approximate
value of w=70031'44", and hence ,4 = 0.052983. To this A in our table
answers log B = 0.0000207 ; from which, log ~ = 1.7914736, and the corrected

value of w= 70031'36".86. The remaining operations of the calculation are "as
follows : —

log tan 4 w 9.8494699

logy 9.9807646

9.9909602

2 log tan 4 w . . . 9.6989398
log 0 9.0251649

log 4 ...... 8.7241047

A= ...... 0.05297911

log B as before,

C= .
4+0= .

0.0001252
1.0425085

'= . 0.9895294

log tan 4 v 9.8211947

$v= ... 33°31'30".02
v= ... 67 3 0 .04

logy 0.0201657

2 C. log cos 4 » .... 0.1580378
log(l + Ayi_p O) . . 0.0180796
C. log (1 ---£4+0) . . 0.0045713

logr 0.2008544

Those which we found above (article 26), v = 67°2'59".78, log r = 0.2008541,
are less exact, and v should properly have resulted = 67° 3' 0".00, with which
assumed value, the value of t had been computed by means of the larger tables.

SECOND SECTION.

RELATIONS PERTAINING SIMPLY TO POSITION IN SPACE.

47.

IN the first section, the motion of heavenly bodies in their orbits is treated
without regard to the position of these orbits in space. For determining this
position, by which the relation of the places of the heavenly body to any other
point of space can be assigned, there is manifestly required, not only the position
of the plane in which the orbit lies with reference to a certain known plane (as,
for example, the plane of the orbit of the earth, the ecliptic), but also the position
of the apsides in that plane. Since these things may be referred, most advanta
geously, to spherical trigonometry, we conceive a spherical surface described
with an arbitrary radius, about the sun as a centre, on which any plane passing
through the sun will mark a great circle, and any right line drawn from the
sun, a point. For planes and right lines not passing through the sun, we draw
through the sun parallel planes and right lines, and we conceive the great circles
and points in the surface of the sphere corresponding to the latter to represent
the former. The sphere may also be supposed to be described with a radius
infinitely great, in which parallel planes, and also parallel right lines, are repre
sented in the same manner.

Except, therefore, the plane of the orbit coincide with the plane of the ecliptic,
the great circles corresponding to those planes (which we will simply call the orbit
and the ecliptic) cut each other in two points, which are called nodes ; in one of
these nodes, the body, seen from the sun, will pass from the southern, through the
ecliptic, to the northern hemisphere, in the other, it will return from the latter to
the former ; the former is called the ascending, the latter the descending node. We
(54)

SECT. 2.] TO POSITION IN SPACE. 55

fix the positions of the nodes in the ecliptic by means of their distance from the
mean vernal equinox (longitude) counted in the order of the signs. Let, in fig. 1,
Q, be the ascending node, A Q B part of the ecliptic, C Q D part of the" orbit ;
let the motions of the earth and of the heavenly body be in the directions from A
towards B and from C towards D, it is evident that the spherical angle which Q, D
makes with Q B can increase from 0 to 180°, but not beyond, without Q ceasing
to be the ascending node : this angle we call the inclination of the orbit to the
ecliptic. The situation of the plane of the orbit being determined by the longi
tude of the node and the inclination of the orbit, nothing further is wanted
except the distance of the perihelion from the ascending node, which we reckon
in the direction of the motion, and therefore regard it as negative, or between
180" and 360°, whenever the perihelion is south of the ecliptic. The following
expressions are yet to be observed. The longitude of any point whatever in
the circle of the orbit is counted from that point which is distant just so far back
from the ascending node in the orbit as the vernal equinox is back from the same
point in the ecliptic : hence, the longitude of the perihelion will be the sum of the
longitude of the node and the distance of the perihelion from the node ; also, the
true longitude in orbit of the body will be the sum of the true anomaly and the
longitude of the perihelion. Lastly, the sum of the mean anomaly and longitude
of the perihelion is called the mean longitude : this last expression can evidently
only occur in elliptic orbits.

48.

In order, therefore, to be able to assign the place of a heavenly body in space
for any moment of time, the following things must be known.

I. The mean longitude for any moment of time taken at will, which is called
the epoch : sometimes the longitude itself is designated by the same name. For
the most part, the beginning of some year is selected for the epoch, namely, noon
of January 1 in the bissextile year, or noon of December 31 preceding, in the
common year.

II. The mean motion in a certain interval of time, for example, in one mean
solar day, or in 365, 365J, or 36525 days.

56 RELATIONS PERTAINING SIMPLY [BOOK I.

III. The semi-axis major, which indeed might be omitted when the mass of
the body is known or can be neglected, since it is already given by the mean
motion, (article 7) ; both, nevertheless, are usually given for the sake of con
venience.

IV. Eccentricity. V. Longitude of the perihelion. VI. Longitude of the
ascending node. VII. Inclination of the orbit.

These seven things are called the elements of the motion of the body.

In the parabola and hyperbola, the time of passage through the perihelion
serves in place of the first element ; instead of II, are given what in these
species of conic sections are analogous to the mean daily motion, (see article
19 ; in the hyperbolic motion the quantity X kl~*, article 23). In the hyperbola,
the remaining elements may be retained the same, but in the parabola, where
the major axis is infinite and the eccentricity = 1, the perihelion distance alone
will be given in place of the elements III. and IV.

49.

According to the common mode of speaking, the inclination of the orbit,
which we count from 0 to 180°, is only extended to 90°, and if the angle made
by the orbit with the arc Q, B exceeds a right angle, the angle of the orbit with
the arc & A, which is its complement to 180°, is regarded as the inclination of
the orbit ; in this case then it will be necessary to add that the motion is retrograde
(as if, in our fiigure, E Q, F should represent a part of the orbit), in order that it
may be distinguished from the other case where the motion is called direct. The
longitude in orbit is then usually so reckoned that in Q it may agree with the
longitude of this point in the ecliptic, but decrease in the direction & F; the initial
point, therefore, from which longitudes are counted contrary to the order of
motion in the direction Q, F, is just so far distant from 8, as the vernal equinox
from the same Q in the direction Q A. Wherefore, in this case the longitude of
the perihelion will be the longitude of the node diminished by the distance of
the perihelion from the node. In this way either form of expression is easily con
verted into the other, but we have preferred our own, for the reason that we
might do away with the distinction between the direct and retrograde motion,

SECT. 2.] TO POSITION IN SPACE. 57

and use always the same formulas for both, while the common form may fre
quently require double precepts.

50.

The most simple method of determining the position, with respect to the
ecliptic, of any point whatever on the surface of the celestial sphere, is by means
of its distance from the ecliptic (latitude], and the distance from the equinox of
the point at which the ecliptic is cut by a perpendicular let fall upon it, (longi
tude). The latitude, counted both ways from the ecliptic up to 90°, is regarded as
positive in the northern hemisphere, and as negative in the southern. Let the
longitude X, and the latitude /?, correspond to the heliocentric place of a celestial
body, that is, to the projection upon the celestial sphere of a right line drawn
from the sun to the body ; let, also, u be the distance of the heliocentric place
from the ascending node (which is called the argument of the latitude], i be the
inclination of the orbit, 8 the longitude of the ascending node; there will exist
between i,u, fi,"k. — 8 , which quantities will be parts of a right-angled spherical
triangle, the following relations, which, it is easily shown, hold good without any
restriction : —

I. tan (X — Q, ) = cos i tan u

II. tan /3 = tan« sin (X — Q)

III. sin {} = sin i sin u

IV. cos u = cos ft cos (X — a )•

When the quantities i and u are given, X — Q will be determined from them by
means of equation I., and afterwards ft by II. or by III., if ft does not approach
too near to + 90° ; formula IV. can be used at pleasure for confirming the cal
culation. Formulas I. and IV. show, moreover, that X — Q, and u always lie in
the same quadrant when i is between 0° and 90° ; X — & and 360° — u, on the
other hand, will belong to the same quadrant when i is between 90° and 180°, or,
according to the common usage, when the motion is retrograde : hence the ambi
guity which remains in the determination of X — 8 by means of the tangent
according to formula I., is readily removed.

8

58 RELATIONS PERTAINING SIMPLY [BoOK I.

The following formulas are easily deduced from the combination of the pre
ceding : —

V. sin (u — X -{- 8 ) = 2 sin2 £ i sin u cos (X — 8 )
VI. sin (u — X -f- 8 ) = tan J z sin ft cos (X — 8 )
VII. sin (« — X -(- 8 ) = tan i z tan ft cos w
VIII. sin (u -\- X — 8 ) = 2 cos2 J j sin « cos (X — 8 )
IX. sin (u -4- X — 8 ) = cotan £ i sin ft cos (X — 8 )

X. sin (w -{- X — 8 ) = cotan £ a tan ft cos w.

The angle u — X -4- 8, when a' is less than 90°, or w -|- X — 8, when i is more
than 90°, called, according to common usage, the reduction to the ecliptic, is, in fact,
the difference between the heliocentric longitude X and the longitude in orbit,
which last is by the former usage 8 + «, by ours 8 -)- u. When the inclination
is small or differs but little from 180°, the same reduction may be regarded as a

^

quantity of the second order, and in this case it will be better to compute first ft
by the formula III., and afterwards X by VII. or X., by which means a greater
precision will be attained than by formula I.

If a perpendicular is let fall from the place of the heavenly body in space
upon the plane of the ecliptic, the distance of the point of intersection from the
sun is called the curtate distance. Designating this by /, the radius vector likewise
by r, we shall have

XI. / = r cos ft.

51.

As an example, we will continue further the calculations commenced in arti
cles 13 and 14, the numbers of which the planet Juno furnished. We had
found above, the true anomaly 315°1'23".02, the logarithm of the radius vector
0.3259877: now let i == 13°6'44".10, the distance of the perihelion from the
node = 241°10'20".57, and consequently u = 196°11'43".59 j finally let 8 =
171° 7'48".73. Hence we have : -
log tan u .... 9.4630573 log sin (X— 8). . . . 9.4348691 «

log cos i .... 9.9885266 log tan i 9.3672305

log tan (X — ») .. 9.4515839 log tan ft ...... 8.8020996 «

SECT. 2.] TO POSITION IN SPACE. 59

Jl — a= 195047'40".25 ft = -3°37'40".02

1= 65528.98 log cos ft 9.9991289

logr 0.3259877 log cos I— Q ... 9.9832852n

log cos ft 9.9991289 9.9824141«

log/ 0.3251166 log cos u 9.9824141«.

The calculation by means of formulas III., VII. would be as follows : -

log sin u .... 9.4454714w log tan i* 9.0604259

log sin » 9.3557570 log tan 0 8.8020995«

log sin ft . "7 .. . 8.8012284^ IogcosM • • • • 9.9824141 n
ft= — 3°37'40".02 log sin (u — I -f Q, ) . 7.8449395

u — l + Q = 0°24' 3".34

I—Q, = 195 47 40.25.

52.

Eegarding i and u as variable quantities, the differentiation of equation III.,
article 50. gives

cotan ft d/5 =: cotan idi-\- cotan wdw,
or

XII. d^ r=sin (X — Q ) d« -(- sin z cos (X — £2 ) dw.

In the same manner, by differentiation of equation I. we get

XIII. d(Jl— Q) = — tan/3cos(Jt— • Q)dt + ^d».
Finally, from the differentiation of equation XI. comes

Ar' = cos ft dr — rsin/fd/3,
or

XIV. dr' = cos/?dr — r sin ft sin (X — Q ) d« — r sin ft sin i cos (X — &) du.

In this last equation, either the parts that contain dz and du are to be divided by
206265", or the remaining ones are to be multiplied by this number, if the
changes of i and u are supposed to be expressed in minutes and seconds.

60 RELATIONS PERTAINING SIMPLY [BOOK I.

53.

The position of any point whatever in space is most conveniently deter
mined by means of its distances from three planes cutting each other at right
angles. Assuming the plane of the ecliptic to be one of these planes, and denot
ing the distance of the heavenly body from this plane by z, taken positively on
the north side, negatively on the south, we shall evidently have s = r tan ft =
r sin ft = r sin i sin u. The two remaining planes, which we also shall consider
drawn through the sun, will project great circles upon the celestial sphere, which
will cut the ecliptic at right angles, and the poles of which, therefore, will lie in
the ecliptic, and will be at the distance of 90° from each other. We call that pole
of each plane, lying on the side from which the positive distances are counted,
the positive pole. Let, accordingly, N and N -\- 90° be the longitudes of the
positive poles, and let distances from the planes to which they respectively
belong be denoted by x and y. Then it will be readily perceived that we have

a; = r'cos(X — N}

= r cos ft cos (X — 8 ) cos (N — 0,}-\-r cos ft sin (X — Q ) sin (^V — Q, )
^ = /sin(Jl— N)

= r cos ft sin (X — Q ) cos (JV — Q, ) — r cos ft cos (X — Q ) sin (N — Q ),

which values are transformed into

x = r cos (N — 8 ) cos u -\- r cos i sin (N — & ) sin u
y = r cosz cos (N — 8) sin u — rsin (N — 8) COSM.

If now the positive pole of the plane of x is placed in the ascending node, so that
N= 8, we shall have the most simple expressions of the coordinates x,y, z, —

x = r cos u

y •=. r cos i sin u
z =. r sin i sin u .

But, if this supposed condition does not occur, the formulas given above will
still acquire a form almost equally convenient, by the introduction of four
auxiliary quantities, a, I, A, B, so determined as to have

SECT. 2.] TO POSITION IN SPACE. 61

cos (N-- Q, ) — a sin A
cos i sin (N — & ) = a cos A
— sin (N — 8 ) = b sin B
cos a cos (^V — 8 ) = & cos 5,

(see article 14, II.). We shall then evidently have

x = ra sin (u -\- A)
y = r b sin (u -j- .Z?)
3 = r sin «' sin M .

54.

The relations of the motion to the ecliptic explained in the preceding article,
will evidently hold equally good, even if some other plane should be substituted
for the ecliptic, provided, only, the position of the plane of the orbit in respect
to this plane be known ; but in this case the expressions longitude and latitude
must be suppressed. The problem, therefore, presents itself: From the known
position of the plane of the orbit and of another new plane in respect to the ecliptic, to
derive the position of the plane of the orbit in respect to the new plane. Let n Q , Q Q ',
n £' be parts of the great circles which the plane of the ecliptic, the plane of the
orbit, and the new plane, project upon the celestial sphere, (fig. 2). In order
that it may be possible to assign, without ambiguity, the inclination of the second
circle to the third, and the place of the ascending node, one direction or the other
must be chosen in the third circle, analogous, as it were, to that in the ecliptic
which is in the order of the signs; let this direction in our figure be from n toward
Q'. Moreover, of the two hemispheres, separated by the circle n&', it will be
necessary to regard one as analogous to the northern hemisphere, the other to
the southern ; these hemispheres, in fact, are already distinct in themselves, since
that is always regarded as the northern, which is on the right hand to one moving
forward* in the circle according to the order of the signs. In our figure, then, Q,
w, &', are the ascending nodes of the second circle upon the first, the third upon
the first, the second upon the third; 180°-- n Q, Q', &n&',nQ,'Q, the inclina-

* In the inner surface, that 5s to say, of the sphere represented by our figure.

62 RELATIONS PERTAINING SIMPLY [BoOK I.

tions of the second to the first, the third to the first, the second to the third.
Our problem, therefore, depends upon the solution of a spherical triangle, in
which, from one side and the adjacent angles, the other parts are to be deduced.
We omit, as sufficiently well known, the common precepts for this case given
in spherical trigonometry : another method, derived from certain equations, which
are sought in vain in our wyorks on trigonometry, is more conveniently employed.
The following are these equations, which we shall make frequent use of in future:
a, b, c, denote the sides of the spherical triangle, and A, B, C, the angles oppo
site to them respectively : —

j sini(& — c) __ sin | (B— C)
sin £ a cos ^ A

-. j sin 1 (b + e) __ cosj (B—C)
sin ^ a sin ^ A

HI COS

cos^a cos

« i : \ ~t - •

cos \ a sin £ A

Although it is necessary, for the sake of brevity, to omit here the demonstration
of these propositions, any one can easily verify them in triangles of which neither
the sides nor the angles exceed 180°. But if the idea of the spherical triangle is
conceived in its greatest generality, so that neither the sides nor the- angles are
confined within any limits whatever (which affords several remarkable advan
tages, but requires certain preliminary explanations), cases may exist in which it
is necessary to change the signs in all the preceding equations ; since the former
signs are evidently restored as soon as one of the angles or one of the sides is
increased or diminished 360°, it will always be safe to retain the signs as we
have given them, whether the remaining parts are to be determined from a side
and the adjacent angles, or from an angle and the adjacent sides ; for, either
the values of the quantities sought, or those differing by 360° from the true val
ues, and, therefore, equivalent to them, will be obtained by our formulas. We
reserve for another occasion a fuller elucidation of this subject : because, in the
meantime, it will not be difficult, by a rigorous induction, that is, by a complete
enumeration of all the cases, to prove, that the precepts which we shall base upon

SECT. 2.] TO POSITION IN SPACE. 63

these formulas, both for the solution of our present problem, and for other pur
poses, hold good in all cases generally.

55.

Designating as above, the longitude of the ascending node of the orbit upon
the ecliptic by 8, the inclination by i ; also, the longitude of the ascending node
of the new plane upon the ecliptic by n, the inclination by t ; the distance of the
ascending node of the orbit upon the new plane from the ascending node of the
new plane upon the ecliptic (the arc nQ,' in fig. 2) by 8', the inclination of the
orbit to the new plane by i' ; finally, the arc from 8 to 8' in the direction of the
motion by A: the sides of our spherical triangle will be & — n, 8', A, and the
opposite angles,/, 180° — i, e. Hence, according to the formulas of the preceding
article, we shall have

sin £ i' sin £ ( 8 ' -\- A] = sin ^ ( 8 — ») sin £ (i -\- e)
sin i i'cos £ ( 8 ' -j- A) = cos i ( & — n) sin J (i — e)
cos £ /sin i (8' — //) = sin k (8 — ?z)cos£ (i-\- e)
cos H' cos i (8' — A} =cos i (8 — w)cosi (/ — «).

The two first equations will furnish i (8' -)-//) and sin i /; the remaining two,
i(S'--J) and cos it"; from ^Q'-j-//) and J(8'— z/) will follow 8' and J ;
from sin i / and cos £ &y (the agreement of which will serve to prove the calcula
tion) will result i'. The uncertainty, whether £ ( 8' + ^) and £ ( Q,' -- A) should
be taken between 0 and 180° or between 180° and 360°, will be removed in this
manner, that both sin \ i', cos J i', are positive, since, from the nature of the case, i'
must fall below 180°.

56.

It will not prove unprofitable to illustrate the preceding precepts by an
example. Let 8 = 172° 28' 13". 7, i = 34°38'l".l ; let also the new plane be
parallel to the equator, so that n = 180° ; we put the angle e, which will be the
obliquity of the ecliptic = 23°27'55".8. We have, therefore,

64 RELATIONS PERTAINING SIMPLY [BOOK 1.

a — »= -7°31'46".3 i(8— n)= -3°45'53".15

»-{-« = 58 556.9 J (»-{-?) = 29 258.45

i — e= 1110 5.3 i(i — e) = 535 2.65

logsini(8— n) . . 8.8173026 n logcosj(8— w) . . 9.9990618

logsini(t + e) . . . 9.6862484 logsin$(t — e) . . . 8.9881405

logcosi(t + e) . . . 9.9416108 logcos i (i— e) . . . 9.9979342.

IK-:1.' f \v • have

logHinifsrai(8'-{-^) 8.5035510» logcos H' sin * (8'—^) 8.7589134«
logsinKcosifa'+J) 8.9872023 logcos Jt" cos i (8'— //) 9.9969960

whence i ( 8'+ J) = 341° 49' 19".01 whence i ( 8 ' — //) = 356° 41' 31".43
log sin it* 9.0094368 log cos H' 9.9977202.

Thus we obtain H' = 5° 51' 56".445, i' = 11° 43'52".89, 8' = 338° 30'50".43,
.-/ =; — 14° 52' 12".42. Finally, the point n evidently corresponds in the celestial
sphere to the autumnal equinox ; for which reason, the distance of the ascending
node of the orbit on the equator from the vernal equinox (its right ascension)
will be 158°30'50".43.

In order to illustrate article 53, we will continue this example still further,
and will develop the formulas for the coordinates with reference to the three
planes passing through the sun, of which, let one be parallel to the equator, and
let the positive poles of the two others be situated in right ascension 0° and 90°:
let the distances from these planes be respectively s, x, y. If now, moreover,
the distances of the heliocentric place in the celestial sphere from the points 8,
8', are denoted respectively by u, u', we shall have u'=n — 4 = u -\- 14° 52'12".42,
and the quantities which in article 53 were represented by i, IV — 8, u, will here
be {, 180° — 8', w7. Thus, from the formulas there given, follow,

log a sin A . . . . 9.9687197 re log b sin B . . . . 9.5638058
logacos.4 .... 9.5546380« logicos^ .... 9.9595519w

whence A = 248° 55' 22".97 whence B = 158° 5' 54".97

log a 9.9987923 log b 9.9920848.

We have therefore,

SECT. 2.] TO POSITION IN SPACE. Go

x = ar sin (M'+ 248855'22'/.97) = ar sm\u -j- 2G3047'35".39)
y = 5rsin(2«'-fl58 5 54 .97) = br sin (M + 172 58 7.39)
z = crsinu' =eram(u-\- 14 5212.42)

in which log e = log sin { = 9.3081870.

Another solution of the problem here treated is found in Von Zach's Monatliche
Corresponded, B. IX. p. 385.

57.

Accordingly, the distance of a heavenly body from any plane passing through
the sun can be reduced to the form krsm(v -\- K}, v denoting the true anomaly;
k will be the sine of the inclination of the orbit to this plane, K the distance
of the perihelion from the ascending node of the orbit in the same plane. So far
as the position of the plane of the orbit, and of the line of apsides in it, and also
the position of the plane to which the distances are referred, can be regarded as
constant, k and K will also be constant. In such a case, however, that method
will be more frequently called into use in which the third assumption, at least, is
not allowed, even if the perturbations should be neglected, which always affect
the first and second to a certain extent. This happens as often as the distances
are referred to the equator, or to a plane cutting the equator at a right angle
in given right ascension: for since the position of the equator is variable, owing to
the precession of the equinoxes and moreover to the nutation (if the true and not
the mean position should be in question), in this case also k and K will be subject
to changes, though undoubtedly slow. The computation of these changes can be
made by means of differential formulas obtained without difficulty : but here
it may be, for the sake of brevity, sufficient to add the differential variations
of/, Q,' and //, so far as they depend upon the changes of & — n and e.

d*w = sine sin8'd(8 — n) — cosS'de

sin i cos A •, , 0 x , sin Q ' ,

C

sin i sin r

Finally, when the problem only is, that several places of a celestial body with

9

66 RELATIONS PERTAINING SIMPLY [BOOK I.

respect to such variable planes may be computed, which places embrace a mod
erate interval of time (oue year, for example), it will generally be most con
venient to calculate the quantities a, A, b, B, c, C, for the two epochs between
which they fall, and to derive from them by simple interpolation the changes for
the particular times proposed.

58.

Our formulas for distances from given planes involve v and r ; when it is
necessary to determine these quantities first from the time, it will be possible to
abridge part of the operations still more, and thus greatly to lighten the labor.
These distances can be immediately derived, by means of a very simple formula,
from the eccentric anomaly in the ellipse, or from the auxiliary quantity F or u
in the hyperbola, so that there will be no need of the computation of the true
anomaly and radius vector. The expression kr sin (v -\- K] is changed ;

I. For the ellipse, the symbols in article 8 being retained, into

ak cosy cos JT sin E-\- ak sin K '(cos E — e).
Determining, therefore, /, L, X, by means of the equations

aksin K= IsinL
ak cos (f cos K=l cos L

.K=i — el

our expression passes into I sin (E -f- L) -\- X, in which I, L, "k will be constant, so
far as it is admissible to regard k, K, e as constant ; but if not, the same precepts
which we laid down in the preceding article will be sufficient for computing their
changes.

We add, for the sake of an example, the transformation of the expression for
# found in article 56, in which we put the longitude of the perihelion = 121° 17'
34% 9 == 14° 13'3r.97, log a = 0.4423790. The distance of the perihelion from
the ascending node in the ecliptic, therefore, = 308° 49' 20".7 = ti — v; hence
K= 212° 36' 56".09. Thus we have,

SECT. 2.] TO POSITION IN SPACE. 67

log a/c ..... 0.4411713 log I sin L .... 0.1727GOOn
logging .... 9.7315887 n log I cos L . . . . 0.3531154 n
log a k cos (f . . . 0.4276456 whence L = 213°25'51".30

log cos K .... 9.9254698 n log^ = 0.4316627

logJl= 9.5632352

1= +0.3657929.

II. In the hyperbola the formula k r sin (v -\- K), by article 21, passes into
X -}- ju tan F -\- v sec F, if we put e b It sin ZT— I, b k tan if cos K= /A, — bk sin K
= v ; it is also, evidently, allowable to bring the same expression under the form

nsm(F-\-N)-{-v
cosF '

If the auxiliary quantity u is used in the place of F, the expression /crsin (v-\-K]
will pass, by article 21, into

in which a, ft, y, are determined by means of the formulas
a = 7, = e b k sin K

y = £ (v — jtt) = — £ ebk sin

III. In the parabola, where the true anomaly is derived directly from the time,
nothing would remain but to substitute for the radius vector its value. Thus,
denoting the perihelion distance by q, the expression kr sin (v -f- -ff") becomes

q k sin (v -\- K)

59.

The precepts for determining distances from planes passing through the sun
may, it is evident, be applied to distances from the earth ; here, indeed, only the
most simple cases usually occur. Let R be the distance of the earth from the sun,
L the heliocentric longitude of the earth (which differs 180° from the geocentric
longitude of the sun), lastly,^, Y, Z, the distances of the earth from three planes
cutting each other in the sun at right angles. Now if

68 RELATIONS PERTAINING SBITLY [BOOK I.

I. The plane of Z is the ecliptic itself, and the longitudes of the poles of the
remaining planes, the distances from which are -X", Y, are respectively N, and
J\r-U90°; then

X=Rcos(L — N), Y = Swci(L — JV), Z=Q.

II. If the plane of Z is parallel to the equator, and the right ascensions of the
poles of the remaining planes, from which the distances are X, Y, are respectively
0° and 90°, we shall have, denoting by « the obliquity of the ecliptic,

X=RcosL, Y=RcoszsinL, Z=RsinssinL.

The editors of the most recent solar tables, the illustrious VON ZACH and DE
LAWBRE, first began to take account of the latitude of the sun, which, produced
by the perturbations of the other planets and of the moon, can scarcely amount
to one second. Denoting by B the heliocentric latitude of the earth, which will
always be equal to the latitude of the sun but affected with the opposite sign, we
shall have,

In Case I.

X = R cos B cos (L — N)

Z=RsinB

In Case

X = R cos B cos L

Y= R cos B cos s sin L — R sin B sin e

Z — R cos B sin g sin L -\- R sin B cos f.

It will always be safe to substitute 1 for cos B, and the angle expressed in parts
of the radius for sin B.

The coordinates thus found are referred to the centre of the earth. If £, 77, £,
are the distances of any point whatever on the surface of the earth from three
planes drawn through the centre of the earth, parallel to those which were drawn
through the sun, the distances of this point from the planes passing through the
sun, will evidently be X -{- £, Y-\- 77, Z -\- L : the values of the coordinates £, 17, C,
are easily determined in both cases by the following method. Let (> be the radius
of the terrestrial globe, (or the sine of the mean horizontal parallax of the sun,)
X the longitude of the point at which the right line drawn from the centre of the
earth to the point on the surface meets the celestial sphere, /? the latitude of the
same point, a the right ascension, d the declination, and we shall have,

SECT. 2.] TO POSITION IN SPACE. 69

In Case I.
= ^> COS /? COS (X

1 = 9 cos /3 sin (X —
' = Q sin |3

In Case IT.

— () COS d COS 05

= Q cos d sin «

— (> sin d.

This point of the celestial sphere evidently corresponds to the zenith of the
place on the surface (if the earth is regarded as a sphere), wherefore, its right
ascension agrees with the right ascension of the mid-heaven, or with the sidereal
time converted into degrees, and its declination with the elevation of the pole ;
if it should be worth while to take account of the spheroidal figure of the earth,
it would be necessary to adopt for d the corrected elevation of the pole, and for
Q the true distance of the place from the centre of the earth, which are deduced
by means of known rules. The longitude and latitude X and /? will be derived
from a and d by known rules, also to be given below : it is evident that X coin
cides with the longitude of the nanagesimal, and 90° — (3 with its altitude.

60.

If x, y, s, denote the distances of a heavenly body from three planes cutting
each other at right angles at the sun; X, Y, Z, the distances of the earth (either
of the centre or a point on the surface), it is apparent that x — X,y — Y, 2 — Z,
would be the distances of the heavenly body from three planes drawn through
the earth parallel to the former; and these distances would have the same relation
to the distance of the body from the earth and its geocentric place,* (that is, the place
of its projection in the celestial sphere, by a right line drawn to it from the earth),
which x, y, z, have to its distance from the sun and the heliocentric place. Let J
be the distance of the celestial body from the earth ; suppose a perpendicular in
the celestial sphere let fall from the geocentric place on the great circle which
corresponds to the plane of the distances z, and let a be the distance of the
intersection from the positive pole of the great circle which corresponds to the

* In the broader sense : for properly this expression refers to that case in which the right line is
drawn from the centre of the earth.

70 RELATIONS PERTAINING SIMPLY [BOOK 1.

plane of the distances x; and, finally, let I be the length of this perpendicular, or
the distance of the geocentric place from the great circle corresponding to the
distances z. Then I will be the geocentric latitude or declination, according as the
plane of the distances e is the ecliptic or the equator ; on the other hand, a -(- N
will be the geocentric longitude or right ascension, if N denotes, in the former
case, the longitude, in the latter, the right ascension, of the pole of the plane of
the distances x. Wherefore, we shall have

x — X = /J cos b cos a
y — Y= z/ cos b sin a
z — Z = A sin b .

The two first equations will give a and A cos b ; the latter quantity (which must
be positive) combined with the third equation, will give I and d.

61.

We have given, in the preceding articles, the easiest method of determining
the geocentric place of a heavenly body with respect to the ecliptic or equator,
either free from parallax or affected by it, and in the same manner, either free
from, or affected by, nutation. In what pertains to the nutation, all the difference
will depend upon this, whether we adopt the mean or true position of the equator;
as in the former case, we should count the longitudes from the mean equinox,
in the latter, from the true, just as, in the one, the mean obliquity of the ecliptic
is to be used, in the other, the true obliquity. It appears at once, that the greater
the number of abbreviations introduced into the computation of the coordinates,
the more the preliminary operations which are required ; on which account, the
superiority of the method above explained, of d-eriving the coordinates immedi
ately from the eccentric anomaly, will show itself especially when it is necessary
to determine many geocentric places. But when one place only is to be com
puted, or very few, it would not be worth while to undertake the labor of calcu
lating so many auxiliary quantities. It will be preferable in such a case not to
depart from the common method, according to which the true anomaly and radius
vector are deduced from the eccentric anomaly; hence, the heliocentric place

SECT. 2.] TO POSITION IN SPACE. 71

with respect to the ecliptic ; hence, the geocentric longitude and latitude ; and
hence, finally, the right ascension and declination. Lest any thing should seeni
to be wanting, we will in addition briefly explain the two last operations.

62.

Let X be the heliocentric longitude of the heavenly body, /? the latitude ; / the
geocentric longitude, b the latitude, r the distance from the sun, A the distance
from the earth ; lastly, let L be the heliocentric longitude of the earth, B the Ia1>
itude, R its distance from the sun. When we cannot put B — 0, our formulas
may also be applied to the case in which the heliocentric and geocentric places
are referred, not to the ecliptic, but to any other plane whatever ; it will only be
necessary to suppress the terms longitude and latitude : moreover, account can
be immediately taken of the parallax, if only, the heliocentric place of the earth
is referred, not to the centre, but to a point on the surface. Let us put, moreover,

r cos /? = r, A cos b = A', R cos B = R ' .

Now by referring the place of the heavenly body and of the earth in space to
three planes, of which one is the ecliptic, and the second and third have their
poles in longitude N and N-\- 90°, the following equations immediately present
themselves: —

/ cos (I — N) — R cos (L — N] = J'cos (l — N]
r sin (X — N) — R sin (L — N}= A' sin (I— N}
/tan/? — M'tanB =/1'tanb,

in which the angle N is wholly arbitrary. The first and second equations will
determine directly I — N and A', whence b will follow from the third ; from b
and A' you will have A. That the labor of calculation may be as convenient as
possible, we determine the arbitrary angle N in the three following ways: —
I. By putting JVr= L, we shall make

^sin(X — L} = P, ^cos(X — L} — 1= Q,
and I — L, -^, and b, will be found by the formulas

RELATIONS PERTAINING SIMPLE [BOOK ].

Q

K sin (l—L) — cos (/ — Z)

*

r'
-JTJ tan p — tan B

tan b = — — p

n. By putting .ZV= X, we shall make

and we shall have,

tan (/ — A) = -£-

^ = _ _•?_ _JL_

r' " sin (I — J.) cos (/ — J.)

r>/

tan j3 p tan 5

tan b = — r , - .

T7

HI. By putting N= % (X -f- _Z/), / and //' will be found by means of the
equations

tan U — £ (X -f- X)j =: r, _ „-, tan i (X — L)

and afterwards 5, by means of the equation given above. The logarithm of the
fraction

r' — R

-7-

TV

is conveniently computed if -7- is put = tan f, whence we have

In this manner the method HL for the determination of / is somewhat shorter
than I. and II.; but, for the remaining operations, we consider the two latter
preferable to the former.

SECT. 2.]

TO POSITION IN SPACE.

73

63.

For an example, we continue further the calculation carried to the helio
centric place in article 51. Let the heliocentric longitude of the earth,
24°19'49".05 = j&, and log R = 9.9980979, correspond to that place; we put
the latitude =0. We have, therefore, Jl — L = — 17° 24'20".07, log R' = R,
and thus, according to method IL,

log sin (X — L] .
log cos (1 — L} .

9.6729813

9.4758653w
9.9796445

l-Q =

. . . 9.6526258

0.4493925
0.5506075

logP ....

9.1488466w
9.7408421

Hence / — X = —
log—;- ....
loo; tan 8

14021'6".75

9.7546117
8.8020996 n

whence 1 =
whence log 4'
log cos b . . .

352°34'22".23
. . . 0.0797283
. . . 99973144

log tan b . . . 9.0474879 n
l = — 6°21'55".07

log// 0.0824139

According to method IH., from log tan £ = 9.6729813, we have f = 25° 13' 6*31,
and thus,

log tan (45° -f Q . . . 0.4441091

logtani(X — L) . . . 9.1848938«

log tan (^— H— 4X) . 9.6290029 n

l-n— kL = - 23° 3'16".79 I whence/=352034'22'/.225.

U+*X== 153739.015J

64.

We further add the following remarks concerning the problem of article 62.
I. By putting, in the second equation there given,

N=l, N=L, N=l,
10

74 RELATIONS PERTAINING SIMPLY [BOOK I.

there results

R sin (l — L) = A' sin (I— X)

/ sin (I — L} = J' sin (I — L)
r' sin (1—1)=. R' sin (l—L).

The first or the second equation can be conveniently used for the proof of the
calculation,, if the method I. or II. of article 62 has been employed. In our
example it is as follows : —

log sin (l — L} . . . 9.4758653 w /— L = — 31°45/26'/.82
log 4 9.7546117

9.7212536«
log sin (l—L) . . . 9.7212536 n

k

II. The sun, and the two points in the plane of the ecliptic which are the
projections of the place of the heavenly body and the place of the earth form a
plane triangle, the sides of which are z/', R', r, and the opposite angles, either
l—L, I— I, 180° --J + Z, or L — I, I — I, and 180°- -L-\-l; from this the
relations given in I. readily follow.

III. The sun, the true place of the heavenly body in space, and the true place
of the earth will form another triangle, of which the sides will be //, R, r : if,
therefore, the angles opposite to them respectively be denoted by

S, T, 18Q° — S—T,
we shall have

sin S s'mT s

/ R

The plane of this triangle will project a great circle on the celestial sphere, in
which will be situated the heliocentric place of the earth, the heliocentric place
of the heavenly body, and its geocentric place, and in such a manner that the
distance of the second from the first, of the third from the second, of the third
from the first, counted in the same direction, will be respectively, S, T, & -|- T.

IV. The following differential equations are derived from known differential
variations of the parts of a plane triangle, or with equal facility from the formu
las of article 62: —

SECT. 2.] TO POSITION IN SPACE. 75

4 J

d ^/' — — / sin (X — T] d \ -\- cos (X —

, , / cos b sin 5 sin (i — /) •, « , r' cos2 6 , - . cos2 b

in which the terms which contain d/ d A' are to be multiplied by 206265, or the
rest are to be divided by 206265, if the variations of the angles are expressed in
seconds.

V. The inverse problem, that is, the determination of the heliocentric from
the geocentric place, is entirely analogous to the problem solved above, on which
account it would be superfluous to pursue it further. For all the formulas of
article 62 answer also for that problem, if, only, all the quantities which relate to
the heliocentric place of the body being changed for analogous ones referring to
the geocentric place, L -\- 180° and — B are substituted respectively for L and B,
or, which is the same thing, if the geocentric place of the sun is taken instead of
the heliocentric place of the earth.

65.

Although in that case where only a very few geocentric places are to be
determined from given elements, it is hardly worth while to employ all the
devices above given, by means of which we can pass directly from the eccentric
anomaly to the geocentric longitude and latitude, and so also to the right ascen
sion and declination, because the saving of labor therefrom would be lost in
the preliminary computation of the multitude of auxiliary quantities ; still, the
combination of the reduction to the ecliptic with the computation of the geocen
tric longitude and latitude will afford an advantage not to be despised. For if the
ecliptic itself is assumed for the plane of the coordinates s, and the poles of
the planes of the coordinates x,y, are placed in 8, 90° -f- 8, the coordinates are
very easily determined without any necessity for auxiliary quantities. We have,

x = r cos u

y = r cos/ sin M

z—rsmismti Z=R'i&nB

76 RELATIONS PERTAINING SIMPLY [BOOK I.

When B = 0, then 1? = R, Z= 0. According to these formulas our example is
solved as follows : —

L — 8 = 213°12'0".32.

logr ...... 0.3259877 log 11' ..... 9.9980979

log cos u ..... 9.9824141 n log cos (L— Q) . . 9.9226027re

log sin u ..... 9.4454714 n log sin ( L — Q, ) . . 9.7384353 n

0.3084018w logJC ..... 9.9207006w

logr sin M .... 9.7714591 n
log cos *f ..... 9.9885266
log sin? ..... 9.3557570

logy ...... 9.7599857w logF ...... 9.7365332«

logz ...... 9.1272161w Z= 0

Hence follows

log(z — X) . . . 0.0795906«

log(y-Y) . . . 8.4807165w

whence (/— Q) = 181°26'33".49 J = 352°34'22".22

logJ' ...... 0.0797283

log tan* ..... 9.0474878 n b= —62155.06

66.

The right ascension and declination of any point whatever in the celestial
sphere are derived from its longitude and latitude by the solution of the spherical
triangle which is formed by that point and by the north poles of the ecliptic and
equator. Let « be the obliquity of the ecliptic, I the longitude, b the latitude, a
the right ascension, 8 the declination, and the sides of the triangle will be e,
90° - - b, 90° - - 6 ; it will be proper to take for the angles opposite the second
and third sides, 90° -f- <*, 90° - - 1, (if we conceive the idea of the spherical triangle
in its utmost generality) ; the third angle, opposite e, we will put = 90° — JS. We
shall have, therefore, by the- formulas, article 54,

SECT. 2.]

TO POSITION IN SPACE.

77

sin (45° - - id) sin } (E -f a) = sin (45° + H) sin (45° — } (e + 5))
sin (45° — J d) cos } (^ + a) = 6os (45° -f £ /) cos (45° — J (e — £))
cos (45°— * «J) sin l(E—a) = cos (45° + H) sin (45° — } (E — 5))
cos (45°— } 8) cos £ (,£ — a) = sin (45° -j- } /) cos (45° — } (e -f 5))

The first two equations will give i(^-)-a) and sin (45° - -i<?); the last two,
l(E—tt) and cos (45° — i d) ; from J (^ + «) and i(j? — o) will be had a, and,
at the same time, E ; from sin (45° — k d] or cos (45° — i $), the agreement of
which will serve for proving the calculation, will be determined 45° — id, and
hence S. The determination of the angles $ (E -\- <*}, $ (E — «) by means of
their tangents is not subject to ambiguity, because both the sine and cosine of the
angle 45° — J 8 must be positive.

The differentials of the quantities a, 8, from the changes of I, b, are found
according to known principles to be,

, sin -Scos 5 n 7 cos E -, -,

&a = - —.— til- --- ^-db

COS 0 COS 0

d d = cos E cosb d /-(- sinJEdb.

67.

Another method is required of solving the problem of the preceding article
from the equations

cos e sin I = sin e tan b -\- cos I tan a

sin d = cos « sin b -|- sin « cos b sin /
cos b cos ^ = cos a cos d .

The auxiliary angle & is determined by the equation

. tan b

tan$= -T-T,

sm/'

and we shall have

cos (s -4- 6) tan /
tan a= —

cos 0
tan d = sin a tan (e -f- d),

to which equations may be added, to test the calculation,

cos b cos I t, cos (e -4- 0) cos 5 sin J

coso=- — ,orcoso = — s — 1-~-. - .

cos a

— -~-.
cos 0 sm a

78 RELATIONS PERTAINING SIMPLY [BoOK 1.

This ambiguity in the determination of a by the second equation is removed by
this consideration, that cos a and cos I must have the same sign.

This method is less expeditious, if, besides a and d, E also is required : the most
convenient formula for determining this angle will then be

sin s cos « sin e cos I

- —;—- — ^r—.

cos b cos o

But E cannot be correctly computed by this formula when + cos E differs but
little from unity ; moreover, the ambiguity remains whether E should be taken
between 0 and 180°, or between 180° and 360°. The inconvenience is rarely
of any importance, particularly, since extreme precision in the value of E is not
required for computing differential ratios ; but the ambiguity is easily removed
by the help of the equation

cos b cos S sin E = cos « — sin b sin d,

which shows that E must be taken between 0 and 180°, or between 180° and
360°, according as cose is greater or less than sin b sind : this test is evidently not
necessary when either one of the angles b, d, does not exceed the limit 66° 32' ;
for in that case sin E is always positive. Finally, the same equation, in the case
above pointed out, can be applied to the more exact determination of E, if it
appears worth while.

68.

The solution of the inverse problem, that is, the determination of the longi
tude and latitude from the right ascension and declination, is based upon the same
spherical triangle ; the formulas, therefore, above given, will be adapted to this
purpose by the mere interchange of b with d, and of I with — «. It will not be
unacceptable to add these formulas also, on account of their frequent use :

According to the method of article 66, we have,

sin (45° - - H) sin } (E— 1} = cos (45° -f } a) sin (45° - - i (e -f <?))
sin (45° — } b) cos l(E—l) = sin (45° -f I a) cos (45° — } (e —
cos (45°— * b) sin } (E+ 1) = sin (45° + } «) sin (45°- - } (e —
cos (45° — j b) cos } (E -f 1) = cos (45° + } «) cos (45° — i (e -f d)) .

SECT. 2.] TO POSITION IN SPACE. 79

As in the other method of article 67, we will determine the auxiliary angle £
by the equation

c. tan d

tan £, = -;—.

since7

and we shall have

7 cos (£ — e) tana

tan I = -

cos f

tan 5 = sin £ tan (£ — e) .
For proving the calculation, may be added,

, _ cos d cos a __ cos (£ — «) cos d sin a

COS 0 - - j - - — - ^ — ; - i - ,

cos i cos f sin I

For the determination of E, in the same way as in the preceding article, the fol
lowing equations will answer : —

j-, sin f cos a sin s cos I

COS-E=- — T— = -

COS 0 COS O

cos b cos $ sin .£" = cos « — sin b sin $ .

The differentials of /, b, will be given by the formulas

d, sin .E cos 5 , , cosl? -. »,
?=- —= — aa-\ --- rdo

COS 0 COS 0

d ^ = — cos E cos $ d a -(- sin .£" d d .

/

69.

We will compute, for an example, the longitude and latitude from the right
ascension 355°43'45".30 = a, the declination — 8° 47' 25" == d, and the obliquity
of the ecliptic 23° 27' 59".26 = e. We have, therefore, 45C + } a = 222° 51' 52".65,
45° . _ $ (e _|_ s) = 37° 39'42".87, 45° — i (e — d) = 28° 52' 17".87 ; hence also,

log cos (45° + i a) . . 9.8650820M log sin (45° -f i a) . . 9.8326803n
logsin(45°--i(e + d)) 9.7860418 log sin (45°— * (e — d)) 9.6838112
log cos (45°— *(« + <*)) 9.8985222 log cos (45° — i (e — <?)) 9.9423572

log sin (45° — ^)sini(^— /) . . 9.6511238 n
log sin (45° — ii)cosi(J?— /) . . 9.7750375 n
whence J (^E1— /) = 216°56'5".39 ; log sin (45° — * J) = 9.8723171

80 RELATIONS PERTAINING SIMPLY [BoOK. L

log cos (45°— Ji)sini(^ + i) . . 9.5164915w
log cos (45° — ifl) cos * (E-\-l) . . 9.7636042 n
whence * (£' + J) = 209° 30'49".94 : log cos (45° — i fl) = 9.8239669.

Therefore, we have E= 426°26'55".33, I — — 7°25'15".45, or, what amounts
to the same thing, E = 66°26'55".33, 1= 352°34'44".55; the angle 45° — i *,
obtained from the logarithm of the sine, is 48°10'58".12, from the logarithm of
the cosine, 48°10'58'/.17, from the tangent, the logarithm of which is their differ
ence, 48° 10'58".14 ; hence b = — 6°2r56".28.

According to the other method, the calculation is as follows : —

log tan d .... 9.1893062« C.logcos£ .... 0.3626190

log sin a . . . . 8.8719792» log cos (C — e) . . 9.8789703

log tan £ .... 0.3173270 log tan a .... 8.8731869w

C= 64°17'6".83 log tan/ ..... 9.1147762w

£ — K= 40497.57 /= 352°34'44".50

log sin J ..... 9.1111232 n

log tan (C — «) . . 9.9363874

log tan b ..... 9.0475106 n
b= — 6°21'56".26.

For determining the angle E we have the double calculation

log sin s . . . . 9.6001144 log sin e ..... 6.6001144

log cos a . . . . 9.9987924 log cos/ ..... 9.9963470

C. log cos* . . . 0.0026859 C. log cos d .... 0.0051313

log cos E . . . 9.6015927 log cos E ..... 9.6015927
whence E = 66° 26' 55".35.

70.

Something is still to be added concerning the parallax and aberration, that
nothing requisite for the computation of geocentric places may be wanting.
We have already described, above, a method, according to which, the place
affected by parallax, that is, corresponding to any point on the surface of the

SECT. 2.] TO POSITION IN SPACE. 81

earth, can be determined directly with the greatest facility ; but as in the com
mon method, given in article 62 and the following articles, the geocentric place is
commonly referred to the centre of the earth, in which case it is said to be free
from parallax, it will be necessary to add a particular method for determining the
parallax, which is the difference between the two places.

Let the geocentric longitude and latitude of the heavenly body with reference
to the centre of the earth be X, ft ; the same with respect to any point whatever
on the surface of the earth be I, b ; the distance of the body from the centre of
the earth, r; from the point on the surface, z/; lastly, let the longitude L, and the
latitude B, correspond to the zenith of this point in the celestial sphere, and let
the radius of the earth be denoted by R. Now it is evident that all the equations
of article 62 will be applicable to this place also, but they can be materially
abridged, since in this place R expresses a quantity which nearly vanishes in
comparison with r and A. The same equations evidently will hold good if K,l,L
denote right ascensions instead of longitudes, and ft, b, B, declinations instead of
latitudes. In this case / — X, b — ft, will be the parallaxes in right ascension and
declination, but in the other, parallaxes in longitude and latitude. If, accord
ingly, R is regarded as a quantity of the first order, I — I, b — ft, /I — r, will be
quantities of the same order ; and the higher orders being neglected, from the
formulas of article 62 will be readily derived : —

L, . __ Rco^BsmQ. — L)
I A — -

r cosp

n. g-8=

HI. J — r= — R cos B sin ft (cotan ft cos (X — L] -\- tan Bj.
The auxiliary angle 6 being so taken that

tan B

tan B =

- — - j^,
cos (i — L) '

the equations II. and III. assume the following form : —

-p, , „ _ B cos B cos (). — Z) sin (|3 — 0) __ .K sin 2? sin (5 — 0)

r cos 0 r sin 0

-pp. . R cos B cos (I — L) cos (|3 — 6) _ R sin B cos (0 — 0)

Mi, /t - T - - • - — - -- ; — — - .

cos 0 sin a

11

82

RELATIONS PERTAINING SIMPLY

[BOOK I.

Further, it is evident, that in I. and II., in order that I — X and b — /? may be
had in seconds, for If, must be taken the mean parallax of the sun in seconds ;
but in III., for R, must be taken the same parallax divided by 206265". Finally,
when it is required to determine in the inverse problem, the 'place free from
parallax from the place affected by it, it will be admissible to use J, /, b, instead
of r, A, ft, in the values of the parallaxes, without loss of precision.

Example. — Let the right ascension of the sun for the centre of the earth
be 220°46'44".65 = 31, the declination,— 15° 49'43'/.94 — ft the distance, 0.9904311
= r: and the sidereal time at any point on the surface of the earth expressed
in degrees, 78°20'38"==X, the elevation of the pole of the point, 45°27'57" = ^,
the mean solar parallax, 8".6 = R. The place of the sun as seen from this point,
and its distance from the same, are required.

log R 0.93450 log.fi1 0.93450

logcos^ 9.84593 log sin B 9.85299

C.logr ...... 0.00418

C. log cos p .... 0.01679

log sin (l — L] . . . 9.78508

C.logr 0.00418

C. lo sin 6 0.10317

Iog<7_3L) . . . . 0.58648
1—1= + 3".86

1= 220°46'48".51

log tan B ..... 0.00706

log cos (X — L) . . . 9.89909«

log tan 6 ~. . . . 0.10797w

6= 127° 57' V"

i — 6= —U34644

log sin (p — 6)

log (b-

. . 9.77152«

. . 0.66636 n

b — fi = - 4"64
b= —15° 49' 4 8". 58

log (*_/}) .... 0.66636 n

log cot (0 — 0) . . . 0.13522

logr 9.99582

logl" 4.68557

log(r — J)
r— // =

. 5.48297 n
• 0.0000304
0.9904615

71.

The aberration of the fixed stars, and also that part of the aberration of com
ets and planets due to the motion of the earth alone, arises from the fact, that
the telescope is carried along with the earth, while the ray of light is passing

SECT. 2.] TO POSITION IN SPACE. 83

along its optical axis. The observed place of a heavenly body (which is called
the apparent, or affected by aberration), is determined by the direction of the
optical axis of the telescope set in such a way, that a ray of light proceeding
from the body on its path may impinge upon both extremities of its axis: but this
direction differs from the true direction of the ray of light in space. Let us con
sider two moments of time t, t', when the ray of light touches the anterior ex
tremity (the centre of the object-glass), and the posterior (the focus of the object-
glass) ; let the position of these extremities in space be for the first moment a, b ;
for the last moment a', b'. Then it is evident that the straight line ab' is the true
direction of the ray in space, but that the straight line ab or ab' (which may be
regarded as parallel) corresponds to the apparent place : it is perceived without
difficulty that the apparent place does not depend upon the length of the tube.
The difference in direction of the right lines b'a, ba, is the aberration such as exists
for the fixed stars : we shall pass over the mode of calculating it, as well known.
This difference is still not the entire aberration for the wandering stars : the
planet, for example, whilst the ray which left it is reaching the earth, itself
changes its place, on which account, the direction of this ray does not correspond
to the true geocentric place at the time of observation. Let us suppose the ray
of light which impinges upon the tube at the time t to have left the planet at the
time T • and let the position of the planet in space at the time T be denoted by
P, and at the time t by p ; lastly, let A be the place of the anterior extremity of
the axis of the tube at the time T. Then it is evident that, —

1st. The right line AP shows the true place of the planet at the time T',

2d. The right line ap the true place at the time t ;

3d. The right line ba or b'a the apparent place at the time t or if (the differ
ence of which may be regarded as an infinitely small quantity) ;

4th. The right line b'a the same apparent place freed from the aberration of
the fixed stars.

Now the points P, a, b', lie in a straight line, and the parts Pa, ab', will be
proportional to the intervals of time t — T, if — t, if light moves with an uni
form velocity. The interval of time if — T is always very small on account of
the immense velocity of light ; within it, it is allowable to consider the motion

84 RELATIONS PERTAINING SIMPLY [BOOK I.

of the earth as rectilinear and its velocity as uniform : so also A, a, a' will lie in a
straight line, and the parts Aa, aa' will likewise be proportional to the intervals
f — T, t' — t. Hence it is readily inferred, that the right lines AP, I'd are paral
lel, and therefore that the first and third places are identical.

The time t — T, within which the light traverses the mean distance of the
earth from the sun which we take for unity, will be the product of the distance
Pa into 493". In this calculation it will be proper to take, instead of the dis
tance Pa, either PA or pa, since the difference can be of no importance.

From these principles follow three methods of determining the apparent place
of a planet or comet for any time t, of which sometimes one and sometimes
another may be preferred.

I. The time in which the light is passing from the planet to the earth may be
subtracted from the given time ; thus we shall have the reduced time T, for which
the true place, computed in the usual way, will be identical with the apparent
place for t. For computing the reduction of the time t — T, it is requisite to
know the distance from the earth ; generally, convenient helps will not be want
ing for this purpose, as, for example, an ephemeris hastily calculated, otherwise it
will be sufficient to determine, by a preliminary calculation, the true distance for
the time t in the usual manner, avoiding an unnecessary degree of precision.

II. The true place and distance may be computed for the instant t, and,
from this, the reduction of the time t--T, and hence, with the help of the daily
motion (in longitude and latitude, or in right ascension and declination), the re
duction of the true place to the time T.

III. The heliocentric place of the earth may be computed for the time t; and
the heliocentric place of the planet for the time T ' : then, from the combination
of these in the usual way, the geocentric place of the planet, which, increased
by the aberration of the fixed stars (to be obtained by a well-known method, or
to be taken from the tables), will furnish the apparent place sought.

The second method, which is commonly used, is preferable to the others,
because there is no need of a double calculation for determining the distance,
but it labors under this inconvenience, that it cannot be used except several
places near each other are calculated, or are known from observation ; otherwise
it would not be admissible to consider the diurnal motion as given.

SECT. 2.] TO POSITION IN SPACE. 85

The disadvantage with which the first and third methods are incumbered, is
evidently removed when several places near each other are to be computed.
For, as soon as the distances are known for some, the distances next following
may be deduced very conveniently and with sufficient accuracy by means of
familiar methods. If the distance is known, the first method will be generally
preferable to the third, because it does not require the aberration of the fixed
stars ; but if the double calculation is to be resorted to, the third is recommended
by this, that the place of the earth, at least, is retained in the second calculation.

What is wanted for the inverse problem, that is, when the true is to be derived
from the apparent place, readily suggests itself. According to method I., you will
retain the place itself unchanged, but will convert the tune t, to which the given
place corresponds as the apparent place, into the reduced time T, to which the
same will correspond as the true place. According to method II, you will retain
the time t, but you will add to the given place the motion in the time t — T, as
you would wish to reduce it to the time t-\- (t — T}. According to the method
III., you will regard the given place, free from the aberration of the fixed stars,
as the true place for the time T, but the true place of the earth, answering to
the time t, is to be retained as if it also belonged to T. The utility of the third
method will more clearly appear in the second book.

Finally, that nothing may be wanting, we observe that the place of the sun is
affected in the same manner by aberration, as the place of a planet : but since
both the distance from the earth and the diurnal motion are nearly constant, the
aberration itself has an almost constant value equal to the mean motion of
the sun in 493s, and so — 20".25; which quantity is to be subtracted from the
true to obtain the mean longitude. The exact value of the aberration is in the
compound ratio of the distance and the diurnal motion, or what amounts to the
same thing, in the inverse ratio of the distance ; whence, the mean value must be
diminished in apogee by 0".34, and increased by the same amount in perigee.
Our solar tables already include the constant aberration — 20".25 ; on which
account, it wih1 be necessary to add 20".25 to the tabular longitude to obtain the
true.

86 RELATIONS PERTAINING SIMPLY [BoOK 1.

72.

Certain problems, which are in frequent use in the determination of the orbits
of planets and comets, will bring this section to a close. And first, we will revert
to the parallax, from which, in article 70, we showed how to free the observed
place. Such a reduction to the centre of the earth, since it supposes the distance
of the planet from the earth to be at least approximately known, cannot be made
when the orbit of the planet is wholly unknown. But, even in this case, it is pos
sible to reach the object on account of which the reduction to the centre of the
earth is made, since several formulas acquire greater simplicity and neatness
from this centre lying, or being supposed to lie, in the plane of the ecliptic,
than they would have if the observation should be referred to a point out of the
plane of the ecliptic. In this regard, it is of no importance whether the obser
vation be reduced to the centre of the earth, or to any other point in the plane
of the ecliptic. Now it is apparent, that if the point of intersection of the
plane of the ecliptic with a straight line drawn from the planet through the true
place of observation be chosen, the observation requires no reduction whatever,
since the planet may be seen in the same way from all points of this line : * where
fore, it will be admissible to substitute this point as a fictitious place of observa
tion instead of the true place. We determine the situation of this point in the
following manner : —

Let X be the longitude of the heavenly body, /? the latitude, // the distance,
all referred to the true place of observation on the surface of the earth, to
the zenith of which corresponds the longitude /, and the latitude b ; let, more
over, n be the semidiameter of the earth, L the heliocentric longitude of the cen
tre of the earth, B its latitude, II its distance from the sun ; lastly, let L' be the
heliocentric longitude of the fictitious place, 1? its distance from the sun, A -j- d

* If the nicest accuracy should be wanted, it would be necessary to add to or subtract from the given
time, the interval of time in which light passes from the true place of observation to the fictitious, or from
the latter to the former, if we are treating of places affected by aberration : but this difference can
scarcely be of any importance unless the latitude should be very small.

SECT. 2.] TO POSITION IN SPACE. 87

its distance from the heavenly body. Then, ^V denoting an arbitrary angle, the
following equations are obtained without any difficulty : —

R cos (L'—N) + d cos ft cos (I —N) = £ cos B cos (L—N) + n cos b cos (l—N)
R sin (L'—N) -f S cos 0 sin (X — N) = li cos .Z? sin (L—N) + « cos 5 sin (l—N)

d sin 0 = 7? sin Z* -|- TT sin i.
Putting, therefore,

L (RsmB-\- it sin b) cotan 0 =ju.,
we shall have

II. E'cos(L' — N) = RcosScos(L — N) + n cosbcos(l— N) — jUCos(X
ILL B sin (I/ — N) = £cosJB sin (Z — N) -\-ncosb sin (l—N) — p sin (X
IV. tf = -£-,,

COS (3

From equations IT. and HI., can be determined R and L', from IV., the inter
val of time to be added to the time of observation, which in seconds will be
= 493 8.

These equations are exact and general, and will be applicable therefore when,
the plane of the equator being substituted for the plane of the ecliptic, Z, L', I, X,
denote right ascensions, and B, b, ft declinations. But in the case which we are
specially treating, that is, when the fictitious place must be situated in the eclip
tic, the smallness of the quantities B, n, L' — L, still allows some abbreviation of
the preceding formulas. The mean solar parallax may be taken for n ; B, for
sin B ; 1, for cos B, and also for cos (I! — L) ; L' — L, for sin (Lr --L). In this
way, making N=. Z, the preceding formulas assume the following form : —
I. fi= (RB -(- n sin b) cotan /3
II. R = R -f- n cos b cos (I — Z) — p,cos(l — Z)

T-I-T j-t j- __ n cos b sin (I — L) — f<sin(l — L)

It?

Here B, n, L' — Z are, properly, to be expressed in parts of the radius ; but it is
evident, that if those angles are expressed in seconds, the equations L, III. can be
retained without alteration, but for II. must be substituted

TV _ n I n cos b cos (I — L) — p cos (J, — L)
•""T 206265"

RELATIONS PERTAINING SIMPLY

[BOOK I.

Lastly, in the formula III., R may always be used in place of the denominator 7?'
without sensible error. The reduction of the time, the angles being expressed
in seconds, becomes

206265". cos /?'

73.

Example. — Let I = 354° 44' 54", 0 = — 4° 59' 32", /=24°29', b = 46° 53',
L'= 12° 28' 54", £ = + 0".49, 7? = 0.9988839, it = 8".60. The calculation is as
follows : —

log,?? 9.99951

log 5 9.69020

log BE 9.68971

Hence log (B R + JT sin b) . 0.83040

logcotan/3 .... 1.05873 n

log ft 1.88913n

logTt 0.93450

log cos* 9.83473

logl" 4.68557

log cos (l—L) . . . 9.99040

logTt 0.93450

log sin b 9.86330

log n sin b

0.79780

logp 1.88913n

logl" 4.68557

log cos (X — L) . . . 9.97886

6.55356w
number — 0.0003577

5.44520
number -f 0.0000279

Hence is obtained R = R -f 0.0003856 == 0.9992695. Moreover, we have

log n cos b 0.76923

log sin (l — L) . . . 9.31794
C.log# 0.00032

1.88913«

log sin (X — L) . . 9.48371 n
G.logtf 0.00032

0.08749

1.37316

number 1".22

number + 23*61

SECT. 2.] TO POSITION IN SPACE. 89

Whence is obtained L' = L — 22".39. Finally we have

log^i 1.88913*

C. log 206265 .... 4.68557

log 493 2.69285

C. log cos 0 0.00165

9.26920 R,
whence the reduction of time = — 0B.186, and thus is of no importance.

74.

The other problem, to deduce the heliocentric place of a heavenly body in its orbit
from the geocentric place and the situation of the plane of the orbit, is thus far similar to
the preceding, that it also depends upon the intersection of a right line drawn
between the earth and the heavenly body with the plane given in position. The
solution is most conveniently obtained from the formulas of article 65, where the
meaning of the symbols was as follows : —

L the longitude of the earth, R the distance from the sun, the latitude B we
put =0, — since the case in which it is not = 0, can easily be reduced to this by
article 72, — whence R = R, I the geocentric longitude of the heavenly body, b
the latitude, A the distance from the earth, r the distance from the sun, u the
argument of the latitude, 8 the longitude of the ascending node, i the inclination
of the orbit. Thus we have the equations

I. r cos u — R cos (L — 8 ) = d cos b cos (I — 8 )
II. r cos i sin u — R sin (L — &)=J cos b sin (I — 8 )

III. r sin i sin u-=/l sin b .

Multiplying equation I. by sin (L — 8 ) sin b, H by — cos (L — 8 ) sin b, III. by
- sin (L — 1} cos b, and adding together the products, we have

cos u sin (L — 8 ) sin b — sin u cos i cos (L — 8 ) sin b — sin u sin i sin (L — I) cos b — 0,
whence

IV. tan«= sin(i-8)sin*

cos i cos (L — £2) s

12

90 RELATIONS PERTAINING SIMPLY [BoOK I.

Multiplying likewise I. by sin (I — 8 ), II. by — cos (I — 8 ); and adding together
the products, we have

~~

sin u cos i cos (/ — & ) — cos w sin (I — Q ) '

The ambiguity in the determination of u by means of equation IV., is removed
by equation III., which shows that u is to be taken between 0 and 180°, or be
tween 180° and 360° according as the latitude b may be positive or negative ;
but if b = 0, equation V. teaches us that we must put u = 180°, or u = 0, accord
ing as sin (L — 1) and sin (I — 8 ) have the same or different signs.

The numerical computation of the formulas l\r. and V. may be abbreviated in
various ways by the introduction of auxiliary angles. For example, putting

i if IAJS \ J^ Aft / A

-' = tan^4.

sin (L — /)

we have

_ sin A tan (L — & )

sin (A -\- i)
putting

tan i sin (L — /)

,, ._ . = tan B,
cos(L-Q)

we have

cos B sin b tan (L — Q )

tanz< = - , ,, i , . .

sin (/»-p 6) cost

In the same manner the equation V. obtains a neater form by the introduction
of the angle, the tangent of which is equal to

., tan(/ — Q)

cos z tan it, or - — ~^- .
cost

Just as we have obtained formula V. by the combination of L, IE., so by a combina
tion of the equations II, III, we arrive at the following : —

r —

sin u (cos t — sin i sin (/ — Q ) cotan b) '

and in the same manner, by the combination of equations L, HI., at this ;

— Q)

T —

cos u — sin u sin t cos (I — Q, ) cotan b'

SECT. 2.] TO POSITION IN SPACE. 91

both of which, in the same manner as V., may be rendered more simple by the
introduction of auxiliary angles. The solutions resulting from the preceding
equations are met with in VON ZACH MonatKche Correspondenz, Vol. V. p. 540, col
lected and illustrated by an example, wherefore we dispense with their further
development in this place. If, besides u and r, the distance J is also wanted, it
can be determined by means of equation in.

f

75.

Another solution of the preceding problem rests upon the truth asserted in arti
cle 64, III., — that the heliocentric place of the earth, the geocentric place of the
heavenly body and its heliocentric place are situated in one and the same great
circle of the sphere. In fig. 3 let these places be respectively T, G, H • further,
let & be the place of the ascending node ; 8, T, 0,11, parts of the ecliptic and
orbit ; GP the perpendicular let fall upon the ecliptic from G, which, therefore,
willbe=;£. Hence, and from the arc PT=L — /will be determined the angle T
and the arc TG. Then in the spherical triangle Q, HT are given the angle Q = i,
the angle T, and the side 8T:=Z — Q, whence will be got the two remaining
sides &H= u and TH. Finally we have HG = TG — TH, and

_Rs,mTG . RsinTH

''~^m~H&> * ~~ smffG '

76.

In article 52 we have shown how to express the differentials of the heliocen
tric longitude and latitude, and of the curtate distance for changes in the argu
ment of the latitude u, the inclination i, and the radius vector r, and subsequently
(article 64, IV.) we have deduced from these the variations of the geocentric
longitude and latitude, I and I : therefore, by a combination of these formulas, d I
and <\l will be had expressed by means of dti, di, d&, dr. But it will be worth
while to show, how, in this calculation, the reduction of the heliocentric place
to the ecliptic, may be omitted in the same way as in article 65 we have
deduced the geocentric place immediately from the heliocentric place in orbit.
That the formulas may become more simple, we will neglect the latitude of

92 RELATIONS PERTAINING SIMPLY [BOOK I.

the earth, which of course can have no sensible effect in differential formulas.
The following formulas accordingly are at hand, in which, for the sake of brevity,
we write w instead of I — 8, and also, as above, A' in the place of A cos b.

A' cos to = r cos u — R cos (L — 8 ) = £
A' sin a) = r cos ismu — R sin (L — & ) = i\
/I' tan b=.r sin i sin u = £ ;
from the differentiation of which result

cos w.d A' — //'sin w.deo = d£

sin w.d^/' -\- A' cos co . d o> = d?j

. -, .

1 cos 6

Hence by elimination,

I _ _ — sin to . d | -f- cos to . fl i;

A'

-, , _ — cos co. sin 5. dj — sin to sini.d)y-(- cosi.d £

A

If in these formulas, instead of £, 77, t, their values are substituted, do*
and d$ will appear represented by dr, dw, d/, dQ; after this, on account of
d/=doj-|-d&, the partial differentials of I and b will be as follows : —

I. A' ( — } = — sin w cos u -(- cos w sin M cos i

-rr ^'/dz\ • •

II. :— I •=- 1 = sin w sm ;« + cos w cos u cos z

r VdM/

TTT ^'/dZ\

ILL T-. ) = —

r \d»/

cos CD sin M sin i

V. ^(^) = — cos w COSM sin b — smto sin u cos i sin b -f- sin M sin i 'cos i

,rT ^/di\ . .

V 1. — ( -j- I = cos w sm M sin o — sin (a cos M cos i sin o -}- cos u sin z cos 0

irrr ^ /<! *\ • • ....

V ll. — IT-. I = sm w sin M sin i sin o -j- sm u cos z cos b

VIII. -^-Q ^| = sin b sin (Z — 8 — w) = sin b sin (Z — /) .

SECT. 2.] TO POSITION IN SPACE. 93

The formulas TV. and VIII. already appear in the most convenient form for cal
culation ; but the formulas L, HI., V., are reduced to a more elegant form by
obvious substitutions, as

.— — cos w tan £

di/

V.* (-:-J = — — cos(Z — Z)sint> = — —, cos (L — 1) sin b cos b.

Finally, the remaining formulas II., VI., VII., are changed into a more simple form
by the introduction of certain auxiliary angles : which may be most conveniently
done in the following manner. The auxiliary angles M, N, may be determined
by means of the formulas

tan M = — " , tan N= sin w tan i = tan M cos w sin i.

COS I '

Then at the same tune we have

cos2 M 14- tan2 N cos2 i -4- sin2 ta sin2 » a

, ^ _ I _ n -. _ I _ i f\ /"iO /|J *

cos2 .AT "~14-tan2J^~ cos2 f -f tan2 w

now, since the doubt remaining in the determination of M, N, by their tangents,
may be settled at pleasure, it is evident that this can be done so that we may

have

cos M ,

and thence

sin

— vj=-.

sin M

These steps being taken, the formulas IT., VI., VII, are transformed into the fol
lowing : —

TT * __

~

m cos

\di ~ 4 sin M

VI* (^) = -^-(coscu smicos(M — w)cos(JV —

"irrr * (^^\ __ r s'n M cos * cos ^ — ^
\d i) ~ A cos N

94 RELATIONS PERTAIXIXG SIMPLY [BOOK I.

These transformations, so far as the formulas II. and VII. are concerned, will detain
no one, but in respect to formula VI., some explanation will not be superfluous.
From the substitution, in the first place, of M — (M — u) for n, in formula VI.,
there results

— ( — } = cos (M — u) (cos to sin M sin b — sin to cos i cos M sin b -j- sin i cos M cos b )
— 8iD.(M — u) (cos to cosJHfsinJ-|-sm w cos z sin J/ sin 5 — smismMcosb).
Now we have

cos w sin M= cos2 i cos to sin M-\- sin2 i cos to sin M
= sin io cos «' cos M-\- sin2 z cos to sin M ;

whence the former part of that expression is transformed into

sin i cos (M — u) (sin i cos to sin M sin b -\- cos Jf cos b)
= sin « cos ( Jf — M) (cos to sin JV^sin J -)- cos to cos iVcos 5)
= cos to sin z cos ( M — M) cos (N — b).
Likewise,

cos JV= cos2 to cos JV-\- sin2 to cos .A7"— cos (a cos J!f -f- sin to cos »' sin 3/;
whence the latter part of the expression is transformed into

— sm(M — M) (cos ^ sin b — sin JV cos b) — sin (M — M) sin (N — b).

The expression VI.* follows directly from this.

The auxiliary angle M can also be used in the transformation of formula I.,
which, by the introduction of M, assumes the form

T*# /^\ _ sino)sin(Jf — u)

Vdr/ ~ A' sin M~

from the comparison of which with formula I.* is derived

- R sin (Z — t) sin M=. r sin to sin (M — 11) ;

hence also a somewhat more simple form may be given to formula II.*, that is,
II.** (^) = - ~ sin (L — 1) cotan (M— M).

That formula VI.* may be still further abridged, it is necessary to introduce
a new auxiliary angle, which can be done in two ways, that is, either by putting

SECT. 2.] TO POSITION IN SPACE. 95

D \&n(M— u) tanfJV— i)

tan P = - . . , or tan 0 = — ^_

cos to sin i cos w sin t '

from which results

VT * * (— } __ rsin(M— u) coa(N'—b — P) __ r sin (N— b) cos (M — u — Q)
VI w/ ^sinP ~dA&~

The auxiliary angles M, N, P, Q, are, moreover, not merely fictitious, and it would
be easy to designate what may correspond to each one of them in the celestial
sphere ; several of the preceding equations might even be exhibited in a more
elegant form by means of arcs and angles on the sphere, on which we are less
inclined to dwell in this place, because they are not sufficient to render superflu
ous, in numerical calculation, the formulas above given.

77.

What has been developed in the preceding article, together with what we
have given in articles 15, 16, 20, 27, 28, for the several kinds of conic sections,
will furnish all which is required for the computation of the differential varia
tions in the geocentric place caused by variations in the individual elements.
For the better illustration of these precepts, we will resume the example treated
above in articles 13, 14, 51, 63, 65. And first we will express dl and db in terms
of dr, du, dzj dS2, according to the method of the preceding article; which cal
culation is as follows : —

logtanw . 8.40113 logsinw . 8.40099« log tan ( M — u) 9.41932w
logcosa . 9.98853 log tan z . 9.36723 logcosw sins' . 9.35562ra

log tan M. 8.41260 log tan N . 7.76822 w log tan P . . 0.06370
M = l°28/52// J\r= 179°39'50" P= 49°11/13'/

M— w=16517 8 N— i =186 145 N—l — P= 1365032

RELATIONS PERTAINING SIMPLY

[BOOK 1.

L*

log sm(L-t) 9.72125
log^ . . 9.99810
C.logJ' . 9.92027

n.**

(*)... 9.63962 log cos w .
log coi(M—<u) 0.58068 n log tan b .

in*

. 9.99986w
. 9.04749w

log(!r) • 0.22030 log(^.)

3 \d«/ = \d i/

. 9.04735»

(*)...
C. log r .

9.63962
9.67401

(D

9.31363

IV.

P . . 9.91837
log cos(Z— T) 9.92956
(**) . . 9.84793

V* VI.**

(**) . . . 9.84793 log^ ... 0.24357
log sin 5 cos 5 9.0421 2 w log sin (M — «) 9.40484
C.logr . . 9.67401 logcos(J\r— J-P) 9.86301 «

C. log sin P

/di\
(H)

0.12099
9.63241«

8.56406

VII* VIII.

log r sin u cosz 9.75999 n (*)... 9.63962

log cos(JV— b) 9.99759 n log sin b cos b 9.04212w

C.logJ. . 9.91759 log/dn 8.68174w
C.logcosJV 0.00001 n

. 9.67518n

These values collected give

d^= + 0.20589 Ar -f 1.66073 Au — 0.11152 dt + 1.70458 dQ
di = + 0.03665 Ar — 0.42895 Au — 0.47335 dt'— 0.04805 d Q .

It will hardly be necessary to repeat here what we have often observed, namely,
that either the variations Al, Ab, Au, Ai, da, are to be expressed in parts of the
radius, or the coefficients of Ar are to be multiplied by 206265", if the former are
supposed to be expressed in seconds.

Denoting now the longitude of the perihelion (which in our example is

SECT. 2.] TO POSITION IN SPACE. 97

52°18'9".30) by II, and the true anomaly by v, the longitude in orbit will be
u-\-Q=v-}-lT, and therefore dw — A v -\-AIT — dS, which value being sub
stituted in the preceding formulas, d/and Ab will be expressed in terms of Ar,
d v, d IT, d a , d i. Nothing, therefore, now remains, except to express d r and d v, ac
cording to the method of articles 15, 16, by means of the differential variations
of the elliptic elements.*

We had in our example, article 14,

log!j = 9.90355 = log Q
log- 0.19290 loSfl ..... °-42244

O « rvt

i nnccKo log tan 9 .... 9.40320

log cos ep .... 9.98652

log sin v .... 9.84931 n
log(T-°) .... 0.17942

= 1.80085
= 0.06018

lof n

. . . 042244

log cos (f .
log cos v

O

. . . 9.98652
. . . 9.84966

log ...... o.24072

log^f ..... 0.19290 los • • • • 0.25862 w

log sin E .... 9.76634 n

log(^) .... 0.19996 n

Hence is collected

dv = -f 1.51154 AM— 1.58475 dg>
dr = — 0.47310 d JfcT — 1.81393 dy + 0.80085 da ;
which values being substituted in the preceding formulas, give

dl= + 2.41287 AM— 3.00531 dg> + 0.16488 da -f 1.66073 AIT

- 0.11152 d» + 0.04385 AQ,

Ab = — 0.66572 d M + 0.61331 dy -f 0.02925 da — 0.42895 d77
— 0.47335 Ai+ 0.38090 d8.

* It will be perceived, at once, that the symbol M, in the following calculation, no longer expresses
our auxiliary angle, but (as in section 1) the mean anomaly.

13

98 RELATIONS PERTAINING SIMPLY [BOOK I.

If the time, to which the computed place corresponds, is supposed to be
distant n days from the epoch, and the mean longitude for the epoch is
denoted by N, the daily motion by T, we shall have M — N -\- nt -- IT, and thus
d M = d N-\- ndf — dI7. In our example, the time answering to the computed
place is October 17.41507 days, of the year 1804, at the meridian of Paris: if,
accordingly, the beginning of the year 1805 is taken for the epoch, then
11= - 74.58493; the mean longitude for that epoch was 41°52'21'/.61, and the
diurnal motion, 824".79S8. Substituting now in the place of d M its value in
the formulas just found, the differential changes of the geocentric place, expressed
by means of the changes of the elements alone, are as follows : —

&l = 2.41287 A.N— 179.96 dr — 0.75214 d/7— 3.00531 dy -f 0.16488 da

- 0.11152 dt-f 0.04385 d8,

AI-- - 0.66572 &N+ 49.65 dr -f 0.23677 d J7 + 0.61331 dq> -f 0.02935 da

- 0.47335 di-f 0.38090 da.

If the mass of the heavenly body is either neglected, or is regarded as
known, r and a will be dependent upon each other, and so either dT or da may
be eliminated from our formulas. Thus, since by article 6 we have

we have also

dr _ 3 da
T * a '

in which formula, if dr is to be expressed in parts of the radius, it will be neces
sary to express r in the same manner. Thus in our example we have

log* . . . . . 2.91635

logl" 4.68557

logf 0.17609

C.loga .... 9.57756

7.35557«,

or, dr = — 0.0022676 da, and da = -- 440.99 dT, which value being substituted
in our formulas, the final form at length becomes : —

SECT. 2.] TO POSITION IN SPACE. 99

•dJ= 2.41287 dJV— 252.67 dr — 0.75214 d/7 — 3.00531 dc;

-0.11152 di-f- 0.04385 da,
db = — 0.66572 d^+ 36.71 dr -f 0.23677 d77 + 0.61331 d</>

- 047335 d» 4- 0.38090 da.

In the developnient of these formulas we have supposed all the differentials d/,
db, dlY, dt, dIT, dq>, di, dQ to be expressed in parts of the radius, but, mani
festly, by reason of the homogeneity of all the parts, the same formulas will
answer, if all those differentials are expressed in seconds.

THIRD SECTION.

RELATIONS BETWEEN SEVERAL PLACES IN ORBIT.

78.

THE discussion of the relations of two or more places of a heavenly body in
its orbit as well as in space, furnishes an abundance of elegant propositions, such
as might easily fill an entire volume. But our plan does not extend so far as to
exhaust this fruitful subject, but chiefly so far as to supply abundant facilities for
the solution of the great problem of the determination of unknown orbits from
observations : wherefore, neglecting whatever might be too remote from our pur
pose, we will the more carefully develop every thing that can in any manner
conduce to it. We will preface these inquiries with some trigonometrical propo
sitions, to which, since they are more commonly used, it is necessary more fre
quently to recur.

I. Denoting by A, B, C, any angles whatever, we have

sin A sin ( C — B} -f- sin B sin (A — C} -\- sin (7 sin (B — A) = 0
cos^sin ( C — B} -|- cosB sin (A — C) -f- cos Csm(B — A) = 0.

IT. If two quantities p, P, are to be determined by equations such as

psin(A — P) = a
psan(B—P) = b,
it may generally be done by means of the formulas

p sin (B — A) sin (H— P} = b sin (H— A} — a sin (H— B}
p sin (B — A) cos (H— P) = b cos (//— A) — a cos (IT— B),

in which If is an arbitrary angle. Hence are derived (article 14, II.) the angle
H — P, and p sin (B — A) ; and hence P and p. The condition added is gen-
(100)

SECT. 3.] RELATIONS BETWEEN SEVERAL PLACES IN ORBIT. 101

erally that p must be a positive quantity, whence the ambiguity in the deter
mination of the angle II — Pby means of its tangent is decided; but without
that condition, the ambiguity may be decided at pleasure. In order that the
calculation may be as convenient as possible, it will be expedient to put the arbi
trary angle H either = A or = B or = i (A -(- B]. In the first case the equa
tions for determining P and p will be

p sin ( A — P) =: a,

i A r>\ b — acos(J3 — A)

p cos (A — P) = -- r—~^ — -f— -f- .

sm (B — A)
In the second case the equations will be altogether analogous ; but in the third

And thus if the auxiliary angle t is introduced, the tangent of which — -r, P will
be found by the formula

tan ( M + } B — P) = tan (45° + £) tan l(B — A),
and afterwards p by some one of the preceding formulas, in which

. . ,.-„ .... I at a sin (450+f) 6 sin (45° + Q

$ (b + a } = sin (45 + O \/ -^— ; s> = — • r /.-> - /•>

'V sm2f sin f^2 coSi\/2

al ocos(45°-fO
-

cos

ITT. If jo and P are to be determined from the equations

every thing said in II. could be immediately applied provided, only, 90° -f- A
90° _|_ B were written there throughout instead of A and B : that their use may
be more convenient, we can, without trouble, add the developed formulas. The
general formulas will be

p sin (B — A) sin (H— P) = — b cos (H— A)-\-a cos (H— B}
p Pin (B — A) cos (H— P)= b sin (H— A) — a sin (H— B} .
Thus 1'or ZT= A, they change into

, *

4a« 3»A*i* A * * ^

102 RELATIONS BETWEEN SEVERAL [BOOK I.

• t \ TJ\ a cos (5 — 4) — b

psin.(A — P) = -- AT-JS- A^~

* ^ sin (B — A)

p cos (-4 — P) = a.

For ff= B, they acquire a similar form ; but for TT= $ ( A -(- B} they become

so that the auxiliary angle t being introduced, of which the tangent = ^, it

becomes

tan(M + i# — P) = tan(C — 45°) cotan i(# — 4).

Finally, if we desire to determine p immediately from a and b without previ
ous computation of the angle P, we have the formula

p sin (B — A) — v/ (aa -\- bb — 2 ab cos (B — A)),
as well in the present problem as in II.

79.

For the complete determination of the conic section in its plane, three things
are required, the place of the perihelion, the eccentricity, and the semi-parameter.
If these are to be deduced from given quantities depending upon them, there
must be data enough to be able to form three equations independent of each
other. Any radius vector whatever given in magnitude and position furnishes
one equation : wherefore, three radii vectores given in magnitude and position are
requisite for the determination of an orbit ; but if two only are had, either one
of the elements themselves must be given, or at all events some other quantity,
with which to form the third equation. Thence arises a variety of problems
which we will now investigate in succession.

Let r, /, be two radii vectores which make, with a right line drawn at pleasure
from the sun in the plane of the orbit, the angles N, N', in the direction of the
motion ; further, let IT be the angle which the radius vector at perihelion makes
with the same straight line, so that the true anomalies N — IT, N' — IT may
answer to the radii vectores r, r ; lastly, let e be the eccentricity, and p the semi-
parameter. Then we have the equations

SECT. 3.] PLACES IN ORBIT. 103

r— 77)

from which, if one of the quantities p, e, IT, is also given, it will be possible to
determine the two remaining ones.

Let us first suppose the semi-parameter p to be given, and it is evident that
the determination of the quantities e and 77" from the equations

ecos(N'— 77)=:^— 1,

can be performed by the rule of lemma III. in the preceding article. We have
accordingly

tan ( N— 77) = cotan ( Nf — N} — -^ — ~(f^2,-

r (p — r) sin (N — N)

r'4-r

P
80.

If the angle 77 is given, p and e will be determined by means of the equations

_ rr' (cos (N— 77) — cos (N'—II))
^n) — r' cos (N1 — 77)
r' — r

_ _

~ r cos (2T^~if) — r' cos (Nf — 77) *

It is possible to reduce the common denominator in these formulas to the form
a cos (A — 77), so that a and A may be independent of 77. Thus letting H de
note an arbitrary angle, we have

rcos(jy— 77)— r'cos(N'— 77)=(rcos(^— H)— /cos(JY'— 7J))cos(7J— 77)

— (r sin(^— 7J)— /sin (N'—H}) sin (77—77)

and so

= a cos (A — 77),

if a and A are determined by the equations

r cos (N— 77) — / cos (Nl — 77) = a cos (4 — 77)
r sin (^— 77) — / sin (Jf — 77) = a sin (4 — 77) .

104: RELATIONS BETWEEN SEVERAL [BOOK 1.

In this way we have

_ 2 r/ sin |(.y' — JV) sin (ijy _[_!#'_ 77)
P ' a cos (A — 77)

/ — r
t> -^— __

a cos (A — 71) *

These formulas are especially convenient when p and e are to be computed for
several values of H ; r, r, N, N' continuing the same. Since for the calculation
of the auxiliary quantities a, A, the angle H may be taken at pleasure, it will be
of advantage to put II ~— J (-N-\- W)> by which means the formulas are changed
into these, —

(/ _ r) cos l(N' — N) = — a cos (A — i N— I N')

And so the angle A being determined by the equation

tan (A — i N — i N') = -^- tan i (N' —
we have immediately

[—±&—

cos i (2V"' _ jy) Cos ( A — 77) '

r1 -\-r

The computation of the logarithm of the quantity -/-__- may be abridged by a
method already frequently explained.

81.

If the eccentricity c is given, the angle IT will be found by means of the
equation

cos (A IT}- _"»(^-*^—m

ecosi(N'—N) '

afterwards the auxiliary angle A is determined by the equation
tan (A — i N— * N') = ^ tan * (W — N}.'

The ambiguity remaining in the determination of the angle A — 77 by its cosine
is founded in the nature of the case, so that the problem can be satisfied by two
different solutions ; which of these is to be adopted, and which rejected, must be
decided in some other way ; and for this purpose the approximate value at least

SECT. 3.] PLACES IN ORBIT. 105

of IT must be already known. After IT is found, p will be computed by the
formulas

p — r (1 + 0 cos (N— IT)) = r' (1 -f- e cos (N' — 77)),

or by this,

_ 2 r/ e sin | (N' — N) sin (£ N'-{^ N— 11)

—

82.

Finally, let us suppose that there are given three radii vectores r, r, r", which
make, with the right line drawn from the sun in the plane of the orbit at pleasure,
the angles N, N', N". We shall have, accordingly, the remaining symbols being
retained, the equations

(I.) £ = 1 -f e cos (N— 77)

£.— l-|_ecos(iV— 77)

2r=l + ecoa(N"— 77),

from which p, 77, e, can be derived in several different ways. If we wish to
compute the quantity p before the rest, the three equations (I.) may be multiplied
respectively by sin (N"- -N'\ -- sin (N" -N), sin (N' • -N\ and the products
being added, we have by lemma I, article 78,

sin (N" — N')— sin ( N" — N) + sin (Nr — N)
i sin (N"—N') - - ^ sin (N"— N) -f ~ sin (N* — N} '

This expression deserves to be considered more closely. The numerator evidently
becomes

2 sin k (N" — N'} cos i (N" — N') — 2 sin } (N" — N'} cos ( } N" + I N' — N)
= 4 sin * (N" — N'} sin * (N" — N) sin * (^' — JV).
Putting, moreover,

/ r" sin (JT — N') = n,r r" sin (iV" — JV) = n', r / sin (JT — JV) = «",

it is evident that i n, k ri & n", are areas of triangles between the second and third
radius vector, between the first and third, and between the first and second.

14

106 RELATIONS BETWEEN SEVERAL [BOOK I.

Hence it will readily be perceived, that in the new formula,

" — N) sin^ (Nr — N).

the denominator is double the area of the triangle contained between the ex
tremities of the three radii vectores, that is, between the three places of the
heavenly body in space. When these places are little distant from each other,
this area will always be a very small quantity, and, indeed, of the third order,
if ' N' — N, N" — N' are regarded as small quantities of the first order. Hence
it is readily inferred, that if one or more of the quantities r, r, r", N, N', N", are
affected by errors never so slight, a very great error may thence arise in the de
termination of p ; on which account, this manner of obtaining the dimensions of
the orbit can never admit of great accuracy, except the three heliocentric places
are distant from each other by considerable intervals.

As soon as the semi-parameter p is found, e and II will be determined by the
combination of any two whatever of the equations I. by the method of article 79.

83.

If we prefer to commence the solution of this problem by the computation
of the angle IT, we make use of the following method. From the second of
equations I. we subtract the third, from the first the third, from the first the sec
ond, in which manner we obtain the three following new equations : —

Any two of these equations, according to lemma II., article 78, will give 77 and -,
whence by either of the equations (I.) will be obtained likewise e and p. If we
select the third solution given in article 78, II., the combination of the first equa-

SECT. 3.] PLACES IN ORBIT. 107

tion with the third gives rise to the following mode of proceeding. The auxil
iary angle £ may be determined by the equation

_ -

/' &mi(N' — N)

r"

and we shall have

tan (* N+ IN'+IN" — II} = tan (45° -f Q tan

Two other solutions wholly analogous to this will result from changing the second
place with the first or third. Since the formulas for - become more complicated
by the use of this method, it will be better to deduce e and p, by the method of
article 80, from two of the equations (I.). The uncertainty in the determination
of IT by the tangent of the angle J JV-f- i N' -(- J N" • -IT must be so decided
that e may become a positive quantity : for it is manifest that if values 180° dif
ferent were taken for 77, opposite values would result for e. The sign of p, how
ever, is free from this uncertainty, and the value of p cannot become negative,
unless the three given points lie in the part of the hyperbola away from the sun,
a case contrary to the laws of nature which we do not consider in this place.

That which, after the more difficult substitutions, would arise from the appli
cation of the first method in article 78, II., can be more conveniently obtained in
the present case in the following manner. Let the first of equations II. be multi
plied by cos 4 (N" — N'\ the third by cos 4 (Nr - N), and let the product of
the latter be subtracted from the former. Then, lemma I. of article 78 being
properly applied,* will follow the equation

cotan

" — N'} — 4 (; — 7) cotan * (N' — N)

By combining which with the second of equations H 77 and - will be found ; thus,
77 by the formula

•Putting, that is, in the second formula. A = %(N"—N'), B=%N-\-%N"— 77, C=$(N—N').

108 RELATIONS BETWEEN SEVERAL [BOOK I.

- - cotan * (N" — N} — - — \) cotan * (JT — N)

Hence, also, two other wholly analogous formulas are obtained by interchanging
the second place with the first or third.

84.

Since it is possible to determine the whole orbit by two radii vectores given
in magnitude and position together with one element of the orbit, the time also
in which the heavenly body moves from one radius vector to another, may be
determined, if we either neglect the mass of the body, or regard it as known :
we shall adhere to the former case, to which the latter is easily reduced. Hence,
inversely, it is apparent that two radii vectores given in magnitude and position,
together with the time in which the heavenly body describes the intermediate
space, determine the whole orbit. But this problem, to be considered among the
most important in the theory of the motions of the heavenly bodies, is not so
easily solved, since the expression of the time in terms of the elements is tran
scendental, and, moreover, very complicated. It is so much the more worthy of
being carefully investigated ; we hope, therefore, it will not be disagreeable to
the reader, that, besides the solution to be given hereafter, Avhich seems to leave
nothing further to be desired, we have thought proper to preserve also the one
of which we have made frequent use before the former suggested itself to me.
It is always profitable to approach the more difficult problems in several ways,
and not to despise the good although preferring the better. We begin with ex
plaining this older method.

85.

We will retain the symbols r, /, N, N', p, e, IT with the same meaning, with
which they have been taken above; we will denote the difference N' --N by A,
and the time in which the heavenly body moves from the former place to the

SECT. 3.] PLACES IN ORBIT. 109

latter by t. Now it is evident that if the approximate value of any one of the
quantities p, e, IT, is known, the two remaining ones can be determined from them,
and afterwards, by the methods explained in the first section, the time corre
sponding to the motion from the first place to the second. If this proves to be
equal to the given time t, the assumed value of p, e, or 77, is the true one, and the
orbit is found ; but if not, the calculation repeated with another value differing a
little from the first, will show how great a change in the value of the time corre
sponds to a small change in the values of p, e-, U; whence the correct value will
be discovered by simple interpolation. And if the calculation is repeated anew
with this, the resulting time will either agree exactly with that given, or at least
differ very little from it, so that, by applying new corrections, as perfect an agree
ment can be attained as our logarithmic and trigonometrical tables allow.

The problem, therefore, is reduced to this, — for the case in which the orbit is
still wholly unknown, to determine an approximate value of any one of the quan
tities p, e, U. We will now give a method by which the value of p is obtained
with such accuracy that for small values of // it will require no further correc
tion ; and thus the whole orbit will be determined by the first computation with
all the accuracy the common tables allow. This method, however, can hardly
ever be used, except for moderate values of z/, because the determination of
an orbit wholly unknown, on account of the very intricate complexity of the
problem, can only be undertaken with observations not very distant from each
other, or rather with such as do not involve very considerable heliocentric
motion.

86.

Denoting the indefinite or variable radius vector corresponding to the true
anomaly v — U by (>, the area of the sector described by the heavenly body in
the time t will be %f() y d v, this integral being extended from v = JY to v = N',
and thus, (k being taken in the meaning of article 6), kt\/p=/i)()dv. Now it
is evident from the fomulas developed by COTES, that if (f x expresses any
function whatever of #, the continually approximating value of the integral
ftpx.dx taken from as = utoz=.u-{-Jis given by the formulas

110

RELATIONS BETWEEN SEVERAL

[BouK 1.

It will be sufficient for our purpose to stop at the two first formulas.
By the first formula we have in our problem,

if we put

w).

Wherefore, the first approximate value of \] p, which we will put = 3 a, will be

, Arr'

\J p = j— - — 3a.
A; t cos 2 w

By the second formula we have more exactly

denoting by R the radius vector corresponding to the middle anomaly

Now expressing p by means of r, R, r, N, N-\- i //,
inula given in article 82, we find

4 sin2 £ A sin \ A

according to the for

_
P — '

and hence

cos^A __ , /_!_ , 1_\ _ 2 sin2 ^ J _ cos to

-B * \ r " ~ 7/~ j9

By putting, therefore,

2 sin' ^ ^f
p

cos eu

we have

P _ cos ^ A \/ (r / cos 2 eu)
— ~~ ^

cos w (1 -- )
p1

whence is obtained the second approximate value of ^ p,

SECT. 3.] PLACES IN ORBIT. Ill

, 2 « COS2 i A COS2 2 O) , 8

= a-\-~ — j — = a-\ -- 5—,

2/1 <->\2 /I °\2 '

cos2o»(l -- r (1 -- r

\ pi \ p>

if we put

2 /cos^^coV e_

\ COS <U /

Writing, therefore, n for y/jt?, 7t will be determined by the equation

which properly developed would ascend to the fifth degree. We may put
TT =: q -\- p, so that q is the approximate value of n, and ^i a very small quantity,
the square and higher powers of which may be neglected : from which substitu
tion proceeds

or

and so

_

(qq-S)

Now we have in our problem the approximate value of n, namely, 3 a, which
being substituted in the preceding formula for q, the corrected value becomes

_243ce4£-}-3«(9«tt — 3) (9«ce-{-73)
(9a«— 3) (27 ace + 5 3)

Putting, therefore,

27~o^= P> (1— 3p)a — y>
the formula assumes this form,

n = —

and all the operations necessary to the solution of the problem are comprehended
in these five formulas : —

I. - = tan (45° + 01)

112 HELATIOXS BETWEEN SEVERAL [BoOK 1.

IL __££!_ = « ••-

Tn 2ein2J 4\/ (rr'cos2iu) «

27 a a cos a>

' (1 — 3f?)cos2aj " '

V.

If we are willing to relinquish something of the precision of these formulas, it
will be possible to develop still more simple expressions. Thus, by making cos ia
and cos 2<o =• 1, and developing the value of y/ p in a series proceeding according
to the powers of J, the fourth and higher powers being neglected, we have,

in which J is to lie expressed in parts of the radius. Wherefore, by making

Arr' _ , ,

we have

VI. » = »'(l — -

In like manner, by developing <J p in a series proceeding according to the powers
of sin /I, putting

we have

VIL ^p =

or

VTII. jo = /' -f- $ sin2 J\Jrr.

The formulas VII. and VIII. agree with those which the illustrious EULER has
given in the Theoria motus plandarum ct cometamm, but formula VI., with that which
has been introduced in the Recherches et calculs sur la vraie orbite elliptigue de la
comete de 1769, p. 80.

SECT. 3.]

PLACES IN ORBIT.

113

87.

The following examples will illustrate the use of the preceding precepts, while
from them the degree of precision can be estimated.

I. Let log r = 0.3307640, log / = 0.3222239, J=T 34' 53".73 = 27293".73,
t = 21.93391 days. Then is found w — — 33'47".90, whence the further compu
tation is as follows : —

log A . .
logrr . .
C. log 3 Jc .
C. log t . . .
C. log cos 2 co

4.4360629
0.6529879
5.9728722
8.6588840
0.0000840

J log r r' cos 2 o>
2 log sin J /t

C. log a a .
C. log cos to .

0.3264519
7.0389972
8.8696662
0.5582180
0.0000210

log a

9.7208910

log/9 ..... 6.7933543
0 = 0.0006213757

log 2 .

.

0.3010300

2 log cos

M .

9.9980976

2 log cos

2w .

9.9998320

C.log(l

-3/3)

0.0008103

2 C. log cos w

0.0000420

logy .

.

0.2998119

r=

1.9943982

21/3 =

0.0130489

1 + y + 21 /3 =

3.0074471

log ...... 0.4781980

log a ..... 9.7208910

C. log (1 + 5/3) . 9.9986528

logy/jo .... 0.1977418

logjo ..... 0.3954836

This value of log p differs from the true value by scarcely a single unit in the
seventh place: formula VI., in this example, gives log p = 0.3954822; formula
VH. gives 0.3954780 ; finally, formula VUL, 0.3954754.

II. Let log r= 0.4282792, log/— 0.4062033, z/ = 62°55'16".64,*— 259.88477
days. Hence is derived <a= — 1°27'20".14, log a = 9.7482348, 0 = 0.04535216,
y = 1.681127, log ^p = 0.2198027, log ^ = 0.4396054, which is less than the true
value by 183 units in the seventh place. For, the true value in this example is
0.4396237; it is found to be, by formula VI., 0.4368730; from formula VII. it

15

RELATIONS BETWEEN SEVERAL [BOOK I.

results 0.4159824 ; lastly, it is deduced from formula VUL, 0.4051103 : the two

last values differ so much from the truth that they cannot even be used as ap
proximations.

The exposition of the second method will afford an opportunity for treating
fully a great many new and elegant relations ; which, as they assume different
forms in the different kinds of conic sections, it will be proper to treat separately ;
we will begin with the ELLIPSR

Let the eccentric anomalies E, E', and the radii vectores r, r, correspond to
two places of the true anomaly v, v', (of which v is first in time) ; let also p
be the semi-parameter, e = sin (p the eccentricity, a the semi-axis major, t the
time in which the motion from the first place to the second is completed ; finally
let us put

Then, the following equations are easily deduced from the combination of for
mulas V., VI., article 8 : —

[1] b smff = sin/, ^rr',

[2] l)M\G = $m.F.\jrr',
p cosy = (cos i v cos i v' . (1 -4- e) -\- sin k v sin i v'. (1 — e}~) y/ r r, or

[3] p cosg = (cos/ -4- e cos F) y/ r r, and in the same way,

[4] p cos £ = (cos F-\- ecosf) \Jrr'.
From the combination of the equations 3 and 4 arise,

[5] cos/, y/r/ — (cosy — e cos G) a,

[6] cos I1. \Jrr'= (cos G — ecosg)a.
From formula III., article 8, we obtain

[7] r — r = 2 a e sin g sin G,

r' -\-r = 2 a — 2aecosg cos G = 2asin2y-|- 2 cos/cosy y/rr';
whence,

2 cos /cos g-jrr'

~

SECT. 3.] PLACES m ORBIT. 115

Let us put

2 cos/

and then will

a

k. — *

also

./ a = _|_

sin 5-

in which the upper or lower sign must be taken, as sin y is positive or negative.
Formula XII., article 8, furnishes us the equation

- =E' — e&a.E' — E + e sin.E = Zg — 2 e siny cos G

a3

= 2ff — sin 2 y -j- 2 cos f sing ^— .

If now we substitute in this equation instead of a its value from 10, and put, for
the sake of brevity,

we have, after the proper reductions,
[12] ±m =

in which the upper or lower sign is to be prefixed to m, as sing is positive or
negative.

When the heliocentric motion is between 180° and 360°, or, more generally,
when cos/ is negative, the quantity m determined by formula 11 becomes im
aginary, and I negative ; in order to avoid which we will adopt in this case, instead
of the equations 9, 11, the following: —

_

2 cos/

- - *i-^ - -=M,
2*(— cos/f (rr'f

whence for 10, 12, we shall obtain these, —

RELATIONS BETWEEN SEVERAL [BOOK I.

[10*] fl = =iC^

[12*] ± M= - (L - sin* | ,) + (L - sin

in which the doubtful sign is to be determined in the same manner as before.

89.

We have now two things to accomplish ; first, to derive the unknown quan
tity g as conveniently as possible from the transcendental equation 12, since it
does not admit of a direct solution ; second, to deduce the elements themselves
from the angle g thus found. Before we proceed to these, we will obtain
a certain transformation, by the help of which the computation of the auxiliary
quantity I or L is more expeditiously performed, and also several formulas after
wards to be developed are reduced to a more elegant form.

By introducing the auxiliary angle w, to be determined by means of the
formula

we have

J !L 4. JL. — 2 _|_ (tan (45° + w) — cotan (45° -f w))2 = 2 -f 4 tan2 2 o>;

whence are obtained

, _ sin2!/ , tan22o» ,- _ ^sin2^/ _ tan2 2 <u

cosy cosy : cosy cosy

90.

We will consider, in the first place, the case in which a value of g not very
great, is obtained from the solution of the equation 12, so that

may be developed in a series arranged according to the powers of sin \ g. The
numerator of this expression, which we shall denote by X, becomes

^ sin8 kg — V- sin5 i y — | sin7 i g — etc. ;

SECT. 3.] PLACES IN ORBIT. 117

and the denominator,

SsinMy — 12 sin5 4^ + 3 sin7 i^ + etc.
Whence X obtains the form

But in order to obtain the law of progression of the coefficients, let us differen
tiate the equation

X sin3^ = 2 g — sin 2 gy
whence results

A TT

3 Xcosff smzff -}- sin8 g — =2 — 2 cos 2^ = 4 sin2^ ;

• y

putting, moreover,

sin2 4 g = x,
We have

— — i in
whence is deduced

AX 8 — GXcosff 4 — 3^(1— 2x)

dx &in*ff 2x(l — x)

and next,

If, therefore, we put

X = |( !-{-« x + /? x x + y 3? + <J a;4 + etc.)
we obtain the equation

f (az-f (2/3 — a)xz + (3f — 2/3)^+(4(J — 3y)^+
= (8 — 4a)» + (8« — 4/5)*3r + (8|8 — 4/)^ + (8y — 4d)*4+ etc.
which should be identical. Hence we get

« =*,/* = f «, f =¥/',* = Hr etc.,
in which the law of progression is obvious. We have, therefore,

v | 4.6 , 4.6.8 , 4.6.8.10 „ , 4. 6.8.10. 12 _,

= * + 3T5a? + 875^**+ 3.5.7.9 ^+ 3.5.7.9.1! ^+ etC'

This series may be transformed into the following continuous fraction : —

118 RELATIONS BETWEEN SEVERAL [BOOK 1.

X- -*-

7.10

, 3.6

"13715*

, 9.12
~X

1 — etc.
The law according to which the coefficients

6 2 5. 8 1.4

5' ~~6T7' 779' 97n' €

proceed is obvious; in truth, the n'h term of this series is, when n is even,

n — 3. n
2n

when n is odd,

the further development of this subject would be too foreign from our purpose.
If now we put

_2_
577*
8.8"

1— etc.
we have

SECT. 3.] PLACES is CEBIT. 119

and

or

sb'gr — |(2gr — sin2gr)(l — f si
^(29 — an2g)

The numerator of this expression is a quantity of the seventh order, the denomi
nator of the third order, and £, therefore, of the fourth order, if g is regarded as
a quantity of the first order, and x as of the second order. Hence it is inferred
that this formula is not suited to the exact numerical computation of £ when g
does not denote a very considerable angle: then the following formulas are
conveniently used for this purpose, which differ from each other in the changed
order of the numerators in the fractional coefficients, and the first of which is
derived without difficulty from the assumed value of a? — £.*

1—

i—

1 — etc.,
or,

5 ' ^ T~Q 7

1 — etc.

In the third table annexed to this work are found, for all values of x from
0 to 0.3, and for every thousandth, corresponding values of £ computed to
seven places of decimals. This table shows at first sight the smallness of £ for

* The derivation of the latter supposes some less obvious transformations, to be explained on another
occasion.

120 RELATIONS BETWEEN SEVERAL [BOOK I.

moderate values of g ; thus, for example, for E' - -E=~LQ°, or y=5°, when
x = 0.00195, is £ = 0.0000002. It would be superfluous to continue the table fur
ther, since to the last term z=Q3 corresponds g = 66° 25', or E' — E= 132° 50'.
The third column of the table, which contains values of | corresponding to nega
tive values of x, will be explained further on in its proper place.

91.

*

Equation 12, in which, in the case we are treating, the upper sign must evi
dently be adopted, obtains by the introduction of the quantity \ the form

Putting, therefore,
and

fnm

H-' + *~
the proper reductions being made, we have

[15] h =

If, accordingly, h may properly be regarded as a known quantity, y can be de
termined from it by means of a cubic equation, and then we shall have

n o~\ "* "' 7
[16] X= I.

L J yy

Now, although h involves the quantity |, still unknown, it will be allowable to
neglect it in the first approximation, and for h to take

t+lf

since £ is undoubtedly a very small quantity in the case we are discussing.
Hence y and x will be deduced by means of equations 15, 16 ; £ will be got
from x by table III., and with its aid the corrected value of h will be obtained by
formula 14, with which the same calculation repeated will give corrected values
of y and x: for the most part these will differ so little from the preceding, that £

SECT. 3.] PLACES ix ORBIT. 121

taken again from table III., will not differ from the first value ; otherwise it would
be necessary to repeat the calculation anew until it underwent no further change.
When the quantity x shall be found, g will be got by the formula sin2 1 g = x.

These precepts refer to the first case, in which cos/ is positive ; in the other
case, where it is negative, we put

and

ri 1^-1 MM

whence equation 12* properly reduced passes into this,

PI CjfeT TT \ •* ~T" A J «* *

[15*] ff=LJ-_2_.

I7" and -£T can be determined, accordingly, by this cubic equation, whence again x
will be derived from the equation

r~i /**n T •"*• -"*•

[16*] x = L YY-

In the first approximation

MM

will be taken for H; £ will be taken from table HI. with the value of x derived
from H by means of the equations 15*, 16*; hence, by formula 14*, will be had
the corrected value of H, with which the calculation will be repeated in the same
manner. Finally, the angle g will be determined from x in the same way as in
the first case.

92.

Although the equations 15, 15*, can have three real roots in certain cases, it
will, notwithstanding, never be doubtful which should be selected in our problem.
Since h is evidently a positive quantity, it is readily inferred from the theory
of equations, that equation 15 has one positive root with two imaginary or two
negative. Now since

m

16

122 RELATIONS BETWEEN SEVERAL [BOOK I.

must necessarily be a positive quantity, it is evident that no uncertainty remains
here. So far as relates to equation 15*, we observe, in the first place, that L is
necessarily greater than 1 ; which is easily proved, if the equation given in article
89 is put under the form

,- __ -• I cos2 i/_i_ tan" 2 at
' — cos/ I — cos/ '

Moreover, by substituting, in equation 12*, Y^ (L — x] in the place of M, we
have

and so

and therefore Y^> ^. Putting, therefore, Y= $ -\- Y', Y' will necessarily be a
positive quantity; hence also equation 15* passes into this,

r» + 2 rr + (i — //) r + ,\ — f //= o,

which, it is easily proved from the theory of equations, cannot have several posi
tive roots. Hence it is concluded that equation 15* would have only one root
greater than i,f which, the remaining ones being neglected, it will be necessary
to adopt in our problem.

93.

In order to render the solution of equation 15 the most convenient possible
in cases the most frequent in practice, we append to this work a special table
(Table II.), which gives for values of h from 0 to 0.6 the corresponding loga
rithms computed with great care to seven places of decimals. The argument
h, from 0 to 0.04, proceeds by single ten thousandths, by which means the
second differences vanish, so that simple interpolation suffices in this part
of the table. But since the table, if it were equally extended throughout,
would be very voluminous, from h = 0.04 to the end it was necessary to proceed
by single thousandths only ; on which account, it will be necessary in this latter
part to have regard to second differences, if we wish to avoid errors of some units

t If in fact we suppose that our problem admits of solution.

SECT. 3.] PLACES IN ORBIT. 123

in the seventh figure. The smaller values, however, of h are much the more fre
quent in practice.

The solution of equation 15, when h exceeds the limit of the table, as also
the solution of 15*, can be- performed without difficulty by the indirect method,
or by other methods sufficiently known. But it will not be foreign to the pur
pose to remark, that a small value of g cannot coexist with a negative value of
cos/, except in an orbit considerably eccentric, as will readily appear from equa
tion 20 given below in article 95.-}-

94.

The treatment of equations 12, 12*, explained in articles 91, 92, 93, rests upon
the supposition that the angle g is not very large, certainly within the limit 66° 25',
beyond which we do not extend table III. When this supposition is not correct,
these equations do not require so many artifices; they can be most securely
and conveniently solved by trial ivithout a change of form. Securely, since the value
of the expression

2 g — sin 2 g
sin8$r '

in which it is evident that 2y is to be expressed in parts of the radius, can, for
greater values of g, be computed with perfect accuracy by means of the trigonomet
rical tables, which certainly cannot be done as long as g is a small angle : c<m-
venieiitli/, because heliocentric places distant from each other by so great an interval
will scarcely ever be used for the determination of an orbit wholly unknown, while
by means of equation .1 or 3 of article 88, an approximate value of g follows
with almost no labor, from any knowledge whatever of the orbit : lastly, from an
approximate value of y, a corrected value will always be derived with few trials,
satisfying with sufficient precision equation 12 or 12*. For the rest, when two
given heliocentric places embrace more than one entire revolution, it is necessary
to remember that just as many revolutions will have been completed by the eccen
tric anomaly, so that the angles^' — E, v' — v, either both lie between 0 and 360°,

| That equation shows, that if cosf is negative, cp must, at least, be greater than 90° — g.

124 RELATIONS BETWEEN SEVERAL [BOOK I.

or both between similar multiples of the whole circumference, and also f and g
together, either between 0 and 180°, or between similar multiples of the semicir-
cumference. If, finally, the orbit should be wholly unknown, and it should not
appear whether the heavenly body, in passing from the first radius vector to the
second, had described a part only of a revolution or, in addition, one entire revo
lution, or several, our problem would sometimes admit several different solutions :
however, we do not dwell here on this case, which can rarely occur in practice.

95.

We pass to the second matter, that is, the determination of the elements from
the angle g when found. The major semiaxis is had here immediately by the
formulas 10, 10*, instead of which the following can also be used : —

rihr-i _2mmcosf^rr'_ kktt

1 / a - — — r~5 — — " — —

yysm'g

FT?*! —2MMcosf\/rr'_ klctt

~TTl\^~ ~4rrr/cos2

The minor semiaxis b = \/ap is got by means of equation 1, which being
combined with 'the preceding, there results

Now the elliptic sector contained between two radii vectores and the elliptic arc
is bkt^p, also the triangle between the same radii vectores and the chord
irr'sin 2/: wherefore, the ratio of the sector to the triangle is asy: 1 or Y: 1.
This remark is of the greatest importance, and elucidates in a beautiful manner
both the equations 12,12*: for it is apparent from this, that in equation 12 the
parts m, (l-{-x)'2, X(l-\-x] , and in equation 12* the parts M, (L — xf, X (L — a?) ,
are respectively proportional to the area of the sector (between the radii vectores
and the elliptic arc), the area of the triangle (between the radii vectores and the
chord), the area of the segment (between the arc and the chord), because the
first area is evidently equal to the sum or difference of the other two, accord
ing a.s v — v lies between 0 and 180°, or between 180° and 360°. In the case

SECT. 3.] PLACES IN ORBIT. 125

where v' — v is greater than 360° we must conceive the area of the whole ellipse
added to the area of the sector and the area of the segment just as many times
as the motion comprises entire revolutions.

Moreover, since b = a cos (f> , from the combination of equations 1, 10, 10*,
follow

sin q tan f

[191 COS CD = aT/i^siX
J--sinar

ri n-fc-i — sin q tan f

[19*] cos 01 = 5-77 — . ,/.,

2(L — sin'^gy

whence, by substituting for I, L, their values from article 89, we have

s'n fsin q

This formula is not adapted to the exact computation of the eccentricity
when the latter is not great : but from it is easily deduced the more suitable
formula

roil f.nn2 4 m — sin^ (/— ff) + *an2 2 M
^-

to which the following form can likewise be given (by multiplying the numerator
and denominator by cos2 2 o>)

T221 tin2 i ro — sini> 2 (f~ff) + cos2 i (/— 9) sin2 2 <»
*<? - - _ --

The angle y can always be determined with all accuracy by either formula, using,
if thought proper, the auxiliary angles of which the tangents are

tan 2 to tan 2 w

™ *(/-?)' sin

for the former, or

sin 2 to sin 2

for the latter.

The following formula can be used for the determination of the angle G,
which rea,dily results from the combination of equations 5, 7, and the following
one not numbered,

T9T1 fin a -

I -io i tan cr — -T--

- - -— — j.
— 2oo8/yrr'

from which, by introducing w,is easily derived

126 RELATIONS BETWEEN SEVERAL [BOOK L

r9 ,-, ^ _ _ sin g sin 2 cu _

~ cos22 o> sin £ (f—g) sin ±(/-f 0) + sin22 <a cosy'

The ambiguity here remaining is easily decided by means of equation 7, which
shows, that G must be taken between 0 and 180°, or between 180° and 360°,
as the numerator in these two formulas is positive or negative.

By combining equation 3 with these, which flow at once from equation II.
article 8,

1 1 2e . , . j-,
--- r = — sin/ smF
r r' p

1 1 2 . 2e , 7,

- -4- -v = -- -- cos / cos F,

r ' / p p

the following will be derived without trouble,
[25] tan.F=^ ^7^1 ^

L J 2cosyyrr — (r-(-r)cos/

from which, the angle cu being introduced, results

[26] tanfc sm/sin2w

I- -1

cos2 2 ojsin£(/ — g) sin| (f-\-g) — sin2 2 cocos/'

The uncertainty here is removed in the same manner as before. — As soon as
the angles F and G shall have been found, we shall have v = F — /, v' = F-\-f,
whence the position of the perihelion will be known; also E= G — g, E'= G-\-g.
Finally the mean motion in the time t will be

kt

— = 2,ff — 2 ecosGsmff,

a*

the agreement of which expressions will serve to confirm the calculation ; also,
the epoch of the mean anomaly, corresponding to the middle time between the
two given times, will be G — e sin G cos g, which can be transferred at pleasure
to any other time. It is somewhat more convenient to compute the mean
anomalies for the two given times by the formulas E — e sin E, E' — e sin E', and
to make use of their difference for a proof of the calculation, by comparing it with

It

SECT. 3.] PLACES IN ORBIT. 127

96.

The equations in the preceding article possess so much neatness, that there
may seem nothing more to be desired. Nevertheless, we can obtain certain
other formulas, by which the elements of the orbit are determined much more
elegantly and conveniently ; but the development of these formulas is a little
more abstruse.

We resume the following equations from article 8, which, for convenience, we
distinguish by new numbers : —

L sin i v V/- = sin lH^(~L-\-e)

IL cos i vu - — cos i.Ey(l — e)

IH. si

W.

We multiply I. by sin i (F-\- g], II. by cos I (F-\-g], whence, the products being
added, we obtain

cos * (f+g) \^ = sin i^sin * (F-\-g)^(l + «) + cos i^cos l^+ff) V(l — e)
or, because

\/ (1 -f- e) = cos i 9 -(- sin i 9, y/ (1 — e) = cos J y — sin £ 9,

cos %(f -\-g}U - = cos i 9003(1^ — kG-\-g] — sin Jycos %(F -\-G}.

In exactly the same way, by multiplying HL by sin i (F — g\ IV. by cos i ( F — g\
the products being added, appears

i-Z'T — % G — g) — sin £ (p cos
The subtraction of the preceding from this equation gives

cos J (f-\-g] (\l -- V / — ^ cos ^ 9 sul^ sm ^ (^ —
or, by introducing the auxiliary angle to,

[27] cos£ (f-\-ff) tan2cu=:sin i ( F — G)cos$(psmg if™.

128 RELATIONS BETWEEN SEVERAL [BOOK I.

By transformations precisely similar, the development of which we leave to the
skilful reader, are found

[29] cos£(/ — g] tan 2 <o = sin. £ (F-\- G) sin

When the first members of these four equations are known, J (F — G] and

will be determined from 27 and 29 ; and also, from 29 and 30, in the same manner,
and

aa

the doubt in the determination of the angles i (F — G), $ (J?-\-G), is to be so
decided that P and Q may have the same sign as sin g. Then \ (f and

will be derived from P and Q. From R can be deduced

and also

sin2/Vr 1*
—-

unless we prefer to use the former quantity, which must be

+ y/ (2 (1+ sin2 Iff) cos/) = + y/ (— 2 (L — sin2 * ff) cos/),
for a proof of the computation chiefly, in which case a and p are most conven
iently determined by the formulas

, sin/Vr/ b 7

0 = — v^ — , a= -- , p = ocosq>.

sing cos gr •*

Several of the equations of articles 88 and 95 can be employed for proving the
calculation, to which we further add the following : —

in 2 co / ri' . .~ .

— * / — = e sin G sin a

s 2o) V aa y

2 tan 2 o)
cos

SECT. 3.] PLACES IN ORBIT. 12'J

2 tan 2 w / pp • n • s

— i / -—, •=• e sin F sin/

cos 2 03 V rr

2 tan 2 <u • /-» • jr • T? •

- = tan tp sin tr sin / — tan a> sin / sm 7 .
cos 2 o>

Lastly, the mean motion and the epoch of the mean anomaly will be found in the
same manner as in the preceding article.

97.

We will resume the two examples of article 87 for the illustration of the
method explained in the 88th, and subsequent articles : it is hardly necessary to
say that the meaning of the auxiliary angle w thus far adhered to is not to be
confounded with that with which the same symbol was taken in articles 86, 87.

I. In the first example we have /= 3° 47' 26".865, also

log ^ = 9.9914599, log tan (45° -f- w) — 9.997864975, a = — 8' 27".006.

Hence, by article 89,

log sin2 i/ . . . 7.0389972 log tan2 2 w . . 5,3832428

log cos/. . . . 9.9990488 log cos/ . . . 9.9990488

7.0399484 5.3841940

= log 0.0010963480 = log 0.0000242211

and thus /= 0.0011205691, | + /=• 0.8344539. Further we have

log** . . . . 9.5766974
21ogjfc* . . . . 9.1533948
C.flogr/ . . . 9.0205181
C. log 8 cos3/ . . 9.0997636

log mm ... 7.2736765
log (| -I-;) . . . 9.9214023

7.3522742

The approximate value, therefore, of h is 0.00225047, to which in our table II.
corresponds logyy = 0.0021633. We have, accordingly,

log m m = 7.2715132, or mm = 0.001868587,
3 yy yy

17

130

RELATIONS BETWEEN SEVERAL

[BOOK I.

whence, by formula 16, x = 0.0007480179 : wherefore, since \ is, by table III,
wholly insensible, the values found for h, y, x, do not need correction. Now, the
determination of the elements is as follows : —

logx 6.8739120

log sin iy . 8.4369560, iy = l°34' 2".0286, i (/+#) = 3° 27'45'/.4611,

* (f—ff) == 19'41".4039. Wherefore, by the formulas 27, 28, 29, 30, is had

log tan 2 o) . . . 7.6916214 n C. log cos 2 w . . . 0.0000052

log cos i(/-j-^) . 9.9992065 logsinj(/+y) . . 8.7810188

log cos ^(/—y) . 9.9999929 log sin l(f—g) . . 7.7579709

log P sin l(F—G) 7.6908279 n
£ 8.7810240

logQsml(F-\-G)

7.6916143 n
7.7579761

1 / ri /°r\

4(P-f £) =

-4°38'41".54
319 21 38 .05

log P = log R cos i
log Q = log R sin £

9 8.7824527
9 7.8778355

F=

v =
v' =
G =
E =
E'=

314 42 56 .51
310 55 29 .64
318 30 23 .37
324 0 19 .59
320 52 15 .53
327 8 23 .65

Hence i 9 =
(p =
log It

7° 6' 0".935
14 12 1 .87
8 TRfrtOfiO

For proying the calculation.

i log 2 cos/. . . . 0.1500394

i log (I -j- x] = log — 8.6357566
y

8.7857960

i log r r . .
log sin/ . .
C. log sin ff .

. . 0.3264939
. . 8.8202909
. . 1.2621765

lo0" sin w . . . .

. 93897262

log 206265 . . .

. 5.3144251

log e in seconds
lo01 sin E . . . .

. 4.7041513

9 8000767 n

log b . . .

. . 0.4089613

log cos 9 . .

. . 9.9865224

log sin E' ...

. 9.7344714 n

. . 03954837

log e sin E . . .
loer e sin E'

. 4.5042280 n
4.4386227 n

lo<r«

0.4224389

SECT. 3.] PLACES IN ORBIT. 131

log£ ... 3.5500066 esin^ = — 31932'/.14 =— S°52'12".14

f log a . . . 0.6336584 esmJE' = — 27455 .08 =— 7 37 35 .08

2.9163482 Hence the mean anomaly for the

logif . . . 1.3411160 first place 329°44'27".67

4.2574642 for tne second = 334 45 58 .73

Difference 5 1 31 .06

Therefore, the mean daily motion is 824".7989. The mean motion in the time

t is I809i".o7 = 5° rsr.07.

II. In the other example we have

/= 31°27'3S".S2, 01 = -21'50".565, 1= 0.08635659, log mm= 9.3530651,
or the approximate value of h = 0.2451454 :

to this, in table n., corresponds logyy = 0.1722663, whence is deduced

— = 0.15163477, x = 0.06527818,
yy

hence from table ITT. is taken I = 0.0002531. Which value being used, the cor
rected values become

h = 0.2450779, logy y = 0.1722303, — = 0.15164737, x = 0.06529078,

I = 0.0002532.

If the calculation should be repeated with this value of £ , differing, by a single
unit only, in the seventh place, from the first ; h, logyy, and x would not suffer
sensible change, wherefore the value of x already found is the true one, and we
may proceed from it at once to the determination of the elements. We shall
not dwell upon this here, as it differs in nothing from the preceding example.

III. It .will not be out of place, to elucidate by an example the other
case also in which cos/ is negative. Let v' — v = 224° 0' 0", or /= 112° 0' 0",
log r = 0.1394892, log / = 0.3978794, t = 206.80919 days. Here we find
w = + 4° 14'43" 78, L = 1.8942298, log MM = 0.6724333, the first approximate
value of log-5^ 0.6467603, whence by the solution of equation 15* is obtained
Y= 1.591432, and afterwards x = 0.037037, to which, in table III., corresponds
£ = 0.0000801. Hence are derived the corrected values log H= 0.6467931,
F= 1.5915107, x— 0.0372195, \ = 0.0000809. The calculation being repeated

132 RELATIONS BETWEEN SEVERAL [BOOK I.

with this value of £, we have x = 0.0372213, which value requires no further cor
rection, since £ is not thereby changed. Afterwards is found % g = 11° 7'25".40,
and hence in the same manner as in example I.

k(F— G)= 3°33'53".59 log P = log fi cos } 9 9.9700507

826 6.38 log Q = logoff sin £9 . 9.8580552

F= 115959.97 £9 = 37°41'34'/.27

v = - 100 0 0 .03 9 = 75 23 8 .54

v' — +1235959.97 log# ...... 0.0717096

G = 4 52 12 .79 For proving the calculation.

-172238.01 . . O.omo97

E'= -f-27 7 3.59

The angle 9 in such eccentric orbits is computed a little more exactly by
formula 19*, which gives in our example 9 = 75° 23' 8".57; likewise the eccen
tricity e is determined with greater precision by the formula

e = 1—2 sin2 (45° — £9),

than by e = sin 9 ; according to the former, e = 0.96764630.

By formula 1, moreover, is found log b = 0.6576611, whence logp= 0.0595967,
log a = 1.2557255, and the logarithm of the perihelion distance

log j^:= tog a (l—«):= log $ tea (45° --*?)== 9.7656496.

It is usual to give the time of passage through the perihelion in place of the
epoch of the mean anomaly in orbits approaching so nearly the form of the
parabola ; the intervals between this time and the times corresponding to the
two given places can be determined from the known elements by the method
given in article 41, of which intervals the difference or sum (according as the
perihelion lies without or between the two given places), since it must agree with
the time t, will serve to prove the computation. The numbers of this third ex
ample were based upon the assumed elements in the example of articles 38, 43,
as indeed that very example had furnished our first place : the trifling differences
of the elements obtained here owe their origin to the limited accuracy of the
logarithmic and trigonometrical tables.

SECT. 3.] PLACES IN OKBIT. 133

98.

The solution of our problem for the ellipse in the preceding article, might be
rendered applicable also to the parabola and hyperbola, by considering the parab
ola as an ellipse, in which a and b would be infinite quantities, (f =. 90°, finally
E, E', ff, and G = 0 ; and in a like manner, the hyperbola as an ellipse, in which a
would be negative, and b,E,E',g,Gr,(p, imaginary: we prefer, however, not to
employ these hypotheses, and to treat the problem for each of the conic sections
separately. In this way a remarkable analogy will readily show itself between
all three kinds.

Retaining in the PARABOLA the symbols p, v, v', F,f, r, r', t with the same sig
nification with which they had been taken above, we have from the theory of the
parabolic motion : —

[2] y/£ = «**(*'+/)

2 Iff

~ = tan * (,P+/) — tan * (I7—/) -f- i tan3 i (I7 +/) — * tan3 * (-F— /)
— (tan } (JP+/) — tan * (F—f)) (l -f- tan } (^+/) tan i (^— /) +
i (tan * ( J'H-/) — tan * (I7—/))2)

2 siny^ »• / /2 cos y^ r / .4 sin2 /V /\
p \ p 3pp /'

whence

rg-| T.4 _- 2sin/cog/.r/ . 4sin»/(r/)^
Further, by the multiplication of the equations 1, 2, is derived

and by the addition of the squares,

[5]

134 RELATIONS BETWEEN SEVERAL [BOOK I.

Hence, cos F being eliminated,

2r/
L°J .?> -->__/_

If, accordingly, we adopt here also the equations 9, 9*, article 88, the first for
cos/ positive, the second for cos/ negative, we shall have,

r7*i . -™1/ 'v'r/

L' J P--—2LcoSf>

which values being substituted in equation 3, preserving the symbols m,M, with
the meaning established by the equations 11, 11*, article 88, there result

[8] w=/

[8*] M= — i*-f |Z§.

These equations agree with 12, 12*, article 88, if we there put g = 0. Hence it is
concluded that, if two heliocentric places which are satisfied by the parabola, are
treated as if the orbit were elliptic, it must follow directly from the application
of the rules of article 19, that x== 0; and vice versa, it is readily seen that, if
by these rules we have x = 0, the orbit must come out a parabola instead of
an ellipse, since by equations 1, 16, 17, 19,20 we should have £ = oo, a=<x>,
(f = 90. After this, the determination of the elements is easily effected. Instead
of p, either equation 7 of the present article, or equation 18 of article 95 f might
be employed : but for F we have from equations 1, 2, of this article

tan J J^= ? ~*^ cotan £ / = sin 2 w cotan i /,

if the auxiliary angle is taken with the same meaning as in article 89.

We further observe just here, that if in equation 3 we substitute instead of
p its value from 6, we obtain the well-known equation

kt = Hr + >•' + cos/, y/r /) (r -(- / — 2 cos/, y/r/ )* ^ 2.

t Whence it is at once evident that y and J" express the same ratios in the parabola as in the
ellipse. See article 95.

SECT. 3.J PLACES IN ORBIT. 135

99.

We retain, in the HYPERBOLA also, the symbols p, v, v',f, F, r, r', t with the
same meaning, but instead of the major semiaxis a, which is here negative, we
shall write — a ; we shall put the eccentricity e = (— r in the same manner as
above, article 21, etc. The auxiliary quantity there represented by u, we shall

f

put for the first place =— , for the second = Cc. whence it is readily inferred
that c is always greater than 1, but that it differs less from one, other things
being equal, in proportion as the two given places are less distant from each
other. Of the equations developed in article 21, we transfer here the sixth and
seventh slightly changed in form,

[2]

[3]

[4]

From these result directly the following : —
[5] faF=ka(0-.

[6] sin/=£a(e — i

[7]

[8]

Again, by equation X. article 21, we have

r , O .

136 RELATIONS BETWEEN SEVERAL [BoOK I.

and hence,

This equation 10 combined with 8 gives

r'-f- r — (c -\- -) cos/, y/ r /

•

Putting, therefore, in the same manner as in the ellipse

/ / r

according as cos/ is positive or negative, we have

8(/_i(v/c
[12] a =

(c— )2

c1

The computation of the quantity / or L is here made with the help of the auxil
iary angle to in the same way as in the ellipse. Finally, we have from equation
XI. article 22, (using the hyperbolic logarithms),

kt . . -. 1 G c , , C

or, C being eliminated by means of equation 8,
tt (c-'-)cos/.y/r/

— -) — 21ogc.

In this equation we substitute for a its value from 12, 12* ; we then introduce

SECT. 3.] PLACES IN ORBIT. 13V

the symbol m or M, with the same meaning that formulas 11, 11*, article 88 give
it ; and finally, for the sake of brevity, we write

c c --- 4 log c

from which result the equations
[13] „ = (/

[13*] M= -(

which involve only one unknown quantity, 2, since Z is evidently a function of s
expressed by the following formula,

_ (1 + 2 «W (* + **)- tog

100.

In solving the equation 13 or 13*, we will first consider, by itself, that case in
which the value of e is not great, so that Z can be expressed by a series proceed
ing according to the powers of z and converging rapidly. Now we have

3 K

and so the numerator of Z is f z T -J- | z . . . ;

3 5

and the denominator, 2 z* -j- 3 z . . . ,
whence,

z=|— 1»....

In order to discover the law of progression, we differentiate the equation

2(0 + «)lZ=(l + 2«r)v/(-ar + ^)-log(

whence results, all the reductions being properly made,

18

138 RELATIONS BETWEEN SEVERAL [BoOK 1.

or

whence, in the same manner as in article 90, is deduced

„ 4.6 . 4.6.8 4.6.8.10 ,, , 4.6.8.10.12 ,

= 3 --Og + 3^77gg---3T5T779-^+ 8.5.7.9.11-^

It is evident, therefore, that Z depends upon — z in axactly the same manner
as X does upon x above in the ellipse ; wherefore, if we put

C also will be determined in the same manner by — z as f, above, by a;, so that
we have

[141 t = _ ^es

1 -f- etc..
or,

1 -\- etc.

In this way the values of £ are computed for s to single thousandths, from z = 0
up to 2 — 0.3, which values are given in the third column of table III.

101.

By introducing the quantity £ and putting

,, rn /(ft \ ^

also

MM

_____

SECT. 3.] PLACES IN ORBIT. 139

equations 13, 13* assume the form,

and so, are wholly identical with those at which we arrived in the ellipse (15, 15*,
article 91). Hence, therefore, so far as h or H can be considered as known, y or
Y can be deduced, and afterwards we shall have

1-1 — -! 7

[iv] « = « ,

l ' - JT

From these we gather, that all the operations directed above for the ellipse serve
equally for the hyperbola, up to the period when y or Y shall have been deduced
from h or H; but after that, the quantity

mm , -,- MM
-y~y- '-TT>

which, in the ellipse, should become positive, and in the parabola, 0, must in the
hyperbola become negative : the nature of the conic section will be defined by
this criterion. Our table will give C from z thus found, hence will arise the cor
rected value of h or H, with which the calculation is to be repeated until all
parts exactly agree.

After the true value of s is found, c might be derived from it by means of the
formula

but it is preferable, for subsequent uses, to introduce also the auxiliary angle n,
to be determined by the equation

hence we have

c = tan 2 n + y/ (1 + tan2 2 n) = tan (45° + n).

140 RELATIONS BETWEEN SEVERAL [BOOK I.

102.

Since y must necessarily be positive, as well in the hyperbola as in the ellipse,
the solution of equation 16 is, here also, free from ambiguity :f but with respect
to equation 16*, we must adopt a method of reasoning somewhat different from
that employed in the case of the ellipse. It is easily demonstrated, from the the
ory of equations, that, for a positive value of H\, this equation (if indeed it has
any positive real root) has, with one negative, two positive roots, which will either
both be equal, that is, equal to

ly/ 5 — 1 = 0.20601,

or one will be greater, and the other less, than this limit. We demonstrate in
the following manner, that, in our problem (assuming that z is not a large
quantity, at least not greater than 0.3, that we may not abandon the use of the
third table) the greater root is always, of necessity, to be taken. If in equation
13*, in place of M, is substituted Y\J (L -\-s\we have

)^>(l + z)^, or
4.6 4. 6.8

whence it is readily inferred that, for such small values of z as we here suppose,
Y must always be > 0.20601. In fact, we find, on making the calculation, that
z must be equal to 0.79858 in order that (\-\-z]Z may become equal to this
limit : but we are far from wishing to extend our method to such great values of z.

103.

When z acquires a greater value, exceeding the limits of table HI., the equa
tions 13, 13* are always safely and conveniently solved by trial in their un
changed form ; and, in fact, for reasons similar to those which we have explained

t It will hardly be necessary to remark, that our table II. can be used, in the hyperbola, as well as
in the ellipse, for the solution of this equation, as long as h does not exceed its limit.

I The quantity H evidently cannot become negative, unless f > £ ; but to such a value of f would
correspond a value of z greater than 2.684, thus, far exceeding the limits of this method.

SECT. 3.] PLACES IN ORBIT. 141

in article 94 for the ellipse. In such a case, it is admissible to suppose the
elements of the orbit, roughly at least, known : and then an approximate value
of n is immediately had by the formula

s'mf\/rr/

tan 2 n = — 4^ — 7..
a^(e e — 1')

which readily follows from equation 6, article 99. z also will be had from n by
the formula

— cos2n sin2n

2 cos 2 n cos 2 n '

and from the approximate value of z, that value will be deduced with a few
trials which exactly satisfies the equation 13, 13*. These equations can also be
exhibited in this form,

( tan 2 ra , , / < i-o i \

•i i „• a~ t hyp. log tan (45 +»)

,. sm*n x8 I fy,j sm-'n ,J Jcos2ra

I

' tan 2 n

and thus, a being neglected, the true value of n can be deduced.

104.

It remains to determine the elements themselves from z, n, or c. Putting
a \j (ee — 1) = (5, we shall have from equation 6, article 99,

Mo sin/^r/
P =— o •
tan 2 ?i

combining this formula with 12, 12*, article 99, we derive,

PI m / /• i \ an an n

[19] y/ (*« — 1) = tan y = -|^_g) ,

n 9*1 tan ty - - tan/tan 2 n

'

whence the eccentricity is conveniently and accurately computed ; a will result
from ft and ^ (ee — 1) by division, and p by multiplication, so that we have,

142 RELATIONS BETWEEN SEVERAL [BOOK. I.

2 (I — z) cos/, v/r/ _ 2mmcos/. y/r/_

2 ~

klctt

_ _

tan2 2 7i y#tan22n ~4yy rr'cos2/tana2n

kktt

— 2(£-|-z)cos/.v/r/ _ - 2 MMcosf. v/ r / _ _ _
tana2n ~"FTtan22n ~ 4 T Tr / cos2/ tan2 2 n»

_ sin/.tan/.y/r/ _ yy sin/, tan/, y/r/ _ _ /yr/sin2/\2
*: 2(/ — z) 27WOT ~\ /!;« /

- — sin/- 1?11/: V^ _ — rrsin/.tan/.y/r/ _ / TV/sinj2/\2
"~ ~V /fci! /'

The third and sixth expressions for p, which are wholly identical with the form
ulas 18, 18*, article 95, show that what is there said concerning the meaning
of the quantities y, Y, holds good also for the hyperbola.

From the combination of the equations 6, 9, article 99, is derived

by introducing therefore y and w, and by putting (7= tan (45° -j-^V), we have

[20] tan2^=2si7ton92(U.
sm/cos 2«u

C being hence found, the values of the quantity expressed by M in article 21, will
be had for both places ; after that, we have by equation III., article 21,

G— c

tan J v =

,

tan j v =

f-fj-. — r- — j

(O-\-c) tan
Oc— 1

or, by introducing for C, c, the angles N, n,

rnn

=

[22] tan^=-™

cos (iv — n) tan ^ i/;

Hence will be determined the true anomalies v, v', the difference of which com
pared with 2/ will serve at once for proving the calculation.

Finally, the interval of time from the perihelion to the time corresponding to
the first place, is readily determined by formula XL, article 22, to be

tan (45°
tan (45°

SECT. 3.] PLACES IN ORBIT. 143

and, in the same manner, the interval of time from the perihelion to the time cor
responding to the second place,

«^ /2 0 cos (.AT — n) sin (N-\- n) , •, / A e-o i 7ir\ , i AS.O i \\

t (~ -Wofe^T J- hyP-log tan (45 + JV) tan (45 +«)).

t

If, therefore, the first time is put = 21 — i tf, and, therefore, the second = T-\- J t,
we have

whence the tune of perihelion passage will be known ; finally,

a

™,n j 2 a 2/etan2n T /^co i \\

[24] t = T (—^ - log tan (4o° + »)) ,

which equation, if it is thought proper, can be applied to the final proof of the
calculation.

105.

To illustrate these precepts, we will make an example from the two places
in articles 23, 24, 25, 46, computed for the same hyperbolic elements. Let,
accordingly,

t/_z, = 48°12/ 0", or/ = 24° 6' 0", log r — 0.0333585, log/ = 0.2008541,
t = 51.49788 days.

Hence is found

w = 2° 45' 28'/.47, I = 0.05796039,

j^P or the approximate value of h = 0.0644371 ; hence, by table H.,
\Q%yy— 0.0560848, m— = 0.05047454, z = 0.00748585,

& »/

to which in table HE. corresponds C = 0.0000032. Hence the corrected value of
h is 0.06443691,

losyy = 0.0560846, -m= 0.05047456, z= 0.00748583,
yy

which values require no further correction, because f is not changed by them.
The computation of the elements is as follows : —

144

RELATIONS BETWEEN SEVERAL

[BOOK L

logz 7.8742399

) 0.0032389

log tan/ 9.6506199

-}-zz) . . 8.9387394
log 2 0.3010300

log tan 2 n

log sin/ . .
log y/ r / . .
C. log tan 2 n

. 9.2397694
9°51'ir.816
4 55 35 .908

. 9.6110118
. 0.1171063

0.7602306

log/3 ..... 0.4883487
log tan y .... 9.8862868

log a ..... 0.6020619
logjo ..... 0.3746355

(they should be 0.6020600 and 0.3746356)

8.7406274
0.0112902
0.4681829

— «) .
C. log cos (ff+ n) .
log cot A y . . .

log tan iw . . . 9.2201005

lv= 9°25'29".97

»= 18 5059.94

(it should be 18° 51' 0")

loge ..... 0.1010184
log tan 2^ . . . 9.4621341
C. log cos 2 n . . 0.0064539

9.5696064

number = 0.37119863
hyp log tan (45° +JV) = 0.28591251

log

tan 2 n

8.9387394
1.2969275

log tan y ..... 9.8862868
y= 37°34'59".77

(it should be 37° 35' 0")

C. log

sin/ . . . 0.6900182

log tan 2 w . . . . 8.9848318

C. log cos 2 w . . . 0.0020156

log sin y 9.7852685

log tan 2 N

N =
N—n =

logsin(JV-)- M)
C. log cos (N — n)
log cot i tf . .

. 9.4621341

16°9'46".253

8 4 53 .127

3 9 17 .219

13 0 29 .035

. 9.3523527

. 0.0006587

0.4681829

log tan it/

v=

... 9.8211943
33031'29".93
672 59 .86

(it should be 67° 3' 0")

loge ...... 0.1010184

log tan 2 w . . . . 9.2397694

C.logcos2JV . . . 0.0175142

9.3583020

number = 0.22819284
hyp log tan (45° +n) = 0.17282621

Difference =

0.08528612

Difference =

0.05536663

SECT. 3.] PLACES IN ORBIT. 145

log ...... 8.9308783 log ...... 8.7432480

| log a ..... 0.9030928 flog a ..... 0.9030928

aiogjfc ..... 1.7644186 C.log£ ..... 1.7644186

logT ..... 1.5983897 loS2 ...... 0.3010300 .

T= 39.66338 log* ...... 1.7117894

t— 51.49788

Therefore, the perihelion passage is 13.91444 days distant from the time
corresponding to the first place, and 65.41232 days from the time corresponding
to the second place. Finally, we must attribute to the limited accuracy of the
tables, the small differences of the elements here obtained, from those, according
to which, the given places had been computed.

106.

In a treatise upon the most remarkable relations pertaining to the motion
of heavenly bodies in conic sections, we cannot pass over in silence the elegant
expression of the time by means of the major semiaxis, the sum r-\-r', and the
chord joining the two places. This formula appears to have been first discovered,
for the parabola, by the illustrious EULER, (Miscell. Berolin, T. VII. p. 20,) who
nevertheless subsequently neglected it, and did not extend it to the ellipse and
hyperbola : they are mistaken, therefore, who attribute the formula to the illus
trious LAMBERT, although the merit cannot be denied this geometer, of having
independently obtained this expression when buried in oblivion, and of having
extended it to the remaining conic sections. Although this subject is treated by
several geometers, still the careful reader will acknowledge that the following
explanation is not superfluous. We begin with the elliptic motion.

We observe, in the first place, that the angle 2/ described about the sun
(article 88, from which we take also the other symbols) may be assumed to be
less than 360° ; for it is evident that if this angle is increased by 360°, the time
is increased by one revolution, or

-=aX 365.25 days.
19

146 RELATIONS BETWEEN SEVERAL [BOOK 1.

Now, if we denote the chord by 9, we shall evidently have

Q () = (r cos if — r cos v)2 -\- (r sin v' — r sin v)z,
and, therefore, by equations VIII., IX., article 8,

Q (> = a a (cos E' — cos Ef -\- a a cos2 y (sin E' — sin E)z

= 4 a a sirfg (sin2 G -(- cos2 (p cos2 G) = 4 a a sin2^ (1 — e e cos2 G).

We introduce the auxiliary angle h such, that cos h =• e cos G ; at the same time,
that all ambiguity may be removed, we suppose h to be taken between 0°-and
180°, whence sin h will be a positive quantity. Therefore, as g lies between the
same limits (for if 2y should amount to 360° or more, the motion would attain to,
or would surpass an entire revolution about the sun), it readily follows from the
preceding equation that ^ = 2« smg sin A, if the chord is considered a positive
quantity. Since, moreover, we have

r-\-r' = 2«(1 — ecos^cos^) = 2a(l — cosy cos h),
it is evident that, if we put h — g = #, h -\-g = t., we have,

[1] r -f r'— <j = 2 a (1 — cos 8} = 4 a sin2 } d,
[2] r-j-/-|-9 = 2o(l — cos e) = 4 a sin2 i t- .

Finally, we have

3 3

Itt = a7 (2^ — 2 <?siny cos 6!) = «- (2^ — 2 siny cos A),
or

^ /
[3] ££=:a*(a — sine

Therefore, the angles d and e can be determined by equations 1, 2, from
>• -)- ^"'? ?> and a ; wherefore, the time t will be determined, from the same equa
tions, by equation 3. If it is preferred, this formula can be expressed thus :

,, f/

k t = a (

\

2a—

2a—(r + r')—o • 2 a— (r-\-r') —Q

arc cos - - — sm arc cos -

2a 2a

_ p .

- arc cos - •£ 4- sm arc cos -

2a 2a

But an uncertainty remains in the determination of the angles <?,e, by their
cosines, which must be examined more closely. It appears at once, that d
must lie between — 180° and + 180°, and e between 0° and 360° : but thus

SECT. 3.] PLACES IN ORBIT. 147

both angles seem to admit of a double, and the resulting time, of a quadruple,
determination. We have, however, from equation 5, article 88,

cos/. \l rr1 =. a (cosy — cos h] = 2 a sin £ d sin £ e :

now, sin & e is of necessity a positive quantity, whence we conclude, that cos/
and sin i $ are necessarily affected by the same sign ; and, for this reason, that
d is to be taken between 0° and 180°, or between — 1 80° and 0° according as cos/
happens to be positive or negative, that is, according as the heliocentric motion
hap'pens to be less or more than 180°. Moreover, it is evident that d must neces
sarily be 0°, for 2/= 180°. In this manner d is completely determined. But
the determination of the angle « continues, of necessity, doubtful, so that two
values are obtained for the time, of which it is impossible to determine the true
one, unless it is known from some other source. Finally, the reason of this
phenomenon is readily seen : for it is known that, through two given points, it
is possible to describe tivo different ellipses, both of which can have their focus
in the same given point and, at the same time, the same major semiaxis;* but
the motion from the first place to the second in these ellipses is manifestly per
formed in unequal times.

107.

Denoting by # any arc whatever between — 180° and -|- 180°, and by s the
sine of the arc $% , it is known that,

Moreover, we have

//I 1.1 5 1.1.3

* sin % = s v/ (1 — ss) = s— i s8 — 274 s5 — ^-j-g
and thus,

* A circle being described from the first place, as a centre, with, the radius 2 a — r, and another,
from the second place, with the radius 2 a — /, it is manifest that the other focus of the ellipse lies in the
intersection of these circles. Wherefore, since, generally speaking, two intersections are given, two dif
ferent ellipses will be produced.

148 RELATIONS BETWEEN SEVERAL [BOOK I.

«•

We substitute in this series for a, successively

__

and we multiply the results by a'2 ; and thus obtain respectively, the series,

l(r + /_^ + ^l(r + /_^ + T^J-(, + /_^+ '

T?ii* (r + r' — e)1 + etc.

the sums of which we will denote by I7, 27 Now it is easily seen, since

the upper or lower sign having effect according as 2/ is less or more than 180°,
that

a*(d — sm8) = ±F,

the sign being similarly determined. In the same manner, if for e is taken the
smaller value, inferior to 180°, we have

a (e — sin e) = 17;

but the other value, which is the complement of the former to 360°, being taken,
we evidently have

a* (e — sin e) = a* 360° — U.

Hence, therefore, are obtained two values for the time t,

a$360° U+T

108.

If the parabola is regarded as an ellipse, of which the major axis is infinitely
great, the expression for the time, found in the preceding article, passes into

SECT. 3.] PLACES IN ORBIT. 140

but since this derivation of the formula might perhaps seem open to some doubts,
we will give another not depending upon the ellipse.
Putting, for the sake of brevity,

tan i v = 6, tan £ if = &', we have r = i p (1 -f 66), r' = i p (1 -f- & &'),

1 — 60 . l — O'tf . 20 20'

= 1-R^JCOS,':.fTW,, S1n^T-^,Sm*':=rfFF.

Hence follow

r'cost/ — r cos# = £jt?(d£ — &' &\ r'smi/ — rsmv=p(&' — 6),
and thus

Now it is readily seen that 6' — 6 = c^ i^^ iv ^s a positive quantity : putting,
therefore,

\/(l-fJ(0'-f£)2) = 77, we have 4,^^(5' — 6)r).
Moreover,

r + / = * j» (2 + ^ + 6' 6') =
wherefore, we have

From the former equation is readily deduced,

as TJ and d' — ^ are positive quantities; but since i (&' — 6} is smaller or greater
than r], according as

=- cos/

COS | f COS

is positive or negative, we must, evidently, conclude from the latter equation that

in which the upper or lower sign is to be adopted, according as the angle de
scribed about the sun is less than 180°, or more than 180°.

150 RELATIONS BETWEEN SEVERAL [BOOK I.

From the equation, which in article 98 follows the second equation, we have,
moreover,

whence readily follows,

the upper or lower sign taking effect, as 2/ is less or more than 180°.

109.

If, in the hyperbola, we take the symbols a, C, c, with the same meaning as in
article 99, we have, from equations VIII., IX., article 21,

/ cos v' — r cos v = — £ (c -- \\G — -~\ a

v/(ee — 1);
and consequently,

Let us suppose that y is a quantity determined by the equation

>+}=<(<>+$••

since this is evidently satisfied by two values, the reciprocals of each other, we
may adopt the one which is greater than 1. In this manner

Moreover,

' r
and thus,

r 4- ^ + ? = « v^r —

SECT. 3.] PLACES IN ORBIT. 151

Putting, therefore,

we necessarily have

but in order to decide the question whether J7- -J- is equal to-|-2w or _ 2w,
it is necessary to inquire whether y is greater or less than c : but it' follows readily
from equation 8, article 99, that the former case occurs when 2/ is less than
180°, and the latter, when 2/ is more than 180°. Lastly, we have, from the same
article,

+ »») — 2 log (y/(l + mm) + m)
± 2 log (y/(l + »«) + »),

the lower signs belonging to the case of 2/> 180°. Now, log (\j(l-}-mm)-\-m)
is easily developed into the following series : —

This is readily obtained from

d
There follows, therefore, the formula

and, likewise, another precisely similar, if mis changed to n. Hence, finally, if we
put

- TrfTT • » (r + ^ + 9) + etc.

152 RELATIONS BETWEEN SEVERAL PLACES IN ORBIT. [BOOK I.

we obtain

which expressions entirely coincide with those given in article 107, if a is there
changed into — a.

Finally, these series, as well for the ellipse as the hyperbola, are eminently
suited to practical use, when a or a possesses a very great value, that is, where the
conic section resembles very nearly the parabola. In such a case, the methods
previously discussed (articles 85-105) might be employed for the solution of the
problem : but as, in our judgment, they do not furnish the brevity of the solution
given above, we do not dwell upon the further explanation of this method.

FOURTH SECTION.

RELATIONS BETWEEN SEVERAL PLACES IN SPACE.

110.

THE relations to be considered in this section are independent of the nature of
the orbit, and will rest upon the single assumption, that all points of the orbit lie
in the same plane with the sun. But we have thought proper to touch here upon
some of the most simple only, and to reserve others more complicated and special
for another book.

The position of the plane of the orbit is fully determined by two places of
the heavenly body in space, provided these places do not lie in the same straight
line with the sun. Wherefore, since the place of a point in space can be assigned
in two ways, especially, two problems present themselves for solution.

We will, in the first place, suppose the two places to be given by means of
heliocentric longitudes and latitudes, to be denoted respectively by X, X', (i, ft' : the
distances from the sun will not enter into the calculation. Then if the longitude
of the ascending node is denoted by 8, the inclination of the orbit to the ecliptic
by i, we shall have,

tan /? = tan i sin (A — Q, ),
tan /?'= tan i sin (X' — & ).

The determination of the unknown quantities & , tan i, in this place, is referred
to the problem examined in article 78, H We have, therefore, according to the
first solution,

tan i sin (A — 8 ) = tan /? ,

,, tanjS' — tanScos(l' — 1)

tan*cos(X— 8) = - sin(/_^v -',

20 (153)

154 RELATIONS BETWEEN SEVERAL [BooK I.

likewise, according to the third solution, we find 8 by equation

and, somewhat more conveniently, if the angles fi, /3', are given immediately, and
not by the logarithms of their tangents : but, for determining i, recourse must be
had to one of the formulas

Finally, the uncertainty in the determination of the angle

X — a, or iX+U' — 8,

by its tangent will be decided so that tant may become positive or negative,
according as the motion projected on the ecliptic is direct or retrograde : this
uncertainty, therefore, can be removed only in the case where it may be ap
parent in what direction the heavenly body has moved in passing from the first
to the second place ; if this should be unknown, it would certainly be impossi
ble to distinguish the ascending from the descending node.

After the angles Q,,i, are found, the arguments of the latitude u,u', will be
obtained by the formulas,

cos t cos t

which are to be taken in the first or second semicircle, according as the corre
sponding latitudes are north or south. To these formulas we add the following,
one or the other of which can, at pleasure, be used for proving the calculation : —

cos u = cos /3 cos (X — 8 ), cos rf = cos /?' cos (X' — Q ),

sinS . , sinj?'

smtt = -^., smw = -TJT,

cvr\ « ' cin t '

COS t COS t

SECT. 4.] PLACES IN SPACE. 155

111.

Let us suppose, in the second place, the two places to be given by means of
their distances from three planes, cutting each other at right angles in the sun ;
let us denote these distances, for the first place, by x, y, z, for the second, by
x, i/', z', and let us suppose the third plane to be the ecliptic itself, also the posi
tive poles of the first and second planes to be situated in N, and 90° -j- N. We
shall thus have by article 53, the two radii vectores being denoted by r, /,

x = r cos u cos (N — 8 ) -f- r sin u sin (JV — Q ) cos i,

y = r sin u cos (N — Q, ) cos i — r cos u sin (N — Q ) ,

z = r sin u sin i

x' = r cos 11 cos (N — 0,}-\-r' sin u' sin (N — & ) cos i,
y = / sin u' cos (N — 8 ) cos i — / cos ut sin (N — Q ),

z' — r sin u' sin i,
Hence it follows that

zy — yz' = rr sin («' — ««) sin (N — Q, ) sin i,
xz — • zx' = rr sin (u' — «) cos ( JV — Q ) sin i,
xy1 — yx' = rr sin (ur — u) cos i.

From the combination of the first formula with the second will be obtained JV — &
and r r' sin (uf — u) sin i, hence and from the third formula, i and rr sin (u' — u)
will be obtained.

Since the place to which the coordinates x', y1 , z' ', correspond, is supposed pos
terior in time, u' must be greater than u : if, moreover, it is known whether the
angle between the first and second place described about the sun is less or greater
than two right angles, rr' sm(u' — w)sinz' and rr'sin(u' — u} must be positive
quantities in the first case, negative in the second : then, accordingly, N — £2
is determined without doubt, and at the same time it is settled by the sign of
the quantity xy' — yx', whether the motion is direct or retrograde. On the othei
hand, if the direction of the motion is known, it will be possible to decide from
the sign of the quantity xy' — y x', whether u' — • u is to be taken less or greater
than 180°. But if the direction of the motion, and the nature of the angle

156 RELATIONS BETWEEN SEVERAL [BOOK I.

described about the sun are altogether unknown, it is evident that we cannot dis
tinguish between the ascending and descending node.

It is readily perceived that, just as cos i is the cosine of the inclination of
the plane of the orbit to the third plane, so sin ( JV — Q ) sin i, cos (N — Q ) sin i,
are the cosines of the inclinations of the plane of the orbit to the first and second
planes respectively ; also that r r sin («' — u) expresses the double area of the tri
angle contained between the two radii vectores, and zy1 — ys', xz — zx', xy' — yz',
the double area of the projections of this triangle upon each of the planes.

Lastly, it is evident, that any other plane can be the third plane, provided,
only, that all the dimensions defined by their relations to the ecliptic, are referred
to the third plane, whatever it may be.

112.

Let x", y", z", be the coordinates of any third place, and u" its argument of
the latitude, r" its radius vector. We will denote the quantities /r"sin(?/' — «'),
rr"sin(n" — u},rr'sin(u' — u), which are the double areas of the triangles be
tween the second and third radii vectores, the first and third, the first and second,
respectively, by «, w', ri'. Accordingly, we shall have for of', y", z", expressions
similar to those which we have given in the preceding article for x, y, z, and
xf, y', z ; whence, with the assistance of lemma I, article 78, are easily derived the
following equations : —

Q = nx — n'x'-\-n"x",

0 = wz — tfV + nV.

Let now the geocentric longitudes of the celestial body corresponding to these
three places be a, a', a"; the geocentric latitudes, ft, ft', ft"; the distances from the
earth projected on the ecliptic, fT, d', 8"; the corresponding heliocentric longitudes
of the earth, L, L', L"; the latitudes, B, B, B', which we do not put equal to
0, in order to take account of the parallax, and, if thought proper, to choose
any other plane, instead of the ecliptic ; lastly, let D, &, D", be the distances of
the earth from the sun projected upon the ecliptic. If, then, x, y, 0, are expressed

SECT. 4.] PLACES IN SPACE. 157

by means of Z, B, D, a, /9, d, and the coordinates relating to the second and third
places in a similar manner, the preceding equations will assume the following
form : —

[1] 0 = n (8 cos a -\- D cos Z) — it (8' cos a' -f V cos Z')
+ n" (8" cos a" -f D" cos Z"),

[2] 0 = w (<? sin a + D sin Z) — ri ($' sin a' -f- V sin Z')

+ n"(«T sin «" + /?" sin Z"),

[3] 0 = n (d tan /} + Z> tan ,5) — w' (d' tan 0' + Z>' tan Z*)
+ n" (d" tan 0" -f D" tan Z"').

If «, /?, Z1, Z, Z1, and the analogous quantities for the two remaining places, are
here regarded as known, and the equations are divided by n', or by n", five un
known quantities remain, of which, therefore, it is possible to eliminate two, or to
determine, in terms of any two, the remaining three. In this manner these three
equations pave the way to several most important conclusions, of which we will
proceed to develop those that are especially important.

113.

That we may not be too much oppressed with the length of the formulas, we
will use the following abbreviations. In the first place we denote the quantity

tan /? sin (a" — a'} -\- tan |3' sin (a — a") -\- tan ft" sin («' — «)

by (0. 1. 2): if, ha this expression, the longitude and latitude corresponding to
any one of the three heliocentric places of the earth are substituted for the longi
tude and latitude corresponding to any geocentric place, we change the number
answering to the latter in the symbol (0. 1. 2.) for the Koman numeral which
corresponds to the former. Thus, for example, the symbol (0. 1. 1.) expresses the
quantity

tan fi sin (Z' — a') -)- tan /?' sin (a — Z') -|- tan B sin («' — a) ,
also the symbol (0. 0. 2), the following,

tan (3 sin (a" — Z) -f- tan B sin (a — a") -f- tan $" sin (Z — a) .
We change the symbol in the same way, if in the first expression any two helio-

158 RELATIONS BETWEEN SEVERAL [BOOK I.

centric longitudes and latitudes of the earth whatever, are substituted for two
geocentric. If two longitudes and latitudes entering into the same expression are
only interchanged with each other, the corresponding numbers should also be
interchanged ; but the value is not changed from this cause, but it only becomes
negative from being positive, or positive from negative. Thus, for example, we
have

(0.1.2)= — (0.2. !) = (!. 2.0) = — (1.0.2) = (2. 0.1) = — (2. 1.0).
All the quantities, therefore, originating in this way are reduced to the nineteen
following : —
(0.1.2)

(0.1.0), (0.1. 1.),. (0.1. II.), (0.0.2), (0.1.2), (O.H.2), (0.1.2), (1. 1.2), (H 1.2),
(0. 0. 1.), (0. 0. II), (0. 1 tt), (1. 0. 1.), (1. 0. II), (1. 1. II.), (2. 0. L), (2. 0. II),
(2. 1. II.),
to which is to be added the twentieth (0. 1. II.).

Moreover, it is easily shown, that each of these expressions multiplied by the
product of the three cosines of the latitudes entering into them, becomes equal
to the sextuple volume of a pyramid, the vertex of which is in the sun, and the
base of which is the triangle formed between the three points of the celestial
sphere which correspond to the places entering into that expression, the radius
of the sphere being put equal to unity. When, therefore, these three places lie in
the same great circle, the value of the expression should become equal to 0 ; and
as this always occurs in three heliocentric places of the earth, when we do not
take account of the parallaxes and the latitudes arising from the perturbations of
the earth, that is, when we suppose the earth to be exactly in the plane of the
ecliptic, so we shall always have, on this assumption, (0. 1. II.) = 0, which is, in
fact, an identical equation if the ecliptic is taken for the third plane. And fur
ther, when B, B', B", each, = 0, all those expressions, except the first, become
much more simple ; every one from the second to the tenth will be made up of
two parts, but from the eleventh to the twentieth they will consist of only one
term.

SECT. 4.] PLACES IN SPACE. 159

114.

By multiplying equation [1] by sin a" tan B" — sin L" tan /?", equation [2]
by cos L" tan /3" — cos a" tan B", equation [3] by sin (L" • — a"), and adding the
products, we get,

[4] 0 = n ((0. 2. II.) d 4- (0. 2. II.) D) —ri ((1. 2. II.) <T + (I. 2. II.) Z>') ;
and in the same manner, or more conveniently by an interchange of the places,
simply

[5] 0 = n ((0. 1. 1.) d 4- (0. 1. 1.) D) -f n" ((2. 1. 1.) d" -f (II. 1. 1.) ZX')
[6] 0 = «' ((1. 0. 0.)<T + (I. 0. 0.)Z>') — n" ((2. 0. 0.)<T + (II. 0. 0.) D").

If, therefore, the ratio of the quantities n, n', is given, with the aid of equation 4,
we can determine df from d, or d from d' ; and so likewise of the equations 5, 6.
From the combination of the equations 4, 5, 6, arises the following,

m (o.2.ii.)a-f(o.2.n.).p (i.o.o.)y+(i.o.o.)zy (2. ij.)
L'-l (o. i.i.)

by means of which, from two distances of a heavenly body from the earth, the
third can be determined. But it can be shown that this equation, 7, becomes
identical, and therefore unfit for the determination of one distance from the other

two, when

B=B'=B"=Q,
and

tan F tan £" sin (L — a) sin (L" — L'} + tan 0" tan 0 sin (I! — a') sin (L — L"}

-\- tan p tan 0' sin (L" — a") sin (I/ — L) = 0.

The following formula, obtained easily from equations 1, 2, 3, is free from this
inconvenience : —

[8] (0. 1. 2.) 8W + (0. 1. 2) Z>cT<r' -}- (0. 1. 2) ZWd" -f (0. 1. TLj'ff'dd'

-}- (o. i. n.) pTTtf -f (o. i. n.) Djyy 4- (0. i. 2) z> w 4- (o. i. n.) DW = o.

By multiplying equation 1 by sin a tan /?" — sin a" tan /T, equation 2 by
cos a" tan /5' — cos «' tan 0", equation 3 by sin (a" — a'), and adding the products,
we get

[9] 0 = n ((0. 1. 2) d 4- (0. 1. 2) D) — n' (L 1.2)I/ + n" (H. 1. 2) 2/'

160 RELATIONS BETWEEN SEVERAL PLACES IN SPACE. [BOOK I.

and in the same manner,

[10] 0 = n (0. 0. 2.) D — ri ((0. 1. 2) <T -f (0. 1 2) ZX) + n" (0. H. 2) ZX',
[11] 0 = » (0. 1. 0) D — n' (0. 1. 1.) Z/ + n" ((0. 1. 2) d"+ (0. l.H.) Z>").

By means of these equations the distances d, d', 8", can be derived from the
ratio between the quantities n, n', n", when it is known. But this conclusion only
holds in general, and suffers an exception when (0.1.2)= 0. For it can be shown,
that in this case nothing follows from the equations 8, 9, 10, except a necessary
relation between the quantities n, n', n", and indeed the same relation from each
of the three. Analogous restrictions concerning the equations 4, 5, 6, will readily
suggest themselves to the reader.

Finally, all the results here developed, are of no utility when the plane of the
orbit coincides with the ecliptic. For if (f, /?', /3", B, B B" are all equal to 0,
equation 3 is identical, and also, therefore, all those which follow.

SECOND BOOK.

INVESTIGATION OF THE ORBITS OF HEAVENLY BODIES FROM GEOCENTRIC

OBSERVATIONS.

FIRST SECTION.

DETERMINATION OF AN ORBIT FROM THREE COMPLETE OBSERVATIONS.

115.

SEVEN elements are required for the complete determination of the motion
of a heavenly body in its orbit, the number of which, however, may be dimin
ished by one, if the mass of the heavenly body is either known or neglected ;
neglecting the mass can scarcely be avoided in the determination of an orbit
wholly unknown, where all the quantities of the order of the perturbations must
be omitted, until the masses on which they depend become otherwise known.
Wherefore, in the present inquiry, the mass of the body being neglected, we re
duce the number of the elements to six, and, therefore, it is evident, that as many
quantities depending on the elements, but independent of each other, are re
quired for the determination of the unknown orbit. These quantities are neces
sarily the places of the heavenly body observed from the earth ; since each one
of which furnishes two data, that is, the longitude and latitude, or the right ascen
sion and declination, it will certainly be the most simple to adopt three geocentric
places which will, in general, be sufficient for determining the six unknown ele
ments. This problem is to be regarded as the most important in this work, and,
for this reason, will be treated with the greatest care in this section.

21 ' (161)

]62 DETERMINATION OF AN ORBIT FROM [BOOK II.

But in the special case, in which the plane of the orbit coincides 'with the
ecliptic, and thus both the heliocentric and geocentric latitudes, from their nature,
vanish, the three vanishing geocentric latitudes cannot any longer be considered
as three data independent of each other: then, therefore, this problem would
remain indeterminate, and the three geocentric places might be satisfied by an
infinite number of orbits. Accordingly, in such a case, four geocentric longitudes
must, necessarily, be given, in order that the four remaining unknown elements
(the inclination of the orbit and the longitude of the node being omitted) may be
determined. But although, from an indiscernible principle, it is not to be ex
pected that such a case would ever actually present itself in nature, nevertheless,
it is easily imagined that the problem, which, in an orbit exactly coinciding with
the plane of the ecliptic, is absolutely indeterminate, must, on account of the
limited accuracy of the observations, remain nearly indeterminate in orbits very
little inclined to the ecliptic, where the very slightest errors of the observations
are sufficient altogether to confound the determination of the unknown quan
tities. Wherefore, in order to examine this case, it will be necessary to select
six data : for which purpose we will show in section second, how to determine an
unknown orbit from four observations, of which two are complete, but the other
two incomplete, the latitudes or declinations being deficient.

Finally, as all our observations, on account of the imperfection of the instru
ments and of the senses, are only approximations to the truth, an orbit based
only on the six absolutely necessary data may be still liable to considerable
errors. In order to diminish these as much as possible,, and thus to reach the
greatest precision attainable, no other method will be given except to accumulate
the greatest number of the most perfect observations, and to adjust the elements,
not so as to satisfy this or that set of observations with absolute exactness, but
so as to agree with all in the best possible manner. For which purpose, we will
show in the third section how, according to the principles of the calculus of
probabilities, such an agreement may be obtained, as will be, if in no one place
perfect, yet in nil the places the strictest possible.

The determination of orbits in this manner, therefore, so far as the heavenly
bodies move in them according to the laws of KEPLER, will be carried to the

SECT. 1.] THREE COMPLETE OBSERVATIONS. 163

highest degree of perfection that is desired. Then it will be proper to undertake
the final correction, in which the perturhations that the other planets cause in the
motion, will he taken account of: we will indicate briefly in the fourth section,
how these may be taken account of, so far at least, as it shall appear consistent
with our plan.

116.

Before the determination of any orbit from geocentric observations, if the
greatest accuracy is desired, certain reductions must be applied to the latter on
account of nutation, precession, parallax, and aberration : these small quantities
may be neglected in the rougher calculation.

Observations of planets and comets are commonly given in apparent (that
is, referred to the apparent position of the equator) right ascensions and declina
tions. Now as this position is variable on account of nutation and precession,
and, therefore, different for different observations, it will be expedient, first of all,
to introduce some fixed plane instead of the variable plane, for which purpose,
.either the equator in its mean position for some epoch, or the ecliptic might be
selected : it is customary for the most part to use the latter plane, but the former
is recommended by some peculiar advantages which are not to be despised.

When, therefore, the plane of the equator is selected, the observations are in
the first place to be freed from nutation, and after that, the precession being-
applied, they are to be reduced to some arbitrary epoch : this operation agrees
entirely with that by which, from the observed place of a fixed star, its mean
place is derived for a given epoch, and consequently does not need explanation
here. But if it is decided to adopt the plane of the ecliptic, there are two courses
Avhich may be pursued : namely, either the longitudes and latitudes, by means of
the mean obliquity, can be deduced from the right ascensions and declinations
corrected for nutation and precession, whence the longitudes referred to the mean
equinox will be obtained ; or, the latitudes and longitudes will be computed more
conveniently from the apparent right ascensions and declinations, using the appar
ent obliquity, and will afterwards be freed from nutation and precession.

The places of the earth, corresponding to each of the observations, are com-

164 DETERMINATION OF AN ORBIT FROM [BoOK II.

puted from the solar tables, but they are evidently to be referred to the same
plane, to which the observations of the heavenly body are referred. For which
reason the nutation will be neglected in the computation of the longitude of the
sun ; but afterwards this longitude, the precession being applied, will be reduced
to the fixed epoch, and increased by 180 degrees ; the opposite sign will be given
to the latitude of the sun, if; indeed, it seems worth while to take account of it :
thus will be obtained the heliocentric place of the earth, which, if the equator is
chosen for the fundamental plane, may be changed into right ascension and decli
nation by making use of the mean obliquity.

117.

The position of the earth, computed in this manner from the tables, is the
place of the centre of the earth, but the observed place of the heavenly body
is referred to a point on the surface of the earth : there are three methods of
remedying this discrepancy. Either the observation can be reduced to the centre
of the earth, that is, freed from parallax ; or the heliocentric place of the earth
may be reduced to the place of observation, which is done by applying the
parallax properly to the place of the sun computed from the tables ; or, finally,
both positions can be transferred to some third point, which is most conveniently
taken in the intersection of the visual ray with the plane of the ecliptic ; the
observation itself then remains unchanged, and we have explained, in article 72,
the reduction of the place of the earth to this point. The first method cannot be
applied, except the distance of the heavenly body from the earth be approxi
mately, at least, known : but then it is very convenient, especially when the
observation has been made in the meridian, in which case the declination only is
affected by parallax. Moreover, it will be better to apply this reduction imme
diately to the observed place, before the transformations of the preceding article
are undertaken. But if the distance from the earth is still wholly unknown,
recourse must be had to the second or third method, and the former will be em
ployed when the equator is taken for the fundamental plane, but the third will
have the preference when all the positions are referred to the ecliptic.

SECT. 1.] THBEE COMPLETE OBSERVATIONS. 165

118.

If the distance of a heavenly body from the earth answering to any observa
tion is already approximately known, it may be freed from the effect of aberra
tion in several ways, depending on the different methods given in article 7L
Let t be the true time of observation ; 6 the interval of time in which light passes
from the heavenly body to the earth, which results from multiplying 493s into the
distance ; I the observed place, t the same place reduced to the time t -\- 6 by
means of the diurnal geocentric motion ; I" the place I freed from that part of the
aberration which is common to the planets and fixed stars ; L the true place of
the earth corresponding to the time t (that is, the tabular place increased by
20".25) ; lastly, 'L the true place of the earth corresponding to the time t — Q.
These things being premised, we shall have

I. I the true place of the heavenly body seen from 'L at the time t — 6.
II. f the true place of the heavenly body seen from L at the time i.
III. t' the true place of the heavenly body seen from L at the time t — &.
By method L, therefore, the observed place is preserved unchanged, but the fic
titious time t — 6 is substituted for the true, the place of the earth being com
puted for the former ; method II., applies the change to the observation alone, but
it requires, together with the distance, the diurnal motion ; in method III., the
observation undergoes a correction, not depending on the distance ; the fictitious
time t — 6 is substituted for the true, but the place of the earth corresponding to
the true time is retained. Of these methods, the first is much the most conven
ient, whenever the distance is known well enough to enable us to compute the
reduction of the time with sufficient accuracy. But if the distance is wholly un
known, neither of these methods can be immediately applied : in the first, to be
sure, the geocentric place of the heavenly body is known, but the time and the
position of the earth are wanting, both depending on the unknown distance ; in
the second, on the other hand, the latter are given, and the former is wanting;
finally, in the third, the geocentric place of the heavenly body and the position
of the earth are given, but the time to be used with these is wanting.

166 DETERMINATION OF AN ORBIT FROM [BOOK II.

What, therefore, is to be done with our problem, if, in such a case, a solution
exact with respect to aberration is required? The simplest course undoubtedly
is, to determine the orbit neglecting at first the aberration, the effect of which can
never be important ; the distances will thence be obtained with at least such pre
cision that the observations can be freed from aberration by some one of the
methods just explained, and the determination of the orbit can be repeated with
greater accuracy. Now, in this case the third method will be far preferable to the
others : for, in the first method all the computations depending on the position of
the earth must be commenced again from the very beginning; in the second (which
in fact is never applicable, unless the number of observations is sufficient to obtain
from them the diurnal motion), it is necessary to begin anew all the computations
depending upon the geocentric place of the heavenly body ; in the third, on the
contrary, (if the first calculation had been already based on geocentric places
freed from the aberration of the fixed stars) all the preliminary computations
depending upon the position of the earth and the geocentric place of the heavenly
body, can be retained unchanged in the new computation. But in this way it
will even be possible to include the aberration directly in the first calculation, if
the method used for the determination of the orbit has been so arranged, that
the values of the distances are obtained before it shall have been necessary to
introduce into the computation the corrected times. Then the double compu
tation on account of the aberration will not be necessary, as will appear more
clearly in the further treatment of our problem.

119.

It would not be difficult, from the connection between the data and unknown
quantities of our problem, to reduce its statement to six equations, or even to less,
since one or another of the unknown quantities might, conveniently enough, be
eliminated : but since this connection is most complicated, these equations woxild
become very intractable ; such a separation of the unknown quantities as finally
to produce an equation containing only one, can, generally speaking, be regarded

SECT. 1.] THREE COMPLETE OBSERVATIONS. 167

as impossible,* and, therefore, still less will it be possible to obtain a complete
solution of the problem by direct processes alone.

But our problem may at least be reduced, and that too in various ways, to the
solution of two equations X=Q, F= 0, in which only two unknown quantities
x, i/, remain. It is by no means necessary that x, y, should be two of the ele
ments : they may be quantities connected with the elements in any manner
whatever, if, only, the elements can be conveniently deduced from them when
found. Moreover, it is evidently not requisite that X, Y, be expressed in explicit
functions of x, y : it is sufficient if they are connected with them by a system of
equations in such manner that we can proceed from given values of x, y, to the
corresponding values of X, Y.

120.

Since, therefore, the nature of the problem does not allow of a further reduc
tion than to two equations, embracing indiscriminately two unknown quantities,
the principal point will consist, first, in the suitable selection of these unknown
quantities and armnr/cment of the equations, so that both X and Y may depend
in the simplest manner upon x, y, and that the elements themselves may follow
most conveniently from the values of the former when known : and then, it will
be a subject for careful consideration, how values of the unknown quantities satis
fying the equations may be obtained by processes not too laborious. If this should
be practicable only by blind trials, as it were, very great and indeed almost intol
erable labor would be required, such as astronomers who have determined the
orbits of comets by what is called the indirect method have, nevertheless, often
undertaken : at any rate, the ' labor in such a case is very greatly lessened, if, in
the first trials, rougher calculations suffice until approximate values of the un
known quantities are found. But as soon as an approximate determination is
made, the solution of the problem can be completed by safe and easy methods,
which, before we proceed further, it will be well to explain in this place.

* When the observations are so near to each other, that the intervals of the times may be treated as
infinitely small quantities, a separation of this kind is obtained, and the whole problem is reduced to the
solution of an algebraic equation of the seventh or eighth degree.

168 DETERMINATION Ot' AX ORBIT FROM [BOOK II.

The equations -X"=0, Y= 0 will be exactly satisfied if for x and y their
true values are taken ; if, on the contrary, values different from the true ones are
substituted for x and y, then X and Y will acquire values differing from 0. The
more nearly x and y approach their true values, the smaller should be the result
ing values of X and Y, and when their differences from the true values are very
small, it will be admissible to assume that the variations in the values of X and Y
are nearly proportional to the variation of x, if y is not changed, or to the varia
tion of y, if x is not changed. Accordingly, if the true values of x and y are
denoted by £, ^, the values of X and Y corresponding to the assumption that
# = £-[" ^j y = t] -j- fi, will be expressed in the form

in which the coefficients a, ft, y, d can be regarded as constant, as long as A and p
remain very small. Hence we conclude that, if for three systems of values of
x, y, differing but little from the true values, corresponding values of X, Y have
been determined, it will be possible to obtain from them correct values of x, y so
far, at least, as the above assumption is admissible. Let us suppose that,
for x = a, y = b we have X = A, Y = B,
x = tt,y = V X=A' Y=ff,

x =a",y = l" X = A" Y= B",

and we shall have

A = ««-

From these we obtain, by eliminating a, ft, y, d,

t __a(A'B" — A"B')-}-a'(A"B—AB")+oi'(AB!—A'B)
A'B" — A"Bt -f- A"B— A B" -\-AH- A'B

_ b(AB" — A"Bi) + V(A"B—AB") -f- 1" (A B? — A'B)
V ~ A'B" — A"B + A"B — A B" -f A B" — A'B

or, in a form more convenient for computation,

,(£ — a)(A'B—A B-') + (a" — a)(A B' — A'B)
A'B"—A"B'-}-A"B—AB"+AB' — A'B '

_ , , (y — 1) (A"B— A B") -f (V — b)(ABr — A'B)
~ A'Br^'i1~r'— T? — A'B '

SECT. 1.] THREE COMPLETE OBSERVATIONS. 169

It is evidently admissible, also, to interchange in these formulas the quantities
a, b, A, B, with «', V, A', B', or with a", b", A", B".

The common denominator of all these expressions, which may be put under

the form (A — A) (B" — B} — (A" — A) (ff — B), becomes

whence it appears that a, a, a", b, b', b" must be so taken as not to make

y— 5— gdj>

otherwise, this method would not be applicable, but would furnish, for the values
of £ and vj, fractions of which the numerators and denominators would vanish at
the same time. It is evident also that, if it should happen that ad — tiy = 0, the
same defect wholly destroys the use of the method, in whatever way a, a, a",
I, b', b", may be taken. In such a case it would be necessary to assume for the
values of X the form

and a similar one for the values of F, which being done, analysis would supply
methods, analogous to the preceding, of obtaining from values of X, Y, computed
for four systems of values of x, y, true values of the latter. But the computation
in this way would be very troublesome, and, moreover, it can be shown that, in
such a case, the determination of the orbit does not, from the nature of the ques
tion, admit of the requisite precision : as this disadvantage can only be avoided
by the introduction of new and more suitable observations, we do not here dwell
upon the subject.

121.

When, therefore, the approximate values of the unknown quantities are ob
tained, the true values can be derived from them, in the manner just now ex
plained, with all the accuracy that is needed. First, that is, the values of X, T,
corresponding to the approximate values (a, b) will be computed : if they do not
vanish for these, the calculation will be repeated with two other values (a, b')
differing but little from the former, and afterwards with a third system (a", b")

22

170 DETERMINATION OF AN ORBIT FROM [BOOK II.

unless X, Y, have vanished for the second. Then, the true values will be de
duced by means of the formulas of the preceding article, so far as the assumption
on which these formulas are based, does not differ sensibly from the truth. In
order that we may be better able to judge of which, the calculation of the values
of X, Y, will be repeated with those corrected values ; if this calculation shows
that the equations .X"= 0, F= 0, are, still, not satisfied, at least much smaller
values of X, Y, will result therefrom, than from the three former hypotheses, and
therefore, the elements of the orbit resulting from them, will be much more exact
than those which correspond to the first hypotheses. If we are not satisfied
with these, it will be best, omitting that hypothesis which produced the greatest
differences, to combine the other two with a fourth, and thus, by the process of
the preceding article, to obtain a fifth system of the values of x, y ; in the same
manner, if it shall appear worth while, we may proceed to a sixth hypothesis,
and so on, until the equations X — 0, Y= 0, shall be satisfied as exactly as the
logarithmic and trigonometrical tables permit. But it will very rarely be neces
sary to proceed beyond the fourth system, unless the first hypotheses were very
far from the truth.

122.

As the values of the unknown quantities to be assumed in the second and third
hypotheses are, to a certain extent, arbitrary, provided, only, they do not differ
too much from the first hypothesis ; and, moreover, as care is to be taken that the
ratio (a" - — a) : (b" • - b) does not tend to an equality with («' — a) : (b' — b], it is
customary to put «'=«, b"=b. A double advantage is derived from this; for, not
only do the formulas for £, 77, become a little more simple, but, also, a part of the
first calculation will remain the same in the second hypothesis, and another part
in the third.

Nevertheless, there is a case in which other reasons suggest a departure from
this custom : for let us suppose X to have the form X' — x, and Y the form
Y'-—y, and the functions X', Y', to become such, by the nature of the problem,
that they are very little affected by small errors in the values of x, y, or that

A! X'\ (dX'\ /dT\ /d T'\
\dx/' \dy/' \dx/' \dy'

SECT. 1.] THREE COMPLETE OBSERVATIONS. 171

may be very small quantities, and it is evident that the differences between the
values of those functions corresponding to the system z=%, y = t], and those
which result from x — «, y = #, can be referred to a somewhat higher order
than the differences £ — a, fj — b ', but the former values are X' = £, Y' = t], and
the latter X' — a -\- A, Y' = b -\- B, \vhence it follows, that a -\- A, b -\- B, are
much more exact values of x, y, than a, b. If the second hypothesis is based
upon these, the equations X= 0, Y= 0, are very frequently so exactly satisfied,
that it is not necessary to proceed any further ; but if not so, the third hypoth
esis will be formed in the same manner from the second, by making

whence finally, if it is still not found sufficiently accurate, the fourth will be ob
tained according to the precept of article 120.

123.

We have supposed in what goes before, that the approximate values of the
unknown quantities x, y, are already had in some way. Where, indeed, the
approximate dimensions of the whole orbit are known (deduced perhaps from
other observations by means of previous calculations, and now to be corrected by
new ones), that condition can be satisfied without difficulty, whatever meaning we
may assign to the unknown quantities. On the other hand, it is by no means a
matter of indifference, in the determination of an orbit still wholly unkno\vn,
(which is by far the most difficult problem,) what unknown quantities we may
use ; but they should be judiciously selected in such a way, that the approximate
values may be derived from the nature of the problem itself. Which can be done
most satisfactorily, when the three observations applied to the investigation of
an orbit do not embrace too great a heliocentric motion of the heavenly body.
Observations of this kind, therefore, are always to be used for the first determina
tion, which may be corrected afterwards, at pleasure, by means of observations
more remote from each other. For it is readily perceived that the nearer the ob
servations employed are to each other, the more is the calculation affected by their
unavoidable errors. Hence it is inferred, that the observations for the first de-

172 DETERMINATION OF AN ORBIT FROM [BOOK II.

termination are not to be picked out at random, but care is to be taken, first, that
tliey be not too near each other, but tJicn, also, that they be not too distant from
each other ; for in the first case, the calculation of elements satisfying the obser
vations would certainly be most expeditiously performed, but the elements them
selves Avould be entitled to little confidence, and might be so erroneous that they
could not even be used as an approximation : in the other case, we should aban
don the artifices which are to be made use of for an approximate determination
of the unknown quantities, nor could we thence obtain any other determination,
except one of the rudest kind, or wholly insufficient, without many more hypoth
eses, or the most tedious trials. But how to form a correct judgment concerning
these limits of the method is better learned by frequent practice than by rules :
the examples to be given below will show, that elements possessing great accu
racy can be derived from observations of Juno, separated from each other only 22
days, and embracing a heliocentric motion of 7° 35'; and again, that our method
can also be applied, with the most perfect success, to observations of Ceres, which
are 260 days apart, and include a heliocentric motion of 62° 55'; and can give,
with the use of four hypotheses or, rather, successive approximations, elements
agreeing excellently well with the observations.

124.

We proceed now to the enumeration of the most suitable methods based upon
the preceding principles, the chief parts of which have, indeed, already been ex
plained in the first book, and require here only to be adapted to our purpose.

The most simple method appears to be, to take for x, y, the distances of the
heavenly body from the earth in the two observations, or rather the logarithms
of these distances, or the logarithms of the distances projected upon the ecliptic
or equator. Hence, by article 64, V., will be derived the heliocentric places and
the distances from the sun pertaining to those places ; hence, again, by article 110,
the position of the plane of the orbit and the heliocentric longitudes in it ; and
from these, the radii vectofes, and the corresponding times, according to the prob
lem treated at length in articles 85-105, all the remaining elements, by which,
it is evident, these observations will be exactly represented, whatever values may

SECT. 1.] THREE COMPLETE OBSERVATIONS. 173

have been assigned to x, y. If, accordingly, the geocentric place for the time of
the third observation is computed by means of these elements, its agreement or
disagreement with the observed place will determine whether the assumed values
are the true ones, or whether they differ from them ; whence, as a double com
parison will be obtained, one difference (in longitude or right ascension) can be
taken for Jf, and the other (in latitude or declination) for Y. Unless, therefore,
the values of these differences come out at once = 0, the true values of x, y, may
be got by the method given in 120 and the following articles. For the rest, it is
in itself arbitrary from which of the three observations we set out : still, it is betr
ter, in general, to choose the first and last, the special case of which we shall speak
directly, being excepted.

This method is preferable to most of those to be explained hereafter, on this
account, that it admits of the most general application. The case must be ex
cepted, in which the two extreme observations embrace a heliocentric motion of
180, or 360, or 540, etc., degrees; for then the position of the plane of the orbit
cannot be determined, (article 110). It will be equally inconvenient to apply the
method, when the heliocentric motion between the two extreme observations
differs very little from 180° or 360°, etc., because an accurate determination of
the position of the orbit cannot be obtained in this case, or rather, because the
slightest changes in the assumed values of the unknown quantities would cause
such great variations in the position of the orbit, and, therefore, in the values of
X, Y, that the variations of the latter could no longer be regarded as propor
tional to those of the former. But the proper remedy is at hand ; which is, that
we should not, in such an event, start from the two extreme observations, but from
the first and middle, or from the middle and last, and, therefore, should take for
-X, Y, the differences between calculation and observation in the third or first
place. But, if both' the second place should be distant from the first, and the
third from the second nearly 180 degrees, the disadvantage could not be removed
in this way ; but it is better not to make use, in the computation of the elements,
of observations of this sort, from which, by the nature of the case, it is wholly
impossible to obtain an accurate determination of the position of the orbit.

Moreover, this method derives value from the fact, that by it the amount of

174 DETERMINATION OF AN ORBIT FROM [BOOK II.

the variations which the elements experience, if the middle place changes while
the extreme places remain fixed, can be estimated without difficulty : in this way,
therefore, some judgment may be formed as to the degree of precision to be
attributed to the elements found.

125.

We shall derive the second from the preceding method by applying a slight
change. Starting from the distances in two observations, we shall determine all
the elements in the same manner as before ; we shall not, however, compute
from these the geocentric place for the third observation, but will only proceed
as far as the heliocentric place in the orbit ; on the other hand we will obtain the
same heliocentric place, by means of the problem treated in articles 74, 75, from
the observed geocentric place and the position of the plane of the orbit; these
two determinations, different from each other (unless, perchance, the true values
of x, y, should be the assumed ones), will furnish us X and Y, the difference be
tween the two values of the longitude in orbit being taken for X, and the differ
ence between the two values of the radius vector, or rather its logarithm, for T.
This method is subject to the same cautions we have touched upon in the -pre
ceding article : another is to be added, namely, that the heliocentric place in orbit
cannot be deduced from the geocentric place, when the place of the earth happens
to be in either of the nodes of the orbit ; when that is the case, accordingly, this
method cannot be applied. But it will also be proper to avoid the use of this
method in the case where the place of the earth is very near either of the nodes,
since the assumption that, to small variations of x, y, correspond proportional
variations of X, Y, would be too much in error, for a reason similar to that which
we have mentioned in the preceding article. But here, also, may be a remedy
sought in the interchange of the mean place with one of the extremes, to which
may correspond a place of the earth more remote from the nodes, except, per
chance, the earth, in all three of the observations, should be in the vicinity of the
nodes.

SECT. 1.] THREE COMPLETE OBSERVATIONS. 175

126.

The preceding method prepares the way directly for the third. In the same
manner as before, by means of the distances of the heavenly body from the earth
in the extreme observations, the corresponding longitudes in orbit together with
the radii vectores may be determined. With the position of the plane of the
orbit, which this calculation will have furnished, the longitude in orbit and the
radius vector will be got from the middle observation. The remaining elements
may be computed from these three heliocentric places, by the problem treated in
articles 82, 83, which process will be independent of the times of the observa
tions. In this way, three mean anomalies and the diurnal motion will be known,
whence may be computed the intervals of the times between the first and second,
and between the second and third observations. The differences between these
and the true intervals will be taken for X and Y.

This method is less advantageous when the heliocentric motion includes a
small arc only. For in such a case this determination of the orbit (as we have
already shown in article 82) depends on quantities of the third order, and does
not, therefore, admit of sufficient exactness. The slightest changes in the values
of x,y, might cause very great changes in the elements and, therefore, in the val
ues of X, Y, also, nor would it be allowable to suppose the latter proportional to
the former. But when the three places embrace a considerable heliocentric mo
tion, the use of the method will undoubtedly succeed best, unless, indeed, it is
thrown into confusion by the exceptions explained in the preceding articles,
which are evidently in this method too, to be taken into consideration.

127.

After the three heliocentric places have been obtained in the way we have
described in the preceding article, we can go forward in the following manner.
The remaining elements may be determined by the problem treated in articles
85-105, first, from the first and second places with the corresponding interval of
time, and, afterwards, in the same manner, from the second and third places and

176 DETERMINATION OF AN ORBIT FROM [BuOK II.

the corresponding interval of time : thus two values will result for each of the
elements, and from their differences any two may be taken at pleasure for X and
Y. One advantage, not to be rejected, gives great value to this method ; it is,
that in the first hypotheses the remaining elements, besides the two which are
chosen for fixing X and Y, can be entirely neglected, and will finally be deter
mined in the last calculation based on the corrected values of x, y, either from
the first combination alone, or from the second, or, which is generally preferable,
from the combination of the first place with the third. The choice of those two
elements, which is, commonly speaking, arbitrary, furnishes a great variety of
solutions ; the logarithm of the semi-parameter, together with the logarithm of
the semi-axis major, may be adopted, for example, or the former with the eccen
tricity, or the latter with the same, or the longitude of the perihelion with any
one of these elements : any one of these four elements might also be combined
with the eccentric anomaly corresponding to the middle place in either calcula
tion, if an elliptical orbit should result, when the formulas -27-30 of article 96,
will supply the most expeditious computation. But in special cases this choice
demands some consideration ; thus, for example, in orbits resembling the parabola,
the semi-axis ma'or or its logarithm would be less suitable, inasmuch as excessive
variations of these quantities could not be regarded as proportional to changes of
x, y: in such a case it would be more advantageous to select -. But we give less
time to these precautions, because the fifth method", to be explained in the follow
ing article, is to be preferred, in almost all cases, to the four thus far explained.

128.

Let us denote three radii vectores, obtained in the same manner as in articles
125, 126, by r, r', r" ; the angular heliocentric motion in orbit from the second to
the third place by If, from the first to the third by 2/, from the first to the
second by 2/", so that we have

' '

next, let

/ r" sin 2f=n,r /' sin 2/' = »', r i> sin 2/" = »" ;

SECT. 1.] THREE COMPLETE OBSERVATIONS. 177

lastly, let the product of the constant quantity It (article 2) into the intervals of
the time. from the second observation to the third, from the first to the third, and
from the first to the second be respectively, 6, 6' &". The double computation of
the elements is begun, just as in the preceding article, both from rr f" and 6",
and from r r",f, 6: but neither computation will be continued to the determina
tion of the elements, but will stop as soon as that quantity has been obtained
which expresses the ratio of the elliptical sector to the triangle, and which is de
noted above (article 91) by y or -- Y. Let the value of this quantity be, in the
first calculation, r", in the second, t]. Accordingly, by means of formula 18, arti
cle 95, we shall have for the semi-parameter^ the two values: —

if'n"

But we have, besides, by article 82, a third value,

4 rr'r" sin /sin/' sin/"

v\ - ___ J J __ ^L_

P- n — n'+ri' '

which three values would evidently be identical if true values could have been
taken in the beginning for x and y. For which reason we should have

(P_ _ »/V'

0 rjn '

'_]_ " — 4 g0"rrV' sin/sin/ sin/7 _ n'dff'

tjif'nn" ~ 2 n n'rr'i" cos/cos/' cos/" '

Unless, therefore, these equations are fully satisfied in the first calculation, we
can put

2 rfrW cos/cos/' cos/"'

This method admits of an application equally general with the second ex
plained in article 125, but it is a great advantage, that in this fifth method the
first hypotheses do not require the determination of the elements themselves, but
stop, as it were, half way. It appears, also, that in this process we find that, as it
can be foreseen that the new hypothesis will not differ sensibly from the truth, it
will be sufficient to determine the elements either from r,r',f",6", alone, or from
r', r",f, 6, or, which is better, from r, r" f, ff.

23

178 DETERMINATION OF AN ORBIT FROM [BOOK II.

129.

The five methods thus far explained lead, at once, to as many others which
differ from the former only in this, that the inclination of the orbit and the lon
gitude of the ascending node, instead of the distances from the earth, are taken
for x and y. The new methods are, then, as follows : —

I. From x and y, and the two extreme geocentric places, according to articles
74, 75, the heliocentric longitudes in orbit and the radii vectores are determined,
and, from these and the corresponding times, all the remaining elements ; from
these, finally, the geocentric place for the time of the middle observation, the
differences of which from the observed place in longitude and latitude will fur
nish X and Y.

The four remaining methods agree in this, that all three of the heliocentric
longitudes in orbit and the corresponding radii vectores are computed from the
position of the plane of the orbit and the geocentric places. But afterwards: —

II. The remaining elements are determined from the two extreme places only
and the corresponding times ; with these elements the longitude in orbit and
radius vector are computed for the time of the middle observation, the differences
of which quantities from the values before found, that is, deduced from the geo
centric place, will produce X and Y:

III. Or, the remaining dimensions of the orbit are derived from all three
heliocentric places (articles 82, 83,) into which calculation the times do not enter:
then the intervals of the times are deduced, which, in an orbit thus found, should
have elapsed between the first and second observation, and between this last
and the third, and their differences from the true intervals will furnish us with
X and Y:

I V. The remaining elements are computed in two ways, that is, both by the
combination of the first place with the second, and by the combination of the
second with the third, the corresponding intervals of the times being used. These
two systems of elements being compared with each other, any two of the differ
ences may be taken for X and Y:

V. Or lastly, the same double calculation is only continued to the values of

SECT. 1.] THREE COMPLETE OBSERVATIONS. 179

the quantity denoted by t/, in article 91, and then the expressions given in the
preceding article for X and Y, are adopted.

In order that the last four methods may be safely used, the places of the earth
for all three of the observations must not be very near the node of the orbit : on
the other hand, the use of the first method only requires, that this condition may
exist in the two extreme observations, or rather, (since the middle place may be
substituted for either of the extremes,) that, of the three places of the earth,
not more than one shall lie in the vicinity of the nodes.

130.

The ten methods explained from article 124 forwards, rest upon the assump
tion that approximate values of the distances of the heavenly body from the
earth, or of the position of the plane of the orbit, are already known. \\ hen
the problem is, to correct, by means of observations more remote from each other,
the dimensions of an orbit, the approximate values of which are already, by
some means, known, as, for instance, by a previous calculation based on other
observations, this assumption will evidently be liable to no difficulty. But it does
not as yet appear from this, how the first calculation is to be entered upon when
all the dimensions of the orbit are still wholly unknown : this case of our problem
is by far the most important and the most difficult, as may be imagined from
the analogous problem in the theory of comets, which, as is well known, has
perplexed geometers for a long time, and has given rise to many fruitless
attempts. In order that our problem may be considered as correctly solved, that
is, if the solution be given in accordance with what has been explained in the
119th and subsequent articles, it is evidently requisite to satisfy the following
conditions : — First, the quantities x, y, are to be chosen in such a manner, that
we can find approximate values of them from the very nature of the problem, at
all events, as long as the heliocentric motion of the heavenly body between the
observations is not too great. Secondly, it is necessary that, for small changes in
the quantities x, y, there be not too great corresponding changes in the quantities
to be derived from them, lest the errors accidentally introduced in the assumed
values of the former, prevent the latter from being considered as approximate.

180 DETERMINATION OF AN ORBIT FROM [BOOK II.

Thirdly and lastly, we require that the processes by which we pass from the quan
tities x, (/, to X, Y, successively, be not too complicated.

These conditions will furnish the criterion by which to judge of the excellence
of any method : this will show itself more plainly by frequent applications. The
method which we are now prepared to explain, and which, in a measure, is to be
regarded as the most important part of this work, satisfies these conditions so that
it seems to leave nothing further to be desired. Before entering upon the ex
planation of this in the form most suited to practice, we will premise certain pre
liminary considerations, and we will illustrate and open, as it were, the way to it,
which might, perhaps, otherwise, seem more obscure and less obvious.

131.

It is shown in article 114, that if the ratio between the quantities denoted
there, and in article 128 by n, ri, n", were known, the distances of the heavenly
body from the earth could be determined by means of very simple formulas.
Now, therefore, if

should be taken for z, y,

L £.

6" 0"

(the symbols 6, 6', 6", being taken in the same -signification as in article 128) im
mediately present themselves as approximate values of these quantities in that
case where the heliocentric motion between the observations is not very great :
hence, accordingly, seems to flow an obvious solution of our problem, if two dis
tances from the earth are obtained from #, y, and after that we proceed agreeably
to some one of the five methods of articles 124-128. In fact, the symbols 17, if
being also taken with the meaning of article 128, and, analogously, the quotient
arising from the division of the sector contained between the two radii vectores
by the area of the triangle between the same being denoted by tf, we shall have,

2L

n'

SECT. 1.] THREE COMPLETE OBSERVATIONS. 181

and it readily appears, that if n, ri, n", are regarded as small quantities of the first
order, 77 — 1, rj' — 1, rf' — 1 are, generally speaking, quantities of the second

order, and, therefore,

e_ er_

6" 6"

the approximate values of x, y, differ from the true ones only by quantities
of the second order. Nevertheless, upon a nearer examination of the sub
ject, this method is found to be wholly unsuitable ; the reason of this we
will explain in a few words. It is readily perceived that the quantity (0. 1. 2),
by which the distances in the formulas 9, 10, 11, of article 114 have been multi
plied, is at least of the third order, while, for example, in equation 9 the quan
tities (0. 1. 2), (I. 1. 2), (II. 1. 2), are, on the contrary, of the first order; hence,
it readily follows, that an error of the second order in the values of the quanti
ties ^, n-^ produces an error of the order zero in the values of the distances.
Wherefore, according to the common mode of speaking, the distances would be
affected by a finite error even when the intervals of the times were infinitely
small, and consequently it would not be admissible to consider either these dis
tances or the remaining quantities to be derived from them even as approximate ;
and the method would be opposed to the second condition of the preceding
article.

. 132.

Putting, for the sake of brevity,

(0.1.2) = 0, (O.L2)1X = — b, (0.0.2)Z>= + o, (O.IL Z)iy'= + d,
so that the equation 10, article 114, may become

ad1 = b -4-c ^, -4- d ^-r,

n n '

the coefficients c and d will, indeed, be of the first order, but it can be easily
shown that the difference c — d is to be referred to the second order. Then it
follows, that the value of the quantity

n+n"

182 DETERMINATION OF AN ORBIT FROM [BuOK II.

resulting from the approximate assumption that n : n" = 6:6" is affected by an
error of the fourth order only, and even of the fifth only when the middle is dis
tant from the extreme observations by equal intervals. For this error is

n" _ Off (d — c) (if — if)

where the denominator is of the second order, and one factor of the numerator
Q6"(d — c] of the fourth, the other rj" — r\ of the second, or, in that special case,
of the third order. The former equation, therefore, being exhibited in this form,

»,/ 7 I c n -4- d n" n -4- n"
ao = b-\- „ . — '— ,

n -j- n n

it is evident that the defect of the method explained in the preceding article does
not arise from the fact that the quantities n, n" have been assumed proportional to
6, 6", but that, in addition to this, n' was put proportional to 6'. For, indeed, in this

way, instead of the factor -Jj — , the less exact value —5 — = 1 is introduced,
from which the true value

2 jyj/VrV cos/cos/' cos/*

differs by a quantity of the second order, (article 128).

133.

Since the cosines of the angles/,/',/", as also the quantities r/, r" differ from
unity by a difference of the second order, it is evident, that if instead of

n+n"

7t

the approximate value

14- 6ff>

1 I 2rrV

is introduced, an error of the fourth order is committed. If, accordingly, in place
of the equation, article 114, the following is introduced,

. Off'

an error of the second order will show itself in the value of the distance $' when

SECT. 1.] THREE COMPLETE OBSERVATIONS. 183

the extreme observations are equidistant from the middle ; or, of the first order in
other cases. But this new form of that equation is not suited to the determina
tion of d', because it involves the quantities r, r', r", still unknown.

Now, generally speaking, the quantities ^,-^, differ from unity by a quantity
of the first order, and in the same manner also the product ^: it is readily
perceived that in the special case frequently mentioned, this product differs
from unity by a quantity of the second order only. And even when the orbit
of the ellipse is slightly eccentric, so that the eccentricity may be regarded as a
quantity of the first order, the difference of T~f-} can be referred to an order one
degree higher. It is manifest, therefore, that this error remains of the same order

fl fl// a off

as before if, in our equation, 2rrV/ is substituted for ^, whence is obtained the
following form,

In fact, this equation still contains the unknown quantity /, which, it is evident
nevertheless, can be eliminated, since it depends only on d' and known quantities.
If now the equation should be afterwards properly arranged, it would ascend to
the eighth degree.

134.

From the preceding it will be understood why, in our method, we are about
to take for x, y, respectively, the quantities

W, and 2 '-1 /'==<?.

For, in the first place, it is evident that if P and Q are regarded as known quanti
ties, d' can be determined from them by means of the equation

A' 7, I c + dP (-[ Q

= b + T+^(l + 2?-*
and afterwards $,d", by equations 4, 6, article 114, since we have

-- -Wl-L.-^ n"- P (l\ Q\
n> — 1-f-PV J-~T2r'8/' ri~~ \-\-P\ ' 2r'V'

In the second place, it is manifest that -j , 66" are, in the first hypothesis, the

184 DETERMINATION OF AN ORBIT FROM [BOOK II.

obvious approximate values of the quantities P, Q, of which the true values are
precisely

__
6 " rS'qtf' cos/cos/' cos/"'

from which hypothesis will result errors of the first order in the determination of
(f, and therefore of ff, d", or of the second order in the special case several times
mentioned. Although we may rely with safety upon these conclusions, generally
speaking, yet in a particular case they can lose their force, as when the quantity
(0. 1. 2), which in general is of the third order, happens to be equal to zero, or so
small that it must be referred to a higher order. This occurs when the geocentric
path in the celestial sphere has a point of contrary flexure near the middle place.
Lastly, it appears to be required, for the use of our method, that the heliocentric
motion between the three observations be not too great : but this restriction, by
the nature of the very complicated problem, cannot be avoided in any way;
neither is it to be regarded as a disadvantage, since it will always be desired to
begin at the earliest possible moment the first determination of the unknown
orbit of a new heavenly body. Besides, the restriction itself can be taken in a
sufficiently broad sense, as the example to be given below will show.

135.

The preceding discussions have been introduced, in order that the principles
on which our method rests, and its true force, as it were, may be more clearly
seen : the practical treatment, however, will present the method in an entirely
different form which, after very numerous applications, we can recommend as
the most convenient of many tried by us. Since in determining an unknown
orbit from three observations the whole subject may always be reduced to
certain hypotheses, or rather successive approximations, it will be regarded as a
great advantage to have succeeded in so arranging the calculation, as, at the
beginning, to separate from these hypotheses as many as possible of the compu
tations which depend, not on P and Q, but only on a combination of the known
quantities. Then, evidently, these preliminary processes, common to each hypoth
esis, can be gone through once for all, and the hypotheses themselves are reduced

SECT. 1.] THREE COMPLETE OBSERVATIONS. 185

to the fewest possible details. It will be of equally great importance, if it
should not be necessary to proceed in every hypothesis as far as the elements,
but if their computation might be reserved for the last hypothesis. In both
these respects, our method, which we are now about to explain, seems to leave
nothing to be desired.

136.

We are, in the first place, to connect by great circles three heliocentric places
of the earth in the celestial sphere, A, A', A" (figure 4), with three geocentric
places of the heavenly body, B, B', B", and then to compute the positions of these
great circles with respect to the ecliptic (if we adopt the ecliptic as the funda
mental plane), and the places of the points B, B', B", in these circles.

Let a, a', a" be three geocentric longitudes of the heavenly body, /?. /T, /?", lat
itudes ; /, ^, I", heliocentric longitudes of the earth, the latitudes of which we put
equal to zero, (articles 117, 72). Let, moreover, /, /, y" be the inclinations to the
ecliptic of the great circles drawn from A, A', A", to B, B', B", respectively ; and,
in order to follow a fixed rule in the determination of these inclinations, we shall
always measure them from that part of the ecliptic which lies in the direction
of the order of the signs from the points A, A', A", so that their magnitudes will
be counted from 0 to 360°, or, which amounts to the same thing, from 0 to 180°
north, and from 0 to — 180° south. We denote the arcs AB, AB1, A'B", which
may always be taken between 0 and 180°, by d,d', 8". Thus we have for the de
termination of y and d the formulas,

[1] tany= .

sm((« — /)

m-i * tan (a — I)

[21 tano = - — .

<- J cos v

To which, if desirable for confirming the calculation, can be added the following,

sin d = -!—*-, cos d = cos S cos (a — I) .
sin 7'

We have, evidently, entirely analogous formulas for determining yf, df, •/', d". Now,
if at the same time /3 = 0. cr — 1= 0 or 180°, that is, if the heavenly body should

24

186 DETERMINATION OF AN ORBIT FROM [BOOK II.

be in opposition or conjunction and in the ecliptic at the same time, y would be
indeterminate. But we assume that this is not the case in either of the three
observations.

If the equator is adopted as the fundamental plane, instead of the ecliptic,
then, for determining the positions of the three great circles with respect to the
equator, will be required the right ascensions of their intersections with the equa
tor, besides the inclinations ; and it will be necessary to compute, in addition to
the distances of the points B, B', B", from these intersections, the distances of the
points A, A', A" also from the same intersections. Since these depend on the
problem discussed in article 110, we do not stop here to obtain the formulas.

137.

The second step will be the determination of the positions of these three great
circles relatively to each other, which depend on their inclinations and the places
of their mutual intersections. If we wish to bring these to depend upon clear
and general conceptions, without ambiguity, so as not to be obliged to use
special figures for different individual cases, it will be necessary to premise some
preliminary explanations. Firstly, in every great circle two opposite directions
are to be distinguished in some way, which will be done if we regard one of them
as direct or positive, and the other as retrograde or negative. This being wholly
arbitrary in itself, we shall always, for the sake of establishing a uniform rule, con
sider the directions from A, A', A" towards B, B',B" as positive; thus, for example,
if the intersection of the first circle with the second is represented by a positive
distance from the point A, it will be understood that it is to be taken from A
towards B (as D" in our figure) ; but if it should be negative, then the distance
is to be taken on the other side of A. And secondly, the two hemispheres, into
which every great circle divides the whole sphere, are to be distinguished by suit
able denominations ; accordingly, we shall call that the superior hemisphere, which,
to one walking on the inner surface of the sphere, in the positive direction along
the great circle, is on the right hand ; the other, the inferior . The superior hemi
sphere will be analogous to the northern hemisphere in regard to the ecliptic or
equator, the inferior to the southern.

SECT. 1.] THREE COMPLETE OBSERVATIONS. 187

These definitions being correctly understood, it will be possible conveniently
to distinguish, loth intersections of the two great circles from each other. In fact,
in one the first circle- tends from the inferior to the superior hemisphere of the
second, or, which is the same thing, the second from the superior to the inferior
hemisphere of the first ; in the other intersection the opposite takes place.

It is, indeed, wholly arbitrary in itself which intersections we shall select for
our problem ; but, that we may proceed here also according to an invariable rule,
we shall always adopt these (D, D1, D", figure 4) where the third circle A"B" passes
into the superior hemisphere of the second A I?, the third into that of the first
AB, and the second into that of the first, respectively. The places of these inter
sections will be determined by their distances from the points A' and A", A and
A", A and A', which we shall simply denote by A'D, A" I). AD', A" I)', AD", AD".

Which being premised, the mutual inclinations of the circles will be the angles
which are contained, at the points of intersection D, Z>', D", between those parts
of the circles cutting each other that lie in the positive direction ; we shall
denote these inclinations, taken always between 0 and 180°, by e, F', a". The de
termination of these nine unknown quantities from those that are known, evi
dently rests upon the problem discussed by us in article 55. We have, conse
quently, the following equations : —

[3] sin * s sin i (A'D -f A'D) = sin } (f — f) sin * (/' -f /),
[4] sin £ e cos * (A'D -f A'D) = cos £ (tf — f) sin } (/' — /),
[5] cos J £ sin * (A'D — A"D) = sin } (f1 — I) cos } (/' -f /),
[6] cos } « cos £ (AD — A'D) = cos } (f — f) cos i (/' — /).

J (A'D-^-A"D) and sin £ E are made known by equations 3 and 4, I (A'D — A'D)
and cos i e by the remaining two ; hence A'D, A"D and e. The ambiguity in the
determination of the arcs £ (A'D -\- A'D), £ (AD — A'D), by means of the tan
gents, is removed by the condition that sin £ f, cos £ f, must be positive, and the
agreement between sin £ e, cos £ t, will serve to verify the whole calculation.

The determination of the quantities AD1, A'D', e', AD", A'D", t" is effected in
precisely the same manner, and it will not be worth while to transcribe here the
eight equations used in this calculation, since, in fact, they readily appear if we
change

188

DETERMINATION OF AN ORBIT FROM

[BOOK II.

A'D

A'D

e

T—t

for AD

A'D1

e'

t'—l

or for AD"

AD'

e"

t —I

y"

respectively.

A new verification of the whole calculation thus far can be obtained from the
mutual relation between the sides and angles of the spherical triangle formed by
joining the three points D, D, D", from which result the equations, true in gen
eral, whatever may be the positions of these points,

sin (AD' — AD') _ sin (A'D— A'D') sin (A'D — A'D)

sine

sm

Finally, if the equator is selected for the fundamental plane instead of the eclip
tic, the computation undergoes no change, except that it is necessary to sub
stitute for the heliocentric places of the earth A, A, A' those points of the equa
tor where it is cut by the circles AB, AB1, A'B" ; consequently, the right ascen
sions of these intersections are to be taken instead of /, I , T ', and also instead of
A'D, the distance of the point D from the second intersection, etc.

138.

The third step consists in this, that the two extreme geocentric places of the
heavenly body, that is, the points B, B", are to be joined by a great circle, and
the intersection of this with the great circle A'B' is to be determined. Let B* be
this intersection, and d' — 0 its distance from the point A ; let a* be its longitude,
and ft* its latitude. We have, consequently, for the reason that B, B*, B" lie in
the same great circle, the well-known equation,

0 = tan ft sin («" - - a*) — tan ft* sin (a" — «) + tan ft" sin (a* — a),
which, by the substitution of tan / sin (a* — I' ) for tan ft*, takes the following
form : —

0 = cos (a* — f) (tan ft sin (a" — ?) — tan ft" sin (a — ? ))

_ sin (a* — t) (tan ft cos (a" — f) -f- tan / sin (a" — a) — tan ft" cos (a —
Wherefore, since tan (a* — f) = cos / tan ((?' - - 0) we shall have,

tan(<T — a) =

tan (3 sin (a" — I') — tan ft" sin (« — Q

cos / (tan § cos («"— /') — tan 0" cos (a — J')) -f sin / sin (a" — a) '

SECT. 1.] THREE COMPLETE OBSERVATIONS. 189

Thence are derived the following formulas, better suited to numerical calculations.
Putting,

[7] tan ft sin (a." — I'} — tan ft" sin (a — /') = S,
[8] tan ft cos (a" — I') — tan ft" cos (a — I') = Tsint,
[9] sin(a" — a) = Tcost,
we shall have (article 14, II.)
[10] tan((T — o)=*r

7 sin (< -{- /)

The uncertainty in the determination of the arc (<?'- — cr) by means of the
tangent arises from the fact that the great circles AB', BE", cut each other in
two points ; we shall always adopt for B* the intersection nearest the point B', so
that 0 may always fall between the limits of — 90° and -f- 90°, by which means
the uncertainty is removed.

For the most part, then, the value of the arc a (which depends upon the
curvature of the geocentric motion) will be quite a small quantity, and even, gen
erally speaking, of the second order, if the intervals of the times are regarded
as of the first order.

It will readily appear, from the remark in the preceding article, what are the
modifications to be applied fo the computation, if the equator should be chosen
as the fundamental plane instead of the ecliptic. It is, moreover, manifest that
the place of the point B* will remain indeterminate, if the circles BB", AB"
should be wholly coincident; this case, in which the four points A,B,B',B" lie in
the same great circle, we exclude from our investigation. It is proper in the
selection of observations to avoid that case, also, where the locus of these four
points differs but little from a great circle ; for then the place of the point B'*,
which is of great importance in the subsequent operations, would be too much
affected by the slightest errors of observation, and could not be determined with
the requisite precision. In the same manner the point B*, evidently, remains
indeterminate when the points B, B" coincide,f in which case the position of the

•fOr when they are opposite to each other; but we do not speak of this case, because our method ia
not extended to observations embracing so great an interval.

190 DETERMINATION OF AN ORBIT FROM [BOOK II.

circle BB" itself would become indeterminate. Wherefore we exclude this case,
also, just as, for reasons similar to the preceding, those observations will be
avoided in which the first and last geocentric places fall in points of the sphere
near to each other.

139.

Let C, C', C", be three heliocentric places of the heavenly body in the celestial
sphere, which will be (article 64, III.) in the great circles AB, AB, A'B", respec
tively, and, indeed, between A and B, A and B', A" and B" ; moreover, the points
C, C', C" will lie in the same great circle, that is, in the circle which the plane
of the orbit projects on the celestial sphere.

We will denote by r, r, r", three distances of the heavenly body from the sun ;
by Q, (/, (/, its distances from the earth ; by R, R, R", the distances of the earth
from the sun. Moreover, we put the arcs C'C", CO", 00' equal to 2/, 2/', 2/",
respectively, and

rr" sin 2/= n, rr" sin 2/' = n', rr sin 2f" = n".
Consequently we have

/' =/ -f /", A O-\- CB = d, A' 0' + O'B1 = df, A" C" -f C"B" = d" ;

also,

sin 8 sin A C sin OB

~r~ Q Ji

sin 8' _ sin A' C' _ sin O'B'

sin y _ sin A" C" _ sin C"B"

i» '' Q" R' '

Hence it is evident, that, as soon as the positions of the points O, C', C" are known,
the quantities r, r, r", Q, Q', Q" can be determined. We shall now show how the
former may be derived from the quantities

from which, as we have before said, our method started.

SECT. 1.] THREE COMPLETE OBSERVATIONS. 191

140.

We first remark, that if JV were any point whatever of the great circle CO' C",
and the distances of the points C, C', C" from the point N were counted in the
direction from 0 to C", so that in general

NC" — NC' = 2/, NO" — N0= 2/', NO' — N0= 2/",
we shall have

I. 0 = sin 2/sin NO — sin 2/' sin NO' -f sin 2f" sin NO".

We will now suppose N to be taken in the intersection of the great circles
BB*B', CO' C", as in the ascending node of the former on the latter. Let us
denote by £, Of, £", £>, 2)', 2>", respectively, the distances of the points C, C', C",
D, D', D" from the great circle B B*B", taken positively on one side, and nega
tively on the other. Then sin d, sin £', sin G", will evidently be proportional to
smNC, mi NO', sin NO", whence equation I. is expressed in the following form: —

0 — sin 2/ sin <£ — sin 2/ sin & -f- sin 2/" sin g" ;
or multiplying by rr'r",

II. 0 = nr sin £ — nY sin <£' + it'i" sin £".

It is evident, moreover, that sin G is to sin 3)', as the sine of the distance of the
point C from B is to that of D1 from B, both distances being measured in the
same direction. We have, therefore,

. ~ sin f sin CB

- Sin li =

. , . n, - vr ,

sm (4 D — oy
in precisely the same way, are obtained,

sin X"sin OB

__
" Sin Vi -

% ~. *~TV/ rr j
sin (A D — d) '

• ff, sinXsinO"7?» sin X" sin C'B*

— Sin G = 7-

(sin ^'ZT— S' + ff) sin (A! If—

_ si

~

sin T sin C"B"

Dividing, therefore, equation II. byr"sinG", there results,

„_ rsmOB sm(A"Df — ^') , SsmC'B* sm(A"D — #') , „

192 DETERMINATION OF AN ORBIT FROM [BooK II.

If now we designate the arc C'ff by s, substitute for r, r\ r" their values in
the preceding article, and, for the sake of brevity, put

nl1 R sin a sin (A"jy—d")_
LUJ R> sin «» sin (AU — d) ~

_,

~

.R" sin 5" sin (A'D — 5' -f a)
our equation will become

, / sin (z — q) . „

HI. 0 = «« — on - — -\-n

sin z

The coefficient £ may be computed by the following formula, which is easily
derived from the equations just introduced : —

— _

a X ^Bin«8in(^'Zy— o'-fq)-

For verifying the computation, it will be expedient to use both the formulas 12
and 13. When sm(A'D" — <?'-(- a) is greater than sm(A'D—d'-\-a), the latter
formula is less affected by the unavoidable errors of the tables than the former,
and so will be preferred to it, if some small discrepancy to be explained in this
way should result in the values of b ; on the other hand, the former formula is
most to be relied upon, when sin (A'D" — <f-|- a) is less than sin (A'D — d'-(- a);
a suitable mean between both values will be adopted, if preferred. The follow
ing formulas can be made to answer for examining the calculation ; their not very
difficult derivation we suppress for the sake, of brevity.

ft _ a sin (I"— I') _ bain (I*— 1) sin (8' — q) , sm(l' — l)

B ~R' ' sin d' ~~K' »

,_ _ -'
~ '

in which (article 138, equation 10,) U expresses the quotient

S

sin(<5' — q) cos(<J'— q) '

141.

From P = — , and equation HI. of the preceding article, we have

/ , ,/, P-\-a , i sin (z — q)

(n-4-n )^H -r = bn - -*-\

' P-\-\ smz

SECT. 1.] THREE COMPLETE OBSERVATIONS. 193

thenco, and from

f\ o/w + w" i\ /s j i Ksmtf
Q = 2 ( — ~- -- 1 1 r 3 and r = —

\ n smz

is obtained,

Qsinz* i P+l . ,

sm * + 2**»* = J P +^ sm (*— °)» or>

Qsm*z /7-P+l \

'»^h^' = \b P^ ~ C°S 0/ Sm ^ ~ <T) ~~ Sm a COS (S — °)'

Putting, therefore, for the sake of brevity,

and introducing the auxiliary angle to such that

sin a

tan to = - „ , l

cos a ,

we have the equation

IV. c Q sin w sin4 g =: sin (2 — w — 0),

from which we must get the unknown quantity z. That the angle w may be
computed more conveniently, it will be expedient to present the preceding for
mula for tan co thus : —

Whence, putting,
5

•a

ri K-I cos ° JT

[ ] x~ii=

COSff

[16]

COSff

we shall have for the determination of to the very simple formula,

tan to =

P+d '

We consider as the fourth step the computation of the quantities a, b, c, d, e,

25

194 DETERMINATION OF AN ORBIT FROM [BOOK II.

by means of the formulas 11-16, depending on given quantities alone. The
quantities b, c, e, will not themselves be required, only their logarithms.

There is a special case in which these precepts require some change. That
is, when the great circle BB" coincides with A'B", and thus the points B, B*
with jy, D, respectively, the quantities a, b would acquire infinite values. Put
ting, in this case,

R sin d sin (A'D' — S' + a) _
JJ'sind'sin^D" — rf) ~ ™ '

in place of equation HI. we shall have

,, n' sin (z — a)

0 = nn —t,

smz
whence, making

?rsin a
tan w =2

•p_j-(l_rtcos<i)'
the same equation IV. is obtained.

In the same manner, in the special case when a = 0, c becomes infinite, and
w = 0, on account of which the factor c sin w, in equation IV., seems to be inde
terminate ; nevertheless, it is in reality determinate, and its value is

as a little attention will show. In this case, therefore, sm z becomes

142.

Equation IV., which being developed rises to the eighth degree, is solved by
trial very expeditiously in its unchanged form. But, from the theory of equa
tions, it can be easily shown, (which, for the sake of brevity, we shall dispense
with explaining more fully) that this equation admits of two or four solutions by
means of real values. In the former case, one value of sin z will be positive ;
and the other negative value must be rejected, because, by the nature of the
problem, it is impossible for r to become negative. In the latter case, among the
values of sin z one will be positive, and the remaining three negative, — when,

SECT. 1.] THREE COMPLETE OBSERVATIONS. 195

accordingly, it will not be doubtful which must be adopted, — or three positive
with one negative ; in this case, from among the positive values those, if there are
any, are to be rejected which give z greater than d', since, by another essential
condition of the problem, (>' and, therefore, sin (d' — z\ must be a positive quantity.
When the observations are distant from each other by moderate intervals of
time, the last case will most frequently occur, in which three positive values of
sin z satisfy the equation. Among these solutions, besides that which is true;
some one will be found making z differ but little from d', cither in excess or
in defect; this is to be accounted for as follows. The analytical treatment of
our problem is based upon the condition, simply, that the three places of the heav
enly body in space must fall in right lines, the positions of which are determined
by the absolute places of the earth, and the observed places of the body. Now,
from the very nature of the case, these places must, in fact, fall in those parts of
the right lines whence the light descends to the earth. But the analytical equa
tions do not recognize this restriction, and every system of places, harmonizing of
course with the laws of KEPLER, is embraced, whether they lie in these right lines
on this side of the earth, or on that, or, in fine, whether they coincide with the
earth itself. Now, this last case will undoubtedly satisfy our problem, since the
earth moves in accordance with these laws. Thence it is manifest, that the equa
tions must include the solution in which the points C. C', C" coincide with A, A', A"
(so long as we neglect the very small variations in the elliptical places of the earth
produced by the perturbations and the parallax). Equation IV., therefore, must
always admit the solution z = d', if true values answering to the places of the
earth are adopted for P and Q. So long as values not differing much from these
are assigned to those quantities (which is always an admissible supposition, when
the intervals of the times are moderate), among the solutions of equation IV.,
some one will necessarily be found which approaches very nearly to the value

z — cr.

For the most part, indeed, in that case where equation IV. admits of three
solutions by means of positive values of sin 2, the third of these (besides the true
one, and that of which we have just spoken) makes the value of z greater than
d', and thus is only analytically possible, but physically impossible ; so that it can-

196 DETERMINATION OF AN ORBIT FROM [BOOK II.

not then be doubtful which is to be adopted. But yet it certainly can happen,
that the equation may admit of two distinct and proper solutions, and thus that
our problem may be satisfied by two wholly different orbits. But in such an
event, the true orbit is easily distinguished from the false as soon as it is possible
to bring to the test other and more remote observations.

143.

As soon as the angle z is got, / is immediately had by means of the equation

, _ K sins'

Further, from the equations P = — and III. we obtain,

nY _ (P+a)J?smff
n b sin (z — a)

«'/_ JL_ nY

«" -~P'~7T'

Now, in order that we may treat the formulas, according to which the posi
tions of the points O, C", are determined from the position of the point C', in such
a manner that their general truth in those cases not shown in figure 4 may
immediately be apparent, we remark, that the sine of the distance of the point
C' from the great circle CB (taken positively in the superior hemisphere, nega
tively in the inferior) is equal to the product of sin e" into the sine of the distance
of the point C' from D", measured in the positive direction, and therefore to

- sin e" sin C'D" = — sin e" sin (0 + A'D" — d') ;

in the same manner, the sine of the distance of the point C" from the same great
circle is — sin t,' sin C"D'. But, evidently, those sines are as sin CO' to sin CO", or
as ^-, to ^p,, or as ri'r" to n'r'. Putting, therefore, C"D' ' — C", we have

Vff • j-// n r sin £ . , \ &f TV/ w\
r sin £" = —.-. -— sm (z 4- A™ — o ) .

if sm e

Precisely in the same way, putting (7ZX = t, is obtained

TTT !- ft' Sin£ . / i Af T\ fc/\

VI. r sin !, = — . -r— 7 sin (z 4- A D — 8} .

n sin e

VH.

SECT. 1.] THREE COMPLETE OBSERVATIONS. 197

By combining equations V. and VI. with the following taken from article 139,
VIII. /' sin ( £" — A"D' -f d") = R" sin d",

IX. r sin (£ — A D1 -\- 8) = R sin d,

the quantities f, £", r, r",will be thence derived by the method of article 78.
That this calculation may be more conveniently effected, it will not be unaccept-
able to produce here the formulas themselves. Let us put

n ^7-1 -^ sin 3

Li7J sm(AJy — <J) =

n «i -ff'sind" _ „

L10J sm(A"D' — d")~

CQS(AD'-<i)
L19J 5 sin* =A>'

[20] ^^--^-l"

sin i

The computation of these, or rather of their logarithms, yet independent of P
and Q, is to be regarded as the fifth and last step in the, as it were, preliminary
operations, and is conveniently performed at the same time with the computation
of a, b, themselves, or with the fourth step, where a becomes equal to 4, •
Making, then,

nr sine . , , ., „ ./,

— .- — , sin (z -\- A D — o ) = »,

i M\ "

—8}=p ,

n sin «'

n'r' sin /
n" ' sin «'

we derive L and r from r sin £ =p, r cos C = q ; also, t" and r" from r" sin "C" =p",
and r" cos £" = q". No ambiguity can occur in determining C and i"", because r
and ;•" must, necessarily, be positive quantities. The complete computation can,
if desired, be verified by equation VII.

There are two cases, nevertheless, where another course must be pursued.
That is, when the point ff coincides with B, or is opposite to it in the sphere,
or when AD' — $ = 0 or 180°, equations VI. and IX. must necessarily be iden-

198 DETERMINATION OF AN ORBIT FROM [BOOK II.

tical, and we should have x = co , \p — 1 = 0, and q, therefore, indeterminate.
In this case, t," and r" will be determined, in the manner we have shown, but
then £ and r must be obtained by the combination of equation VII. with VI. or
IX. We dispense with transcribing here the formulas themselves, to be found
in article 78; we observe, merely, that in the case where AD' — d is in fact
neither = 0 nor = 180°, but is, nevertheless, a very small arc, it is preferable
to follow the same method, since the former method does not then admit of the
requisite precision. And, in fact, the combination of equation VII. with VI. or IX.
will be chosen according as sin (AD" — AD') is greater or less than sin (AD'— (T).

In the same manner, in the case in which the point Z>', or the one opposite to
it, either coincides with B" or is little removed from it, the determination of £"
and r" by the preceding method would be either impossible or unsafe. In this
case, accordingly, C and r will be determined by that method, but C" and /•" by
the combination of equation VII. either with V. or with VIII., according as sin
(A"D — A"Dr) is greater or less than sin (A'D1 — d"}.

There is no reason to fear that D' will coincide at the same time with the points
J5, B", or with the opposite points, or be very near them ; for the case in which
B coincides with B", or is but little remote from it, we excluded above, in article
138, from our discussion.

144.

The arcs £ and C" being found, the positions of the points C, C", will be given,
and it will be possible to determine the distance CO"— 2/' from £, £" and t'.
Let u, u", be the inclinations of the great circles AB, A"JB" to the great circle CO"
(which in figure 4 will be the angles C"CDr and 180° -- CC"D, respectively),
and we shall have the following equations, entirely analogous to the equations
3-6, article 137 : -

sin/' sin £ («" + «) = sin \ e' sin * (f + £"),
sin/' cos i (u" -(- u) = cos £ t' sin £ (c — f"),
cos/' sin k (u" — u) = sin $ e' cos i (C + <•"")>
cos/' cos £ (u" — u) = cos J e' cos i (t — C").

SECT. 1.] THREE COMPLETE OBSERVATIONS. 199

The two former will give i (n"-\- u) and sin/', the two latter £ (u" — 11) and cos/';
from sin/' and cos/' we shall have/'. It will be proper to neglect in the first
hypotheses the angles I («"-)-??) and \ (»"--?<), which will be used in the last
hypothesis only for determining the position of the plane of the orbit.

hi the same way, exactly,/ can be derived from a, C'D and C"D; also/"
from t", CD" and C'D" ; but the following formulas are used much more con
veniently for this purpose : —

in which the logarithms of the quantities ^ , ^-, are already given by the pre
ceding calculations. Finally, the whole calculation finds a new verification in
this, that we must have

if by chance any difference shows itself, it will not certainly be of any impor
tance, if all the processes have been performed as accurately as possible. Never
theless, occasionally, the calculation being conducted throughout with seven
places of decimals, it may amount to some tenths of a second, which, if it appear
worth while, we may with the utmost facility so distribute between 2 /and 2f"
that the logarithms of the sines may be equally either increased or diminished,
by which means the equation

p _ r sin 2/" _ n"
r"sin2/ n

will be satisfied with all the precision that the tables admit. When /and/" differ a
little, it will be sufficient to distribute that difference equally between 2/ and 2/".

145.

After the positions of the heavenly body in the orbit have been determined in
this manner, the double calculation of the elements will be commenced, both by
the combination of the second place with the third, and the combination of the
first with the second, together with the corresponding intervals of the times.

200 DETERMINATION OF AN ORBIT FROM [BOOK II.

Before this is undertaken, of course, the intervals of the times themselves require
some correction, if it is decided to take account of the aberration agreeably to the
third method of article 118. In this case, evidently, for the true times are to be
substituted fictitious ones anterior to the former, respectively, by 493(>, 493(/,
493</' seconds. For computing the distances (),(/, (>", we have the formulas: —

— s!n~(C— Aiy-{-6)~ -Bind

, _ Jfsm(d' — z) _ / sin (9 — z)

Q - . - . ^ ,

sin z sin o

But, if the observations should at the beginning have been freed from
aberration by the first or second method of article 118, this calculation may be
omitted ; so that it will not be necessary to deduce the values of the distances (t,
(>', (>", unless, perhaps, for the sake of proving that those values, upon which the
computation of the aberration was based, were sufficiently exact. Finally, it is
apparent that all this calculation is also to be omitted whenever it is thought
preferable to neglect the aberration altogether.

146.

The calculation of the elements — on the one hand from /, r", 2/ and the
corrected interval of the time between the second and third observations, the
product of which multiplied by the quantity k, (article 1,) we denote by 6, and
on the other hand from r, r, 2/" and the interval of time between the first and
second observations, the product of which by k will be equal to &" - - is to be car
ried, agreeably to the method explained in articles 88-105, only as far as the
quantity there denoted by y, the value of which in the first of these combinations
we shall call i], in the latter rf'. Let then

* ryoer'

9rj'~ ' r^t? cos/cos/' cos/""

and it is evident, that if the values of the quantities P, Q, upon which the whole
calculation hitherto is based, were true, we should have in the result P' = P,

SECT. 1.] THREE COMPLETE OBSERVATIONS. 201

Qf = Q. And conversely it is readily perceived, that if in the result P' = P,
Q' = Q, the double calculation of the elements from both combinations would, if
completed, furnish numbers entirely equal, by which, therefore, all three observa
tions will be exactly represented, and thus the problem wholly satisfied. But
when the result is not P = P, Q' = Q, let P'—P, Q'— Q be taken for X and Y,
if, indeed, P and Q were taken for x and y; it will be still more convenient to put

log P = x, log Q = y, log F — log P = X, log $ — log Q = Y.
Then the calculation must be repeated with other values of x, y.

147.

Properly, indeed, here also, as in the ten methods before given, it would be
arbitrary what new values we assume for x and y in the second hypothesis, if
only they are not inconsistent with the general conditions developed above ; but
yet, since it manifestly is to be considered a great advantage to be able to set out
from more accurate values, in this method we should act with but little prudence
if we were to adopt the second values rashly, as it were, since it may easily be
perceived, from the very nature of the subject, that if the first values of P and Q
were affected with slight errors, P' and Q' themselves would represent much more
exact values, svipposing the heliocentric motion to be moderate. "Wherefore, we
shall always adopt P and Q' themselves for the second values of P and Q, or
log P', log Q' for the second values of x and y, if log P, log Q are supposed to
denote the first values.

Now, in this second hypothesis, where all the preliminary work exhibited
in the formulas 1-20 is to be retained without alteration, the calculation will be
undertaken anew in precisely the same manner. That is, first, the angle o»
will be determined; after that e, r', n~, "-£-, £, r, ?', r", /', /, /". From the dif
ference, more or less considerable, between the new values of these quantities
and the first, a judgment will easily be formed whether or not it is worth while
to compute anew the correction of the times on account of aberration ; in the
latter case, the intervals of the times, and therefore the quantities & and 6", will
remain the same as before. Finally, 1], if are derived from /, r, r",f", r, r and

26

202 DETERMINATION OF AN ORBIT FROM [BOOK II.

the intervals of the times ; and hence new values of P and Q', which commonly
differ much less from those furnished by the first hypothesis, than the latter from
the original values themselves of P and Q. The second values of X and Y will,
therefore, be much smaller than the first, and the second values of P, Q', will be
adopted as the third values of P, Q, and with these the computation will be
resumed anew. In this' manner, then, as from the second hypothesis more exact
numbers had resulted than from the first, so from the third more exact numbers
will again result than from the second, and the third values of P', Q' can be taken
a.s the fourth of P, Q, and thus the calculation be repeated until an hypothesis
is arrived at in which X and Y may be regarded as vanishing ; but when the
third hypothesis appears to be insufficient, it will be preferable to deduce the val
ues of P, Q, assumed in the fourth hypothesis from the first three, in accordance
with the method explained in articles 120, 121, by which means a more rapid
approximation will be obtained, and it will rarely be requisite to go forward to
the fifth hypothesis.

148.

When the elements to be derived from the three observations are as yet

wholly unknown (to which case our method is especially adapted), in the first

ff1

hypothesis, as we have already observed, — , 6 6", are to be taken for approximate

values of P and Q, where & and to" are derived for the present from the interv.als
of the times not corrected. If the ratio of these to the corrected intervals is
expressed by /n : 1 and u" : 1, respectively, we shall have in the first hypothesis,

X==\og[i — log u" -f log r\ — log if,

Y= log u -(- log fi" - - log t] — log r" -j- Comp. log cos/-|- Comp. log cos /'
-|- Comp. log cos/" -|- 2 log r' — log r — log r".

The logarithms of the quantities p, u", are of no importance in respect to the re
maining terms ; log »; and log r", which are both positive, in X cancel each other
in some measure, whence X possesses a small value, sometimes positive, some
times negative ; on the other hand, in Y some compensation of the positive terms
Comp. log cos/, Comp. log cos/', Comp. log cos/" arises also from the negative

SECT. 1.] THREE COMPLETE OBSERVATIONS. 203

terms log?}, log?/', but less complete, for the former greatly exceed the latter. In

r'r'

general, it is not possible to determine any thing concerning the sign of log —r,.

Now, as often as the heliocentric motion between the observations is small, it
will rarely be necessary to proceed to the fourth hypothesis ; most frequently the
third, often the second, will afford sufficient precision, and we may sometimes be
satisfied with the numbers resulting from even the first hypothesis. It will be
advantageous always to have a regard to the greater or less degree of precision
belonging to the observations; it would be an ungrateful task to aim at a pre
cision in the calculation a hundred or a thousand times greater than that which
the observations themselves allow. In these matters, however, the judgment is
sharpened more by frequent practical exercise than by rules, and the skilful
readily acquire a certain faculty of deciding where it is expedient to stop.

149.

Lastly, the elements themselves will be compiited in the final hypothesis,
either from/, r, r", or from/", r, /, carrying one or the other of the calculations
through to the end, which in the previous hypotheses it had only been requisite
to continue as far as t], r" ; if it should be thought proper to finish both, the
agreement of the resulting numbers will furnish a new verification of the whole
work. It is best, nevertheless, as soon as /,/',/", are got, to obtain the elements
from the single combination of the first place with the third, that is, from f,r, r".
and the interval of the time, and finally, for the better confirmation of the com
putation, to determine the middle place in the orbit by means of the elements
found.

In this way, therefore, the dimensions of the conic section are made known,
that is, the eccentricity, the semi-axis major or the semi-parameter, the place
of the perihelion with respect to the heliocentric places C, 0', C", the mean
motion, and the mean anomaly for the arbitrary epoch if the orbit is elliptical, or
the time of perihelion passage if the orbit is hyperbolic or parabolic. It only
remains, therefore, to determine the positions of the heliocentric places in the
orbit with respect to the ascending node, the position of this node with reference
to the equinoctial point, and the inclination of the orbit to the ecliptic (or the

204 DETERMINATION OF AN ORBIT FROM [BOOK II.

equator). All this may be effected by the solution of a single spherical tri
angle. Let 8 be the longitude of the ascending node ; i the inclination of the
orbit ; g and g" the arguments of the latitude in the first and third observations ;
lastly, let I — & = h, I" - - Q, = li . Calling, in figure 4, & the ascending node,
the sides of the triangle Q, AC will be AD' — c, g, h, and the angles opposite to
them, respectively, i, 180° — y, u. We shall have, then,

sin i i sin i (g -\- h] = sin i (A!? — t) sin J (y -j- u)
sin J i cos £ (g -\- h) = cos i (AD' — £) sin i (y — u)
cos i z sin k (g — h} = sin i ( AZ/ — £) cos I (y -(- w)
cos J z'cos % (y — h} = cos i (AZ/ — £) cos £ (y — ?;).

The two first equations will give i (#-|-A) and sin ^ the remaining two i (y — Ji)
and cos H; fromy will be known the place of the perihelion with regard to the
ascending node, from h the place of the node in the ecliptic ; finally, i will be
come known, the sine and the cosine mutually verifying each other. We can
arrive at the same object by the help of the triangle &A"C', in which it is only
necessary to change in the preceding formulas the symbols g, h, A, L, y, u into y",
h", A", £", y", u". That still another verification may be provided for the whole
work, it will not be unserviceable to perform the calculation in both ways ;
when, if any very slight discrepancies should show themselves between the values
of i, Q, , and the longitude of the perihelion in the orbit, it will be proper to take
mean values. These differences rarely amount to OM or 0'.2, provided all the
computations have been carefully made with seven places of decimals.

When the equator is taken as the fundamental plane instead of the ecliptic,
it will make no difference in the computation, except that in place of the points
A, A" the intersections of the equator with the great circles AB, A'B" are to be
adopted.

SECT. 1.]

THREE COMPLETE OBSERVATIONS.

205

150.

We proceed now to the illustration of this method by some examples fully
explained, which will show, in the plainest manner, how generally it applies, and
how conveniently and expeditiously it leads to the desired result*

The new planet Juno will furnish us the first example, for which purpose we
select the following observations made at Greenwich and communicated to us by
the distinguished MASKELYNE.

Mean Time, Greenwich.

App. Right Ascension.

App. Declination S.

1804, Oct.

5 10* 51m 6'
17 9 58 10
27 9 16 41

357° 10' 22".35
355 43 45 .30
355 11 10 .95

6° 40' 8"
8 47 25
10 2 28

From the solar tables for the same times is found

Longitude of the Sun
from App. Equin.

Nutation.

Distance from
the Earth.

Latitude of
the Sun.

Appar. Obliquity of
the Ecliptic.

Oct. 5
17
27

192° 28' 53".72
204 20 21 .54
214 16 52 .21

-4- 15".43
4-15 .51
-f 15 .60

0.9988839
0.99539G8
0.9928340

— 0".49
-f 0.79
— 0.15

23° 27' 59".48
59 .26
59 .00

We will conduct the calculation as if the orbit were wholly unknown : for
which reason, it will not be permitted to free the places of Juno from parallax,
but it will be necessary to transfer the latter to the places of the earth. Accord
ingly we first reduce the observed places from the equatoi to the ecliptic, the
apparent obliquity being employed, whence results,

* It is incorrect to call one method more or less exact than another. That method alone can be con
sidered to have solved the problem, by which any degree of precision whatever is, at least, attainable.
Wherefore, one method excels another in this respect only, that the same degree of precision may be
reached by one more quickly, and with less labor, than by the other.

206

DETERMINATION OF AX ORBIT FROM

[BOOK 11.

App. Longitude of Juno.

App. Latitude of Juno.

Oct. 5

17

27

354° 44' 54".27
352 34 44.51 •
351 34 51 .57

— 4°59'31".59
— 6 21 56.25

— 7 17 52.70

We join directly to this calculation the determination of the longitude and
latitude of the zenith of the place of observation in the three observations : the
right ascension, in fact, agrees with the right ascension of Juno (because the
observations have been made in the meridian) but the declination is equal to the
altitude of the pole, 51° 28' 39". Thus we get

Long, of the Zenith. , Lat. of the Zenith.

Oct. 5

17
27

24° 29'
23 25
23 1

46° 53'
47 24
47 36

Now the fictitious places of the earth in the plane of the ecliptic, from which
the heavenly body would appear in the same manner as from the true places of
the observations, will be determined according to the precepts given in article 72.
In this way, putting the mean parallax of the sun equal to 8".6, there results,

Reduction of Longitude.

Reduction of Distance.

Reduction of Time.

Oct. 5

— 22" .39

4- 0.0003856

— 0'.19

17

— 27 .21

-f- 0.0002329

— 0 .12

27

— 35 .82

-(- 0.0002085

— 0 .12

The reduction of the time is added, only that it may be seen that it is wholly
insensible.

After this, all the longitudes, both of the planet and of the earth, are to be
reduced to the mean vernal equinox for some epoch, for which we shall adopt
the beginning of the year 1805 ; the nutation being subtracted the precession is
to be added, which, for the three observations, is respectively 11".87, 10".23, 8". 8 6,

SECT. 1.]

THREE COMPLETE OBSERVATIONS.

207

so that — 3".56 is to be added for the first observation, — 5".28 for the second,
— 6". 74 for the third.

Lastly the longitudes and latitudes of Juno are to be freed from the aberra
tion of the fixed stars ; thus it is found by well-known rules, that we must sub
tract from the longitudes respectively 19".12, 17".ll, 14".82, but add to the lati
tudes 0".53, 1".18, 1".75, by which addition the absolute values are diminished,
since south latitudes are considered as negative.

151.

All these reductions being properly applied, we have the correct data of the
problem as follows : —
Times of the observations reduced

to the meridian of Paris
Longitudes of Juno, a, a', a" .

Latitudes, p, p', p"

Longitudes of the earth, /, I', I"
Logs, of the distances, R, R, R"

Oct. 5.458644

354°44'3r.60

-4 59 31 .06

12 28 27 .76

9.9996826

17.421885

352034'22".12

-6 21 55 .07

24 19 49 .05

9.9980979

27.393077

351°34'30".01

-7 17 50 .95

34 16 9 .65

9.9969678

Hence the calculations of articles 136, 137, produce the following numbers,

, y"

logarithms of the sines
A' D, AD', AD" . .
A"D, A" I/. AD" . .

«,*',«",

logarithms of the sines
log sin $ e' ....
loo; cos i e'

196° 0' S".36
18 23 59 .20
9.4991995
232 6 26 .44
241 51 15 .22
2 19 34 .00
8.6083885

32 19 24 .93
9.7281105
213 12 29 .82
234 27 0 .90
7 13 37 .70
9.0996915
8.7995259
9.9991357

Moreover, according to article 138, we have

log tan/? .... 8.9412494 n log tan p" .... 9.1074080 n
log sin («"—?') . 9.7332391 n log sin (a — I'} . . 9.6935181 n
log cos (a" — *') . 9.9247904 log cos (a — I'} . . 9.9393180

191° 58' 0".33

190°41'40".17
43 11 42 .05
9.8353631
209 43 7 .47
221 13 57 .87
4 55 46 .19
8.9341440

208 DETERMINATION OF AN OHBIT FROM [BOOK II.

Hence

log (tan 0 cos (a" — /') — tan /?" cos (a — I'}) = log Tsm t 8.5786513

logsin(«" — a)=logrcosi! .......... 8.7423191«

Hence t — 145° 32' 57".78 log T ....... 8.8260683

= 337 30 58.11 log sin (* + /) .... 9.5825441 n

Lastly

log (tan 0 sin (a" — f ) — tan (3" sin (a — f)) = log £ . . 8.2033319 n
log T sin (* + /) .............. 8.4086124 n

whence log tan (dr — a) ............ 9.7947195

<T _ a = 31° 56' 11".81, and therefore a = 0° 23' 13".12.
According to article 140 we have

y — d" = 191° 15' 18".85 log sin 9.2904352 n log cos 9.9915661 »
^— <? =1944830.62 « " 9.4075427 n « « 9.9853301 »

>_^" =1983933.17 " " 9.5050667 n
> — tf'-f a = 200 10 14 .63 « « 9.5375909«
>" — d =191 19 8.27 « " 9.2928554 w
A'D"—d' + a = lW 17 46 .06 « « 9.2082723 n

Hence follow,

log a . . . 9.5494437, a =+0.3543592
log* . . . 9.8613533.

Formula 13 would give log b = 9.8613531, but we have preferred the former
value, because sin (A'D — d' -\-o) is greater than sin (AD" - — 8'-\-a).
Again, by article 141 we have,

3 log # sin d' . . . 9.1786252
log 2 ...... 0.3010300

log sin a ..... 7.8295601

7.3092153 and therefore log c = 2.6907847

log* 9.8613533

log cos a 9.9999901

9.8613632

SECT. 1.] THREE COMPLETE OBSERVATIONS. 209

whence — = 0.7267135. Hence are derived

COSff

d = — 1.3625052, log e = 8.3929518 n
Finally, by means of formulas, article 143, are obtained,
logx .... 0.0913394 »
log*" .... 0.5418957 n
log! . . . . 0.4864480 n
. 0.1592352 n

152.

The preliminary calculations being despatched in this way, we pass to the
first hypothesis. The interval of time (not corrected) between the second and
third observations is 9.971192 days, between the first and second is 11.963241.
The logarithms of these numbers are 0.9987471, and 1.0778489, whence

log 6 = 9.2343285, log &" = 9.3134303.
We will put, therefore, for the first hypothesis,

x = log P= 0.0791018
y — log Q= 8.5477588

Hence we have P = 1.1997804, P -{- a = 1.5541396, P -4- d= — 0.1627248 ;

loge . . . 8.3929518 n

log(P + a). 0.1914900

C.log(P + rf) O'.7885463w

log tan w . . 9.3729881, whence to — -f- 13°16'51".89, co -f a — -j- 13°40' 5".01.

logQ . . . 8.5477588

lose 2.6907847

-

log sin w . . 9.3612147
log Qc sin (» . 0.5997582

The equation

Qc sin w sin4 s= sin (z — 13°40' 5".01)

is found after a few trials to be satisfied by the value z = 14° 35' 4".90, whence
we have log sin z = 9.4010744, log / = 0.3251340. That equation admits of three
other solutions besides this, namely,

27

210 DETERMINATION OF AN ORBIT FROM [BOOK II.

e = 32° 2' 28"
2=137 27 59
z = 193 4 18

The third must be rejected because sin s is negative ; the second because s is
greater than d' ; the first answers to an approximation to the orbit of the earth
of which we have spoken in article 142.

Further, we have, according to article 143,

...... 9.8648551

log (P -fa) ..... 0.1914900
C. log sin (z — o). . . . 0.6103578

....... 0.6667029

logP ........ 0.0791018

0.5876011

47' r.51 = 214°22' 6".41; log sin = 9.7516736 n
54 32 .94 = 203 29 37 .84; log sin = 9.6005923 n
Hence we have \ogp = 9.9270735 n, log /'= 0.0226459 n, and then

log q — 0.2930977 n, log q" = 0.2580086 n,
whence result

C = 203° 17' 31".22 log r = 0.3300178
£"=110 10 58 .88 logr"= 0.3212819
Lastly, by means of article 144, we obtain

i («" + «)= 205° 18' 10".53

$(u" — «)= — 3 14 2 .02

/'= 3 48 14 .66

log sin 2/' . . . 9.1218791 log sin 2/' . . . 9.1218791

"

logr 0.3300178 logr" 0.3212819

C.log— 9.3332971 C.log^ 9.4123989

*— ' 9t. *— ' VI

log sin 2 / . . . 8.7851940 log sin 2 /" . . . 8.8555599
2/= 3°29"46'.03 2/" = 4°6'43".28

The sum 2/-J-2/" differs in this case from 2f only by 0".01.

SECT. 1.]

THREE COMPLETE OBSERVATIONS.

211

Now, in order that the times may be corrected for aberration, it is necessary to
compute the distances (>, (>', (>" by the formulas of article 145, and afterwards to
multiply them by the time 493', or Orf.005706. The following is the calculation,

logr . . . . 0.33002 logr' . . . 0.32513 log/' .... 0.32128

log sin (<T — z) 9.48384
C. log sin y . 0.27189

logsm(AZX— £) 9.23606
0.50080

C. log sin d

logsin (4"ZX— • 'C") 9.61384
0.16464

C. log sin 9" .

log^ ... 0.06688
log const. . . 7.75633

log(/ . . . 0.08086
7.75633

log?". . . . 0.09976
7.75633

log of reduction 7.82321
reduction = 0.006656

7.83719
0.006874

7.85609
0.007179

Observations.

Corrected times.

Intervals.

Logarithms.

I.

Get. 5.451988

II.

17.415011

11*963023

1.0778409

in.

27.385898

9 .970887

0.9987339

The corrected logarithms of the quantities 6, &", are consequently 9.2343153 and
9.3134223. By commencing now the determination of the elements from /, /,
r", & we obtain log TJ = 0.0002285, and in the same manner from /", r, /, 6"we
get log if = 0.0003191. We need not add here this calculation explained at
length in section III. of the first book.
Finally we have, by article 146,

iogr . .

. . 9.3134223

2 log/ . . .

. 0.6502680

C.logd . .

. . 0.7656847

C.logr/' . .

. 9.3487003

log rj . .

. . 0.0002285

logdd" . . .

. 8.5477376

C. log if .

. . 9.9996809

C. log 1717" . .

. 9.9994524

logP' . .

. . 0.0790164

C. log cos/ . .

. 0.0002022

C. log cos/' . .

. 0.0009579

C. log cos/" .

. 0.0002797

log(X.

8.5475981

The first hypothesis, therefore, results in X = — 0.0000854, Y— — 0.0001607.

212

DETERMINATION OF AN ORBIT FROM

[BOOK II.

153.

In the second hypothesis we shall assign to P, Q, the very values, which in the
first we have found for Pf) Q', We shall put, therefore,

x = log P = 0.0790164
y = log Q = 8.5475981

Since the calculation is to be conducted in precisely the same manner as in
the first hypothesis, it will be sufficient to set down here its principal results : —

210° 8'24".9S
0.3307676
0.3222280
205 22 15 .58
-3 14 4 .79
7 34 53 .32

3 29 0 .18

4 5 53 .12

It would hardly be worth while to compute anew the reductions of the times
on account of aberration, for they scarcely differ Is from those which we have
got in the first hypothesis.

The further calculations furnish log ij = 0.00022 70, logi?" = 0.0003173, whence
are derived

to

13°15'38".13

t"

(a -\- a

13 38 51 .25

loo* T .

log Q c sin w . .
z

0.5989389
14 33 19 .00

log/' . . . .
*(«" + «) . . .

k>f r .

0.3259918

i (u — u} . . .

OC£>7C-| QO

2f .

l°g „ ....

.DO ioiyo

2f

, n ' f

log-,,- ....

0.5885029

2/" .

C .

203 16 38 .16

log ^=0.0790167
log (X= 8.5476110

X= + 0.0000003
Y = 0.0000129

From this it appears how much more exact the second hypothesis is than the

first.

154.

In order to leave nothing to be desired, we will still construct the third hypothe
sis, in which we shall again choose the values of P', Q', obtained in the second

w

13°15'38".39

L"

Wl— ff

13 38 51 51

lo°" T .

log Qc sin o) . .

0.5989542
14 33 19 .50

log/' . . . .

locr /

0.3259878

In n'r>

OeftV-M ZA

2/'

l°s— • . • .

.00 ( OlO*

>

2/

loo-W//

0.5884987

2 f"

71

203 16 38 .41

"j

SECT. 1.] THREE COMPLETE OBSERVATIONS. 213

hypothesis, as the values of P, Q. Putting, therefore,

z = log P — 0.0790167
# = log (2 = 8.5476110

the following are found to be the principal results of the calculation : —

210° 8'25".65
0.3307640
0.3222239
205 22 14 .57
—3 14 4 .78
7 34 53 .73

3 29 0 .39

4 5 53 .34

All these numbers differ so little from those which the second hypothesis fur
nished, that we may safely conclude that the third hypothesis requires no further
correction.* We may, therefore, proceed to the determination of the elements
from 2/', r, r", 6', which we dispense with transcribing here, since it has already
been given in detail in the example of article 97. Nothing, therefore, remains
but to compute the position of the plane of the orbit by the method of article
149, and to transfer the epoch to the beginning of the year 1805. This computa
tion is to be based upon the following numbers : —

' — C= 9°55'5r.41

18 13 .855
i(y_M)=_6 18 5 .495
whence we obtain

i(0-|-A) = 196°43'14".62
l(g — h) = — 4 37 24 .41
it = 6 33 22 .05

* If the calculation should be carried through in the same manner as in the preceding hypotheses,
we should obtain X=0, and T= -(-0.0000003, which value must be regarded as vanishing, and,
in fact, it hardly exceeds the uncertainty always remaining in the last decimal place.

214 DETERMINATION OF AN OKBIT FROM [BoOK II.

We have, therefore, h = 201° 20' 39".03, and so Q= I — h = 171° 7' 48".73 ; fur
ther, ff — 192° 5' 50".21, and hence, since the true anomaly for the first observa
tion is found, in article 97, to be 310°55/29".64, the distance of perihelion from
the ascending node in the orbit, 241° 10'20".57, the longitude of the perihelion
52° 18' 9".30; lastly, the inclination of the orbit, 13° 6'44".10. If we prefer to
proceed to the same calculation from the third place, we have,

A"D'—L"= 24°18'35".25
i (/'+«")= 196 24 54 .98
i (/'_«") = — 5 43 14 .81

Thence are derived

i(/_[-A")= 2H°24'32".45
i(/_ A")= — 11 43 48 .48
i i 633 22 .05

and hence the longitude of the ascending node, I" — h" = 171° 7'48".72, the lon
gitude of the perihelion 52° 18' 9".30, the inclination of the orbit 13° 6'44".10,
just the same as before.

The interval of time from the last observation to the beginning of the year
1805 is 64.614102 days; the mean heliocentric motion corresponding to which is
53293".66 =14° 48' 13".66 ; hence the epoch of the mean anomaly at the begin
ning of the year 1805 for the meridian of Paris is 349° 34' 12".3S, and the epoch
of the mean longitude, 41° 52' 21".68.

155.

That it may be more clearly manifest what is the accuracy of the elements
just found, we will compute from them the middle place. For October 17.415011
the mean anomaly is found to be 332° 28' 54".77, hence the true is 315° 1' 23".02
and log r", 0.3259877, (see the examples of articles 13, 14); this true anomaly
ought to be equal to the true anomaly in the first observation increased by the
angle 2/", or to the true anomaly in the third observation diminished by the
angle 2/, that is, equal to 315° 1' 22".98; and the logarithm of the radius vector
should be 0.3259878 : the differences are of no consequence. If the calculation

SECT. 1.]

THREE COMPLETE OBSERVATIONS.

215

for the middle observation is continued to the geocentric place, the results dif
fer from observation only by a few hundredths of a second, (article 63 ;) these
differences are absorbed, as it were, in the unavoidable errors arising from the
want of strict accuracy in the tables.

We have worked out the preceding example with the utmost precision, to
show how easily the most exact solution possible can be obtained by our method.
In actual practice it will rarely be necessary to adhere scrupulously to this
type. It will generally be sufficient to use six places of decimals throughout;
and in our example the second hypothesis would have given results not less accu
rate than the third, and even the first would have been entirely satisfactory. We
imagine that it will not be unacceptable to our readers to have a comparison of
the elements derived from the third hypothesis with those which would result
from the use of the second or first hypothesis for the same object. We exhibit
the three systems of elements in the following table : —

From hypothesis III.

From hypothesis II.

From hypothesis I.

Epoch of mean long. 1805
Mean daily motion . .

41°52'21".68
824".7989
52 18 9 .30

41°52'18".40
824".7983
52 18 6 .66

42°12'37".83
823".5025
52 41 9 .81

14 12 1 .87

14 11 59 .94

14 24 27 .49

Log of semi-axis major .
Ascending node
Inclination of the orbit .

0.4224389
171 7 48 .73
13 6 44 .10

0.4224392
171 7 49 .15
13 6 45 .12

0.4228944
171 5 48 .86
13 2 37 .50

By computing the heliocentric place in orbit for the middle observation from
the second system of elements, the error of the logarithm of the radius vector is
found equal to zero, the error of the longitude in orbit, 0".03 ; and in comput
ing the same place by the system derived from the first hypothesis, the error of
the logarithm of the radius 'Vector is 0.0000002, the error of the longitude in
orbit, 1".31. And by continuing the calculation to the geocentric place we have,

216

DETERMINATION OF AN ORBIT FROM

[BOOK II.

From hypothesis II.

From hypothesis I.

p

Geocentric longitude

352° 34' 22".26
0 .14

352° 34' 19".97
2 .15

Geocentric latitude .

6 21 55 .06
0 01

6 21 54 .47
0 .GO

156.

We shall take the second example from Pallas, the following observations of
which, made at Milan, we take from VON ZACH'S Monatliche Corrcsporidmz, Vol.
XIV., p. 90.

Mean Time, Milan.

App. Right Ascension.

App. Declination S.

1805, Nov. 5*1 4* 14m 4s
Dec. 6 11 51 27
1806, Jan. 15 8 50 36

78° 20' 37".8
73 8 48 .8
67 14 11 .1

27° 16' 56".7
32 52 44.3

28 38 8 .1

We Avill here take the equator as the fundamental plane instead of the
ecliptic, and we will make the computation as if the orbit were still wholly un
known. In the first place we take from the tables of the sun the following data
for the given dates : — «

Longitude of the Sun

Distance from

Latitude of

from mean Equinox.

the Earth.

the Sun.

Nov. 5

223° 14' 7".61

0.9804311

4- 0".59

Dec. 6

254 28 42 .59

0.9846753

-f 0.12

Jan. 15

295 5 47 .62

0.9838153

— 0.19

We reduce the longitudes of the sun, the precessions -j-7".59, -|-3".36, — 2".ll,
being added, to the beginning of the year 1806, and thence we afterwards derive
the right ascensions and declinations, using the mean obliquity 23° 27' 53".53 and
taking account of the latitudes. In this way we find

SECT. 1.]

THREE COMPLETE OBSERVATIONS.

217

Right ascension of the Sun.

Deol. of the Sun S.

Nov. 5
Dec. 6
Jan. 15

220° 46' 44".65
253 9 23 .26
297 2 51 .11

15°49'43".94
22 33 39 .45
21 8 12 .98

These places are referred to the centre of the earth, and are, therefore, to be
reduced by applying the parallax to the place of observation, since the places of
the planet cannot be freed from parallax. The right ascensions of the zenith to
be used in this calculation agree with the right ascensions of the planet (because
the observations have been made in the meridian), and the declination will be
throughout the altitude of the pole, 45° 28'. Hence are derived the following
numbers : —

Bight asc. of the Earth.

Decl. of the Earth N.

Log of dist. from the Sun.

Nov. 5
Dec. 6
Jan. 15

40° 46' 48".ol
73 9 23 .26
117 2 46 .09

15° 49' 48".59
22 33 42 .83
21 8 17 .29

9.9958575
9.9933099
9.9929259

The observed places of Pallas are to be freed from nutation and the aberra
tion of the fixed stars, and afterwards to be reduced, by applying the precession,
to the beginning of the year 1806. On these accounts it will be necessary to
apply the following corrections to the observed places : —

Observation I.

Observation II.

Observation HI.

Bight asc.

Declination.

Right asc.

Declination.

Right asc.

Declination.

Nutation
Aberration
Precession

— 12".86
— 18.13
+ 5.43

— 3".08
— 9 .89
-f- 0.62

— 13".68
— 21.51
+ 2.55

— 3".42
— 1.63
-f 0.39

— 13".06

— 15 .60
— 1 .51

— 3".75
+ 9.76
— 0.33

Sum

— 25 .56

— 12 .35

— 32 .64

— 4.66

— 30.17

-f- 5.68

28

218

DETERMINATION OF AN ORBIT FROM

[BOOK II.

Hence we have the following places of Pallas, for the basis of the compu
tation : —

Mean Time, Paris.

Right Ascension.

Declination.

Nov. 5.574074
36.475035
76.349444

78° 20' 12".24
73 8 16 .16
67 13 40 .93

— 27° 17' 9".05
— 32 52 48 .96
— 28 38 2 .42

157.

Now in the first place we will determine the positions of the great circles
drawn from the heliocentric places of the earth to the geocentric places of the
planet. We take the symbols 2t, 2f, 21", for the intersections of these circles
with the equator, or, if you please, for their ascending nodes, and we denote the
distances of the points B, B, B" from the former points by J, z/', J". In the
greater part of the work it will be necessary to substitute the symbols 2(, 21', 21",
for A, A', A', and also //, //', A" for d, 8', 8" ; but the careful reader will readily
understand when it is necessary to retain A, A, A', d, d', 8", even if we fail to
advise him.

The calculation being made, we find
Riffht ascensions of the

233° 54' 57".10
51 17 15 .74
215 58 49 .27
56 26 34 .19
23 54 52 .13
33 3 26 .35
47 1 54 .69
9.8643525

points 2t, 21', 21" .

, 21 77,
, 3TZX, W

logarithms of the sines
log sin
log cos

e

e'

253° 8'57".01
90 1 3 .19

212 52 48 .96
55 26 31 .79

30 18 3 .25

31 59 21 .14
89 34 57 .17

9.9999885
9.8478971
9.8510614

276° 40' 25".87

131 59 58 .03

220 9 12 .96

69 10 57 .84

29 8 43 .32

22 20 6 .91

42 33 41 .17

9.8301910

SECT. 1.] THREE COMPLETE OBSERVATIONS. 219

The right ascension of the point 2T is used in the calculation of article 138
instead of I'. In this manner are found

log T sin t 8.4868236 n

log T cost 9.2848162 n

Hence ^ = 189° 2'48".83, log T = 9.2902527; moreover, #-f / = 2 79° 3'52".02,

log 8 9.0110566 n

log Tsin (* + /). . . 9.2847950 n
whence Jf— o = 208° 1' 55".64, and 0 = 4° 50' 53".32.

In the formulas of article 140 sin 8, sin d', sin 8" must be retained instead of
a, b and -, and also in the formulas of article 142. For these calculations we
have

WD' — A" = 171° 50' 8".18 log sin 9.1523306 log cos 9.9955759 n

%jy—J =1741913.98 « « 8.9954722 « « 9.9978629 »

WZ>— A" =172 54 13. .39 « « 9.0917972

2t'Z> — J'+a = 175 52 56 .49 « « 8.8561520

W — A — 173 9 54 .05 « « 9.0755844

St'ZX'— J' + o- =174 18 11 .27 " « 8.9967978

Hence we deduce

log* =0.9211850, logJl = 0.0812057 n

log x" = 0.8112762, log X" = 0.0319691 »

log a = 0.1099088, a = -f- 1.2879790

log b =0.1810404,
log* =0.0711314,

whence we have log b = 0.1810402. We shall adopt log b = 0.1810403 the
mean between these two nearly equal values. Lastly we have

log c = 1.0450295
d = -f 0.4489906
log e=9.2102894

with which the preliminary calculations are completed.

220 DETERMINATION OF AN ORBIT FROM [BoOK II.

The interval of time between the second and third observations is 39.874409
days, between the first and second 30.900961 : hence we have
log 6 = 9.8362757, log d" = 9.7255533.
We put, therefore, for the first hypothesis,

x = log P= 9.8892776
y = log Q = 9.5618290
The chief results of the calculation are as follows : —

w + <j = 20° 8'46".72
log Qc sin co = 0.0282028

Thence the true value of z is 21°11/24".30, and of log/, 0.3509379. The three
remaining values of z satisfying equation IV., article 141, are, in this instance,

z= 63° 41' 12"
z = 101 12 58
2=199 24 7

the first of which is to be regarded as an approximation to the orbit of the earth,
the deviation of which, however, is here much greater than in the preceding
example, on account of the too great interval of time. The following numbers
result from the subsequent calculation : —

£ 195° 12' 2".48

C" 196 57 50 .78

logr 0.3647022

log/' .... 0.3355758

*K + w) ... 266 4750 .47

*(M" — «) . . .—43 39 5 .33

2/' 22 32 40 .86

2/ 13 541.17

2/" 9 27 0 .05

"We shall distribute the difference between 2/' and 2/-J-2/", which in this case
is 0".36, between 2 /and 2/" in such a manner as to make 2/= 13° 5'40".96,
and2/"=9°26'59".90.

The times are now to be corrected for aberration, for which purpose we are to

SECT. 1.]

put in the formulas of article 145,

THREE COMPLETE OBSERVATIONS.

221

— £" = 2TZX —

8" — C

We have, therefore,

logr . . . . 0.36470

log / . .

. 0.35094

log/' . .

. . 0.33557

log sin (AZ/— f) 9.76462

log sin (dr —

z) 9.75038

log sin ( A"D

'—C") 9.84220

C.logsind . . 0.07918

C. log sin df

. 0.08431

C. log sin 6"

. . 0.02932

log const. . . 7.75633

log const. .

. 7.75633

log const.

. . 7.75633

7.96483

7.94196

7.96342

reduction of) 0009222

0.008749

0.009192

the time j

Corrected times.

Nov. 5.564852
36.466286
76.340252

Intervals.

30d.901434

39.873966

Logarithms.

1.4899785
1.6006894

Hence follow,

Observations.

L

n.
in.

whence are derived the corrected logarithms of the quantities 6, &" respectively
9.8362708 and 9.7255599. Beginning, then, the calculation of the elements
from /, r", 2/, 6, we get log i] — 0.0031921, just as from r, r', 2/", 6" we obtain
log rf' = 0.0017300. Hence is obtained

log F = 9.8907512 log Q' = 9.5712864,

and, therefore,

X= +0.0014736 Y= +0.0094574

The chief results of the second hypothesis, in which we put

x — log P= 9.8907512
y = log Q = 9.5712864

are the following : •

w -4- <J - •
log Qcsmw

3 . . . .

log/

20° 8' 0".87
0.0373071

21 12 6 .09
0.3507110

C 195° 16' 59".90

£" 196 52 40 .63

logr .... 0.3630642

log/' . . . . 0.3369708

222 DETERMINATION OF AN ORBIT FROM [BOOK IE.

• 267° 6'10".75
._43 39 4 .00

22° 32' 8".69

2/ 13 1 54 .65

2/" 9 30 14 .38

The difference 0."34, between 2/' and 2/-f2/"is to be so distributed, as to
make 2/= 13° 1' 54".45, 2/" = 9° 30' 14".24.

If it is thought worth while to recompute here the corrections of the times,
there will be found for the first observation, 0.009169, for the second, 0.008742,
for the third, 0.009236, and thus the corrected times, November 5.564905, Novem
ber 36.466293, November 76.340280. Hence we have

logd 9.8362703 logr/' 0.0017413

log 6" 9.7255594 logP7 9.8907268

log TJ 0.0031790 i log^ 9.5710593

Accordingly, the results from the second hypothesis are

.X= — 0.0000244, F= — 0.0002271.
Finally, in the third hypothesis, in which we put
x — log P = 9.8907268
y = log 0 = 9.5710593
the chief results of the calculation are as follows : —

w+ff . . . . 20° 8' 1".62 log/' .... 0.3369536

log^csinw . . 0.0370857 i(tt"-ftt). . . 267 553.09

z 21 12 4 .60 i(«" — u) . . .—43 39 4.19

log/ 0.3507191 2/' 22 32 7 .67

C 195 16 54 .08

C" . . 196 52 44 .45

2/ 13 1 57 .42

2/" 9 30 10 .63

logr 0.3630960

The difference 0".38 will be here distributed in such a manner as to make
2/= 13° 1' 57".20, 2/" = 9° 30' 10".47.*

* This somewhat increased difference, nearly equal in all the hypotheses, has arisen chiefly from
this, that a had been got too little by almost two hundredths of a second, and the logarithm of 6 too
great by several units.

SECT. 1.] THREE COMPLETE OBSERVATIONS. 223

Since the differences of all these numbers from those which the second
hypothesis furnished are very small, it may be safely concluded that the third
hypothesis requires no further correction, and, therefore, that a new hypothesis
would be superfluous. Wherefore, it will now be proper to proceed to the calcu
lation of the elements from 2/', $', r, r" : and since the processes comprised in
this calculation have been most fully explained above, it will be sufficient to add
here the resulting elements, for the benefit of those who may wish to perform the
computation themselves : —

Right ascension of the ascending node on the equator .... 158° 40' 38".93

Inclination of the orbit to the equator 11 42 49 .13

Distance of the perihelion from the ascending node 323 14 56 .92

Mean anomaly for the epoch 1806 335 4 13 .05

Mean daily (sidereal) motion 770".2662

Angle of eccentricity, y 14 9 3 .91

Logarithm of the semi-axis major 0.4422438

158.

The two preceding examples have not yet furnished occasion for using the
method of article 120 : for the successive hypotheses converged so rapidly that
we might have stopped at the second, and the third scarcely differed by a sensible
amount from the truth. We shall always enjoy this advantage, and be able to do
without the fourth hypothesis, when the heliocentric motion is not great and the
three radii vectores are not too unequal, particularly if, in addition to this, the
intervals of the times differ from each other but little. But the further the con
ditions of the problem depart from these, the more will the first assumed values
of P and Q differ from the correct ones, and the less rapidly will the subsequent
values converge to the truth. In such a case the first three hypotheses are to
be completed in the manner shown in the two preceding examples, (with this
difference only, that the elements themselves are not to be computed in the third
hypothesis, but, exactly as in the first and second hypotheses, the quantities 17, rj",
P', Q', X, Y) ; but then, the last values of P', Q' are no longer to be taken as

224

DETERMINATION OF AN ORBIT FROM

[BOOK II.

the new values of the quantities P, Q in the new hypothesis, but these are to
be derived from the combination of the first three hypotheses, agreeably to the
method of article 120. It will then very rarely be requisite to proceed to the
fifth hypothesis, according to the precepts of article 121. We will now explain
these calculations further by an example, from which it wih1 appear how far our
method extends.

159.

For the third example we select the following observations of Ceres, the first
of which has been made by OLBERS, at Bremen, the second by HARDING, at Got-
tingen, and the third by BESSEL, at Lilienthal.

Mean time of place of observation.

Right Ascension.

North declination.

1805, Sept. 5" 13* 8m 54'
1806, Jan. 17 10 58 51
1806, May 23 10 23 53

95° 59' 25"
101 18 40.6
121 56 7

22° 21' 25"
30 21 22.3

28 2 45

As the methods by which the parallax and aberration are taken account of,
when the distances from the earth are regarded as wrholly unknown, have already
been sufficiently explained in the two preceding examples, we shah1 dispense
with this unnecessary increase of labor in this third example, and with that
object will take the approximate distances from VON ZACH'S Monatlielie Corre-
ispondenz, Vol. XL, p. 284, in order to free the observations from the effects of
parallax and aberration. The following table shows these distances, together
with the reductions derived from them : —

J.111HJ 111 W 111U11 Lilt; llli

o

Eeduced time of observation .
Sidereal time in degrees
Parallax in right ascension
Parallax in declination

.he earth . . .

2.899

1.638

2.964

reaches the earth

23m49'

13m28J

24m21'

ation

12A45m 5'

10445m23'

9459m32'

355° 55'

97° 59'

210° 41'

on

-4- 1".90

-4- 0".22

— 1".97

1

i

— 2.08

— 1.90

— 2.04

SECT. 1.]

THREE COMPLETE OBSERVATIONS.

225

Accordingly, the data of the problem, after heing freed from parallax and
aberration, and after the times have been reduced to the meridian of Paris, are as
follows : —

Times of the observations.

Right Ascension.

Declination.

1805, Sept. 5, 12s 19"1
1806, Jan. 17, 10 15
1806, May 23, 9 33

14'
2
18

95° 59' 23".10
101 18 40.38
121 56 8.97

22° 21' 27".08
30 -21 24.20
28 2 47.04

From these right ascensions and declinations have been deduced the longi
tudes and latitudes, using for the obliquity of the ecliptic 23° 27' 55".90, 23° 27'
54".59, 23° 27' 53".27 ; the longitudes have been afterwards freed from nutation,
which was for the respective times -j- 17".31, -f- 17".88, -|- 18".00, and next re
duced to the beginning of the year 1806, by applying the precession -\- 15".98,
— 2".39, — 19".6S. Lastly, the places of the sun for the reduced times have
been taken from the tables, in which the nutation has been omitted in the longi
tudes, but the precession has been added in the same way as to the longitudes of
Ceres. The latitude of the sun has been wholly neglected. In this manner have
resulted the following numbers to be used in the calculation: —

Times, 1805, September

a, a, a

5.51336

95° 32' 18".56

— 0 59 34 .06

342 54 56 .00

0.0031514

i, i', i" ......

log R, log K, log R' .

The preliminary computations explained in articles 136-140 furnish the fol-

139.42711

99° 49' 5".87
+ 7 16 36 .80
117 12 43 .25
9.9929861

265.39813
118° 5'2S".85
7 38 49 .39
241 58 50 .71

0.0056974

lowing : —

AD, AD', AD" .
A'D, A"D', A'D".

358°55'28".09
112 37 9 .66

15 32 41 .40
138 45 4 .60

29 18 8 .21

29

156052'11".49

18 48 39 .81

252 42 19 .14

6 26 41 .10

170 32 59 .08

170°48'44".79
123 32 52 .13
136 2 22 .38
358 5 57 .00
156 6 25 .25

226

DETERMINATION OF AN ORBIT FROM

[BOOK II.

log e = 0.8568244

log x = 0.1611012
logx"= 9.9770819 n
log \ = 9.9164090 n
log X"= 9.7320127 n

o = 8° 52' 4".05

log a = 0.1840193 n, a = — 1.5276340
log £ = 0.0040987
log c = 2.0066735
d= 117.50873

The interval of time between the first and second observations is 133.91375
days, between the second and third, 125.97102 : hence

log 4 = 0.3358520, log 6"= 0.3624066, log -£ = 0.0265546, log fid" = 0.6982586.

We now exhibit in the following table the principal results of the first three
hypotheses : —

i.

n.

ni.

log P = x

0.0265546

0.0256968

0.0256275

log Q = y

0.6982586

0.7390190

0.7481055

w -\-a

7°15'13".523

7°14'47".139

7°14'45".071

log Qc sin o)

1.1546650 w

1.1973925w

1.2066327 n

2

7 3 59 .018

7 2 32 .870

7 2 16 .900

log/

0.4114726

0.4129371

0.4132107

C

160 10 46 .74

160 20 7 .82

160 22 9 .42

C"

262 6 1 .03

262 12 18 .26

262 14 19 .49

log r

0.4323934

0.4291773

0.4284841

log/'

0.4094712

0.4071975

0.4064697

*(«"+«)

262 55 23 .22

262 57 6 .83

262 57 31 .17

k(u"-,i,

273 28 50 .95

273 29 15 .06

273 29 19 .56

2/'

62 34 28 .40

62 49 56 .50

62 53 57 .06

2/

31 8 30 .03

31 15 59 .09

31 18 13 .83

2/"

31 25 58 .43

31 33 57 .32

31 35 43 .32

log7?

0.0202496

0.0203158

0.0203494

log if

0.0211074

0.0212429

0.0212751

logP'

0.0256968

0.0256275

0.0256289

log*?

0.7390190

. 0.7481055

0.7502337

X

— 0.0008578

— 0.0000693

+ 0.0000014

r

+ 0.0407604

+ 0.0090865

+ 0.0021282

SECT. 1.] THREE COMPLETE OBSERVATIONS. 227

If we designate the three values of X by A, A', A"; the three values of Y by
B, B, B"; the quotients arising from the division of the quantities A'B"-—A"B.
A'B — AB", AB1 — A'B, by. the sum of these quantities, by k, k', k", respectively,
so that we have R-{-tf-\-tfr=l; and, finally, the values of log Pf and log Q' in the
third hypothesis, by M and N, (which would become new values of x and y if it
should be expedient to derive the fourth hypothesis from the third, as the third
had been derived from the second) : it is easily ascertained from the formulas of
article 120, that the corrected value of x is M — k (A' -\- A") — /c'A", and the cor
rected value of y, N — k (B -j- B') — k'B". The calculation being made, the
former becomes 0.0256331, the latter, 0.7509143. Upon these corrected values
we construct the fourth hypothesis, the chief results of which are the following : —

w + a . . . . 7°14'45".247
log Qc sin CD . . 1.2094284 B

0 7 2 12 .736

log/ 0.4132817

log/' .... 0.4062033

*(«" + «) . . . 262°57'38".78

-M) . . . 273 29 20 .73

2/' 62 55 16 .64

2/ 31 19 1 .49

2/" 31 36 15 .20

£ 160 22 45 .38

£" 262 15 3 .90

logr 0.4282792

The difference between 2/' and 2/-J- 2/" proves to be 0".05, which we shall
distribute in such a manner as to make 2/= 31° 19' 1".47, 2/"= 31° 36' 15".17.
If now the elements are determined from the two extreme places, the following
values result : —

True anomaly for the first place 289° 7' 39".75

True anomaly for the third place 352 2 56 .39

Mean anomaly for the first place 297 41 35 .65

Mean anomaly for the third place 353 15 22 .49

Mean daily sidereal motion 769".6755

Mean anomaly for the beginning of the year 1806 . . 322 35 52 .51

Angle of eccentricity, y 4 37 57 .78

Logarithm of the semi-axis major 0.4424661

By computing from these elements the heliocentric place for the time of the

228 DETERMINATION OF AN ORBIT FROM [BOOK II.

middle observation, the mean anomaly is found to be 326° 19' 25".72, the loga
rithm of the radius vector, 0.4132825, the true anomaly, 320° 43' 54".87 : this last
should differ from the true anomaly for the first place by the quantity If", or
from the true anomaly for the third place by the quantity 2/, and should, there
fore, be 320° 43' 54".92, as also the logarithm of the radius vector, 0.4132817 :
the difference 0".05 in the true anomaly, and of eight units in the logarithm, is
to be considered as of no consequence.

If the fourth hypothesis should be conducted to the end in the same way as
the three preceding, we would have X= 0, Y= 0.0000168, whence the follow
ing corrected values of x and y would be obtained,

x =• logP = 0.0256331, (the same as in the fourth hypothesis,)
y = \og Q= 0.7508917.

If the fifth hypothesis should be constructed on these values, the solution would
reach the utmost precision the tables allow: but the resulting elements would
not differ sensibly from those which the fourth hypothesis has furnished.

Nothing remains now, to obtain the complete elements, except that the posi
tion of the plane of the orbit should be computed. By the precepts of article
149 we have

From the first place. From the third place.

g 354° 9' 44".22 /'.... 57° 5' 0".91

h 261 56 6 .94 A" .... 161 0 1 .61

i 10 37 33 .02 10 37 33 .00

8 80 58 49 .06 80 58 49 .10

Distance of the perihelion I ^ g ^ 65 g 4 ^

from the ascending node j

Longitude of the perihelion 146 0 53 .53 146 0 53 .62

The mean being taken, we shall put i= 10° 37' 33".01, Q = 80° 58' 49".08, the
longitude of the perihelion = 146° 0' 53".57. Lastly, the mean longitude for
the beginning of the year 1806 will be 108° 36' 46".08.

SECT. 1.] THREE COMPLETE OBSERVATIONS. 229

160.

In the exposition of the method to which the preceding investigations have
been devoted, we have come upon certain special cases to which it did not apply,
at least not in the form in which it has been exhibited by us. We have seen
that this defect occurs first, when any one of the three geocentric places coincides
either with the corresponding heliocentric place of the earth, or with the oppo
site point (the last case can evidently only happen when the heavenly body
passes between the sun and earth) : second, when the first geocentric place of the
heavenly body coincides with the third ; third, when all three of the geocentric
places together with the second heliocentric place of the earth are situated in the
same great circle.

In the first case the position of one of the great circles AB, A'B', A'B", and in
the second and third the place of the point JB*, will remain indeterminate. In
these cases, therefore, the methods before explained, by means of which we have
shown how to determine the heliocentric from the geocentric places, if the quan
tities P, Q, are regarded as known, lose their efficacy : but an essential distinction
is here to be noted, which is, that in the first case the defect will be attributable
to the method alone, but in the second and third cases to the nature of the prob
lem; in the first case, accordingly, that determination can imdoubtedly be effected
if the method is suitably altered, but in the second and third it will be absolutely
impossible, and the heliocentric places will remain indeterminate. It will not be
uninteresting to develop these relations in a few words : but it would be out of
place to go through all that belongs to this subject, the more so, because in all
these special cases the exact determination of the orbit is impossible where it
would be greatly affected by the smallest errors of observation. The same defect
will also exist when the observations resemble, not exactly indeed, but nearly,
any one of these cases ; for which reason, in selecting observations this is to be
recollected, and properly guarded against, that no place be chosen where the
heavenly body is at the same time in the vicinity of the node and of opposition
or conjunction, nor such observations as where the heavenly body has nearly re
turned in the last to the geocentric place of the first observation, nor, finally, such

230 DETERMINATION OF AN ORBIT FROM [BOOK II.

as where the great circle drawn from the middle heliocentric place of the earth to
the middle geocentric place of the heavenly body makes a very acute angle with
the direction of the geocentric motion, and nearly passes through the first and
third places.

161.

We will make three subdivisions of the first case.

L If the point B coincides with A or with the opposite point, 8 will be equal
to zero, or to 180° ; y, t', s" and the points I/, D", will be indeterminate ; on the
other hand, /, /', e and the points D, £*, will be determinate ; the point 0 will
necessarily coincide with A. By a course of reasoning similar to that pursued in
article 140, the following equation will be easily obtained : —

, sin (z — a) R sin y sin ( A"D — 3") „
sin z R' sin b" sin (AD— fl'-f a) U '

It will be proper, therefore, to apply in this place all which has been explained in
articles 141, 142, if, only, we put a — 0, and b is determined by equation 12,

H'/*' fi 'y'

article 140, and the quantities z, r, -—, — ^, will be computed in the same manner
as before. Now as soon as z and the position of the point C' have become
known, it will be possible to assign the position of the great circle CO', its inter
section with the great circle A'B", that is the point C", and hence the arcs CC',
CO", C'C", or 2/", 2/', 2/. Lastly, from these will be had

_ n'r'sm2f „ nVsin 2/"

: ~~nsin2f' T ~ ri'smZf

n. Every thing we have just said can be applied to that case in which B"
coincides with A" or with the opposite point, if, only, all that refers to the first
place is exchanged with what relates to the third place.

III. But it is necessary to treat a little differently the case in which B' coin
cides with A' or with the opposite point. There the point C' will coincide with
A' ; /, e, e" and the points D, D", B*, will be indeterminate : on the other hand,
the intersection of the great circle BB" with the ecliptic,f the longitude of which

t More generally, with the great circle AA" : but for the sake of brevity we are now considering
that case only where the ecliptic is taken as the fundamental plane.

SECT. 1.] THREE COMPLETE OBSERVATIONS. 231

may be put equal to I' -\- n, may be determined. By reasonings analogous to
those which have been developed in article 140, will be obtained the equation

„_ R sin S sin (A'D — 5") , / , sin n \ "

~ H '">'— rf ~\ H T R' sin V'—l' — n ~"~ n '

Let us designate the coefficient of n, which agrees with a, article 140, by the
same symbol a, and the coefficient of n'r' by ft : a may be here also determined
by the formula

.g sin (*'+« — Q
K' sin V'—l'—n

"We have, therefore,

Q = an

which equation combined with these,

P = ^

produces

whence we shall be able to get /, unless, indeed, we should have ft = 0, in which
case nothing else would follow from it except P ==. — a. Further, although we
might not have ,'9 = 0 (when we should have the third case to be considered in
the following article), still ft will always be a very small quantity, and therefore
P will necessarily differ but little from — a : hence it is evident that the deter
mination of the coefficient

P+a

is very uncertain, and that /, therefore, is not determinable with any accuracy.
Moreover, we shall have

«V_ _P+« »y_ P-\-a.
~n~'' (J ' n" ' ~JP~'~

after this, the following equations will be easily developed in the same manner as
in article 143,

232 DETERMINATION OF AN ORBIT FROM [BOOK II.

„ . w. n'/sinv . ,,, ,,

'"

r sin (C - A D'} = r"P sin (?-

from the combination of which with equations VIII. and IX. of article 143, the
quantities r, C, r", £" can be determined. The remaining processes bf the calcula
tion will agree with those previously described.

162.

In the second case, where B" coincides with B, D" will also coincide with them
or with the opposite point. Accordingly, we shall have AD1 — d and A" I? — d"
either equal to 0 or 180° : whence, from the equations of article 143, we obtain

n'r' _ I sins'^ffsinii

n — sin E sin (z -(- A'D — ff) '

n'r1 sin «' R' sin 5"

»" '" — sine" sin (z + ArD' — if) '
R sin d sin e" sin (s + yl'Z>" — d') = P7T sin d" sin e sin (z + vl'Z> — d').

Hence it is evident that z is dcterminable by P alone, independently of Q, (un
less it should happen that A'D" — A'D, or = ^l'Z> + 180°, when we should have
the third case) : 2 being found, r will also be known, and hence, by means of
the values of the quantities

n'r' n'r1 , n , n"

— , —„-, also — and — :

n ' n" n n' '

and, lastly, from this also

Evidently, therefore, P and Q cannot be considered as data independent of each
other, but they will either supply a single datum only, or inconsistent data. The
positions of the points O, C" will in this case remain arbitrary, if they are only
taken in the same great circle as O'.

In the third case, where A', B, B1, B", lie in the same great circle, D and D" will
coincide with the points B", B, respectively, or with the opposite points : hence is

SECT. 1.] THREE COMPLETE OBSERVATIONS. 233

obtained from the combination of equations VII., VIII., IX., article 143,

p_ 7? sin 5 sine" _ Ssm(l' — l)
~ R" sin 8" sin* lt"l^ (F^l7) '

In this case, therefore, the value of P is had from the data of the problem, and,
therefore, the positions of the points 0, C', C", will remain indeterminate.

163.

The method which we have fully explained from article 136 forwards, is prin
cipally suited to the first determination of a wholly imknown orbit : still it is em
ployed with equally great success, where the object is the correction of an orbit
already approximately known by means of three observations however distant
from each other. But in such a case it will be convenient to change some things.
When, for example, the observations embrace a very great heliocentric motion, it

nff

will no longer be admissible to consider — and 66" as approximate values of the
quantities P, Q : but much more exact values will be obtained from the very
nearly known elements. Accordingly, the heliocentric places in orbit for the
three times of observation will be computed roughly by means of these elements,
whence, denoting the true anomalies by v, v', v", the radii vectores by r, r, r", the
semi-parameter by p, the following approximate values will result : —

p _ r sin (v ' — v) ,, 4 r'* sin ^ (vr — v) sin ^ («/' — v')

~r" sin (»"—»')' y~ p cos ± (v" — v) '

With these, therefore, the first hypothesis will be constructed, and with them, a
little changed at pleasure, the second and third : it would be of no advantage
to adopt P' and Q1 for the new values, since we are no longer at liberty to sup
pose that these values come out more exact. For this reason all three of the
hypotheses can be most conveniently despatched at the same time: the fourth will
then be formed according to the precepts of article 120. Finally, we shall not
object, if any person thinks that some one of the ten methods explained in arti
cles 124-129 is, if not more, at least almost equally expeditious, and prefers to

use it.

30

SECOND SECTION.

DETERMINATION OF AN ORBIT PROM FOUR OBSERVATIONS, OF WHICH TWO

ONLY ARE COMPLETE.

164.

WE have already, in the beginning of the second book (article 115), stated
that the use of the problem treated at length in the preceding section is lim
ited to those orbits of which the inclination is neither nothing, nor very small,
and that the determination of orbits slightly inclined must necessarily be based
on four observations. , But four complete observations, since they are equivalent
to eight equations, and the number of the unknown quantities amounts only to
six, would render the problem more than determinate : on which account it will
be necessary to set aside from two observations the latitudes (or declinations),
that the remaining data may be exactly satisfied. Thus a problem arises to
which this section will be devoted : but the solution we shall here give will ex
tend not only to orbits slightly inclined, but can be applied also with equal suc
cess to orbits, of any inclination however great. Here also, as in the problem of
the preceding section, it is necessary to separate the case, in which the approxi
mate dimensions of the orbit are already known, from the first determination
of a wholly unknown orbit : we will begin with the former.

165.

The simplest method of adjusting a known orbit to satisfy four observations
appears to be this. Let x, y, be the approximate distances of the heavenly body
from the earth in two complete observations : by means of these the correspond
ing heliocentric places may be computed, and hence the elements; after this,
(234)

SECT. 2.] DETERMINATION OF AN ORBIT. 235

from these elements the geocentric longitudes or right ascensions for the two
remaining observations may be computed. If these happen to agree with the
observations, the elements will require no further correction: but if not, the
differences X, T, will be noted, and the same calculation will be repeated twice,
the values of x, y being a little changed. Thus will be obtained three systems
of values of the quantities x, y, and of the differences X, Y, whence, according
to the precepts of article 120, will be obtained the corrected values of the quan
tities x, y, to which will correspond the values X= 0, Y= 0. From a similar
calculation based on this fourth system elements will be found, by which all four
observations will be correctly represented.

If it is in your power to choose, it will be best to retain those observations
complete from which the situation of the orbit can be determined with the great
est precision, therefore the two extreme observations, when they embrace a helio
centric motion of 90° or less. But if they do not possess equal accuracy, you
will set aside the latitudes or declinations of those you may suspect to be the
less accurate.

166.

Such places will necessarily be used for the first determination of an entirely
unknown orbit from four observations, as include a heliocentric motion not too
great ; for otherwise we should be without the aids for forming conveniently the
first approximation. The method which we shall give directly admits of such
extensive application, that observations comprehending a heliocentric motion of
30° or 40° may be used without hesitation, provided, only, the distances from the
sun are not too unequal : where there is a choice, it will be best to take the
intervals of the times between the first and second, the second and third, the
third and fourth but little removed from equality. But it will not be necessary
to be very particular in regard to this, as the annexed example will show, in
which the intervals of the times are 48, 55, and 59 days, and the heliocentric
motion more than 50°.

Moreover, our solution requires that the second and third observations be
complete, and, therefore, the latitudes or declinations in the extreme observations

236 DETERMINATION OF AN OKBIT FROM FOUR OBSERVATIONS, [BuoK II.

are neglected. We have, indeed, shown above that, for the sake of accuracy, it is
generally better that the elements be adapted to two extreme complete observa
tions, and to the longitudes or right ascensions of the intermediate ones ; never
theless, we shall not regret having lost this advantage in the first determination
of the orbit, because the most rapid approximation is by far the most important,
and the loss, which affects chiefly the longitude of the node and the inclina
tion of the orbit, and hardly, in a sensible degree, the other elements, can after
wards easily be remedied.

We will, for the sake of brevity, so arrange the explanation of the method,
as to refer all the places to the ecliptic, and, therefore, we will suppose four longi
tudes and two latitudes to be given : but yet, as we take into account the latitude
of the earth in our formulas, they can easily be transferred to the case in which
the equator is taken as the fundamental plane, provided that right ascensions and
declinations are substituted in the place of longitudes and latitudes.

Finally, all that we have stated in the preceding section with respect to nuta
tion, precession, and parallax, and also aberration, applies as well here : unless,
therefore, the approximate distances from the earth are otherwise known, so that
method I., article 118, can be employed, the observed places will in the beginning
be freed from the aberration of the fixed stars only, and the times will be cor
rected as soon as the approximate determination of the distances is obtained in
the course of the calculation, as will appear more clearly in the sequel.

167.

We preface the explanation of the solution with a list of the principal sym
bols. We will make

t, t', t", t'", the times of the four observations,

a, a', a", a"', the geocentric longitudes of the heavenly body,

(1, /?', ft", p'", their latitudes,

r, r, r", r", the distances from the sun,

(), (>', (/', (>'", the distances from the earth,

/, I', I", I'", the heliocentric longitudes of the earth,

SECT. 2.] OF WHICH TWO ONLY ARE COMPLETE. 237

B, B', B", B'", the heliocentric latitudes of the earth,
R, R', R", R'", the distances of the earth from the sun,

(wOl), (n 12), (n 23), (H 02), (H 13), the duplicate areas of the triangles which
are contained between the sun and the first and second places of the heavenly
body, the second and third, the third and fourth, the first and third, the second
and fourth respectively; (rj 01), (vj 12), (17 23) the quotients arising from the
division of the areas i (n 01), i (n 12), i (n 23), by the areas of the correspond
ing sectors ;

,_0L12) ,,_(n!2)
~ ~(n23)'

v, v', v", v'", the longitudes of the heavenly body in orbit reckoned from an arbi
trary point. Lastly, for the second and third observations, we will denote the
heliocentric places of the earth in the celestial sphere by A', A", the geocentric
places of the heavenly body by B', B", and its heliocentric places by C', C".

These things being understood, the first step will consist, exactly as in the
problem of the preceding section (article 136), in the determination of the posi
tions of the great circles AC'B', A" C"B", the inclinations of which to the eclip
tic we denote by /, y": the determination of the arcs A'£'= d', A'B"= 3" will be
connected at the same time with this calculation. Hence we shall evidently have

/ = v (eY + 2 9'R cos s' + Rtf}

r"= y/ (e'V 4- 2 Q"R" cos d" -f R"R"\
or by putting ^ -f R cos 8' — of, ()" -J- R" cos d" = x", R sin d' = d, R" sin d" — a",

r' = \l (of of + a'a')

168.

By combining equations 1 and 2, article 112, the following equations in sym
bols of the present discussion are produced : —

0 = (n 12) R cos B sin (I— a] — (n 02) (9' cos ? sin (of— a) -f- .R'cos.B'sin (f—a))
-f (n 01) Xv" cos (1" sin (a" — a) + R" cos £" sin (/" — a)),

238 DETERMINATION OF AN ORBIT FROM FOUR OBSERVATIONS, [Book II.

0 = (» 23) (</ cos p sin (a'"— a'} -f R cos B sin (a'"— J'))
- (n 13) (^"cos /?"sin (a'"— a") -f 7?" cos B" sin (a'"— /" ))

-f (n 12) 72"' cos £"' sin (a'" — I'"}.
These equations, by putting

B' cos B' sin (/' — a) r,/ «,, 7,
„, — ,-f -- r2- - It COS 0 = I'

cos p sin (a — a)

"cousin («'" — «")

cos sn « — TV x,

=*'

-

cos j?' sin (or — a)

B cos 5 sin (^ — a) _ .
cousin («» — «) ~ ^ '

R"co&H"sm(af" — I'") _
~~

~~^^8in(«"' — a')
cos ^ sin (a' — a) _

_ . „
~

cos f sin («"—«) r:

cos p sin («'" — g")_ „
cos (3' sin («'" — «') " '

and all the reductions being properly made, are transformed into the following:

— " I "I

1+

1+

or, by putting besides,
into these,

SECT. 2.] OF WHICH TWO ONLY ARE COMPLETE. 239

With the aid of these two equations x' and x" can be determined from a', 5', c', tf,
Q'. a", b", c", d", Q". If, indeed, x' or x" should be eliminated from them, we should
obtain an equation of a very high order : but still the values of the unknown
quantities x', x", will be deduced quickly enough from these equations by indi
rect methods without any change of form. Generally approximate values of
the unknown quantities result if, at first, Q' and Q" are neglected ; thus : —

j _<!'+ d" (V -f- Q -f- d'd"V
1—d'd" '

„ _ c' 4- d' (V + c") -f d'd'V
x —~ l — d'd"

But as soon as the approximate value of either unknown quantity is obtained,
values exactly satisfying the equations will be very easily found. Let, for ex
ample, £' be an approximate value of x', which being substituted in equation I.,
there results x" = £" ; in the same manner from x" = £" being substituted in
equation II., we may have x' = X.' ' ; the same processes may be repeated by sub
stituting for x in I., another value £' -\- v', which may give x" = £" -(- v" ; this
value being substituted in H, may give x' = X' -\- N'. Thereupon the corrected
value of x will be

t' [ IS — •*• )r S •" — -"• y

and the corrected value of a/',

£" + jy-v •

If it is thought worth while, the same processes will be repeated with the cor
rected value of x' and another one slightly changed, until values of x', x" satisfy
ing the equations I., II. exactly, shall have been found. Besides, means will not
be wanting even to the moderately versed analyst of abridging the calculation.

In these operations the irrational quantities (x'x' -\- a' a'}'1, (x"x" -\-a"a"} , are
conveniently calculated by introducing the arcs z', /', of which the tangents are

240 DETERMINATION OF AN ORBIT FROM FOUft OBSERVATIONS, [BOOK II.

respectively ^, ^,, whence come

These auxiliary arcs, which must be taken between 0° and 180°, in order that
/, r", may come out positive will, manifestly, be identical with the arcs C'B', C"B",
whence it is evident that in this way not only / and /', but also the situation of
the points C', C", are known.

This determination of the quantities at, x" requires a', a", b', b", c, c", d', tf', Q',
Q" to be known, the first four of which quantities are, in fact, had from the data
of the problem, but the four following depend on P , P". Now the quantities
P1, P", Q', Q", cannot yet be exactly determined j but yet, since

TTT iy _'—'<* 01)

-7=7PF)>

TV P"— f~f
-"

V. Q' -- - } Jck (f--f) (f — if) ^ (]? oi) (, 12) cos 1 (v1 — v) cos £ («"— ») cos 1 (i* — v7] '

VI. Q" -- = J kk (f— t)(t"—t"}7X

7X (7 12) (, 23) cos 1 (J— v') cosi (v"' - v') cos i («"'

the approximate values are immediately at hand,

" f—<

Q1 = i Jck (f — t) (f — if), Q!' =tkk(f— t') (f — i"),
on which the first calculation will be based.

169.

The calculation of the preceding article being completed, it will be necessary
first to determine the arc C' C". Which may be most conveniently done, if, as
in article 137, the intersection D of the great circles A C'B', A'C"B", and their
mutual inclination « shall have been previously determined: after this, will be
found from e, C'D = z -f- B'D, and C"D = z' -f B"D, by the same formulas

SKOT. 2.] OF WHICH TWO ONLY ARE COMPLETE. 241

which we have given in article 144, not only C'C" = v" — v', but also the angles
(u, u",) at which the great circles Alt', A'B", cut the great circle C'C".

After the arc v" — v' has been found, v' — v, and r will be obtained from a
combination of the equations

P' /sin(j/' —

~ —

• , i // /x l + P'

rsm(v — v + v" — v'}= ^~

14- —

-TT*

and in the same manner, /" and v'" — v" from a combination of these : —

sn

All the numbers found in this manner would be accurate if we could set out in
the beginning from true values of P', Q', I*", Q" : and then the position of the
plane of the orbit might be determined in the same manner as in article 149,
either from A' ' C, u' and /, or from A"C", u" and y"; and the dimensions of the
orbit either from r, r", t', t", and v" — v, or, which is more exact, from r, r'", t,
f, v'" — v. But in the first calculation we will pass by all these things, and will
direct our attention chiefly to obtaining the most approximate values of P', P",
(X, Q". We shall reach this end, if by the method explained in 88 and the fol
lowing articles,

from r, r, v' — v, f — t we obtain (rj 01)

« r',r",v" — v',t" — t' « (ij!2)

« r",r'",v"'—v",t'"— t" * (17 23).

We shall substitute these quantities, and also the values of r, /, r", /", cos k (v' — ?'),
etc., in formulas III.- VI., whence the values of P1, Q', P", Q" will result much
more exact than those on which the first hypothesis had been constructed. With
these, accordingly, the second hypothesis will be formed, which, if it is carried to
a conclusion exactly in the same manner as the first, will furnish much more
exact values of P1, Q', P", Q", and thus lead to the third hypothesis. These
processes will continue to be repeated, until the values of P', Q', P", Q" seem to

31

242 DETERMINATION OF AN ORBIT FROM FOUR OBSERVATIONS, [BOOK II.

require no further correction, how to judge correctly of which, frequent practice
will in time show. When the heliocentric motion is small, the first hypothesis
generally supplies those values with sufficient accuracy : but if the motion in
cludes a greater arc, if, moreover, the intervals of the times are very unequal,
hypotheses several times repeated will be wanted ; but in such a case the first
hypotheses do not demand great preciseness of calculation. Finally, in the last
hypothesis, the elements themselves will be determined as we have just indicated.

170.

It will be necessary in the first hypothesis to make use of the times /, t', t", t'",
uncorrected, because the distances from the earth cannot yet be computed : as
soon, however, as the approximate values of the quantities x', x" have become
known, we shall be able to determine also those distances approximately. But
yet, since the formulas for Q and (>'" come out here a little more complicated, it
will be well to put off the computation of the correction of the times until the
values of the distances ha,ve become correct enough to render a repetition of the
work unnecessary. On which account it will be expedient to base this operation
on those values of the quantities x', x", to which the last hypothesis but one leads,
so that the last hypothesis may start with corrected values of the times and of
the quantities P1, P", Q', Q". The following are the formulas to be employed
for this purpose : —

vn. </ = /—
vni. Q"=3f— i

IX. ^008/9 = — R cos B cos (a — /)

ttt' — a\ -I- tf cos J? cos (I'— a)}

-p, ((>"cos /3" cos (a"— a) -f Kr cos B" cos (*"— a)),

X. <> sin /J = — R sin B 4- _1+Z1 (,/ sin ft' -4- K sin J?)

^(1 + ^)
i r'8?y

— p ((/'sin jT+JZ" sin #')»

SE<JT. 2.] OF WHICH TWO ONLY ARE coMrLETE. 243

XI. ?'" cos $'"• = — R'" cos B"' cos («'" —I'"}

H 1+P"^y (?" cos 0" cos («'" — «")+ ,5" cos ,5" cos (a'" — I"])

**(!+$)

- jL (<?' cos 0' cos (a'" — a') + # cos £' cos (a'" — I' )),

XII. o'" sin |3'" = — #" sin B" -4- 1 + P" =, fo" sin 0" 4- #' sin B"}

*"(! + £)

-•^(e'sin/S'-f JZ'sin.ff').

The formulas IX.-XII. are derived without difficulty from equations 1, 2, 3, article
112, if, merely, the symbols there used are properly converted into those we here
employ. The formulas will evidently come out much more simple if B, B', B"
vanish. Not only (), but also /? will follow from the combination of the formulas
IX. and X., and, in the same manner, besides /", also ft'" from XI. and XII. : the
values of these, compared with the observed latitudes (not entering into the
calculation), if they have been given, will show with what degree of accuracy
the extreme latitudes may be represented by elements adapted to the six remain
ing data.

171.

A suitable example for the illustration of this investigation is taken from Vesta,
which, of all the most recently discovered planets, has the least inclination to
the ecliptic.* We select the following observations made at Bremen, Paris,
Lilienthal, and Milan, by the illustrious astronomers OLBERS, BOUVARD, BESSEL, and
ORIANI : —

* Nevertheless this inclination is still great enough to admit of a sufficiently safe and accurate deter
mination of the orbit based upon three observations: in fact the first elements which had been derived
in this way from observations only 19 days distant from each other (see TON ZACH'S Monatliche Cor-
respondenz, Vol. XV. p. 595), approach nearly to those which were here deduced from four observa
tions, removed from each other 162 days.

244

DETERMINATION OF AN OKBIT FROM FOUR OBSERVATIONS, [BOOK II.

Mean time of place of observation.

Right Ascension.

Declination.

1807, March 30, 12* 33m 17'
May 17, 8 16 5
July 11, 10 30 19
Sept. 8, 7 22 16

183° 52' 40".8
178 36 42.3
189 49 7.7
212 50 3.4

11° 54'27".ON.
11 39 46.8
3 9 10 .IN.
8 38 17 .OS.

We find for the same times from the tables of the sun,

1

Lonpitude of the Sun
fromapp. Equinox.

Nutation.

Distance from
the Earth.

Latitude of
the Sun.

Apparent obliquity
of the Ecliptic.

March 30

9° 21' 59".5

-16.8

0.9996448

+ 0".23

23° 27' 50".82

May 17

55 56 20 .0

-16.2

1.0119789

— 0.63

49 .83

July 11

108 34 53 .3

-17.3

1.0165795

— 0.46

49 .19

Sept. 8

165 8 57 .1

-16.7

1.0067421

+ 0.29

23 27 49 .26

The observed places of the planets have, the apparent obliquity of the eclip
tic being used, been converted into longitudes and latitudes, been freed from
nutation and aberration of the fixed stars, and, lastly, reduced, the precession
being subtracted, to the beginning of the year 1807 ; the fictitious places of the
earth have then been derived from the places of the sun by the precepts of arti
cle 72 (in order to take account of the parallax), and the longitudes transferred
to the same epoch by subtracting the nutation and precession ; finally, the times
have been counted from the beginning of the year and reduced to the meridian
of Paris. In this manner have been obtained the following numbers : —

« , «, a, a

i', r,

89.505162
178° 43' 38".87
12 27 6 .16
189 21 33 .71

9.9997990

Hence we deduce

y'=168032'41".34, d' — 62° 23' 4".88,
y"=173 5 15 .68, d"= 100 45 1 .40,

137.344502

174° 1'30".08

10 8 7 .80

235 56 0 .63

0.0051376

192.419502
187°45'42".23

6 47 25 .51
288 35 20 .32
0.0071739

251.288102
213°34'15".63

4 20 21 .63

345 9 18 .69

0.0030625

log a' = 9.9526104,
log a" =9.9994839,

SECT. 2.] OF WHICH TWO ONLY ARE COMPLETE. 245

b' = — 11.009449, x' = — 1.083306, log A = 0.0728800, log/*' = 9.7139702w
j" = _ 2.082036, x* = + 6.322006, log Jl'"= 0.0798512ra log/*"= 9.8387061

MD= 37°17'51".50, A"D = 89° 24' 11".84, « = 9°5'5".48

£'D = — 25 513.38, #7) = — 11 20 49 .56.

These preliminary calculations completed, we enter upon the first hypothesis.
From the intervals of the times we obtain

log & (f — t] — 9.9153666
log k (t" — 0=9.9765359
log k (t"f — O = 0.0054651,
and hence the first approximate values

log P' = 0.06117, log (1 -f P') — 0.33269, log Qt = 9.59087
logP"= 9.97107, log (1 + P") — 0.28681, log Q"= 9.67997,
hence, further,

c' = — 7.68361, log d' = 0.04666 n
c"= + 2.20771, logrf"= 0.12552.

With these values the following solution of equations I., II., is obtained, after a
few trials : —

x' = 2.04856, z' = 23° 38' 17", log r' = 0.34951
x"= 1.95745, s"=27 2 0, logr"^ 0.34194.
From 0', /' and e, we get

C'C" = i/' — i/ = ir r 5":

hence v' — v, r, v'" — v", r", will be determinable by the following equations : —
log r sin (v' — v}= 9.74942, log r sin (v' — v + 17° 7' 5") = 0.07500
log/-'" sm(v'"—v")= 9.84729, log/" sin (z/"— v"+ 17 7 5") = 0.10733
whence we derive

v' __ v — 14° 14' 32", log r = 0.35865
v'"— v"= 18 48 33, log/"=: 0.33887.
Lastly, is found

log (H 01) = 0.00426, log (n 12) = 0.00599, log (n 23) = 0.00711,
and hence the corrected values of P', P", Q', Q",

246 DETERMINATION OF AN ORBIT FROM FOUR OBSERVATIONS, [BOOK II.

log P' — 0.05944, log Q' = 9.60374,
log P" — 9.97219, log Q"= 9.69581,

upon which the second hypothesis will be constructed. The principal results of this
are as follows : —

c' — — 7.67820, log d' = 0.045736 n
c"= + 2.21061, logrf"= 0.126054
of = 2.03308, z' = 23° 47' 54", log / = 0.346747,
af'= 1.94290, z"=27 12 25, log r" = 0.339373
C'C"=v" — v =\T 8' 0"
v' — v = 14° 21' 36", log r = 0.354687
v'"—v"=18 5043, logr'" = 0.334564

log (n 01) = 0.004359, log (n 12) = 0.006102, log (» 23) = 0.007280.
Hence result newly corrected values of F, P", Q', Q",

log P1 == 0.059426, log Q' = 9.604749
log P" = 9.972249, log Q" = 9.697564,

from which, if we proceed to the third hypothesis, the following numbers result : -
c' =--7.67815, logrf == 0.045729 n
c" = -- + 2.21076, log d"= 0.126082
x' = 2.03255, 0' = 23° 48' 14", log / = 0.346653
z" = 1.94235, z"=27 12 49, log r"= 0.339276
C'0" — if'—ff=lT 8' 4"
v' — v= 14° 21' 49", logr =0.354522
v'"—v"=l% 51 7, log/" =0.334290

log (n 01) = 0.004363, log (n 12) = 0.006106, log (n 23) = 0.007290.
If now the distances from the earth are computed according to the precepts of
the preceding article, there appears : —

(/ = 1.5635, 9" =2.1319

log Q cos 0 = 0.09876 log (>'" cos /?'" = 0.42842

log Q sin ft = 9.44252 log <>"' sin /?'" = 9.30905

0 = 12° 26' 40" p'" = 4° 20' 39"

log ? = 0.10909 log <;/" = 0.42967.

SECTt 2.] OF WHICH TWO ONLY ARE COMPLETE. 247

Hence are found

Corrections of the Times.

Corrected Times.

I.

0.007335

89.497827

n.

0.008921

135.335581

IH.

0.012165

192.407337

IV.

0.015346

251.272756

whence will result newly corrected values of the quantities f, P", Q', Q",

log P' — 0.059415, log Q' = 9.604782,
logP"= 9.972253, log Q" = 9.697687.

Finally, if the fourth hypothesis is formed with these new values, the following
numbers are obtained : —

c' = — 7.678116, log cf = 0.045723

c"= + 2.210773, log rf"= 0.126084

of = 2.032473, / = 23° 48' 16". 7, log / = 0.346638

x"= 1.942281, 0"= 27 12 51 .7, log /'= 0.339263

i/'—i/ = ir 8' 5".l, i («"+ iO == 176° 7'50".5, * («"— w') = 4° 33'23".6

v' — v= 14 21 51 .9, log r = 0.354503

v'"— t/' =18 51 9 .5, log/"= 0.334263

These numbers differ so little from those which the third hypothesis furnished,
that we may now safely proceed to the determination of the elements. In
the first place we get out the position of the plane of the orbit. The inclina
tion of the orbit 7° 8' 14".8 is found by the precepts of article 149 from /, u',
and A'C' = d' — z, also the longitude of the ascending node 103° 16'37".2, the
argument of the latitude in the second observation 94° 36' 4". 9, and, there
fore, the longitude in orbit 197° 52' 42".l ; in the same manner, from y", u", and
A"C" = 3"—J', are derived the inclination of the orbit = 7° 8'14".8, the longi
tude of the ascending node 103° 16' 37".5, the argument of the latitude in the
third observation 111°44'9".7, and therefore the longitude in orbit 215° 0'47".2.
Hence the longitude in orbit for the first observation will be 183° 30' 50".2, for
the fourth 233° 51' 56".7. If now the dimensions of the orbit are determined
from f" — t, r, r", and v'" — v = 50° 21' 6".5, we shall have,

248 DETERMINATION OF AN ORBIT FROM FOUR OBSERVATIONS. [BoOK II.

True anomaly for the first place 293° 33' 43".7

True anomaly for the fourth place 343 54 50 .2

Hence the longitude of the perihelion 249 57 6 .5

Mean anomaly for the first place 302 33 32 .6

Mean anomaly for the fourth place 346 32 25 .2

Mean daily sidereal motion 978".7216

Mean anomaly for the beginning of the year 1807 . 278 13 39 .1

Mean longitude for the same epoch 168 10 45 .6

Angle of eccentricity y 5 2 58 .1

Logarithm of the semi-axis major 0.372898

If the geocentric places of the planet are computed from these elements
for the corrected times t, t', t", t"', the four longitudes agree with a, a', a", a'", and
the two intermediate latitudes with ft', ft", to the tenth of a second ; but the
extreme latitudes come out 12° 26' 43".7 and 4° 20' 40".l. The former in error
22".4 in defect, the latter 18".5 in excess. But yet, if the inclination of the
orbit is only increased 6", and the longitude of the node is diminished 4' 40", the
other elements remaining the same, the errors distributed among all the latitudes
will be reduced to a few seconds, and the longitudes will only be affected by the
smallest errors, which will themselves be almost reduced to nothing, if, in addition.
2" is taken from the epoch of the longitude.

THIRD SECTION.

THE DETERMINATION OF AN ORBIT SATISFYING AS NEARLY AS POSSIBLE ANY
NUMBER OF OBSERVATIONS WHATEVER.

172.

IF the astronomical observations and other quantities, on which the computa
tion of orbits is based, were absolutely correct, the elements also, whether deduced
from three or four observations, would be strictly accurate (so far indeed as the
motion is supposed to take place exactly according to the laws of KEPLER), and.
therefore, if other observations were used, they might be confirmed, but not cor
rected. But since all our measurements and observations are nothing more than
approximations to the truth, the same must be true of all calculations resting
upon them, and the highest aim of all computations made concerning concrete
phenomena must be to approximate, as nearly as practicable, to the truth. But
this can be accomplished in no other way than by a suitable combination of
more observations than the number absolutely requisite for the determination of
the unknown quantities. This problem can only be properly undertaken when
an approximate knowledge of the orbit has been already attained, which is after
wards to be corrected so as to satisfy all the observations in the most accurate
manner possible.

It then can only be worth while to aim at the highest accuracy, when the
final correction is to be given to the orbit to be determined. But as long as it
appears probable that new observations will give rise to new corrections, it will
be convenient to relax more or less, as the case may be, from extreme precision,
if in this way the length of the computations can be considerably diminished.
We will endeavor to meet both cases.

32 (249)

250 DETERMINATION OF AN ORBIT FROM [BOOK II.

173.

In the first place, it is of the greatest importance, that the several positions of
the heavenly body on which it is proposed to base the orbit, should not be
taken from single observations, but, if possible, from several so combined that the
accidental errors might, as far as may be, mutually destroy each other. Obser
vations, for example, such as are distant from each other by an interval of a few
days, — or by so much, in some cases, as an interval of fifteen or twenty days, —
are not to be used in the calculation as so many different positions, but it would
be better to derive from them a single place, which would be, as it were, a mean
among all, admitting, therefore, much greater accuracy than single observations
considered separately. This process is based on the following principles.

The geocentric places of a heavenly body computed from approximate ele
ments ought to differ very little from the true places, and the differences between
the former and latter should change very slowly, so that for an interval of a
few days they can be regarded as nearly constant, or, at least, the changes may
be regarded as proportional to the times. If, accordingly, the observations should
be regarded as free from all error, the differences between the observed places
corresponding to the times t, t', f, t'", and those which have been computed from
the elements, that is, the differences between the observed and the computed
longitudes and latitudes, or right ascensions and declinations, would be quanti
ties either sensibly equal, or, at least, uniformly and very slowly increasing or de
creasing. Let, for example, the observed right ascensions a, «', a", a", etc., cor
respond to those times, and let a -\- $, a' -\- <$', a" -\- d", a'" -\- d'", etc., be the
computed ones ; then the differences d, 8', 8", 8'", etc. will differ from the true
deviations of the elements so far only as the observations themselves are errone
ous : if, therefore, these deviations can be regarded as constant for all these ob
servations, the quantities d, d', d", 8'", etc. will furnish as many different determi
nations of the same quantity, for the correct value of which it will be proper to
take the arithmetical mean between those determinations, so far, of course, as
there is no reason for preferring one to the other. But if it seems that the same
degree of accuracy cannot be attributed to the several observations, let us assume

SECT. 3.] ANY NUMBER OF OBSERVATIONS. 251

that the degree of accuracy in each may be considered proportional to the num
bers e, e, e", e", etc. respectively, that is, that errors reciprocally proportional to
these numbers could have been made in the observations with equal facility;
then, according to the principles to be propounded below, the most probable
mean value will no longer be the simple arithmetical mean, but

ee 8 -\- e'e'8 -f e"e"8' -\- e'"e'"d'" -f- etc.
~ee+ ~e'e'~+ e"e" -\-e'"e'" -f- etc. '

Putting now this mean value equal to //, we can assume for the true right ascen
sions, a -\- d — J, of -j- ()''- — _/, ft"- j- d" - — .J, a'"- j- d'"- — A, respectively, and then
it will be arbitrary, which we use in the calculation. But if either the observa
tions are distant from each other by too great an interval of tune, or if suffi
ciently approximate elements of the orbit are not yet known, so that it would
not be admissible to regard their deviations as constant for all the observations, it
will readily be perceived, that no other difference arises from this except that the
mean deviation thus found cannot be regarded as common to all the observa
tions, but is to be referred to some intermediate time, which must be derived from
the individual times in the same manner as A from the corresponding deviations,
and therefore generally to the time

eet + e'eY + e'W -}- e'"e'"t"> + etc.
~~e e -f e'e' + e V + e'"e'" + etc. '

Consequently, if we desire the greatest accuracy, it will be necessary to compute
the geocentric place from the elements for the same time, and afterwards to free
it from the mean error A, in order that the most accurate position may be ob
tained. But it will in general be abundantly sufficient if the mean error is
referred to the observation nearest to the mean time. What we have said here
of right ascensions, applies equally to declinations, or, if it is desired, to longitudes
and latitudes : however, it will always be better to compare the right ascensions
and declinations computed from the elements immediately 'with those observed ;
for thus we not only gain a much more expeditious calculation, especially if we
make use of the methods explained in articles 53-60, but this method has the
additional advantage, that the incomplete observations can also be made use of;
and besides, if every thing should be referred to longitudes and latitudes, there

252 DETERMINATION OF AN ORBIT FROM [BOOK II.

would be cause to fear lest an observation made correctly in right ascension,
but badly in declination (or the opposite), should be vitiated in respect to both
longitude and latitude, and thus become Avholly useless. The degree of precision
to be assigned to the mean found as above will be, according to the principles to
be explained hereafter,

^ (ee 4. e'e> + e"e" + /"/" + etc.) ;

so that four or nine equally exact observations are required, if the mean is to
possess a double or triple accuracy.

174.

If the orbit of a heavenly body has been determined according to the methods
given in the preceding sections from three or four geocentric positions, each one
of which has been derived, according to the precepts of the preceding article,
from a great many observations, that orbit will hold a mean, as it were, among
all these observations ; and in the differences between the observed and computed
places there will remain no trace of any law, which it would be possible to re
move or sensibly diminish by a correction of the elements. Now, when the whole
number of observations does not embrace too great an interval of time, the best
agreement of the elements with all the observations can be obtained, if only
three or four normal positions are judiciously selected. How much advantage
we shall derive from this method in determining the orbits of new planets or
comets, the observations of which do not yet embrace a period of more than
one year, will depend on the nature of the case. When, accordingly, the orbit
to be determined is inclined at a considerable angle to the ecliptic, it will be
in general based upon three observations, which we shall take as remote from
each other as possible : but if in this way we should meet with any one of the
cases excluded above (articles 160-162), or if the inclination of the orbit should
seem too small, we shall prefer the determination from four positions, which, also,
we shall take as remote as possible from each other.

But when we have a longer series of observations, embracing several years,
more normal positions can be derived from them ; on which account, we should

SECT. 3.] ANY NUMBER OF OBSERVATIONS. 253

not insure the greatest accuracy, if we were to select three or four positions only
for the determination of the orbit, and neglect all the rest. But in such a case,
if it is proposed to aim at the greatest precision, we shall take care to collect
and employ the greatest possible number of accurate places. Then, of course,
more data will exist than are required for the determination of the unknown
quantities : but all these data will be liable to errors, however small, so that it
will generally be impossible to satisfy all perfectly. Now as no reason exists,
why, from among those data, we should consider any six as absolutely exact, but
since we must assume, rather, upon the principles of probability, that greater or
less errors are equally possible in all, promiscuously ; since, moreover, generally
speaking, small errors oftener occur than large ones ; it is evident, that an orbit
which, while it satisfies precisely the six data, deviates more or less from the
others, must be regarded as less consistent with the principles of the calculus of
probabilities, than one which, at the same time that it differs a little from those
six data, presents so much the better an agreement with the rest. The investiga
tion of an orbit having, strictly speaking, the maximum probability, will depend
upon a knowledge of the law according to which the probability of errors de
creases as the errors increase in magnitude : but that depends upon so many
vague and doubtful considerations — physiological included — which cannot be
subjected to calculation, that it is scarcely, and indeed less than scarcely, possible
to assign properly a law of this kind in any case of practical astronomy. Never
theless, an investigation of the connection between this law and the most prob
able orbit, which we will undertake in its utmost generality, is not to be regarded
as by any means a barren speculation.

175.

To this end let us leave our special problem, and enter upon a very general
discussion and one of the most fruitful in every application of the calculus to
natural philosophy. Let V, V, V", etc. be functions of the unknown quantities
p, q, r. s, etc., u, the number of those functions, v the number of the unknown
quantities ; and let us svippose that the values of the functions found by direct
observation are V = M, V = M', V" = M", etc. Generally speaking, the

254 DETERMINATION OF AX ORBIT FROM [BOOK II.

determination of the unknown quantities will constitute a problem, indetermi
nate, determinate, or more than determinate, according as p<^v, [i =v, or
/j > v* We shall confine ourselves here to the last case, in which, evidently, an
exact representation of all the observations would only be possible when they
were all absolutely free from error. And since this cannot, in the nature of
things, happen, every system of values of the unknown quantities p, q, r, s, etc.,
must be regarded as possible, which gives the values of the functions V — M,
V - M', V" — M", etc., within the limits of the possible errors of observation ;
this, however, is not to be understood to imply that each one of these systems
would possess an equal degree of probability.

Let us suppose, in the first place, the state of things in all the observations to
have been such, that there is no reason why we should suspect one to be less
exact than another, or that we are bound to regard errors of the same magnitude
as equally probable in all. Accordingly, the probability to be assigned to each
error A will be expressed by a function of A which we shall denote by (f A. Now
although we cannot precisely assign the form of this function, we can at least
affirm that its value should be a maximum for A = 0, equal, generally, for equal
opposite values of A, and should vanish, if, for A is taken the greatest error, or a
value greater than the greatest error: yd, therefore, would appropriately be re
ferred to the class of discontinuous functions, and if we undertake to substitute
any analytical function in the place of it for practical purposes, this must be of
such a form that it may converge to zero on both sides, asymptotically, as it were,
from A =• 0, so that beyond this limit it can be regarded as actually vanishing.
Moreover, the probability that an error lies between the limits A and A -(- d A
differing from each other by the infinitely small difference d A, will be expressed
by (pJdJ; hence the probability generally, that the error lies between D and

* If, in the third case, the functions V, V, V" should be of such a nature that [i -j- 1 — v of them,
or more, might be regarded as functions of the remainder, the problem would still be more than determi
nate with respect to these functions, but indeterminate with respect to the quantities p, q, r, s, etc. ; that
is to say, it would be impossible to determine the values of the latter, even if the values of the func
tions V, V, V", etc. should be given with absolute exactness : but we shall exclude this case from our
discussion.

SECT. 3.] ANY NUMBER OF OBSERVATIONS. 255

D', will be given by the integral / (f J.dJ extended from J = D to J = I/.
This integral taken from the greatest negative value of J to the greatest positive
value, of more .generally from z/ = — cc to // = -|- co must necessarily be equal
to unity. Supposing, therefore, any determinate system of the values of the
quantities p, q, r, s, etc., the probability that observation would give for V the
value M, will be expressed by y (M-- V), substituting in V for p, q, r, s, etc.,
their values ; in the same manner 9 (M'--V), (f (M"--V"\ etc. will express the .
probabilities that observation would give the values M', M", etc. of the func
tions V, V", etc. Wherefore, since we are authorized to regard all the observa
tions as events independent of each other, the product

(f(M—V) (f(M'—V) <f(M"—V") etc., =Sl

will express the expectation or probability that all those values will result to
gether from observation.

176.

Now in the same manner as, when any determinate values whatever of the
unknown quantities being taken, a determinate probability corresponds, previ
ous to observation, to any system of values of the functions V, V, V", etc.; so,
inversely, after determinate values of the functions have resulted from observa
tion, a determinate probability will belong to every system of values of the un
known quantities, from which the values of the functions could possibly have
resulted : for, evidently, those systems will be regarded as the more probable in
which the greater expectation had existed of the event which actually occurred.
The estimation of this probability rests upon the following theorem : —

If, any hypothesis H being made, the probability of any determinate event E is h, and
if, another hypothesis H' 'being made excluding the former and equally probable in itself, the
probability of the same event is h' : then I say, wlien the event E has actually occurred, that
the probability that H was the true hypothesis, is to the probability that H' was the true
hypothesis, as h to h'.

For demonstrating which let us suppose that, by a classification of all the cir
cumstances on which it depends whether, with II or II' or some other hypothesis,

256

DETERMINATION OF AN ORBIT FROM

[BOOK II.

the event E or some other event, should occur, a system of the different cases is
formed, each one of which cases is to be considered as equally probable in itself
(that is, as long as it is uncertain whether the event E, or some other, will occur),
and that these cases be so distributed,

that among them
may be found

iu which should be assumed
- the hypothesis

in such a mode as would give
occasion to the event.

m

H

E

n

H

different from E

m'

H'

E

n'

H'

different from E

m"

different from /Tand H'

E

n"

different from H and H'

different from E

Then we shall have

m

j •

m -\- n

moreover, before the event was known the probability of the hypothesis II was

m -\- n
m _|_ n_|_,n'_|_ w'_|_ m" _|_n">

but after the event is known, when the cases n, n, n" disappear from the number
of the possible cases, the probability of the same hypothesis will be

in the same way the probability of the hypothesis H' before and after the event,
respectively, will be expressed by

— ™' + n' and m'

i i " / i r~\ Ti i fr cm*-! / i 7/ •

tn — (— n — }— w* — f- n — j— w — j— w wz — j— ni -j— w

since, therefore, the same probability is assumed for the hypotheses H and If
before the event is known, we shall have

m -j- n = m' -\- nf,

whence the truth of the theorem is readily inferred.

Now, so far as we suppose that no other data exist for the determination of
the unknown quantities besides the observations V=M, V = M', V" = M",

SECT. 3.] ANY NUMBER OF OBSERVATIONS. 257

etc., and, therefore, that all systems of values of these unknown quantities were
equally probable previous to the observations, the probability, evidently, of any
determinate system subsequent to the observations will be proportional to £2.
This is to be understood to mean that the probability that the values of the un
known quantities lie between the infinitely near limits p and p-\-dp, q and g-\-dq,
r and r-\-dr, s and s-(-ds, etc. respectively, is expressed by

A.&djod^drds , etc.,

where the quantity A will be a constant quantity independent of p, q, r, s, etc. :

. *

and, indeed, ^ will, evidently, be the value of the integral of the order v,

fv£2dpdgdrds , etc.,

for each of the variables p, q, r, s, etc., extended from the value - - oo to the
value -|- oo .

177.

Now it readily follows from this, that the most probable system of values of
the quantities p, q, r, s, etc. is that in which 12 acquires the maximum value, and,
therefore, is to be derived from the v equations

- = 0, ~ = 0, i== 0, =£?= 0, etc.

dp dy dr ' ds

These equations, by putting

V— M= v, V— M' = v', V"— M" = v", etc., and ^~ = 9' 4,
assume the following form : —

dv , . dv' , f I dv" i n \ , r>

dv , . dvf , , , dt/' / /, . A

TqVv + djVv+^Vv +eto.= Q,

dv , | dv' , , , d«/' , „ i A

dT 9 v + j; 9 v ' + -^ y v '4- etc. = 0,

dv , . dv' , , , dv' i n \ rv

r.V v + dTVv+d^Vv +eta=a

Hence, accordingly, a completely determinate solution of the problem can be
obtained by elimination, as soon as the nature of the function y' is known. Since

33

258 DETERMINATION OF AN ORBIT FROM [BOOK II.

this cannot be defined a priori, we will, approaching the subject from another
point of view, inquire upon what function, tacitly, as it were, assumed as a
base, the common principle, the excellence of which is generally acknowledged,
depends. It has been customary certainly to regard as an axiom the hypothesis
that if any quantity has been determined by several direct observations, made
under the same circumstances and with equal care, the arithmetical mean of the
observed values affords the most probable value, if not rigorously, yet very
nearly at least, so that it is always most safe to adhere to it. By putting,
therefore,

V=V'=V" Qte.=p,
we ought to have in general,

9' (M—p) + <?' (Mf —p) + 9' (M" — p) + etc. = 0,
if instead of p is substituted the value

wnatever positive integer /a expresses. By supposing, therefore,

M"= etc. =M—

we shall have in general, that is, for any positive integral value of

whence it is readily inferred that ^ must be a constant quantity, which we will
denote by Jc. Hence we have

-\- Constant,

denoting the base of the hyperbolic logarithms by e and assuming

Constant = log K.

Moreover, it is readily perceived that Tt must be negative, in order that /2 may
really become a maximum, for which reason we shall put

i# — — hh;
and since, by the elegant theorem first discovered by LAPLACE, the integral

SECT. 3.] ANY NUMBER OF OBSERVATIONS. 259

from J = — oo to A = -)- oo is ^-, (denoting by TT the semicircumference of
the circle the radius of which is unity), our function becomes

178.

The function just found cannot, it is true, express rigorously the probabilities
of the errors : for since the possible errors are in all cases confined within certain
limits, the probability of errors exceeding those limits ought always to be zero.
while our formula always gives some value. However, this defect, which every
analytical function must, from its nature, labor under, is of no importance in
practice, because the value of our function decreases so rapidly, when hJ has
acquired a considerable magnitude, that it can safely be considered as vanishing.
Besides, the nature of the subject never admits of assigning with absolute rigor
the limits of error.

Finally, the constant h can be considered as the measure of precision of the
observations. For if the probability of the error J is supposed to be expressed
in any one system of observations by

and in another system of observations more or less exact by

h' --h'h'AA

V/rt

the expectation, that the error of any observation in the former system is con
tained between the limits — d and -)- d will be expressed by the integral

taken from // = — <? to // — -|- d ; and in the same manner the expectation, that
the error of any observation in the latter system does not exceed the limits — d'
and -(- d' will be expressed by the integral

\jn
extended from A = — d' to 4 = -j- d' : but both integrals manifestly become

260 DETERMINATION OF AN ORBIT FROM [BoOK II.

equal when we have Ad = h'S'. Now, therefore, if for example h' = 2 h, a double
error can be committed in the former system with the same facility as a single
"error in the latter, in which case, according to the common way of speaking, a
double degree of precision is attributed to the latter observations.

179.

We will now develop the conclusions which follow from this law. It is evi
dent, in order that the product

may become a maximum, that the sum

vv + v'v' + v"v" + etc.,

must become a minimum. Therefore, that will be the most probable system of values of
the unknown quantities p, q, r, s, etc., in which the sum of the squares of the differences
between the observed and computed values of the functions V, V, V", etc. is a minimum, if
the same degree of accuracy is to be presumed in all the observations. This prin
ciple, which promises to be of most frequent use in all applications of the mathe
matics to natural philosophy, must, everywhere, be considered an axiom with
the same propriety as the arithmetical mean of several observed values of the
same quantity is adopted as the most probable value.

This principle can be extended without difficulty to observations of unequal
accuracy. If, for example, the measures o'f precision of the observations by
means of which V=M, V = 3/', V" = M", etc. have been found, are expressed,
respectively, by h, h', h", etc., that is, if it is assumed that errors reciprocally pro
portional to these quantities might have been made with equal facility in those
observations, this, evidently, will be the same as if, by means of observations of
equal precision (the measure of which is equal to unity), the values of the func
tions hV, h'V, h"V", etc., had been directly found to be hM, h'M',h"M", etc.:
wherefore, the most probable system of values of the quantities p, q, r, s, etc.,
will be that in which the sum of hhvv -f- h'h'v'v' -\- h"h"v"v" -)- etc , that is, in which
/lie sum of the squares of tlie differences between the actually observed and computed values
multiplied by numbers tJiat measure the degree of precision, is a minimum. In this way it

SECT. 3.] ANY NUMBER OF OBSERVATIONS. 261

is not even necessary that the functions V, V, V", etc. relate to homogeneous
quantities, but they may represent heterogeneous quantities also, (for example,
seconds of arc and time), provided only that the ratio of the errors, which might
have been committed with equal facility in each, can be estimated.

180.

The principle explained in the preceding article derives value also from this,
that the numerical determination of the unknown quantities is reduced to a very
expeditious algorithm, when the functions V, V, V", etc. are linear. Let us
suppose

V — M = v=. — m -\- ap -f- bq -(- cr -\- ds -J- etc.
V— M' ^v'= — m' -f a'p 4- b'q -j- c'r -\- d's -f etc.
V"— M"=v"= — m"+ ap + b"q + c"r -f d"s + etc.
etc., and let us put

av-\- a'v' -f a"v" -f- etc. = P
Iv -\- I'v' -f l"v" + etc. = Q
cv -f c'v' -j- c"v" -\- etc. = R
dv -f d'v -J- d"v"-\- etc. = 8

etc. Then the v equations of article 177, from which the values of the unknown
quantities must be determined, will, evidently, be the following : —

P = 0, Q= 0, ft = 0, S — 0, etc.,

provided we suppose the observations equally good ; to which case we have shown
in the preceding article how to reduce the others. We have, therefore, as many
linear equations as there are unknown quantities to be determined, from which
the values of the latter will be obtained by common elimination.

Let us see now, whether this elimination is always possible, or whether the
solution can become indeterminate, or even impossible. It is known, from the
theory of elimination, that the second or third case will occur when one of the
equations

P — 0, Q = 0, R = 0, S = 0, etc.,
being omitted, an equation can be formed from the rest, either identical with the

262 DETERMINATION OF AN ORBIT PROM [BoOK II.

omitted one or inconsistent with it, or, which amounts to the same thing, when
it is possible to assign a linear function

aP 4- 0 @ _j_ y# -{- $S 4- etc.,

which is identically either equal to zero, or, at least, free from all the unknown
quantities p, q, r, s, etc. Let us assume, therefore,

«P _|_ 0 § 4. yj{ _j_ #8 _|_ etc. = x.

We at once have the identical equation

(i, _|_ m) v 4. (vr 4. w/) v' 4- (v" _)_ m") v" -f etc. = pP + q Q -\- rR -j- sS + etc.
If, accordingly, by the substitutions

p = a x, q = (9 x, r = y x, s = d x, etc.
we suppose the functions v, v, v", to become respectively,

— m -j- "L x, — m' -\- \'x, — m" - \- H'x, etc.,
we shall evidently have the identical equation

(I I _|_ XT _|_ x"X" + etc.) xx — (\m 4- I'm' -f l"m" etc.) * = x*,
that is,

1 1 _|_ XT -f X'T -f etc. = 0, x + X m 4- XV + X"WZ" + etc. = 0 :

hence it must follow that X = 0, X' = 0, X" = 0, etc. and also x = 0. Then it is
evident, that all the functions V, V V", are such that their values are not
changed, even if the quantities p, q, r, s, etc. receive any increments or decre
ments whatever, proportional to the numbers a, ft, y, d, etc. : but we have already
mentioned before, that cases of this kind, in which evidently the determination
of the unknown quantities would not be possible, even if the true values of the
functions V, V, V", etc., should be given, do not belong to this subject.

Finally, we can easily reduce to the case here considered, all the others in
which the functions V, V, V", etc. are not linear. Letting, for instance, n, x, (,'>
o, etc., denote approximate values of the unknown quantities jo, q, r, s, etc., (which
we shall easily obtain if at first we only use v of the p, equations V=M, V = M\
V" — M", etc.), we will introduce in place of the unknown quantities the others,
/> q', r', s', etc., putting p = n -\-p, q = % -(- /, r = (> -f- r', s — a -)- *', etc. : tin-
values of these new unknown quantities will evidently be so small that their

SECT. 3.] ANY NUMBER OF OBSERVATIONS. 263

squares and products may be neglected, by which means the equations become
linear. If, after the calculation is completed, the values of the unknown quanti
ties j/, </', /, /, etc., prove, contrary to expectation, to be so great, as to make it
appear unsafe to neglect the squares and products, a repetition of the same pro
cess (the corrected values of p, q, r, s, etc. being taken instead of n, %, (>, o, etc.),
will furnish an easy remedy.

181.

When we have only one unknown quantity p, for the determination of which
the values of the functions ap -\- n, up -\- n', a"p -|- n", etc. have been found, re
spectively, equal to M, M', M", etc., and that, also, by means of observations
equally exact, the most probable value of p will be

, __ a m -|- a'mf -f- a"m" -{- etc.

- ~

putting m, m, m", respectively, for M — n, M' — n', M" — n", etc.

In order to estimate the degree of accuracy to be attributed to this value, let
us suppose that the probability of an error A in the observations is expressed by

Hence the probability that the true value of p is equal to 4 -\-p will be propor
tional to the function

g-hh ((ap— mf+(a'p— m'?+(a"p-m"f+ etc.)

if A -\-p' is substituted for p. The exponent of this function can be reduced to
the form,

— hh (aa -\- ctct -f cl'ct' + etc.) (pp — 2pA-{- B),

in which B is independent of p : therefore the function itself will be propor
tional to

It is evident, accordingly, that the same degree of accuracy is to be assigned to
the value A as if it had been found by a direct observation, the accuracy of which
would be to the accuracy of the original observations as h^ (aa-\- a'a'-}-a"a"-\- etc.)
to h, or as y/ (a a -(- do! -\- d'd' -j- etc.) to unity.

264 DETERMINATION OF AN ORBIT FROM [BoOK 11.

182.

\

It will be necessary to preface the discussion concerning the degree of accu
racy to be assigned to the values of the unknown quantities, when there are sev
eral, with a more careful consideration of the function v v -j- v'v' -j- v"v" -f- etc.,
which we will denote by W.

I. Let us put

, AW

etc.,
uf

also

(t

and it is evident that we have p' = P, and, since

AW' _ AW 2/d/ „

dp dp a dp

that the function W is independent of p. The coefficient a = aa-\-a'a' -\-a"a"-\-
etc. will evidently always be a positive quantity.
II. In the same manner we will put

also

and we shall have

, i AW p'Ap' B , , AW"

q — 5 -, *-•£-= Q — *- n and -r- = 0,

Aq a Aq a1 ' Aq

whence it is evident that the function W" is independent both of p and q.
This would not be so if ft' could become equal to zero. But it is evident
that W is derived from vv-\- v'v -\- v"v" -\- etc., the quantity p being eliminated
from v, v', v", etc., by means of the equation p' = 0 ; hence, ft' will be the sum of
the coefficients of qq in vv, v'v', v"v", etc., after the elimination; each of these
coefficients, in fact, is a square, nor can all vanish at once, except in the case
excluded above, in which the unknown quantities remain indeterminate. Thus
it is evident that ft' must be a positive quantity.

SECT. 3.] ANY NUMBER OF OBSERVATIONS. 265

III. By putting again,

i^ = / = r + /V + <r*-fetc., and W'—^= W",
we shall have

/=*_!/_/ j-,

also W" independent of p, and q, as well as r. Finally, that the coefficient of y"
must be positive is proved in the same manner as in II. In fact, it is readily per
ceived, that y" is the sum of the coefficients of rr in vv, v'v', v"if', etc., after the
quantities p and q have been eliminated from v, v', v", etc., by means of the equa
tions /== 0, q' = 0.

IV. In the same way, by putting

we shall have

> n i i j

iS' — — — n n r

—— f^j p .1 i/ i/ i «

a P /

W" independent of p, q, r, s, and 8'" a positive quantity.

V. In this manner, if besides p, q, r, s, there are still other unknown quanti
ties, we can proceed further, so that at length we may have

'' '

+ s's'+ etc' + Constant,

in which all the coefficients will be positive quantities.

VI. Now the probability of any system of determinate values for the quan
tities p, q, r, s, etc. is proportional to the function e~hhw; wherefore, the value of
the quantity p remaining indeterminate, the probability of a system of determi
nate values for the rest, will be proportional to the integral

fe~hhWAp
extended from jt>— — oo to p=-^-ao , which, by the theorem of LAPLACE, becomes

therefore, this probability will be proportional to the function e~hhw'. In the
same manner, if, in addition, q is treated as indeterminate, the probability of a

34

260 DETERMINATION OF AN ORBIT FROM [BOOK II.

system of determinate values for r, s, etc. will be proportional to the integral

extended from g=: — oo up to ^ = -j- co , which is

or proportional to the function e~hhw". Precisely in the same way, if r also is
considered as indeterminate, the probability of the determinate values for the rest,
s, etc. will be proportional to the function e~hhw'", and so on. Let us suppose the
number of the unknown quantities to amount to four, for the same conclusion

will hold good, whether it is greater or less. The most probable value of s will

• i if
be -- YT-,, and the probability that this will differ from the truth by the quantity

0, will be proportional to the function e~hH"'a<! • whence we conclude that the
measure of the relative precision to be attributed to that determination is ex
pressed by \/d'", provided the measure of precision to be assigned to the original
observations is put equal to unity.

183.

By the method of the preceding article the measure of precision is conven
iently expressed for that unknown quantity only, to which the last place has
been assigned in the work of elimination ; in order to avoid which disadvantage,
it will be desirable to express the coefficient 8'" in another manner. From the
equations

P=p'

it follows, that/, /, r', s', can be. thus expressed by means of P, Q, R, S,

SECT. 3.] ANY NUMBER OF OBSERVATIONS. 267

S3" Q + STP,

so that S(, 51', S3', 21", S3", £" may be determinate quantities. We shall have,
therefore (by restricting the number of unknown quantities to four),

)'" 31" 33" S"

Hence we deduce the following conclusion. The most probable values of the
unknown quantities p, q, r, s, etc., to be derived by elimination from the equations

P= 0, Q = 0, R = 0, 8= 0, etc.,

will, if P, Q) R, S, etc., are regarded for the time as indeterminate, be expressed
in a linear form by the same process of elimination by means of P, Q, R, 8, etc.,
so that we may have

p = L+ AP + BQ+ CR + DS+ etc.

q = L' + AP + B'Q+C'R+D'S-\- etc.

r = L"-\-A'P-\-B"Q + C"R+&'S-}- etc.

s =L'"+A"P+B"'Q + C'"R+iy"S+ etc.

etc.

This being done, the most probable values of p, q, r, s, etc., will evidently be
L, L', L", L'", etc., respectively, and the measure of precision to be assigned to
these determinations respectively will be expressed by

_L J_ J_ 1

p' ^£" v/c"" Jiy7" €

the precision of the original observations being put equal to unity. That which
we have before demonstrated concerning the determination of the unknown
quantity s (for which -^ answers to D'") can be applied to all the others by the
simple interchange of the unknown quantities.

184.

In order to illustrate the preceding investigations by an example, let us sup
pose that, by means of observations in which equal accuracy may be assumed,
we have found

268 DETERMINATION OF AN ORBIT FROM [BOOK II.

p — 0-|-2r = 3

?+4r=21,

but from a fourth observation, to which is to be assigned one half the same
accuracy only, there results

We will substitute in place of the last equation the following : —

-P + 3 1 + 3 r = 14>

and we will suppose this to have resulted from an observation possessing equal
accuracy with the former. Hence we have

Pr=27/>-f 60 — 88

Q= 6^+15^4-r — 70
R= ? + 54r_i07,

and hence by elimination,

19899jo = 49154 + 809 P — 324 Q -\- Q Jt

737?= 2617- 12 P+ 540 — 7?
6633 r = 12707+ 2P- 9 0 -f 123 /?.

The most probable values of the unknown quantities, therefore, will be

p = 2.470
q = 3.551
r = 1.916

and the relative precision to be assigned to these determinations, the precision of
the original observations being put equal to unity, will be

19899

-

=3.69

SECT. 3.] ANY NUMBER OF OBSERVATIONS. 269

185.

The subject we have just treated might give rise to several elegant analytical
investigations, upon which, however, we will not dwell, that we may not be too
much diverted from our object. For the same reason we must reserve for another
occasion the explanation of the devices by means of which the numerical calcu
lation can be rendered more expeditious. I will add only a single remark.
When the number of the proposed functions or equations is considerable, the
computation becomes a little more troublesome, on this account chiefly, that the
coefficients, by which the original equations are to be multiplied in order to ob
tain P, Q, R, S, etc., often involve inconvenient decimal fractions. If in such
a case it does not seem worth while to perform these multiplications in the most
accurate manner by means of logarithmic tables, it will generally be sufficient
to employ in place of these multipliers others more convenient for calculation,
and differing but little from them. This change can produce sensible errors in
that case only in which the measure of precision in the determination of the
unknown quantities proves to be much less than the precision of the original
observations.

186.

In conclusion, the principle that the sum of the squares of the differences
between the observed and computed quantities must be a minimum may, in the
following manner, be considered independently of the calculus of probabilities.

When the number of unknown quantities is equal to the number of the ob
served quantities depending on them, the former may be so determined as exactly
to satisfy the latter. But when the number of the former is less than that of the
latter, an absolutely exact agreement cannot be obtained, unless the observations
possess absolute accuracy. In this case care must be taken to establish the best
possible agreement, or to diminish as far as practicable the differences. This idea,
however, from its nature, involves something vague. For, although a system of
values for the unknown quantities which makes all the differences respectively

270 DETERMINATION OF AN ORBIT FROM [BoUK II.

less than another system, is without doubt to be preferred to the latter, still the
choice between two systems, one of which presents a better agreement in some
observations, the other in others, is left in a measure to our judgment, and innu
merable different principles can be proposed by which the former condition is
satisfied. Denoting the differences between observation and calculation by A,
,/, ,/', etc., the first condition will be satisfied not only Mi. A A -f A' A' -)- A" A" +
etc., is a minimum (which is our principle), but also if //4 -f- ./* -(- //"4-J- etc., or
j« _|_ j'6 _|_ //"6 -|- etc., or in general, if the sum of any of the powers with an
even exponent becomes a minimum. But of all these principles ours is the most sim
ple ; by the others we should be led into the most complicated calculations.

Our principle, which we have made use of since the year 1795, has lately
been published by LEGENDRE in the work Nouvclles mcthodes pour la determination des
orbites des cometes, Paris, 1806, where several other properties of this principle have
been explained, which, for the sake of brevity, we here omit.

If we were to adopt a power with an infinite even exponent, we should be
led to that system in which the greatest differences become less than in any other
system.

LAPLACE made use of another principle for the solution of linear equations the
number of which is greater than the number of the unknown quantities, which
had been previously proposed by BOSCOVICH, namely, that the sum of the errors
themselves taken positively, be made a minimum. It can be easily shown, that a
system of values of unknown quantities, derived from this principle alone, must
necessarily* exactly satisfy as many equations out of the number proposed, as
there are unknown quantities, so that the remaining equations come under consid
eration only so far as they help to determine the choice : if, therefore, the equation
V = M, for example, is of the number of those which are not satisfied, the sys
tem of values found according to this principle would in no respect be changed,
even if any other value N had been observed instead of M, provided that, denot
ing the computed value by n, the differences M — n, N — n, were affected by the
same signs. Besides, LAPLACE qualifies in some measure this principle by adding

* Except the special cases in which the problem remains, to some extent, indeterminate.

SECT. 3.] ANY NUMBER OF OBSERVATIONS. 271

a new condition : he requires, namely, that the sum of the differences, the signs
remaining unchanged, be equal to zero. Hence it follows, that the number of
equations exactly represented may be less by unity than the number of unknown
quantities ; but what we have before said will still hold good if there are only
two unknown quantities.

187.

From these general discussions we return to our special subject for the sake
of which they were undertaken. Before the most accurate determination of
the orbit from more observations than are absolutely requisite can be com
menced, there should be an approximate determination which will nearly satisfy
all the given observations. The corrections to be applied to these approximate
elements, in order to obtain the most exact agreement, will be regarded as the
objects of the problem. And when it can be assumed that these are so small
that their squares and products may be neglected, the corresponding changes,
produced in the computed geocentric places of a heavenly body, can be obtained
by means of the differential formulas given in the Second Section of the First
Book. The computed places, therefore, which we obtain from the corrected ele
ments, will be expressed by linear functions of the corrections of the elements,
and their comparison with the observed places according to the principles before
explained, will lead to the determination of the most probable values. These
processes are so simple that they require no further illustration, and it appears at
once that any number of observations, however remote from each other, can
be employed. The same method may also be used in the correction of the parcir
lolic orbits of comets, should we have a long series of observations and the best
agreement be required.

188.

The preceding method is adapted principally to those cases in which the
greatest accuracy is desired: but cases very frequently occur where we may,
without hesitation, depart from it a little, provided that by so doing the calcula-

272

DETERMINATION OF AN ORBIT FROM

[BOOK II.

tion is considerably abridged, especially when the observations do not embrace a
<Teat interval of time ; here the final determination of the orbit is not yet
proposed. In such cases the following method may be employed with great
advantage.

Let complete places L and L' be selected from the whole number of observa
tions, and let the distances of the heavenly body from the earth be computed
from the approximate elements for the corresponding times. Let three hypothe
ses then be framed with respect to these distances, the computed values being
retained in the first, the first distance being changed in the second hypothesis,
and the second in the third hypothesis ; these changes can be made in proportion
to the uncertainty presumed to remain in the distances. According to these
three hypotheses, which we present in the following table,

Hyp. I.

Hyp. II.

Hyp. HI.

Distance * corresponding to the first place,

D

D-\-S

D

Distance corresponding to the second place,

D'

n

ix+5

let three sets of elements be computed from the two places I/, L', by the methods
explained in the first book, and afterwards from each one of these sets the geo
centric places of the heavenly body corresponding to the times of all the remain
ing observations. Let these be (the several longitudes and latitudes, or right
ascensions and declinations, being denoted separately),

in the first set .... M, M', M", etc.

in the second set . . . M-\-a, M' -(-«', M"-\-a", etc.

in the third set . . . . M + /?, M' +/?', M"-}- p", etc.
Let, moreover, the observed

places be respectively N, N', N", etc.

Now, so far as proportional variations of the individual elements correspond

* It will be still more convenient to use, instead of the distances themselves, the logarithms of the
curtate distances.

SECT. 3.] ANY NUMBER OF OBSERVATIONS. 273

to small variations of the distances D, I/, as well as of the geocentric places
computed from them, we can assume, that the geocentric places computed from
the fourth system of elements, based on the distances from the earth D-\-xd.
D' -f y <T, are respectively M-\- a x -f /ty, M1 -f a'x -\- (t'y, M" -f a"x -f 0'>, etc.
Hence, x, y, will be determined, according to the preceding discussions, in such a
manner (the relative accuracy of the observations being taken into account), that
these quantities may as far as possible agree with N, N', N", etc., respectively.
The corrected system of elements can be derived either from L, L' and the dis
tances D -\- x d, D' -\- x §', or, according to well-known rules, from the three first
systems of elements by simple interpolation.

189.

This method differs from the preceding in this respect only, that it satisfies
two geocentric places exactly, and then the remaining places as nearly as possi
ble ; while according to the other method no one observation has the preference
over the rest, but the errors, as far as it can be done, are distributed among all.
The method of the preceding article, therefore, is only not to be preferred to the
former when, allowing some part of the errors to the places L, L', it is possible to
diminish considerably the errors in the remaining places : but yet it is generally
easy, by a suitable choice of the observations L, L', to provide that this difference
cannot become very important. It will be necessary, of course, to take care that
such observations are selected for L, L', as not only possess the greatest accuracy,
but also such that the elements derived from them and the distances are not
too much affected by small variations in the geocentric places. It will not. there
fore, be judicious to select observations distant from each other by a small inter
val of time, or those to which correspond nearly opposite or coincident heliocen
tric places.

35

FOURTH SECTION.

ON THE DETERMINATION OF ORBITS, TAKING INTO ACCOUNT THE

PERTURBATIONS.

190.

THE perturbations which the motions of planets suffer from the influence of
other planets, are so small and so slow that they only become sensible after a
long interval of time ; within a shorter time, or even within one or several entire
revolutions, according to circumstances, the motion would differ so little from the
motion exactly described, according to the laws of KEPLER, in a perfect ellipse,
that observations cannot show the difference. As long as this is true, it would
not be worth while to undertake prematurely the computation of the perturba
tions, but it will be sufficient to adapt to the observations what we may call an
osculating conic section: but, afterwards, when the planet has been accurately
observed for a longer time, the effect of the perturbations will show itself in such
a manner, that it will no longer be possible to satisfy exactly all the observations
by a purely elliptic motion ; then, accordingly, a complete and permanent agree
ment cannot be obtained, unless the perturbations are properly connected with
the elliptic motion.

Since the determination of the elliptic elements with which, in order that the
observations may be exactly represented, the perturbations are to be combined,
supposes a knowledge of the latter; so, inversely, the theory of the perturbations
cannot be accurately settled unless the elements are already very nearly known :
the nature of the case does not admit of this difficult tusk being accomplished
with complete success at the first trial : but the perturbations and the elements
can be brought to the highest degree of perfection only by alternate corrections
(274)

SECT. 4.] ON THE DETERMINATION OF ORBITS. 275

often repeated. Accordingly, the first theory of perturbations will be constructed
upon those purely elliptical elements which have been approximately adjusted to
the observations ; a new orbit will afterwards be investigated, which, with the
addition of these perturbations, may satisfy, as far as practicable, the observa
tions. If this orbit differs considerably from the former, a second determination
of the perturbations will be based upon it, and the corrections will be repeated
alternately, until observations, elements, and perturbations agree as nearly as
possible.

191.

Since the development of the theory of perturbations from given elements is
foreign to our purpose, we will only point out here how an approximate orbit
can be so corrected, that, joined with given perturbations, it may satisfy, in
the best manner, the observations. This is accomplished in the most simple
way by a method analogous to those which we have explained in articles 124,
165, 188. The numerical values of the perturbations will be computed from the
equations,for the longitudes in orbit, for the radii vectores, and also for the helio
centric latitudes, for the times of all the observations which it is proposed to use,
and which can either be three, or four, or more, according to circumstances : for
this calculation the materials will be taken from the approximate elliptic ele
ments upon which the theory of perturbations has been constructed. Then two
will be selected from all the observations, for which the distances from the earth
will be computed from the same approximate elements : these will constitute the
first hypothesis, the second and third will be formed by changing these distances
a little. After this, in each of the hypotheses, the heliocentric places and the
distances from the sun will be determined from two geocentric places; from those,
after the latitudes have been freed from the perturbations, will be deduced the
longitude of the ascending node, the inclination of the orbit, and the longi
tudes in orbit. The method of article 110 with some modification is useful in
this calculation, if it is thought worth while to take account of the secular varia
tion of the longitude of the node and of the inclination. If p, ft', denote the
heliocentric latitudes freed from the periodical perturbations; \, If, the heliocen-

276 ON THE DETERMINATION OF ORBITS, [BOOK II.

trie longitudes; Q, & -j- J, the longitudes of the ascending node; i,i-\-d, the
inclinations of the orbit ; the equations can be conveniently given in the follow
ing form : —

tan ft = tan i sin (A. — & ),

tun i ,»/ . . / • / j *~k \

,. i ,. tan a = tan t sin (A — A — Q),

tan (i -\- 8) v

This value of - r-^- acquires all the requisite accuracy by substituting an
approximate value for i: i and Q, can afterwards be deduced by the common
methods.

Moreover, the sum of the perturbations will be subtracted from the longitudes
in orbit, and also from the two radii vectores, in order to produce purely elliptical
values. But here also the effect, which the secular variations of the place of the
perihelion and of the eccentricity exert upon the longitude in orbit and radius
vector, and which is to be determined by the differential formulas of Section I.
of the First Book, is to be combined directly with the periodical perturbations,
provided the observations are sufficiently distant from each other to make it
appear worth while to take account of it. The remaining elements will be deter
mined from these longitudes in orbit and corrected radii vectores together with
the corresponding times. Finally, from these elements will be computed the
geocentric places for all the other observations. These being compared with the
observed places, in the manner we have explained in article 188, that set of
distances will be deduced, from which will follow the elements satisfying in the
best possible manner all the remaining observations.

192.

The method explained in the preceding article has been principally adapted
to the determination of the first orbit, including the perturbations : but as soon
as the mean elliptic elements, and the equations of the perturbations have both
become very nearly known, the most accurate determination will be very con
veniently made with the aid of as many observations as possible by the method
of article 187, which will not require particular explanation in this place. Now
if the number of the best observations is sufficiently great, and a great interval

SECT. 4.] TAKING INTO ACCOUNT THE PERTURBATIONS. 277

of time is embraced, this method can also be made to answer in several cases for
the more precise determination of the masses of the disturbing planets, at least
of the larger planets. Indeed, if the mass of any disturbing planet assumed in
the calculation of the perturbations does not seem sufficiently determined, besides
the six unknown quantities depending on the corrections of the elements, yet
another, p, will be introduced, putting the ratio of the correct mass to the assumed
one as 1 -f- p to 1 ; it will then be admissible to suppose the perturbations them
selves to be changed in the same ratio, whence, evidently, in each one of the com
puted places a new linear term, containing /*, will be produced, the development
of which will be subject to no difficulty. The comparison of the computed places
with the observed according to the principles above explained, will furnish, at the
same time with the corrections of the elements, also the correction p. The
masses of several planets even, which exert very considerable perturbations, can
be more exactly determined in this manner. There is no doubt but that the mo
tions of the new planets, especially Pallas and Juno, which suffer such great per
turbations from Jupiter, may furnish in this manner after some decades of years,
a most accurate determination of the mass of Jupiter ; it may even be possible
perhaps, hereafter, to ascertain, from the perturbations which it exerts upon the
others, the mass of some one of these new planets.

APPENDIX.

1.*

THE value of t adopted in the Solar Tables of HANSEN and OLUFSEN, (Copen
hagen, 1853,) is 365.2563582. Using this and the value of /n,

l
fJ''' "354936'

from the last edition of LAPLACE'S Syst&me du Monde, the computation of k is

Iog2jt 0.7981798684

Compl. log* 7.4374022154

Compl. log ^(1-fj*) . . . 9.9999993882

log£ 8.2355814720

h = 0.01720210016.

11.

The following method of solving the equation

M=E — esin E,

is recommended by ENCKE, Berliner Astronomisches Jahrbuch, 1838.
Take any approximate value of E, as e, and compute

M ' = £ — e" sin « ,

' The numbering of the Notes of the Appendix designates the articles of the original work to

which they pertain.

(279)

280 APPENDIX.

e" being used to denote c expressed in seconds, then we have

or

M — M ' = E — s — e" (sin E— sin e )
= (E — t) (1 — ecoss),

if E — e is regarded as a small quantity of the first order, and quantities of
the second order are neglected for the present : — so that the correction of K is

M— M1

1 — e cos s '

and a new approximate value of £ is

. M— M'

' 1 — e cos s'

with which we may proceed in the same manner until the true value is obtained.
It is almost always unnecessary to repeat the calculation of 1 — e cos e. Gener
ally, if the first £ is not too far from the truth, the first computed value of
1 — e cos £ may be retained in all the trials.

This process is identical with that of article 11, for X is nothing more than

. _ d log sin E _ cos E

<i i: ~ shTlr

if we neglect the modulus of BIUGGS'S system of logarithms, which would subse
quently disappear of itself, and

d (e" sin E)

therefore,

n — ). i — i
and

n M— M'

—.- ~,

' p + /I 1 — e cos E "

and the double sign is to be used in such a way that >. shall always have the same
sign as cos E. In the first approximations when the value of £ differs so much
from E that the differences of the logarithms are uncertain, the method of this
note will be found most convenient. But when it is desired to insure perfect
agreement to the last decimal place, that of article 11 may be used with
advantage.

APPENDIX.

281

As an illustration, take the data of the example in article 13.
Assume £ = 326°, and we find

log sin £ 9.74756 n log cose 9.91857

loge

log/' 4.70415
log e"sin£ 4.45171 n

e" sin £ = — 28295" = — 7° 51' 35"
' = e — e" sin e = 333° 51' 35"
M— M' — — 4960"

9.38973

loge cos £

9.30830
cos e = .79662
log(l — ecos£) 9.90125
logJf— M' 3.69548n

1 — e cos s

— e cos

= _1°43'46".
And for a second approximation,

£ = 326° — 1° 43' 46" = 324° 16' 14"

log sine 9.7663820»

loge" 4.7041513
loge" sine 4.4705333 n

e" sin £ = — 29548".36 = — 8° 12' 28".36

M' = 332° 28' 42".36 log (l — e COSE) 9.90356

M— M' = + 12".41 log (M— M') 1.09377

£=¥- = + 15".50 bg^^- 1.19021

1 — e cos E ° 1 — e cos e

which gives

H= 324° 16' 14" 15".50 = 324° 16'29".50.

Putting

we have

18.

q — lp =. perihelion distance,

log x = 8.0850664436,
r =

tan i v -\- i tan3 i y = x 1

T = — (3 tan i v -f- tan8

36

282 APPENDIX.

a table may be computed from this formula, giving v for values of t as the argu
ment, which will readily furnish the true anomaly corresponding to any time
from the perihelion passage. Table Ila is such a table. It is taken from the
first volume of Annales dc I' Observatoire Imperiale de Paris, (Paris, 1855,) and differs
from that given in DELAMBRE'S Astronomy, (Paris, 1814,) Vol. III., only in the
intervals of the argument, the coefficients for interpolation, and the value of k
with which it was computed.

The true anomaly corresponding to any value of the argument is found by
the formula

v = z-o + A! (T — TO) + A2 (* ~ To)2 + (T — T0)3 A3 -f A± (t — T0)4.

The signs of A1, A2, A3, are placed before the logarithms of these quantities
in the table.

BURCKHARDT'S table, BOWDITCH'S Appendix to the third volume of the Mecanique
Celeslc, is similar, except that log t is the argument instead of T.

Table lla contains the true anomaly corresponding to the time from peri
helion passage in a parabola, the perihelion distance of which is equal to the
earth's mean distance from the sun, and the mass ju, equal to zero. For if we put
H = 1 , u = 0 , we have t — t .

By substituting the value of /c in the equation

T = — (3 tan %v -f- tan3 £ v)

it becomes

T = 27.40389544 (3 tan kv + tan3 } v)

= 1.096155816 (75 tan i » -f 25 tan3 irj
and therefore, if we put x'== 0.9122790G1,

75 tan i v -4- 25 tan3 4 v — *' t

log x' = 9.9601277069

BARKER'S Table, explained in article 19, contains v' t for the argument v.
The Mean daily motion or the quantity M, therefore, of BARKER'S Table may be
obtained from table IIa, for any value of v, by multiplying the corresponding
value of T by x'.

The following examples will serve to illustrate the use of the table.
Given, the perihelion distance <? = 0.1; the time after perihelion passage
t— 0".590997, to find the true anomaly.

APPENDIX. 283

Assuming p = 0, we find

r = 208.42561

TO = 200.
T — TO = 8.42561

w0 = 110° 24' 46".69
AI(V — T0)=+l°14'42".42
**(* — *o)2 = - 2'20".19
,13(T-T0)3 = + 4".76

At (T — T0)4 = — Q".16

v = 1110 37' 13".52
or

r = 208.42561

T0 = 210.
T — TO = —1.57439

t'o = 111° 50' 16".87
Ai(r — TO) = - 12'58".96

— TO)» = - 4".35

— T0)8 = - 0".03
_r* = _ O^.OQ

t; = 111° 37' 13".53

The latter form of calculation is to be preferred because the value of T — TO
is smaller, and therefore the terms depending on (T — r0), (T — T0)2, (T — T0)3, are
smaller, and that depending on (T — T0)4 is insensible ; and it is the only form
of which all the appreciable terms are to be found in the table.

Beyond T = 40000, the limit of the table, we can use the formula,

v = 180° - - [6.0947259] Q*— [6.87718] Q — [7.313] (^)f, etc.,

in which the coefficients expressed in arc are given by their logarithms.
For T = 40000, for example, we have

v = 180° — 10° 6' 6".87 — 3' 8".4 1 — 0".44
= 169050'44".28.

If v is given, and it is required to find T, we have

284 APPENDIX.

For a first approximation the terms depending on the square and third power
of T — T0 may be neglected, and the value of T — TO thus found can be corrected
so as to exactly satisfy the equation.

If v exceeds 169°, the formula

r = [1.9149336] tan i v -f- [1.4378123] tan8 } v

may be used instead of the table.
Thus, for v = 169° 50' 44".28,

log tan i». .1.0513610
1.9149336

925.33 2.9662946

log tan3 iy. .3.1540830

1.4378123

39074.67 4.5918953

7 = 40000.00

This method will often be found more convenient than the table, even where
v is less than 169°.

35.

Table Va contains BESSEL'S table here referred to, in a slightly modified
form ; and also a similar table by POSSELT, for the coefficients v' and v" in the
formula of article 34,

to = v + d v' -4- dd v" + d3 v'" -f etc.,

it is taken from ENCKE'S edition of OLBERS Abhandlung iiber die IcicMcste und bcquemste
Mdhodc die Bahn cities Cometen zu berechnen (Weimar, 1847). The following
explanation of its construction and use is taken from the same work, with
such changes as are needed to adapt it to the notation of the preceding
articles : —
If we put

# = tan ^ w
t = tan i v

APPENDIX. 285

the formulas of article 34 become

, A* — A*1

I - A * - A 0" + li 0* + <H ^ + M ^9 + A 0" v2
!24

The second equation, in which v is expressed in terms of w, is that given by
BESSEL, Monatliche Correspondenz, Vol. XII., p. 197. He also gives the third coeffi
cient of the series, but has computed a table of only the first two. POSSELT, in
the Zeitschrlft fur Astronomic und verwandte Wissenschaflcn, Vol. V., p. 161, has given
the first equation ; he has also given three coefficients of the series, but a table of
the second only, since BESSEL'S table will give the first coefficient simply by
changing the sign. POSSELT has changed the sign of the second coefficient also.

Instead of the logarithms as given in the tables of BESSEL and POSSELT, the
corresponding numbers are given in table Va, and to avoid large numbers, O.OL
is taken as the unit of d.

Patting

tan i x = £
the table contains

T>_ - A § — A r

10000(1+ ?)4

•1 .fc I « t8 I -1 t6 I 41 W 1 t9 19 til

TV _ ~T5"S~TTB'^ "t~ Tff * I '8Tnr > 3?^ ~fSU ?

-"

So that when x = iv we have

y = w4-
And when x = v,

w = v — A (100 8} — B' (100 3f

It seems unnecessary to recompute the table in order to be certain of the
accuracy of the last place, or to extend it further, as its use is limited. For

286 APPENDIX.

absolute values of S greater than 0.03, and for values of x considerably greater
than 90°, the terms here given woitld not be sufficient. In such cases the
method of 37 and the following articles should be used.
Example. — For HALLEY'S cornet^

logtf = 8.5099324, and t = 63".43592, we have

by table IIff, w = 99° 36' 55".91

and by table Va, A = •• -f 417.45 1st cor. + 22' 30".63

#= + 3.111 2d cor. -f 32".57

v = 99° 59' 59".ll

which, rigorously, should be 100°; so that d is in this case too great.
Inversely, we find, for v= 100°,

v = 100° 0'00".00

4 = 4-426.78 1st cor. 23' 0".83

B = + 0.297 2d cor. 3".ll

w= 99°36'56".06

which agrees nearly with the preceding value. The change of the table to the
present form has been made under the supervision of D' ARREST.

39.

When table Ha is used instead of BARKER'S table, to is the value of v, which
corresponds to the argument

at

40.

If we put

l

E —
j-^t —

1-jA+O

-i

the formulas for computing the true anomaly and radius vector are

tan i v = E, y tan £ w

APPENDIX. 287

Table la for the Ellipse contains log Ev and log E, for the argument A , to
gether with the logarithms of their differences corresponding to a change of a unit
in the seventh decimal place of the argument. It was computed by Prof. J. S.
HUBBAKD, and has been used by him for several years. Since it was in type, a
similar table, computed by Mr. A. MARTH, has appeared in the Astronomische Nach-
ricMen, Vol. XLIIL, p. 122. The example of article 43 will furnish an illustra
tion of its use.

Formulas expressing the differentials of the true anomaly and radius vector
in a very eccentric ellipse, in terms of the differentials of the time of perihelion
passage, the perihelion distance and the eccentricity may be obtained from the
equations of this article.

If we put £ = I, C= 0, we have, article 39,

tan i iv -|- | tan3 i w = ^
which, by article 20, gives

dw a. -., 3 at 7 . t ,

~n — = ^dt — -^-fr: aq -4- -—da.

4> 2

75 2q75 2 75

We also have, article 40,

log tan i v = log tan lw — Hog(l — | (5 tan2 i iv) -f- log y
and, therefore,

2 sin I v cos ^ w 2 sin £ w cos8 £ w (1 -

^f •> a cos2 1- «? , , Sat cos2 \ w •,

sinv 75taniw(l— § A) ~2? 75 tan 1 w (1 — f ^) ^

w , .rfj", ^^4 rf|3

.-*j)flfa"T~T~r-f3rriT

which, by putting

•rr (t COS2 1

'75tanlw(l — f ^t)

L— 3

Z-

288 APPENDIX.

p_ 10.

is reduced to

^ = — KdT— KLtdq + \KMt~ N— 0 PI de,

smv

observing that d t = — dT, if T denotes the time of perihelion passage.
If we differentiate the equation

r==

1 -f- e cos v

we find

r , I 2 o2 sin2 i v 7 , r2 e sin v ,

dr = - do -\ -- ., . „ de-\ — 7—- — r dv.

2 r

q

These formulas are given by NlCOLAI, (Monatliche Correspondenz, Vol. XXVIL,
p. 212). The labor of using them is greatly abridged by the fact that K, L,
M, etc., are computed once for all, and that the quantities needed for this pur
pose are those required for computing the true anomaly and radius vector.

If the ellipse so nearly approaches the parabola that, in the coefficients, we
may assume

tan kv = y tan | w

,~ _ k Y/ 2 cos2 £ v
2 q% tan $ v

the values of dv and dr assume a much more simple form. In this case we
should have

ifsjn v _ ^ y/ 2 cos8 \v sin \ v _ k ^ 2 cos4 £ v _ k \j 2 q

(1

and consequently,

sn

8] -

+9 e)

APPENDIX. 289

This form is given by ENCKE (Berliner Astronomisches Jahrfawh, 1822, page 184.)
If we put e = 1 in the coefficient of de it becomes

dv , kt

If we substitute the value of dv in the expression for dr given above, it
may be reduced to the form

7 k . i m \ 7 / o k t sin tf .

\ i

t> )de,

41.

The time t may be found from table IIa, by multiplying the value of r cor
responding to w by

J B

45.

Table I« for the hyperbola is similar to that for the ellipse, and contains
log E, and log Er for the formulas

tan bv = Ev-y tan i w
r = fir sec2 i w .

The differential formulas of article 40, of the Appendix, can be applied to
the hyperbola also, by changing the sign of A and of 1 — e in the coefficients.

56.

As the solution here referred to may sometimes be found more convenient
than the one given in articles 53-57, the formulas sufficient for the use of prac
tical computers are given below.

Using the notation of 50 and the following articles, the expressions for the
rectangular coordinates referred to the equator are, —

x = r cos u cos Q — r sin u sin Q, cos i

(1) y = r cosn sin & cose -f-rsin ticos & cos i cose — r.smu sin i sin e
z = r cos M sin Q sin e -f- r sin u cos Q cos * sin e -j- r sin u sin i cos e

37

290 APPENDIX.

which can be put in the form

x = r sin a sin ( A -j- u)

(2) y = r sin b sin (B -\- u}

s = r sin c sin ( 0 -\- u)

or

x = r sin a sin A cos t« -j- r sin a cos ^4 sin u

(3) ^ — r sin & sin 5 cos u -\- r sin b cos .B sin M
z =. r sin c sin (7 cos M -(- r sin c cos C" sin M

equations (3), compared with (1) give

sin a sin 4 = cos Q, sin a cos A = — sin & cos i

(4) sin b sin 5 = sin Q, cos e sin i cos B = cos S cos i cos e — sin? sine
sin c sin (7 — sin S sin e sin c cos C' = cos 8 cos ? sin e -j- sin * cos e .

By introducing the auxiliary angle E

tan t

we shall find

cotan A = — tan Q cos »

tun Q cos .& cos «

cotan (7= ™--'^+l)_
tan £2 <'°* -asm s

_ cos Q _ sin a cos

Dill t* - . — ; - ~r -

— ; - ~r - --

sm A cos ^.

„ j _ si" S2 cos e cos Q cos i cos « — sin f sin e
bill c> . — - . — y. — z^i - — -
sin B cos .5

_ sin Q fin e cos Q cos i sin « 4- sin f coss
sin c — - : — -~ — --- — - .
sin U cos C

sin a, sin i, sine are always positive, and the quadrants in which A, B, C are to
be taken, can be decided by means of equations (4).

The following relations between these constants, easily deducible from the
foregoing, are added, and may be used as checks :

tan ; _ ain5sincsin(O— B)
sin a sin A

APPENDIX. 291

cos a = sin 8 sin i

cos b = — cos 8 sin i cos £ — cos i sin e

cos c = — cos 8 sin i sin e -\- cos i cos «

sin2 a -f- sin2 £ -f- sin2 c = 2

cos2 a -f- cos2 b -f- cos2 e = 1
cos ( A — B) = — cotan a cotan b
cos (B — G} = — cotan b cotan c
cos (A — C) = — cotan a cotan c.

58.

If in the formulas of article 56 of the Appendix, the ecliptic is adopted as
the fundamental plane, in which case e = 0 ; and if we put

n = long, of the perihelion
sin a = kx A = KC — (n — 8 )
sii\b = ky B = Ky — (n — 8)
sine — Jcz C=KZ — (n — 8)
we shall have

kx sin (Kx — (n — Q )) = cos 8

Jcx cos (Kx — (n — 8 )) = — sin 8 cos i
Jcx sin Kx = cos 8 cos (n — 8 ) — sin 8 sin (it — 8 ) cos f
£zcos Kx = — [cos 8 sin (it — Q, ) -|- sin Q cos (JT — 8 ) cosz]

which can easily be reduced to the form,

&x sin Kx = cos2 k i cos TT -J- sin2 J z cos (TT — 2 8 )
#z cos Kx = — [cos2 J z sin n -j- sin2 ^ ism (it — 2 8 )]

and in like manner we should find

ks sin Ky = cos2 i z sin n — sin2 i z sin (it — 2 8 )
= cos2 J / cos it — sin2 J i cos (TT — 2 8 )
#z sin _ff^ = sin i sin (TT — 8 )
kz cos ^ = sin i sin (JT — 8 )

292 APPENDIX.

If these values are substituted in the general expression for coordinates,

a k cos (f cos jfTsin E -j- a k sin l£(cos E — e]
and if we put

a cos (f = b

n , . Tl I 21 -COS (a - 2 £2)1

a cos2 i i cos TI 1 4- tan2 i a - = ^

L cos a J

— b cos2 * » sin * [l + tan2 4 1 8in(«-28)1 = #

sin n \

2 1 • • 2 i -sin (« — 2Q)1 j/

a cos2 4 z sin nil — tan- i z - = A

L sin a J

, n . . o , .COS(« - 28)1 i-.,

b cos2 i a cos n 1 — bur J » - == -»

L cos n J

a sin « sin (n — & ) = J."
i sin e cos (it — & ) = B"

the- coordinates will be

x = A (cosE — e)-\-B sinE = ^l (1 — esecE)+JB sin E
y = A' (cosE — e)-\-£' smE = Af (1 — esecE) -(-^ sinE
z = A" (cos E — e) 4- B" sin E = A" (l — e sec E) + B" sin E.

If the equator is adopted as the fundamental plane instead of the ecliptic,
the same formulas may be used, if Q,,n, and i are referred to the equator by
the method of article 55. Thus, if Qe denote the right ascension of the node
on the equator, for Q, n, and i, we must use 8E, Qe-{-(n — 8) — .4, and i
respectively.

This form has been given to the computation of coordinates by Prof. PEIRCE,
and is designed to be used with ZECH'S Tables of Addition and Subtraction Logarithms.

Example. — The data of the example of articles 56 and 58, furnish
Q ==158°30'50".43, TT = = 122° 12'23".55, t=ll° 43' 52".89 when the equator
is adopted as the fundamental plane ; and also log b — 0.4288533.

Whence we find

log cos (n — 2 Q, ) 9.9853041 n log sin (n — 2 Q) 9.4079143

log sec n 0.2732948 n logcosecTt 0.0725618

log tan2 H 8.0234332 log tan2 U 8.0234332

logo 8.2820321 logs' 7.5039093

APPENDIX.

293

add. log -

0.0082354

C. sub. log i

9.9916052

log cos n

9.7267052 »

log COS 71

9.7267052

log cos2 i i

9.9954404

log cos2 i i

9.9954404

log a

0.4423790

log 6

0.4288533

log A

0.1727600 n

log 5'

0.1426041 n

add. log -

C

0.0013836

C'. sub. log ->

9.9986120

log sin TT

9.9274382

log sin n

9.9274382

log cos2 i *

9.9954404

log cos2 i *

9.9954404

log 6

0.4288533

log a

0.4423790

log B

0.3531155 n

log A'

0.3638696

This method may

also be used to

compute k and K for the

general formula

of article 57. Thus:

—

acW. log -

0.0082354

(7. sw5. log -

9.9916052

log cos n

9.7267052 »

log cos TC

9.7267052 «

log cos2 i »

9.9954404

log cos2 i i

9.9954404

log /^ sin JE^.

9.7303810 n

log ky cos ^"y

9.7137508 n

rttfo?. log -

0.0013836

(7. s»5. log -

9.9986120

log sin n .

9.9274382

log sin Tt

9.9274382

log cos2 i z

9.9954404

log cos2 i z .

9.9954404

log kx cos -ff"z

9.9242622 n

lOg ky Sin jffy

9.9214906

log tan Kx

9.8061188

log tan Ky

0.2077398 n

log cos .ffl

9.9254698 n

log sin JT..

9.9294058

log A, = 9.9987924
r= 212°36'56".l

log ky= 9.9920848
, = 121° 47' 28".l

It will not be necessary to extend the example to the final expressions for
z,>/,s,sis illustrations of similar applications of the Addition and Subtraction
Logarithms are given in the directions accompanying ZECH'S Tables.

294 APPENDIX.

59.

If r, b, and / denote the radius vector, the heliocentric latitude and longitude
of any planet, the rectangular coordinates referred to three axes, — of which
that of x is directed towards the vernal equinox, that of 0, parallel to the earth's
axis, and that of y, 90° of right ascension in advance of x, — will be as in case II.

x = r cos I cos I

y = r cos b sin I cos t — r sin b sin e
z •=. r cos b sin e sin l-\- r sin b cos «
and by putting

cos u = cos b cos I

sin 5 sin ? cos b
Sin U = -.-- = -

sin 0 cos o

. tan b

tan 6 = -^— ,

fin I

they assume the following forms convenient for computation : —

x = r cos u

y := r sin M cos (6 -f- e)

2 =z r sin ?< sin (0 -j- c) .

74.

The following are the solutions and examples from the Monatltche Correspon
dent referred to in this article, adopting the notation of article 74, and using I!
to denote the longitude of the Sun.

Given, &, L', I, b, i, R, to find u, r, 4 , and the auxiliary angles A, JB, C, etc.

L

9 sin (L' — l) tan t _ cos -B sin 6 tan (/,' — Q ) _

^i« , F / , , — tcin JL> — — — — -- —

, F / , , — c J — . — ^ -^ — j — ir -- i —

oos (/y — Q ) sm (B -\- b) cos %

3. ^ ^- 8 > !»* = tan C -^2Pr?- ~^ ' •= tan u

B\n(L' — Qtani sm(0-\-L — Q ) cos i

cos (L'—Q) tan 4 _ sin .P tan (Z,' — Q ) co*(L' — l) _

- FT/ - y\ *i • - Lclll X/ — 7"VT~i - *•/ - iu -- • - " - will ((

cos (U — I) tan i sin (D -f- L' — /) cos i

APPENDIX.

295

The angle u is to be taken between 0° and 180° when b is positive, and be
tween 180° and 360° when b is negative. When b = 0°, the body is in one of the
nodes of its orbit, in the ascending node when sin (L' — /) and sin (I — a) have
the same sign ; and in the descending node when they have opposite signs.

It is immaterial in which of the two quadrants that give the same tangent,
the auxiliary angles A , B , C, etc., are taken. In the following examples they
are always taken between -4- 90° and — 90°.

II.

5.

6.
7.
8.
9.
10.
11.

19,

t^5 — tanZ?

sinZ£sin(Z' — a) r

sm (i — a )

tan i sin (I — a ) = tan F

sin (i — E) sin u R
cosZ^sin (Z/ — a) sin* r

sin (F — b) sin u cos i R
cosGsm(L'-l) _ r

sin (/ — a — (?) cos M R
sin Z/sin {L' — T) r

COS »

tan6 tin T

• / IT \ ' // /-v \ r>

sin ( -/i/ — u } sin it — ^ i jt
sin Zcos (L' — a ) r

:, .-. , Idll J.

sim cos (t — a )

sin(w — Z) R
cos K sin b cos (Z/ — a) r

sin G sin (L — I) r

\ ' — 4-n-ri j.

sin (AT — 6) cos u R
sin Z r

cos ( C4- L' — I) tan (Z/ — a ) cos » ~
sin Z) cos (Z' — a) . . M

sin (u—L) cos (Z'— a ) -ff
sin J/ r

III.

13.
14.
15.

r sin M sm t
sin b

sin (I! — a)s>n»_ ficosEs\n(L' — asn . A
~ sin (»' — ^) sin (Z — Q ) cos i

sin (i, — E) sin b

7? cos .Fsin (Z/ — Q) tan i _ Z^ sin .fsin (L' — a) sin U — Q) _ ./
sin (>— J) ^ sin (-f— 6)

Other expressions for // may be obtained by combining 13 with all the
formulas II.

Examples : —

Given, a= 80°59'12".07, z7=281°l'34".99, ^=:53023'2".46, »= 10°37'9".55,
5 = — 3° 6' 33".561, log Z?= 9.9926158.

296

APPENDIX.

log tan b
log cos (L' — 8 )
Clog sin (L' — b)
log tan A

8.7349698 n
9.9728762 »
0.1313827 n

8.8392287 »

L = — 3°57'2".136
(= 6°40'7".414

log sin A
log tan (L' — 8)
flog sin (J.-J-?)
log tan u

8.8381955«
9.5620014

9.3352577 n
u = — 12° 12' 37".942

2°.

log sin (Lr — I)

log tan i

9.8686173 w
9.2729872
(7.log cos (77— 8) 0.0271238 n
log tan B 9.1687283

£ = 8°23'21".888
= 5°16'48".327

log cos B

log sin b

log tan (L' — Q)

C. log cos i
log tan M

9.9953277
8.7343300 n
9.5620014
1.0360961
0.0075025
9.3352577 n

log sin (II — 8)
log tan i

a. log sin (X' — /)
C. log tan z

log tan C

9.5348776 »
8.7349698 n
0.1313827 n
0.7270128

log sin 6"
log sin (Lr — 8 )
. C. log sin ( C-\- L' — i
C. log cos i

9.1243583 n
9.5348776 n
J)0.6685194w
0.0075025

9.1282429 n

«7 = — 7° 39' 7".058
04-17 — 8 = 192° 23' 15".864

log tan «<

9.3352578 n

4°.

log cos (Z' — 8)
log tan i
(7. log cos (L'—l)
C. log tan i
log tan Z>

9.9728762 n
8.7349698 n
0.1714973 n
0.7270128
9.60G3561n
.0= -21°59'51".182
D + L' — l= 205° 38' 41". 348

log sin D 9.5735295 n

log tan (Z'— 8) 9.5620014
log cos (Z' — I) 9.8285027 R

C'.logsin(Z>-|-r— /) 0.3637217 R
£ log cos*' 0.0075025

log tan M 9.3352578 n

APPENDIX.

5°.

log tan b

8.7349698 n

iOf

log sin (I— Q )

9.6658973 »

IOC

log tan E

9.0690725

C!

E—&

5 41' 12".412

a

i—n=y

> 55' 57".138

loj

297

log sin (If— S)
C. log sin (i—E]

C. log sin M

9.0661081
9.5348776 n
1.1637907
0.6746802 n

0.4394566

~ J.ti

r=\og R _j-log^= 0.4320724

log tan i
log sin (I — Q, )
log tan F

9.2729872
9.6658973 »

8.9388845 n

' 57' 53".955
'51'20".394

log cos _F

log sin b

log sin (Z' — Q)

£ log sin (F — b)

C. log sin M

<7. log cos z

9.9983674
8.7343300 n
9.5348776 n
1.4896990 n
0.6746802 n
0.0075025 it

0.4394567

7°.

log cos i
log tan M
log tan G

a=—

9.9924975
9.3352577 n
9.3277552w
12° 0'27".118

15° 35' 42".492

log cos G

log sin (L' — l)

C, log cos u

9.9903922
9.8686173 n
0.5705092 n
0.0099379
0.4394566

log tan (I— Q)
log cos i
log tan H

II=— 28°

9.7183744 n
9.9924975
9.7258769 «
0' 39".879

H—u=— 15° 48' 1".937

log sin H

log sin (L' — l)
C. log sin (H — w)

log sin (/ —

9.6717672 n
9.8686173 n
0.5649695 n
0.3341027 M
0.4394567

38

298

APPENDIX.

9°.

log tan b
C. log sin i
C. log cos (l-

log tan /

1 =

u — I =

log sin i
log cos (I — S
log tan M
log tan K
K--

K—b--

8.7349698 n
0.7345153

8) 0.0542771
9.5237622 n

• 18° 23' 55".334
6°11'17".392

9.2654847
) 9.9475229
9.3352577 M
875482653 n
-2°1'26".344

1°5' 7".217

log sin I
log sin (U — 8
C. log sin (u — /)

10°.

log cos K

log sin b

log cos (E — 8)
£ log sin (K—b)
C. log cos M

. 9.4991749 n
9.9728762 n
0.9674054

0.4394565

9.9997290
8.7343300 n
9.9728762 n
1.7225836
0.0099379

0.4394567

11°.

tf 4- 1! — I = 219° 59' 25".474

log sin C 9.1243583 M

log sin (L' — t) 9.8686173 n

C. log coa(G-{-If—I) 0.1156850 n

Clog tan (I/— 8) 0.4379986

C log cost 0.0075025

log tan L 9.5541617 n
L = — 19° 42' 32".533

M -L==

7° 29' 54".591

12°.
D+L'— 8= 178° 2' 31".738

log sin D

log cos (I! — Q)
£logcos(Z>+i'—
Clog cos»

log tan M(= L}

9.5735295 n
9.9728762 n
) 0.0002536 n
0.0075025
9.5541618 n

log sin L
C. log sin (M — L)
C. log cos (If— Q

logr
log sin u
log sin i
C. log sin b

13°

9.5279439 n
0.8843888
0.0271238 M

0.4394565

0.4320724
9.3253198 n
9.2654847
1.2656700 n
02885469

APPENDIX. 299

76.

If in the equations of article 60,

x — X= A cosd cos a
y — Y -= A cosd sin a
z — Z = A sin 8

a denoting the right ascension, and 8 the declination, we suppose X, Y, Z known,

we have

dx = cos a cosd d A — A sin a cost? da — A cos a sin$ dd
d y = sin a cos d d A -\- A cos a cos 8 da — A sin a sin d dd
d z = sin d d A -\- A cos d dd.

Multiply the first of these by sin a , and subtract from it the second multiplied by
cos a , and we find

A cos d d a = — dx sin a -j- d y sin a .

Multiply the first by cos a and add to it the second multiplied by sin a , and
we find

dx cos a -\- dy sin a •=. cos d d A — A sin (J dd.

Multiply this equation by — sin d and add it to the third of the differential equa
tions above multiplied by cos d and we find

— dx cos a sin d — dy sin a sin d -\- dz cos d = A dd

and, therefore,

d, sin a. , . cos « 7
d a =. -j-ax -\ — -j- dy

-, ,5, cos a sin 8 -, sin a sin 8 , , cos 3 7

a o = -. d x -; a y -\ -r- dz.

d d A

From the formulas of article 56 of the Appendix are obtained

dx x dy y dz z

dr r' dr r' dr r'

-^ = x cotan (A -f- u) , -^=y cotan (B -f- M) , ^ = s cotan ( C-{- «)

rfa; . rf« . , dz

— - = x sin u cos a , -r-. = r smwcoso, -r-. = r sinwcos c,
di d^ di

and the partial differentials

dx . dy dz

r-r — — ^cose — s sins, - = 2 cose, --=xsins

300 APPENDIX.

whence

dx = -dr -[-# cotan (A -|-«) d v -\- x cotan (vl-f-«) dn

— [x cotan (A -}- M) -\-y cos e -(- 0 sin e] </ & -|- r sin M cos a rfz

dy = y-dr -\- y cotan (.Z? -f- w) e?p -(-y cotan (i? -(- M) J n

— \_y cotan (B -f- M) — a; cos e] d & ~f- r sin u cos i «?»

ds = -dr — s cotan ( C'-j-w) rfw-f- 2 cotan (O-\-u) dn

— [s cotan ( C-\- u] — x sin e] d Q, -f- f sin M cos c di.

These formulas, as well as those of 56 may be found in a small treatise
Ueber die Differentialformeln far Cometem-Balmen, etc., by G. D. E. WEYER, (Berlin,
1852). They are from BESSEL'S Abhandlung liber den Olbers'schen Cometen.

90.

GAUSS, in the Berliner Astronomisches Jahrbuch for 1814, p. 256, has given an
other method of computing £, and also C of article 100. It is as follows : -
We have

c_ 5. 10

~ + =

This fraction, by substituting for X the series of article 90, is readily trans
formed into

f- 8 <^(-\ I2-8 | 3.8.10^ , 4.8.10.12^ , 5.8.10.12.14 4

'los^v1 ~9~' " 9.11 ^ 9.H.13 : ' 9.nm7ur* •

Therefore, if we put

* 1 I 2 • O lO.O.ll/oi ,

^==l + __^ + ___^ + etc,
we shall have

by means of which 5 can always be found easily and accurately.

APPENDIX. 301

For C, article 100, it is only necessary to write g in place of x in the pre
ceding formulas.

A may be computed more conveniently by the following formula : —

a/ 1.5 1.3.5.7 ,, 1.3.5.5.7.9

A=(l-x] H1 +279^ + 2^

. 4.6. 9. 11.

142.

PROF. ENCKE, on the 13th of January, 1848, read a paper before the Royal
Academy of Sciences at Berlin, entitled Ueber den Ausnahmefall einer doppetten
Bahnbestimmung ans denselben drei geocentrischen Oertern, in which he entered into a
full discussion of the origin of the ambiguous case here mentioned, and the
manner in which it is to be explained. The following paragraphs, containing
useful instructions to the practical computer, embody the results of his in
vestigation : —

By putting

m = c Q sin w
0 = (oi-f a),

Equation IV., 141, becomes, for r'^>Hf

m sin4 s = sin (0 — q)
and for / <^ R

m sin4 s = sin (z -)- q)
m is always positive.

The number and the limits of the roots of this equation may be found by
examining both forms.

Take the first form, and consider the curves, the equations of which are

y — m sin4 z, y' = sin (z — q)

y and y' being ordinates, and z abscissas.
The first differential coefficients are

dy . „ dt/ , .

^| = 4 m sin4 z cos z, ~- = cos (z — q),

302 APPENDIX.

There will, therefore, be a contact of the curves when we have

m sin4 z = sin (z — q)

and

4 m sin8 s cos z = cos (z — q)

or when

4 sin (z — <?) cos s = cos (s — q) sin«

which may be more simply written

sin (20 — q] = £ sin q.

When the value of z deduced from this equation satisfies

m sin4 z = sin (z — q)

then there is a contact of the curves, or the equation has two equal roots. These
equal roots constitute the limits of possibility of intersection of the curves, or the
limits of the real roots of the equation.

For the delineation of both curves it is only necessary to regard values of
a — q between 0° and 180°, since for values between 180° and 360° the solution
is impossible ; and beyond 360° these periods are repeated.

The curve

/ = sin (z — q)

is the simple sine-curve, always on the positive side of /, and concave to the axis of
abscissas, and has a maximum for

„ — q — 90°.

The curve

y •=. sin4z

is of the fourth order, and since it gives

-^ = 4 m sin3 z cos z = m sin 2 z — J m sin 4 z
dz

-r-
it lias a maximum for

-r-j- = 12 m sin2 z cos2 z — 4 m sin4 z

dz'

= 4 m sin2 z (1 -f- 2 cos 2 z] = 2 m (cos 2 z — cos 4 z}
^J. = _ 4ra(sin2z — 2sin4z)

dz*

-r-£ = — 8 m (cos 2z — 4 cos 4 z)

APPENDIX. 303

and a point of contrary flexure for

z = 60°, and 2 = 120°.

From s— 0° to s— 60°, it is convex to the axis of abscissas, from 60° to
120° it is concave, and convex from 120° to 180°.
For oscillation, the three equations,

m sin4 3 = sin (z — q)
4 m sin8 z cos z = cos (z — q)
4 m sin2 2(1 -f-2 cos 2 2)= — sin (2 — q)
must coexist, or

m sin4 z = sin (z — q)
sin (2 3 — q] = f sin q

cos 22 = — f .
In this case we should have

sin (2s — q) = | cos ^ -f- I snl ?>
consequently,

tan£ = f
and

mn? = £,
or

* = 46°H-isin-1f.

From these considerations we infer that for the equation

m sin4 z = sin (2 — q)
or even when it is in the form

nf sin8 z — 2 m cos ^ sin5 2 -)- sin2 2 — sin2 q = 0

of the eighth degree, there can only be four real roots ; because, in the whole
period from z — <^=0°to z — q = 360°,only four intersections of the two curves
are possible on the positive side of the axis of ordinates.

Of these, three are between 2=0° and z = 180°, and one between 180°
and 180° -\-q; or, inversely, one between 0° and 180°, and three between 180°
and 180° -\-q; consequently, there are three positive and one negative roots, or
three negative and one positive roots for sin 2.

304 APPENDIX.

Contact of the curves can exist only when for a given value of q,

z1 = i q -j- i sin""1 f sin q
and

, sin (/ — q)

sin4 z/

If the contact of the curve of the fourth order with the sine-curve is with
out the latter, then will m' constitute the upper limit, — for m greater than this
values of the roots will be impossible. There would then remain only one positive
and one negative root.

If the contact is within the sine-curve, then will the corresponding m" con
stitute the lower limit, and for m less than this, the roots again would be re
duced to two, one positive and one negative.

If q is taken negative, or if we adopt the form

m sin4 2 = sin (z -j- q)

180° - — z must be substituted for z.
The equation

m2 sin8 z — 2m cos q sin6 z -j- sin2 z — sin2 q •=. 0

shows, moreover, according to the rule of DESCARTES, that, of the four real
roots three can be positive only when q, without regard to sign is less than
90°, because m is always regarded as positive. For q greater than 90°, there is
always only one real positive root Now since one real root must always cor
respond to the orbit of the Earth, that is, to r' ' = R ; and since sin<5", in the
equation, article 141, —

R sin &
sin z = — -; —

is always positive, so that it can be satisfied by none but positive values
of z ; an orbit can correspond to the observations only when three real roots are
positive, or when q without regard to its sign is less than 90°. These limits are
still more narrowly confined, because, also, there can be four real roots only
when m lies between m' and m", and when we have

| Bin q < 1, or sin q < f , q < 36° 52' 11".64
in order that a real value of / may be possible.

APPENDIX. 305

Then the following are the conditions upon which it is possible to find a
planet's orbit different from that of the earth, which shall satisfy three complete
observations.

First. The equation

m sin4 z = sin (z -\- q)

must have four real roots. The conditions necessary for this are, that we must
have, without regard to sign,

sin q < |

and m must lie between the limits m' and m".

/Second. Of these four real roots three must be positive and one negative.

For this it is necessary that cos q should remain positive for all four of those
values for which

sin q < ± § ,

the two in the second and third quadrants are excluded, and only values between
- 36° 52' and + 36° 52' are to be retained.

If both these conditions are satisfied, of the three real positive roots, one must
always correspond to the Earth's orbit, and consequently will not satisfy the
problem. And generally there will be no doubt which of the other two will
give a solution of the problem. And since by the meaning of the symbols, arti
cles 139, 140, we have

sin z sin (8' — z) sin &

IT' ~tf~ :~7~

not only must z and d' be always less than 180°, but, also, sin(d' — z) must be
positive, or we must have

y>a.

If, therefore, we arrange the three real positive roots in the order of their
absolute magnitudes, there may be three distinct cases. Either the smallest root
approaches most nearly the value of d', and corresponds, therefore, to the Earth's
orbit, in which case the problem is impossible; because the condition d' >2 can
never be fulfilled. Or the middle root coincides with d', then will the problem
be solved only by the smallest root. Or, finally, the greatest of the three roots
differs least from d'. in which case the choice must lie between the two smaller

39

305 APPENDIX.

roots. Each of these will give a planetary orbit, because each one fulfils all
the conditions, and it will remain to be determined, from observations other than
the three given ones, which is the true solution.

As the value of m must lie between the two limits m' and m", so also must
all four of the roots lie between those roots as limits which correspond to m and
m". In Table IVa. are found, therefore, for the argument q from degree to degree,
the roots corresponding to the limits, arranged according to their magnitude, and
distinguished by the symbols z\ z", zm, z". For every value of m which gives a
possible solution, these roots will lie within the quantities given both for m and
ni", and we shall be enabled in this manner, if 8' is found, to discern at the first
glance, whether or not, for a given m and q, the paradoxical case of a double orbit
can occur. It must, to be sure, be considered that, strictly speaking, 8' would
only agree exactly with one of the z's, when the corrections of P and Q belong
ing to the earth's orbit had been employed, and, therefore, a certain difference
even beyond the extremest limit might be allowed, if the intervals of time should
be very great.

The root s", for which sin s is negative, always falls out, and is only intro
duced here for the sake of completeness. Both parts of this table might have
been blended in one with the proviso of putting in the place of z its supplement ;
for the sake of more rapid inspection, however, the two forms sin (z — </) and
sin (.? -|- </) have been separated, so that q is always regarded as positive in the
table.

To explain the use of Table IV«. two cases are added ; one, the example of Ceres
in this Appendix, and the other, the exceptional case that occurred to Dr. GOULD,
in his computation of the orbit of the fifth comet of the year 1847, an account of
wJiich is given in his AstronomicalJournal, Vol. I., No. 19.

I. In our example of Ceres, the final equation in the first hypothesis is

[0.9112987] sin4z = sin (*. — 7° 49' 2".0)
and

8'= 24°19'53".34

the factor in brackets being the logarithm. By the table, the numerical factor
lies between m and m", and this d' answers to z", concerning which there can be
no hesitation, since zu must lie between 10°. 27' and 87° 34'. Accordingly, we

APPENDIX. 307

have only to choose for the £ which occurs in this case, and which, as we per
ceive, is to be sought between 7° 50' and 10° 27'.

The root is in fact

2 = r 59' 30".3,
and the remaining roots,

«" = 26 24 3

if* = 148 2 35
^=18740 9

are all found within the limits of the table.

2. In the case of the fifth comet of 1847, Dr. GOULD derived from his first
hypothesis the equation

[9.7021264] sin4* = sin (s -f- 32° 53' 28".5).
He had also

V = 133° 0' 31".

Then we have sin q <^ -f , and the inspection of the table shows that the factor
in the parenthesis lies between m' and m" ; therefore, there will be four real roots.
of which three will be positive. The given d' approximates here most nearly to
sia, about which, at any rate, there can be no doubt.

Consequently, the paradoxical case of the determination of a double orbit
occurs here, and the two possible values of s will lie between

88° 29' - - 105° 59'
and

105 59 -131 7
In fact, the four roots are,

2' = 95° 31' 43".5
z" == 117 31 13 .1
zra = 137 38 16 .7
a" =329 58 35 .5.

By a small decrease of m without changing q, or by a small decrease of q
without changing m, a point of osculation will be obtained corresponding to
nearly a mean between the second and third roots ; and on the contrary, by a
small increase of m without changing q, or a small increase of q without changing
m, a point of osculation is obtained corresponding to nearly a mean between the
first and second roots.

;;08 APPENDIX.

"We have, therefore, the choice between the two orbits. The root used by Dr.
GOULD was z", which gave him an ellipse of very short period. The other obser
vations showed him that this was not the real orbit. M. D'ARREST was involved in
a similar difficulty with the same comet, and arrived also at an ellipse. An ellipse
of eighty-one years resulted from the use of the other root.

" Finally, both forms of the table show that the exceptional case can never
occur when 8' < 63° 26'.

" It will also seldom occur when d' < 90°. For then it can only take place
with the first form sin (s — q), and since here for all values of q either the limits
are very narrow, or one of the limits approximates very nearly to 90°, so it will
be perceived that the case where there are two possible roots for d'< 90° will
very seldom happen. For the smaller planets, therefore, which for the most part
are discovered near opposition, there is rarely occasion to look at the table. For
the comets we shall have more frequently d' > 90° ; still, even here, on account
of the proximity to the sun, d' > 150° can, for the most part, be excluded. Con
sequently, it will be necessary, in order that the exceptional case should occur,
that we should have in general, the combination of the conditions d' ^> 90° and
<l between 0° and 32° in the form sin (z — q), or between 22° and 36° 52' in the
form sin (z -j- q]."

Professor PEIRCE has communicated to the American Academy several methods
of exhibiting the geometrical construction of this celebrated equation, and of
• others which, like this, involve two parameters, some of which are novel and
curious. In order to explain them, let us resume the fundamental equation,

m sin4 g = sin (z — q).

1. The first method of representation is by logarithmic curves ; the logarithm
of the given equation is

log m -\- 4 log sin z = log sin (2 — §•).
If AVC construct the curve

y = 4 log sin z,

APPENDIX. 309

and also the same curve on another scale, in which y is reduced to one fourth of

its value, so that

y = log sin s,

it is plain that if the second curve is removed parallel to itself by a distance equal
to q in the direction of the axis of z, and by a distance equal to — logm in the
direction of the axis of y, the value of z on the first curve where the two curves
intersect each other will be a root of the given equation ; for, since the point of
intersection is on the first curve, -its coordinates satisfy the equation,

y = 4 log sin 3,
and because it is on the second curve its coordinates satisfy the equation,

y -f- log m = log sin (z — q) ;

and by eliminating y from these two equations we return to the original equation,

m sin4 2 = sin (z — q).

A diagram constructed on this principle is illustrated by figure 5, and it will
be readily seen how, by moving one curve upon the other, according to the
changeable values of q and m, the points of intersection will be exhibited, and also
the limits at which they become points of osculation.

On this and all the succeeding diagrams, we may remark, once for all, that
two cases are shown, one of which is the preceding example of the planet Ceres,
in which the four roots of the equation will correspond in all the figures to the
four points of intersection D, D', D", D"', and the other of which is the very
remarkable case that occurred to Dr. GOULD, approaching the two limits of
the osculation of the second order, the details of which are given in No. 19 of his
Astronomical Journal, and the points of which are marked on all our diagrams
G, G', G", G'".

2. The second method of representation is by a fixed curve and straight line,
as follows.

(a.) The fundamental equation, developed in its second member, and divided
by in cos z, assumes the form

sin4 z cos q

cosz

= -— (tan;? — tan q)

m \ i'

By putting

x = tan z, b = tan q, a = — -

310 APPENDIX.

the roots of the equation will correspond to the points of intersection of the

curve

_ sin4 z _ x*

with the straight line

y = a(x — b}. [Figs. 6 and 6'.]

It will be perceived that the curve line, in this as in all the following cases
under this form, is not affected by any change in the values of m and q, and that
the position of the straight line is determined by its cutting the axis of x at
the distance tan q from the origin, and the axis of y at the distance — ^^

m

from the origin. The tangent of its inclination to the axis is obviously equal to
'—, which may in some cases answer more conveniently for determining its
position than its intersection with the axis of y.

(b.) The development of the fundamental equation divided by m sin z, is

sin8 z = -— (cotan q — cotan z) ;

and by .putting

x = cotan 2

b = cotan q

the roots of the equation correspond to the intersection of the curve

y = sin8 * = (1 -|- «*)""" t
with the straight line

y = a(b — x}. [Fig. 7.]

The position of the straight line is determined by its cutting the axis of x at a
distance equal to cotan q from the origin, and the axis of y at a distance equal to ^-^
from the origin. This form of construction is identical with that given by M.
Binet in the Journal de FEcok Poll/technique, 20 Cahier, Tome XIII. p. 285. His
method of fixing the position of the straight line is not strictly accurate. This
mode of representation is not surpassed by either of the others under this form.

(c.) The fourth root of the fundamental equation developed, and divided by
cos (z — q\ assumes the form

cos ? (tan (z — q\ 4- tan?) = »n

cos (z —

q)

APPENDIX. oil

By putting

x = tan (z — q)

b = tan q
a = \j m cos q
the roots of the equation correspond to the intersection of the curve

=

cos z — q)

with the straight line

y = a(x + b). [Fig. 8.]

The straight line cuts the axis of x at a distance equal to — tan q, and the axis
of u at a distance equal to ^ m sin q, from the origin.

(d.) The development of the fourth root of the fundamental equation divided
by sin (0 — q) is,

3

^ m sin q (cotan (z — q) -f- cotan q) = cosec (s — qy

By putting

x = cotan (z — q}

1) = cotan £
a — ^ m sin g1

the roots of the equation correspond to the intersection of the curve

with the straight line

y = a(x-\-l). [Figs. 9 and 9'.]

The straight line cuts the axis of x at a distance equal to — cotan q, and the
axis of y at a distance equal to $ m cos q, from the origin.

(e.) From the reciprocal of the fundamental equation multiplied by m, its
roots may be seen to correspond to the intersection of the curve

r = cosec4 s

with the straight line

r = m cosec (z — q}. [Figs. 10 and 10'.]

Both these equations are referred to polar coordinates, of which r is the radius
vector, z the angle which the radius vector makes with the polar axis, m the dis
tance of the straight line from the origin, and q the inclination of the line to the
polar axis.

312 APPENDIX.

(/). From the reciprocal of the fourth root of the fundamental equation, its
roots may be seen to correspond to the intersection of the curve

r = cosec^ 9
with the straiht line

in which

y = 2 — q. [Fig. 11.]

Both these equations are referred to polar coordinates, of which (p is the
an ale which the radius vector r makes with the polar axis, \1 - the distance of the

T m

straight line from the origin, and q the inclination of the line to the polar axis.

3. The third method of representation is by a curve and a circle.

(«.) The roots of the fundamental equation correspond to the intersection
of the curve

sin4 z

with the circle

r = - sin (z — z}. [Fig. 12.1

m V. 1 L O J

Both these equations are referred to polar coordinates, of which r is the radius
vector, 0 the angle which the radius vector makes with the polar axis, — the

in

radius of the circle which passes through the origin, and 90° -(- q is the ano-le
which the diameter drawn to the origin makes with the polar axis.

(b.) From the fourth root of the fundamental equation it appears that its
roots correspond to the intersection of the equation

r — ^ sin <f
with the circle

[Fig. 13],

in which 9 — (2 — q) is the inclination of the radius vector to the polar axis,
^ m is the diameter of the circle which passes through the origin, and 90° — q
is the inclination of the diameter drawn through the origin of the polar axis.

In these last two delineations the curve I K I' K' I" incloses a space, within
which the centre of the circle must be contained, in order that there should be
four real roots, and therefore that there should be a possible orbit. The curve

APPENDIX.

313

itself corresponds to the limiting points of osculation denoted by Professor ENCKE'S
m' and m", and the points K and K' correspond to the extreme points of oscula
tion of the second order, for which ENCKE has given the values q •= =p 36° 52'
and m' = 4.2976, and m" — 9.9999.

On the delineations, 8 is the centre of the circle for our example of Ceres,
and 8' the same for Dr. GOULD'S exceptional case. A careful examination of the
singular position of the point 8' will illustrate the peculiar difficulties attending
the solution of this rare example.

159.

"We add another example, which was prepared with great care to illustrate the
Method of Computing an Orbit from three observations published in pamphlet
form for the use of the American Ephemeris and Nautical Almanac in 18-52. It
furnishes an illustration of the case of the determination of two orbits from the
same three geocentric places, referred to in article 142.

We take the following observations, made at the Greenwich Observatory,
from the volume for the year 1845, p. 36.

Mean Time, Greenwich.

Apparent Right Ascension.

Apparent Declination.

1845. July 30, H 5 10.8
Sept. 6, 11 5 56.8
Oct. 14, 8 19 35.9

o / //
339 51 15.15

332 22 39.30
328 7 51.45

S. 23 31 34.60
27 10 23.13
26 49 57.23

From the Nautical Almanac for the same year, we obtain

Date.

Longitude of the Sun
from App. Equinox.

Nutation.

Distance from the
Earth.

Latitude of the
Sun.

Apparent Obliquity
of the Ecliptic.

July 30.
Sept. G.
Oct. 14.

o / //

127 40 11.32
164 9 40.85
201 21 12.49

-f-14.99
4-14.06
-j-12.16

0.0064168

0.0031096
9.9984688

' — 0.17

4-0.21

-j-0.53

0 / //

23 27 28.13
28.41
28.05

The computation is arranged as if the orbit were wholly unknown, on which
account we are not at liberty to free the places of Ceres from parallax, but must
transfer it to the places of the earth.

40

APPENDIX.

Reducing the observed places of the planet from the equator to the ecliptic,
we find

Date.

App. Longitude of Ceres.

App. Latitude of Cores.

July 30.
Sept. 6.
Oct. 14.

332 28 28.02
324 35 58.87
321 4 54.55

S. 13 54 52.47
14 45 30.00
13 5 35.33

And also,

Date.

Longitude of Zenith,

Latitude of Zenith.

July 30.
Sept 6.
Oct. 14.

o /

11 6
4 49
1 4

ST. 53 26

56 22

58 4

The method of article 72 gives

Date.

Reduction of Longitude.

Reduction of Distance.

Reduction of Time.

July 30.
Sept. 6.
Oct. 14.

+16.32
— 7.10
—26.95

+0.0001368
1421

0907

—0.070
—0.065
—0.071

The reduction of time is merely added to show that it is wholly insensible.

All the longitudes, both of the planet and of the earth, are to be reduced to
the mean vernal equinox for the beginning of the year 1845, which is taken as
the t'poch ; the nutation, therefore, being applied, we are still to subtract the
precession, which for the three observations is 28".99, 34".20, and 39".41, re
spectively ; so that for the first observation it is necessary to add — 43".98, for
the second, — 48".26, and for the third, — 51".57.

Finally, the latitudes and longitudes of Ceres are to be freed from the aber
ration of the fixed stars, by subtracting from the longitudes 18".76, 19".69,.and
10".40, respectively, and adding to the latitudes —2.02, +1.72, and +4.02,
numbers which are obtained from the following formulas of Prof. PEIRCE : —

d a = m cos ( O — « ) sec ft

d ft =^ m sin ( O — « ) sin a ;

where O = sun's longitude, and m = aberration of Q.

APPENDIX.

315

The longitudes of the sun were corrected for aberration by adding 20".06,
20".21, and 20".43, respectively, to the numbers given in the Nautical
Almanac.

These reductions having been made, the correct data of the problem are as
follows : —

Times of observation.

For Washington Meridian.

Ceres'slong. a, a', a"
latitudes p, 0', 0"
Earth's long. I, t, I"
logs, of dist. R, R, R'

July 30. 372903.

330° 27' 25".28
- 13 54 54 .49
307 39 43 .66
0.0064753

Sept. 6. 248435.

324 34 50.92

• 14 45 28.28

344 8 45.49

0.0031709

By the formulas of Arts. 136 and 137, we find

7,7,7

d,d',S"

log d, d', d" sines
A D,Aiy,AD"
A'D,A"V,A'D",

f ff
£, I , £ ,

log e, s', e" sines, . .
log sin i K
log cos i e'

And by article 138,

wherefore

329° 25' 34".81
28 12 56 .84

9.6746717

199° 45' 41".00

233 54 11 .72

27 32 45 .72

9.6650753

log T sin t
log Tcost

218° 11' 22".38
24 19 53 .34

9.6149131

204° 8'25".14

233 31 23 .54

142 37 25 .44

9.7832221

9.9764767

9.5057153

6.2654993 n
9.2956278 n

Whence

*=180° 3' 12".63, log T . . . 9.2956280

= 38°14/35".01,logsin(<-f /) 9.7916898

log S ...... 8.6990834

logrsin^ + y) . . 9.0873178
log tan (<T — a) . . . 9.6117656
6' — a = 22° 14' 47".47 and a = 2° 5' 5".87.

Oct. 14. 132915.
321 3 52.58
• 13 5 31.31
21 19 53.97
9.9985083

194 59 35 .15
61 6 50.78
9.9422976
203° 56' 46".56
199 30 24 .04
115 4 41 .lu
9.956992

816 APPENDIX.

By articles 140-143, we find

A" D — 8" = 172° 24' 32".76 log sin 9.1208995 log cos 9.9961773 n
AD' — 8 =175 55 28.30 8.8516890 9.9989004 n

A'D — S" =172 47 20.94 9.0987168

AD — d' + o =177 30 53.53 8.6370904

AD" — d =175 43 49.72 8.8718546

AD" — $' + a=lll 15 36.57 8.6794373

log a ..... 0.0095516, a =1.0222370

log 4 ..... 0.1389045.

Formula 13, which serves as a check, would give log b = 0.1389059. We
prefer the latter value, because sin ( A' D — $' -j- o) is less than sin (A D"
-tf' + a).

The interval of the time (not corrected) between the second and third obser
vations is 37.884480 days, and between the first and second 37.875532 days.
The logarithms of these numbers are 1.5784613 and 1.5783587 ; the logarithm
of k is 8.2355814 ; whence log 6 = 9.8140427, log d" = 9.8139401.

We shall put, therefore, for the first hypothesis

x = log P = ? = 9.9998974

y — log Q = 6 6" = 9.6269828
and we find

01 = 5° 43' 56".13

<o + 0 = 7 49 2 .00
log Qc sin w = 0.9112987

It is found, by a few trials, that the equation

Q c sin w sin4 z = sin (z -j- 7° 49' 2".00)
is satisfied by the value

0 = 7° 59' 30".30,
whence log sin z = 9.1431101, and

/= = 0.474939.

sin z

APPENDIX. 317

Besides this solution, the equation admits of three others, —

0 = 26° 24' 3"
g=148 2 35
0=187 40 9

The third must be rejected, because sin z is negative ; the second, because z is
greater than 8' ; the first answers to the approximation to the orbit of the earth,
of which we have spoken in article 142.*

The manner of making these trials is as follows. On looking at the table of
sines we are led to take for a first approximation for one of the values, 0 = 8°
nearly, or 8° -f- x. Then we have

log sin z ....... 9.14356 -|- 89 x

log sin4 z ....... 6.57424 -f 356 x

log^csinw ...... 0.91130

;sin(0 — w — o] . . . 7.48554 -+- 356 x
e — (a — o = 0° 10' 52" + ftfr x
o) + ff = T 49 3

0=7 59 55-f-iV** nearly =8° -f-ar.
For the second approximation, we make

0=7° 59' 30" + / ; and have

log sin 0 9.1431056 -f- 150 /

log sin4 0 6.5724224 + 600 of,

Q.csmw 0.9112987

log sin (0 — a. — 0) . 7.4837211 + 600^
g — a, _ 0 = 0° 10' 28".27 -f TV of nearly,
w -f o = 7 49 2. 00

0=759 30. 27 + TV af = 7° 59' 30".30.
The process is the same for the other roots.

* See article 142 of the Appendix.

318 APPENDIX.

Again, by art. 143 we obtain

f=185010'31".7S
£"=189 25 30.25
log f = 0.4749722
log r"= 0.4744748

i (*"-(-«) = 264° 21' 48".61 .

i(w"_w) = 288 49 5.19
2/ = 6 57 7 .46
2/" = 6 56 32 .68

The sum 2/-|-2/", which is a check, only differs by 0".20 from 2/', and the

equation

p_rsin2/" _i£
•^ : ~ i" sin 2/ ~~ n

is sufficiently satisfied by distributing this 0".2 equally between 2/ and 2/", so
that 2/= 6°59'7".36, and 2/" = 6°56'32".58.

Now, in order that the times may be corrected for aberration, the distances
(j, ()', Q" must be computed by the formulas of Art 145, and then multiplied into
the time 493' or Od.005706, as follows : —

logr 0.47497

log sin (AD — Q .... 9.51187

comp. log sin d 0.32533

log 9 0.31217

log const 7.76054*

log of reduction 8.07271
Reduction == 0.011823

log /, 0.47497

log sin (d — z) 9.44921

comp log sin if, 0.38509

log of reduction 0.30927
Reduction, 0.011744.

* The constant of aberration is that of M. Struve.

APPENDIX. o!9

logr" . . 0.47447

log sin ( A" D' — C") • . . 9.84253

log sin d" 0.05770

log of reduction 0.37470

Reduction =0.013653

Observations. Corrected Times. Intervals. Logarithms.

I. July 30. 361080

IJ. Sept. 6. 236691 37.875611 1.5783596

in. Oct. 14. 119260 37.882569 1.5784395

Hence the corrected logarithms of the quantities &, 6" become 9.8140209,
and 9.8139410.

We are now, according to the precept of Art. 146, to commence the determi
nation of the elements from the quantities/, /, r", (3, and to continue the calcula
tion so far as to obtain rj, and again from the quantities /", r, /, 6" so as to
obtain ij".

log*? 0.0011576

log 77" 0.0011552

logP' .... 9.9999225
log </ .... 9.6309476

From the first hypothesis, therefore, there results X == 0.0000251, and
Y= 0.0029648.

In the second hypothesis, we assign to P and Q the values which we find
in the first hypothesis for P and $. We put, therefore,

x = log P — 9.9999225,
y — log $=9.6309476.

Since the computation is to be performed in precisely the same manner as in
the first hypothesis, it is sufficient to set down here its principal results: —

0 . 7° 59' 34" 98

<« 5° 43' 56" .10

c.j + a 7 49 1 .97

log (Jcsmoi 0.9142633

log/ 0.4749037

log n-' 0.7724177

320

APPENDIX.

nV
n"

.. 0.7724952

185° 10' 39" 64

189 25 42 .36

0.4748696

logr" 0.4743915

*(M + M) . . . . 264° 21' 50" .64
* («" — «) .... 288 49 5 .57

2/' 13 53 58 82

2/ . 6 57 15 58

2/" 6 56 43 41

In this case we distribute the difference 0".17so as to make 2/= 6° 51' 15".49
and 2/"= 6° 56' 43".33.

It would not be worth while to compute anew the reductions of the time on
account of the aberration, for they scarcely differ 1" from those which we de
rived from the first hypothesis.
Further computations furnish

log T? = 0.0011582, log?;" = 0.0011558, whence are deduced
log ^=9.9999225, X= 0.0000000
log q = 9.6309955, T = 0.0000479 .

From which it is apparent how much more, exact the second hypothesis is than
the first.

For the sake of completing the example, we will still construct the third
hypothesis, in which we shall adopt the values of P and Q' derived from the
second hypothesis for the values of P and Q.

Putting, therefore,

x = log P= 9.9999225

y = log Q == 9.6309955
the following are obtained for the most important parts of the computation : —

»' 5°43'56".10

w + o 7 49 1.97

log Qc sin w .... 0.9143111

z 7°59'35".02

log/ 0.4749031

log^ 0.7724168

n
nV

. 0.7724943
185° 10' 39".69

f" 189°25'42".45

logr 0.4748690

logr" 0.4743909

iw"M .... 264°21'50".64

(a"— «)

288 49 5 .57

2/' 13 53 58 .94

2/ 6 57 15 .65

2/" 6 56 43 .49

APPENDIX. 321

The difference 0".2 between 2/' and 2/-f-2/" is divided as in the first
hypothesis, making 2/ = 6° 57' 15".55, and 2/"= 6° 56' 43".39.

All these numbers differ so little from those given by the second hypothesis
that it may safely be concluded that the third hypothesis requires no further cor
rection ; if the computation should be continued as in the preceding hypotheses,
the result would be X= 0.0000000, F— 0.0000001, which last value must be
regarded as of no consequence, and not exceeding the unavoidable uncertainty
belonging to the last decimal figure.

We are, therefore, at liberty to proceed to the determination of the elements
from 2/', r, r", 6' according to the methods contained in articles 88-97.

The elements are found to be as follows : —

Epoch of the mean longitude, 1845, .... 278° 47' 13".79

Mean daily motion, .... .... 771".5855

Longitude of the perihelion, 148° 27' 49".70 .

Angle of eccentricity, 4 33 28 .35

Logarithm of the major semi-axis .... 0.4417481

Longitude of the ascending node, .... 80° 46' 36".94

Inclination of the orbit, 10 37 7 .98

The computation of the middle place from these elements gives

«'= 324° 34' 51".05, /?'= — 14° 45' 28".31
which differ but little from the observed values

«'== 324° 34' 50".92, fl'= — 14° 45' 28".28.

41

322 APPENDIX.

FORMULAS FOE COMPUTING THE ORBIT OF A COMET.

Given

Mean times of the observations in days, t', f, if"

Observed longitudes of the comet, «', a", a'"

Observed latitudes of the comet, ft', ft", ft'"

Longitudes of the sun, A', A", A'"

Distances of the sun from the earth, R, R", R"

Required

The curtate distances from the earth, 9', (>", Q'"

Compute

L

tan (3" ,, _ If"— if' TO sin (a! — A") — tan/T

~8in(a"— A") ' if'—tf tan/3"'~— msin(a"'— A")

and by means of this, approximately,

n.

R" cos (A'"— A') — K = ffcos(G — A')
R" sin (A'"— A) —ffwa(G — A')

g is the chord of the earth's orbit between the first and third places of the earth.
G the longitude of the first place of the earth as seen from the third place.

III.

M — cos (a'"— a') = h cos £ cos (H— a'")
sin («'"_ a') — h cos £ sin (II— a'")
Mian ft'"— tan ft' •= h sin f .

h is always positive. If JVis a point, the coordinates of which, referred to the
third place of the earth, are

(/ cos a', (/ sin a', ^» tan /3,
then are

A?', ^ C,

APPENDIX. 323

the polar coordinates of the third place of the comet, (that is, the distance, longi
tude and latitude,) referred to the point N as the origin.

IV.

cos C cos ( G — H] = cos (f ffsirnp=A

cos ft' cos («' — A') — cos if)' B sin y'= ff

cos ft'" cos («'" — A") = cos y '" #" sin y'" = ff"
By means of 9, i//, r/", -4, -B', -B"', Olbers's formulas, become : -

F =(^9'— <7COS9)2-f-yl2

r'2 =(Q'sec|3'— R' cos yj + ff2

r'"z = (Mo sec ft"' — R" cos i^'")2 + B"'*

The computation would be somewhat easier by

V.

h cos (i'=f, g cos (f — /' R cos y'= c'

=/'" ^ cos v» — /'" 7T" cos /"= c'"

/

in which

u=^h ()' — g cos y

VI.

A value of u is to be found by trial which will satisfy the equation

(/ + ,"+ *)*-(/+ /"-*)* - ^,

in which

log »»'= 0.9862673

If no approximate value for (>' or for / or r" is otherwise known, by means
of which an approximate value of u can be found, we may begin with

324 APPENDIX.

This trial will be facilitated by Table ITTa, which gives fj, corresponding to

by means of which is found k, which corresponds rigorously to r, r'", and if" — i!\ _

x(r-Q

-(/ + /")! /*»

in which

log x = 8.5366114.

The process may be as follows : For any value of « compute k, r, r'", by V,
and with /, r", compute rj, with which /* is to be taken from Table IIIa, and a value
of k is to be computed which corresponds to the /, r'", f- — i! used. And u is to
be changed until the second value of k shall agree exactly with that computed
byV.

Then we have

,__

'

vn.

(>' cos («' — A') — & = / cos V cos (f — A')
</ gin («' — A') = r' cos b' sin (t — A')

q' tan /J' = / sin V

cos («'" — A") — R" = r'" cos V" cos (r — A")
(>'" sin (of" - A"} = r'" cos V" sin (f"—A'")

FIRST CONTROL.

The values of r', r'", obtained from these formulas, must agree exactly with
those before computed.

/, b' ; I", b'", are heliocentric longitudes and latitudes of the comet.

The motion is direct when f"- - f is positive, and retrograde when r — f is
negative.

APPENDIX. 325

VIII.

± tan U = tan i sin (t — Q )
tan If" — tan 6' cos (Z"7— Z')

rin(r-0 = tan i COB (f — 8)

i the inclination is always positive, and less than 90°. The upper signs are to be
used when the motion is direct ; the lower when it is retrograde.

IX.

= tan (L' - Q ), **«"-*) = tan (£'"- fi ).

COS « v

COS 4

'"

L' and L"' are the longitudes in orbit.

SECOND CONTROL.

The value of k before computed must be exactly

k = y/ [V2 + r'"* — 2 / /" cos (II" — £')].

/

X.

1 _ cos ^ (L' — n)

cos (If "—L')

V// V7" V'?

TT, the longitude of the perihelion, is counted from a point in the orbit from which
the distance, in the direction of the order of the signs, to the ascending node, is
equal to the longitude of the ascending node.

XL

The true anomalies are

v' = L' — n, v'" = L'"—n.

With these the corresponding M' and M'" are to be taken from BARKER'S
Table, and we have then the time of perihelion passage

T= f =F M' q* n = f' =F M'" q% n,

326 APPENDIX.

in which M' and M'" have the sign of v and v'" ; the constant log n is

log n = 0.0398723.

The upper signs serve for direct, the lower for retrograde motion.
For the use of Table Ha instead of BARKER'S Table, see Article 18 of the
Appendix.

THIRD CONTROL.

The two values of T, from it, and f", must agree exactly.

XII.

With T, q,n, 8 , i, I", A", £", compute a" and (i", and compare them with the
observed values. And also compute with these values the formula

tan/?"
~ Sm (a" — A")'

If this value agrees with that of m of formulas I., the orbit is exactly deter
mined according to the principles of Olbers's Method. That is, while it satisfies
exactly the two extreme places of the comet, it agrees with the observations in
the great circle which connects the middle place of the Comet with the middle
place of the Sun.

If a difference is found, M can be changed until the agreement is complete.

TABLES.

TABLE I. (See articles 42, 45.)

ELLIPSE.

HYPERBOLA.

A

LogB

C

T

LogB

c

T

0.000

0

0

0.00000

0

0

0.00000

.001

0

0

.00100

0

0

.00100

.002

0

2

.00200

0

2

.00200

.003

1

4

.00301

1

4

.00299

.004

1

7

.00401

1

7

.00399

0.005

2

11

0.00502

2

11

0.00498

.006

3

16

.00603

3

16

.00597

.007

4

22

.00704

4

22

.00696

.008

5

29

.00805

5

29

.00795

.009

6

37

.00907

6

37

.00894

0.010

7

46

0.01008

7

46

0.00992

.011

9

56

.01110

9

55

.01090

.012

11

66

.01212

11

66

.01189

.013

13

78

.01314

13

77

.01287

.014

15

90

.01416

15

89

.01384

0.015

17

103

0.01518

17

102

0.01482

.016

19

118

.01621

19

116

.01580

.017

22

133

.01723

21

131

.01677

.018

24

149

.01826

24

147

.01774

.019

27

166

.01929

27

164

.01872

0.020

30

184

0.02032

30

182

0.01968

.021

33

203

.02136

33

200

.02065

.022

36

223

.02239

36

220

.02162

.023

40

244

.02343

39

240

.02258

.024

43

265

.02447

43

261

.02355

0.025

47

288

0.02551

46

283

0.02451

.026

51

312

.02655

50

306

.02547

.027

55

336

.02760

54

330

.02643

.028

59

362

.02864

58

355

.02739

.029

63

388

.02969

62

381

.02834

0.030

67

416

0.03074

67

407

0.02930

.031

72

444

.03179

71

435

.03025

.032

77

473

.03284

76

463

.03120

.033

82

503

.03389

80

492

.03215

.034

87

535

.03495

85

523

.03310

0.035

92

567

0.03601

91

554

0.03404

.036

97

600

.03707

96

585

.03499

.037

103

634

.03813

101

618

.03593

.038

108

669

.03919

107

652

.03688

.039

114

704

.04025

112

686

.03782

.040

120

741

.04132

118

722

.03876

TABLE 1,

ELLIPSE.

HYPERBOLA.

A

LogB

C

T

LogB

c

T

0.040

120

741

0.041319

118

722

0.038757

.041

126

779

.042387

124

758

.039695

.042

133

818

.043457

130

795

.040632

.043

139

858

.044528

136

833

.041567

.044

146

898

.045601

143

872

.042500

0.045

152

940

0.046676

149

912

0.043432

.046

159

982

.047753

156

953

.044363

.047

166

1026

.048831

163

994

.045292

.048

173

1070

.049911

170

1037

.046220

.049

181

1116

.050993

177

1080

.047147

0.050

188

1162

0.052077

184

1124

0.048072

.051

196

1210

.053163

191

1169

.048995

.052

204

1258

.054250

199

1215

.049917

.053

212

1307

.055339

207

1262

.050838

.054

220

1358

.056430

215

1310

.051757

0.055

228

1409

0.057523

223

1358

0.052675

.056

236

1461

.058618

231

1407

.053592

.057

245

1514

.059714

239

1458

.054507

.058

254

1568

.060812

247

1509

.055420

.059

263

1623

.061912

256

1561

.056332

0.0 GO

272

1679

0.063014

265

1614

0.057243

.061

281

1736

.064118

273

1667

.058152

.062

290

1794

.065223

282

1722

.059060

.063

300

1853

.066331

291

1777

.059967

.064

309

1913

.067440

301

1833

.060872

0.065

319

1974

0.068551

310

1891

0.061776

.066

329

2036

.069664

320

1949

.062678

.067

339

2099

.070779

329

2007

.063579

.068

350

2163

.071896

339

2067

.064479

.069

360

2228

.073014

349

2128

.065377

0.070

371

2294

0.074135

359

2189

0.066274

.071

381

2360

.075257

370

2251

.067170

.072

392

2428

.076381

380

2314

.068064

.073

403

2497

.077507

390

2378

.068957

.074

415

2567

.078635

401

2443

.069848

0.075

426

2638

0.079765

412

2509

0.070738

.076

437

2709

.080897 •

423

2575

.071627

.077

449

2782

.082030

434

2643

.072514

.078

461

2856

.083166

445

2711

.073400

.079

473

2930

.084303

457

2780

.074285

.080

485

3006

.085443

468

2850

.075168

TABLE I,

ELLIPSE.

HYPERBOLA.

A

LogB

C

T

LogB

C

T

0.080

485

3006

0.085443

468

2850

0.075168

.081

498

3083

.086584

480

2921

.076050

.082

510

3160

.087727

492

2992

.076930

.083

523

3239

.088872

504

3065

.077810

.084

535

3319

.090019

516

3138

.078688

0.085

548

3399

0.091168

528

3212

0.079564

.086

561

3481

.092319

540

3287

.080439

.087

575

3564

.093472

553

3363

.081313

.088

588

3647

.094627

566

3440

.082186

.089

602

3732

.095784

578

3517

.083057

0.090

615

3818

0.096943

591

3595

0.083927

.091

629

3904

.098104

604

3674

.084796

.092

643

3992

.099266

618

3754

.085663

.093

658

4081

.100431

631

3835

.086529

.094

672

4170

.101598

. 645

3917

.087394

0.095

687

4261

0.102766

658

3999

0.088257

.096

701

4353

.103937

672

4083

.089119

.097

716

4446

.105110

686

4167

.089980

.098

731

4539

.106284

700

4252

.090840

.099

746

4634

.107461

714

4338

.091698

0.100

762

4730

0.108640

728

4424

0.092555

.101

777

4826

.109820

743

4512

.093410

.102

793

4924

.111003

758

4600

.094265

.103

809

5023

.112188

772

4689

.095118

.104

825

5123

.113375

787

4779

.095969

0.105

841

5224

0.114563

802

4870

0.096820

.106

857

5325

.115754

817

4962

.097669

.107

873

5428

.116947

833

5054

.098517

.108

890

5532

• .118142

848

5148

.099364

.109

907

5637

.119339

864

5242

.100209

0.110

924

5743

0.120538

880

5337

0.101053

.111

941

5850

.121739

895

5432

.101896

.112

958

5958

.122942

911

5529

.102738

.113

975

6067

.124148

928

5626

.103578

.114

993

6177

.125355

944

5724

.104417

0.115

1011

6288 .

0.126564

960

5823

0.105255

.116

1029

6400

.127776

977

5923

.106092

.117

1047

6513

.128989

994

6024

.106927

.118

1065

6627

.130205

1010

6125

.107761

.119

1083

6742

.131423

1027

6228

.108594

.120

1102

6858

.132643

1045

G331

.109426

TABLE 1.

ELLIPSE.

HYPERBOLA.

A

LogB

C

T

LogB

C

T

0.120

1102

6858

0.132643

1045

6331

0.109426

.121

1121

6976

.133865

1062

6435

.110256

.122

1139

7094

.135089

1079

6539

.111085

.123

1158

7213

.136315

1097

6645

.111913

.124

1178

7334

.137543

1114

6751

.112740

0.125

1197

7455

0.138774

1132

6858

0.113566

.126

1217

7577

.140007

1150

6966

.114390

.127

1236

7701

.141241

1168

7075

.115213

.128

1256

7825

.142478

1186

7185

.116035

.129

1276

7951

.143717

1205

7295

.116855

0.130

1296

8077

0.144959

1223

7406

0.117675

.131

1317

8205

.146202

1242

7518

.118493

.132

1337

8334

.147448

1261

7631

.119310

.133

1358

8463

.148695

1280

7745

.120126

.134

1378

8594

.149945

1299

7859

.120940

0.135

1399

8726

0.151197

1318

7974

0.121754

.136

1421

8859

.152452

1337

8090

.122566

.137

1442

8993

.153708

1357

8207

.123377

.138

1463

9128

.154967

1376

8325

.124186

.139

1485

9264

.156228

1396

8443

.124995

0.140

1507

9401

0.157491

1416

8562

0.125802

.141

1529

9539

.158756

1436

8682

.126609

.142

1551

9678

.160024

1456

8803

.127414

.143

1573

9819

.161294

1476

8925

.128217

.144

1596

9960

.162566

1497

9047

.129020

0.145

1618

10102

0.163840

1517

9170

0.129822

.146

1641

10246

.165116

1538

9294

.130622

.147

1G64

10390

.166395

1559

9419

.131421

.148

1687

10536

.167676

1580

9545

.132219

.149

1710

10683

.168959

1601

9671

.133016

0.150

1734

10830

0.170245

1622

9798 .

0.133812

.151

1757

10979

.171533

1643

9926

.134606

.152

1781

11129

.172823

1665

10055

.135399

.153

1805

11280

.174115

1686

10185

.136191

.154

1829

11432

.175410

1708

10315

.136982

0.155

1854

11585

0.176707

1730

10446

0.137772

.156

1878

11739

.178006

1752

10578

.138561

.157

1903

11894

.179308

1774

10711

.139349

.158

1927

12051

.180612

1797

10844

.140135

.159

195-2

12208

.181918

1819

10978

.140920

.160

1977

12366

.183226

1842

11113

.141704

TABLE I.

5

ELLIPSE.

HYPERBOLA.

A

LogB

C

T

Log B

C

T

0.1 GO

1977 .

12366

0.183226

1842

11113

0.141704

.161

2003

12526

.184537

1864

11249

.142487

.162

2028

12686

.185850

1887

11386

.143269

.163

2054

12848

.187166

1910

11523

.144050

.164

2080

13011

.188484

1933

11661

.144829

0.165

2106

13175

0.189804

1956

11800

0.145608

.166

2132

13340

.191127

1980

11940

.146385

.167

2158

13506

.192452

2003

12081

.147161

.168

2184

13673

.193779

2027

12222

.147937

.169

2211

13841

.195109

2051

12364

.148710

0.170

2238

14010

0.196441

2075

12507

0.149483

.171

2265

14181

.197775

2099

12651

.150255

.172

2292

14352

.199112

2123

12795

.151026

.173

2319

14525

.200451

2147

12940

.151795

.174

2347

14699

.201793

2172

13086

.152564

0.175

2374

14873

0.203137

2196

13233

0.153331

.176

2402

15049

.204484

2221

13380

.154097

.177

2430

15226

.205832

2246

13529

.154862

.178

2458

15404

.207184

2271

13678

.155626

.179

2486

15583

.208538

2296

13827

.156389

0.180

2515

15764

0.209894

2321

13978

0.157151

.181

2543

15945

.211253

2346

14129

.157911

.182

2572

16128

.212614

2372

14281

.158671

.183

2601

16311

.213977

2398

14434

.159429

.184

2630

16496

.215343

2423

14588

.160187

0.185

2660

16682

0.216712

2449

14742

0.160943

.186

2689

16868

.218083

2475

14898

.161698

.187

2719

17057

.219456

2502

15054

.162453

.188

2749

17246

.220832

2528

15210

.163206

.189

2779

17436

.222211

2554

15368

.163958

0.190

2809

17627

0.223592

2581

15526

0.164709

.191

2839

17820

.224975

2608

15685

.165458

.192

2870

18013

.226361

2634

15845

.166207

.193

2900

18208

.227750

2661

16005

.166955

.194

2931

18404

.229141

2688

16167

.167702

0.195

2962

18601

0.230535

2716

16329

0.168447

.196

2993

18799

.231931

2743

16491

.169192

.197

3025

18998

.233329

2771

16655

.169935

.198

3056

19198

.234731

2798

16819

.170678

.199

3088

19400

.236135

2826

16984

.171419

.200

3120

19602

.237541

2854

17150

.172159

6

TABLE I,

ELLIPSE.

HYPERBOLA.

A

LogB

c

T

LogB

C

T

1

0.200

3120

19602

0.237541

2854

17150

0.172159

.201

3152

19806

.238950

2882

17317

.172899

.202

3184

20011

.240361

2910

17484

.173637

.203

3216

20217

.241776

2938

170.32

.174374

.204

3249

20424

.243192

2967

17821

.175110

0.205

3282

20(532

0.244612

2995

17991

0.175845

.206

3315

20842

.246034

3024

18161

.176579

.207

3348

21052

.247458

3053

18332

.177312

.208

3381

21264

.248885

3082

18504

.178044

.209

3414

21477

.250315

3111

18677

.178775

0.210

3448

21690

0.251748

3140

18850

0.179505

.211

3482

21905

.253183

3169

19024

.180234

.212

3516

22122

.254620

3199

19199

.180962

.213

3550

22339

.256061

3228

19375

.181688

.214

3584

22557

.257504

3258

19551

.182414

0.215

3618

22777

0.258950

3288

19728

0.183139

.216

3653

22998

.260398

3318

19906

.183863

.217

8688

23220

.261849

3348

20084

.184585

.218

3723

23443

.263303

3378

20264

.185307

.219

3758

23667

.264759

3409

20444

.186028

0.220

3793

23892

0.266218

3439

20625

0.186747

.221

3829

24119

.267680

3470

20806

.187466

.222

3865

24347

.269145

3500

20988

.188184

.223

3900

24576

.270612

3531

21172

.188900

.224

393C

24806

.272082

3562

21355

.189616

0.225

3973

25037

0.273555

3594

21540

0.190331

.226

4009

25269

.275031

3625

21725

.191044

.227

4046

25502

.276509

3656

21911

.191757

.228

4082

25737

.277990

3688

22098

.192468

.229

4119

25973

.279474

3719

22285

.193179

0.230

4156

26210

0.280960

3751

22473

0.193889

.231

4194

2G448

.282450

3783

22662

.194597

.232

4231

26687

.283942

3815

22852

.195305

.233

4269

26928

.285437

3847

23042

.196012

.234

4306

27169

.286935

3880

23234

.196717

0.235

4344

27412

0.288435

3912

23425

0.197422

.236

4382

27656

.289939

3945

23618

.198126

.237

4421

27:ioi

.291445

3977

23811

.198829

.238

4459

28148

.292954

4010

24005

.199530

.239

4498

28395

.294466

4043

24200

.200231

.210

4537

28644

.295980

4076

24396

.200931

TABLE I.

ELLIPSE.

HYPERBOLA.

A

LogB

C

T

LogB

c

T

0.240

4537

28644

0.295980

4076

24396

0.200931

.241

4576

28894

.297498

4110

24592

.201630

.242

4615

29145

.299018

4143

24789

.202328

.243

4654

29397

.300542

4176

24987

.203025

.244

4694

29651

.302068

4210

25185

.203721

0.245

4734

29905

0.303597

4244

25384

0.204416

.246

4774

30161

.305129

4277

25584

.205110

.247

4814

30418

.306664

4311

25785

.205803

.248

4854

30676

.308202

4346

25986

.206495

.249

4894

30935

.309743

4380

26188

.207186

0.250

4935

31196

0.311286

4414

26391

0.207876

.251

4976

31458

.312833

4449

26594

.208565

.252

5017

31721

.314382

4483

26799

.209254

.253

5058

31985

.315935

4518

27004

.209941

.254

5099

32250

.317490

4553

27209

.210627

0.255

5141

32517

0.319048

4588

27416

0.211313

.256

5182

32784

.320610

4623

27623

.211997

.257

5224

33053

.322174

4658

27830

.212681

.258

5266

33323

.323741

4694

28039

.213364

.259

5309

33595

.325312

4729

28248

.214045

0.260

5351

33867

0.326885

4765

28458

0.214726

.261

5394

34141

.328461

4801

28669

.215406

.262

5436

34416

.330041

4838

28880

.216085

.263

5479

34692

.331623

4873

29092

.216763

.264

5522

34970

.333208

4909

29305

.217440

0.265

5566

35248

0.334797

4945

29519

0.218116

.266

5609

35528

.336388

4981

29733

.218791

.267

5653

35809

.337983

5018

29948

.219465

.268

5697

36091

.339580

5055

30164

.220138

.269

5741

36375

.341181

5091

30380

.220811

0.270

5785

36659

0.342785

5128

30597

0.221482

.271

5829

36945

.344392

5165

30815

.222153

.272

5874

37232

.346002

5202

31033

.222822

.273

5919

37521

.347615

5240

31253

.223491

.274

5964

37810

.349231

5277

31473

.224159

0.275

6009

38101

0.350850

5315

31693

0.224826

.276

6054

38393

.352473

5352

31915

.225492

.277

6100

38686

.354098

5390

32137

.226157

.278

6145

3*981

.355727

5428

32359

.226821

.279

6191

39277

.357359

5466

32583

.227484

.280

6237

39573

.358994

5504

32807

.228147

TABLE I,

ELLIPSE.

HYPERBOLA.

A

LogB

C

T

LogB

C

T

0.280

6237

39573

0.358994

5504

32807

0.228147

.281

6283

39872

.360632

5542

33032

.228808

.282

6330

40171

.362274

5581

33257

.229469

.283

6376

40472

.363918

5619

33484

.230128

.284

6423

40774

.365566

5658

33711

.230787

0.285

6470

41077

0.367217

5697

33938

0.231445

.286

6517

41381

.368871

5736

34167

.232102

.287

6564

41687

.370529

5775

34396

.232758

.288

6612

41994

.372189

5814

34626

.233413

.289

6660

42302

.373853

5853

34856

.234068

0.290

6708

42611

0.375521

5893

35087

0.234721

.291

6756

42922

.377191

5932

35319

.235374

.292

6804

43233

.378865

5972

35552

.236025

.293

6852

43547

.380542

6012

35785

.236676

.294

6901

43861

.382222

6052

36019

.237326

0.295

6950

44177

0.383906

6092

36253

0.237975

.290

6999

44493

.385593

6132

36489

.238623

.297

7048

44812

.387283

6172

36725

.239271

.298

7097

45131

.388977

6213

36961

.239917

.299

7147

45452

.390673

6253

37199

.240563

.300

7196

45774

.392374

6294

37437

.241207

TABLE II. (See Article 93.)

h

i°gyy

h

logyy

h

logyy

0.0000

0.0000000

0.0040

0.0038332

0.0080

0.0076133

.0001

.0000965

.0041

.0039284

.0081

.0077071

.0002

.0001930

.0042

.0040235

.0082

.0078009

.0003

.0002894

.0043

.0041186

.0083

.0078947

.0004

.0003858

.0044

.0042136

.0084

.0079884

0.0005

0.0004821

0.0045

0.0043086

0.0085

0.0080821

.0006

.0005784

.0046

.0044036

.0086

.0081758

.0007

.0006747

.0047

.0044985

.0087

.0082694

.0008

.0007710

.0048

.0045934

.0088

.0083630

.0009

.0008672

.0049

.0046883

.0089

.0084566

0.0010

0.0009634

0.0050

0.0047832

0.0090

0.0085502

.0011

.0010595

.0051

.0048780

.0091

.0086437

.0012

.0011556

.0052

.0049728

.0092

.0087372

.0013

.0012517

.0053

.0050675

.0093

.0088306

.0014

.0013478

.0054

.0051622

.0094

.0089240

0.0015

0.0014438

0.0055

0.0052569

0.0095

0.0090174

.0016

.0015398

.0056

.0053515

.0096

.0091108

.0017

.0016357

.0057

.0054462

.0097

.0092041

.0018 .0017316

.0058

.0055407

.0098

.0092974

. |>19 .0018275

.0059

.0056353

.0099

.0093906

0.0020

0.0019234

0.0060

0.0057298

0.0100

0.0094838

.0021

.0020192

.0061

.0058243

.0101

.0095770

.0022

.0021150

.0062

.0059187

.0102

.0096702

.0023

.0022107

.0063

.0060131 .

.0103

.0097633

.0024

.0023064

.0064

.0061075

.0104

.0098564

0.0025

0.0024021

0.0065

0.0062019

0.0105

0.0099495

.0026

.0024977

.0066

.0062962

.0106

.0100425

.0027

.0025933

.0067

.0063905

.0107

.0101355

.0028

.0026889

.0068

.0064847

.0108

.0102285

.0029

.0027845

.0069

.0065790

.0109

.0103215

0.0030

0.0028800

0.0070

0.0066732

0.0110

0.0104144

.0031

.0029755

.0071

.0067673

.0111

.0105073

.0032

.0030709

.0072

.0068614

.0112

.0106001

.0033

.0031663

.0073

.0069555

.0113

.0106929

.0034

.0032617

.0074

.0070496

.0114

.0107857

0.0035

0.0033570

0.0075

0.0071436

0.0115

0.0108785

.0036

.0034523

.0076

.0072376

.0116

.0109712

.0037

.0035476

.0077

.0073316

.0117

.0110639

.0038

.0036428

.0078

.0074255

.0118

.0111565

.0039

.0037380

.0079

.0075194

.0119

.0112491

.0040

.0038332

.0080

.0076133

.0120

.0113417

10

TABLE II.

h

logyy

h

logyy

h

log y y

0.0120

0.0113417

0.0160

0.0150202

0.0200

0.0186501

.0121

.0114343

.0161

.0151115

.0201

.0187403

.0122

.0115268

.0162

.0152028

.0202

.0188304

.0123

.0116193

.0163

.0152941

.0203

.0189205

.0124

.0117118

.0164

.0153854

.0204

.0190105

0.0125

0.0118043

0.0165

0.0154766

0.0205

0.0191005

.0126

.0118967

.0166

.0155678

.0206

.0191905

.0127

.0119890

.0167

.0156589

.0207

,0192805

.0128

.0120814

.0168

.0157500

.0208

.0193704

.0129

.0121737

.0169

.0158411

.0209

.0194603

0.0130

0.0122660

0.0170

0.0159322

0.0210

0.0195502

.0131

.0123582

.0171

.0160232

.0211

.0196401

.0132

.0124505

.0172

.0161142

.0212

.0197299

.0133

.0125427

.0173

.0162052

.0213

.0198197

.0134

.0126348

.0174

.0162961

.0214

.0199094

0.013,5

0.0127269

0.0175

0.0163870

0.0215

0.0199992

.0136

.0128190

.0176

.0164779

.0216

.0200889

.0137

.0129111

.0177

.0165688

.0217

.0201785

.0138

.0130032

.0178

.0166596

.0218

.0202682

.0139

.0130952

.0179

.0167504

.0219

.02035 7 H

0.0140

0.0131871

0.0180

0.0168412

0.0220

0.0204474

.0141

.0132791

.0181

.0169319

.0221

.0205369

.0142

.0133710

.0182

.0170226

.0222

.0206264

.0143

.0134629

.0183

.0171133

.0223

.0207159

.0144

.0135547

.0184

.0172039

.0224

.0208054

0.0145

0.0136465

0.0185

0.0172945

0.0225

0.0208948

.0146

.0137383

.0186

.0173851

.0226

.0209842

.0147

.0138301

.0187

.0174757

.0227

.0210736

.0148

.0139218

.0188

.0175662

.0228

.0211630

.0149

.0140135

.0189

.0176567

.0229

.0212523

0.0150

0.0141052

0.0190

0.0177471

0.0230

0.0213416

.0151

.0141968

.0191

.0178376

.0231

.0214309

.0152

.0142884

.0192

.0179280

.0232

.0215201

.0153

.0143800

.0193

.0180183

.0233

.0216093

.0154

.0144716

.0194

.0181087

.0234

.0216985

0.0155

0.0145631

0.0195

0.0181990

0.0235

0.0217876

.0156

.0146546

.0196

.0182893

.0236

.0218768

.0157

.0147460

.0197

.0183796

.0237

.0219659

.0158

.0148374

.0198

.0184698

.0238

.0220549

.0159

.0149288

.0199

.0185600

.0239

.0221440

.0160

.0150202

.0200

.0186501

.0240

.0222330

TABLE II.

11

h

i°gyy

h

logyy

h

logyy

0.0240

0.0222330

0.0280

0.0257700

0.0320

0.0292626

.0241

.0223220

.0281

.0258579

.0321

.0293494

.0242

.0224109

.0282

.0259457

.0322

.0294361

.0243

.0224998

.0283

.0260335

.0323

.0295228

.0244

.0225887

.0284 .0261213

.0324

.0296095

0.0245

0.0226776

0.0285

0.0262090

0.0325

0.0296961

.0246

.0227664

.0286

.0262967

.0326

.0297827

.0247

.0228552

.0287

.0263844

.0327

.0298693

.0248

.0229440

.0288

.0264721

.0328

.0299559

.0249

.0230328

.0289

.0265597

.0329

.0300424

0.0250

0.0231215

0.0290

0.0266473

0.0330

0.0301290

.0251

.0232102

.0291

.0267349

.0331

.0302154

.0252

.0232988

.0292

.0268224

.0332

.0303019

.0253

.0233875

.0293

.0269099

.0333

.0303883

.0254

.0234761

.0294

.0269974

.0334

.0304747

0.0255

0.0235647

0.0295

0.0270849

0.0335

0.0305611

.0256

.0236532

.0296

.0271723

.0336

.0306475

.0257

.0237417

.0297

.0272597

.0337

.0307338

.0258

.0238302

.0298

.0273471

.0338

.0308201

.0259

.0239187

.0299

.0274345

.0339

.0309064

0.0260

0.0240071

0.0300

0.0275218

0.0340

0.0309926

.0261

.0240956

.0301

.0276091

.0341

.0310788

.0262

.0241839

.0302

.0276964

.0342

.0311650

.0263

.0242723

.0303

.0277836

.0343 .0312512

.0264

.0243606

.0304

.0278708

.0344 .0313373

0.0265

0.0244489

0.0305

0.0279580

0.0345 0.0314234

.0266

.0245372

.0306

.0280452

.0346 .0315095

.0267

.0246254

.0307

.0281323

.0347 .0315956

.0268

.0247136

.0308

.0282194

.0348 .0316816

.0269

.0248018

.0309

.0283065

.034!) .0317676

0.0270

0.0248900

0.0310

0.0283936

0.0350 0.0318536

.0271

.0249781

.0311

.0284806

.0351 .0319396

.0272

.0250662

.0312

.0285676

.0352 .0320255

.0273

.0251543

.0313

.0286546

.0353 .0321114

.0274

.0252423

.0314

.0287415

.0354

.0321973

0.0275

0.0253303

0.0315

0.0288284

0.0355

0.0322831

.0276

.0254183

.0316

.0289153

.0356 .0323689

.0277

.0255063

.0317

.0290022

.0357 .0324547

.0278

.0255942

.0318

.0290890

.0358 .0325405

.0279

.0256821

.0319

.0291758

.0359

.0326262

.0280

.0257700

.0320

.0292626

.0360

.0327120

12

TABLE II.

h

i°gyy

h

i°gyy

h

logyy

0.0360

0.0327120

0.040

0.0361192

0.080

0.0681057

.0861

.0327976

.041

.0369646

.081

.0688612

.0863

.0328833

.042

.0378075

.082

.0696146

.0:! 63

.0329689

.043

.0386478

.083

.0703661

.0364

.0330546

.044

.0394856

.084

.0711157

0.0365

0.0331401

0.045

0.0403209

0.085

0.0718633

.0366

.0332257

.046

.0411537

.086

'.0726090

.0367

.0333112

.047

.0419841

.087

.0733527

.0368

.0333967

.048

.0428121

.088

.0740945

.0369

.0334822

.049

.0436376

.089

.0748345

0.0370

0.0335677

0.050

0.0444607

0.090

0.0755725

.0371

.0336531

.051

.0452814

.091

.0763087

.0372

.0337385

.052

.0460997

.092

.0770430

.0373

.0338239

.053

.0469157

.093

.0777754

.0374

.0339092

.054

.0477294

.094

.0785060

0.0375

0.0339946

0.055

0.0485407

0.095

0.0792348

.0376

.0340799

.056

.0493496

.096

.0799617

.0377

.03416.51

.057

.0501563

.097

.0806868

.0378

.0342504

.058

.0509607

.098

.0814101

.0379

.0343356

.059

.0517628

.099

.0821316

0.0380

0.0344208

0.060

0.0525626

0.100

0.0828513

.0381

.0345059

.061

.0533602

.101

.0835693

.0382

.0345911

.062

.0541556

.102

.0842854

.0383

.0346762

.063

.0549488

.103

.0849999

.0384

.0347613

.064

.0557397

.104

.0857125

0.0385

0.0348464

0.065

0.0565285

0.105

0.0864235

.0386

.0349314

.066

.0573150

.106

.0871327

.0387

.0350164

.067

.0580994

.107

.0878401

.0388

.0351014

.068

.0588817

.108

.0885459

.0389

.0351864

.069

.0596618

.109

.0892500

0.0390

0.0352713

0.070

0.0604398

0.110

0.0899523

.031(1

.0353562

.071

.0612157

.111

.0906530

.0392

.0354411

.072

.0619895

.112

.0913520

.0393

.0355259

.073

.0627612

.113

.0920494

.0394

.0356108

.074

.0635308

.114

.0927451

0.0395

0.0356956

0.075

0.0642984

0.115

0.0934391

.0396

.0357804

.076

.0650639

.116

.0941315

.0397

.0358651

.077

.0658274

.117

.0948223

.0398

.0359499

.078

.0665888

.118

.0955114

.0399

.0360346

.079

.0673483

.119

.0961990

.0400

.0361192

.080

.0681057

.120

.0968849

TABLE II.

IS

h

logyy

h

logyy

h

logyy

0.120

0.0968849

0.160

0.1230927

0.200

0.1471869

.121

.0975692

.161

.1237192

.201

.1477653

.122

.0982520

.162

.1243444

.202

.1483427

.123

.0989331

.163

.1249682

.203

.1489189

.124

.0996127

.164

.1255908

.204

.1494940

0.125

0.1002907

0.165

0.1262121

0.205

0.1500681

.126

.1009672

.166

.1268321

.206

.1506411

.127

.1016421

.167

.1274508

.207

.1512130

.128

.1023154

.168

.1280683

.208

.1517838

.129

.1029873

.169

.1286845

.209

.1523535

0.130

0.1036576

0.170

0.1292994

0.210

0.1529222

.131

.1043264

.171

.1299131

.211

.1534899

.132

.1049936

.172

.1305255

.212

.1540565

.133

.1056594

.173

.1311367

.213

.1546220

.134

.1063237

.174

.1317466

.214

.1551865

0.135

0.1069865

0.175

0.1323553

0.215

0.1557499

.136

.1076478

.176

.1329628

.216

.1563123

.137

.1083076

.177

.1335690

.217

.1568737

.138

.1089660

.178

.1341740

.218

.1574340

.139

.1096229

.179

.1347778

.219

.1579933

0.140

0.1102783

0.180

0.1353804

0.220

0.1585516

.141

.1109323

.181

.1359818

.221

.1591089

.142

.1115849

.182

.1365821

.222

.1596652

.143

.1122360

.183

.1371811

.223

.1602204

.144

.1128857

.184

.1377789

.224

.1607747

0.145

0.1135340

0.185

0.1383755

0.225

0.1613279

.146

.1141809

.186

.1389710

.226

.1618802

.147

.1148264

.187

.1395653

.227

.1624315

.148

.1154704

.188

.1401585

.228

.1629817

.149

.1161131

.189

.1407504

.229

.1635310

0.150

0.1167544

0.190

0.1413412

0.230

0.1640793

.151

.1173943

.191

.1419309

.231

.1646267

.152

.1180329

.192

.1425194

.232

.1651730

.153

.1186701

.193

.1431068

.233

.1657184

.154

.1193059

.194

.1436931

.234

.1662628

0.155

0.1199404

0.195

0.1442782

0.235

0.1668063

.156

.1205735

.196

.1448622

.236

.1673488

.157

.1212053

.197

.1454450

.237

.1678903

.158

.1218357

.198

.1460268

.238

.1684309

.159

.1224649

.199

.1466074

.239

.1689705

.160

.1230927

.200

.1471869

.240

.1695092

TABLE II.

h

logyy

h

logyy

h

logyy

0.240

0.1695092

0.280

0.1903220

0,320

0.2098315

.241

.1700470

.281

.1908249

.321

.2103040

.242

.1705838

.282

.1913269

.322

.2107759

.243

.1711197

.283

.1918281

.323

.2112470

.244

.1716547

.284

.1923286

.324

.2117174

0.245

0.1721887

0.285

0.1928282

0.325

0.2121871

.246

.1727218

.286

.1933271

.326

.2126562

.247

.1732540

.287

.1938251

.327

.2131245

.248

.1737853

.288

.1943224

.328

.2135921

.249

.1743156

.289

.1948188

.329

.2140591

0.250

0.1748451

0.290

0.1953145

0.330

0.2145253

.251

.1753736

.291

.1958094

.331

.2149909

.252

.1759013

.292

.1963035

.332

.2154558

.253

.1764280

.293

.1967968

.333

.2159200

.254

.1769538

.294

.1972894

.334

.2163835

0.255

0.1774788

0.295

0.1977811

0.335

0.2168464

.256

.1780029

.296

.1982721

.336

.2173085

.257

.1785261

.297

.1987624

.337

.2177700

.258

.1790484

.298

.1992518

.338

.2182308

.259

.1795698

.299

.1997406

.339

.2186910

0.260

0.1800903

0.300

0.2002285

0.340

0.2191505

.261

.1806100

.301

.2007157

.341

.2196093

.262

.1811288

.302

.2012021

.342

.2200675

.263

.1816467

.303

.2016878

.343

.2205250

.264

.1821638

.304

.2021727

.344

.2209818

0.265

0.1826800

0.305

0.2026569

0.345

0.2214380

.266

.1831953

.306

.2031403

.346

.2218935

.267

.1837098

.307

.2036230

.347

.2223483

.268

.1842235

.308

.2041050

.348

.2228025

.269

.1847363

.309

.2045862

.349

.2232561

0.270

0.1852483

0.310

0.2050667

0.350

0.2237090

.271

.1857594

.311

.2055464

.351

.2241613

.272

.1862696

.312

.2060254

.352

.2246130

.273

.1867791

.313

.2065037

.353

.2250640

.274

.1872877

.314

.2069813

.354

.2255143

0.275

0.1877955

0.315

0.2074581

0.355

0.2259640

.276

.1883024

.316

.2079342

.356

.2264131

.277

.1888085

.317

.2084096

.357

.2268615

.278

.1893138

.318

.2088843

.358

.2273093

.279

.1898183

.319

.2093582

.359

.2277565

.280

.1903220

.320

.2098315

.360

.2282031

TABLE II.

15

h

logyy

h

log y y

h

logyy

0.360

0.2282031

0.400

0.2455716

0.440

0.2620486

.361

.2286490

.401

.2459940

.441

.2624499

.362

.2290943

.402

.'2464158

.442

.2628507

.363

.2295390

.403

.2468371

.443

.2632511

.364

.2299831

.404

.2472578

.444

.2636509

0.365

0.2304265

0.405

0.2476779

0.445

0.2640503

.366

.2308694

.406

.2480975

.446

.2644492

.367

.2313116

.407

.2485166

.447

.2648475

.368

.2317532

.408

.2489351

.448

.2652454

.369

.2321942

.409

.2493531

.449

.2656428

0.370

0.2326346

0.410

0.2497705

0.450

0.2660397

.371

.2330743

.411

.2501874

.451

.2664362

.372

.2335135

.412

.2506038

.452

.2668321

.373

.2339521

.413

.2510196

.453

.2672276

.374

.2343900

.414

.2514349

.454

.2676226

0.375

0.2348274

0.415

0.2518496

0.455

0.2680171

.376

.2352642

.416

.2522638

.456

.2684111

.377

.2357003

.417

.2526775

.457

.2688046

.378

.2361359

.418

.2530906

.458

.2691977

.379

.2365709

.419

.2535032

.459

.2695903

0.380

0.2370053

0.420

0.2539153

0.460

0.2699824

.381

.2374391

.421

.2543269

.461

.2703741

.382

.2378723

.422

.2547379

.462

.2707652

.383

.2383050

.423

.2551485

.463

.2711559

.384

.2387370

.424

.2555584

.464

.2715462

0.385

0.2391685

0.425

0.2559679

0.465

0.2719360

.386

.2395993

.426

.2563769

.466

.2723253

.387

.2400296

.427

.2567853

.467

.2727141

.388

.2404594

.428

.2571932

.468

.2731025

.389

.2408885

.429

.2576006

.469

.2734904

0.390

0.2413171

0.430

0.2580075

0.470

0.2738778

.391

.2417451

.431

.2584139

.471

.2742648

.392

.2421725

.432

.2588198

.472

.2746513

.393

.2425994

.433

.2592252

.473

.2750374

.394

.2430257

.434

.2596300

.474

.2754230

0.395

0.2434514

0.435

0.2600344

0.475

0.2758082

.396

.2438766

.436

.2604382

.476

.2761929

.397

.2443012

.437

.2608415

.477

.2765771

.398

.2447252

.438

.2612444

.478

.2769609

.399

.2451487

.439 .2616467

.479 .2773443

.400

.2455716

.440 .2620486

.480

.2777272

16

TABLE II.

h

i°gyy

h

i°gyy

h

i°gyy

0.480

0.2777272

0.520

0.2926864

0.560

0.3069938

.481

.2781096

.521

.2930518

.561

.3073437

.482

.2784916

.522

.2934168

.562

.3076931

.483

.2788732

.523

.2937813

.563

.3080422

.484

.2792543

.524

.2941455

.564

.3083910

0.485

0.2796349

0.525

0.2945092

0.565

0.3087394

.486

.2800151

.526

.2948726

.566

.3090874

.487

.2803949

.527

.2952355

.567

.3094350

.488

.2807743

.528

.2955981

.568

.3097823

.489

.2811532

.529

.2959602

.569

.3101292

0.490

0.2815316

0.530

0.2963220

0.570

0.3104758

.491

.2819096

.531

.2966833

.571

.3108220

.492

.2822872

.532

.2970443

.572

.3111678

.493

.2826644

.533

.2974049

.573

.3115133

.494

.2830411

.534

.2977650

.574

.3118584

0.495

0.2834173

0.535

0.2981248

0.575

0.3122031

.496

.2837932

.536

.2984842

.576

.3125475

.497

.2841686

.537

.2988432

.577

.3128915

.498

.2845436

.538

.2992018

.578

.3132352

.499

.2849181

.539

.2995600

.579

.3135785

0.500

0.2852923

0.540

0.2999178

0.580

0.3139215

.501

.2856660

.541

.3002752

.581

.3142641

.502

.2860392

.542

.3006323

.582

.3146064

.503

.2864121

.543

.3009890

.583

.3149483

.504

.2867845

.544

.3013452

.584

.3152898

0.505

0.2871565

0.545

0.3017011

0.585

0.3156310

.506

.2875281

.546

.3020566

.586

.3159719

.507

.2878992

.547

.3024117

.587

.3163124

.508

.2882700

.548

.3027664

.588

.3166525

.509

.2886403

.549

.3031208

.589

.3169923

0.510

0.2890102

0.550

0.3034748

0.590

0.3173318

.511

.2893797

.551

.3038284

.591

.3176709

.512

.2897487

.552

.3041816

.592

.3180096

.513

.2901174

.553

.3045344

.593

.3183481

.514

.2904856

.554

.3048869

.594

.3186861

0.515

0.2908535

0.555

0.3052390

0.595

0.3190239

.516

.2912209

.556

.3055907

.596

.3193612

.517

.2915879

.557

.3059420

.597

.3196983

.518

.2919545

.558

.3062930

.598

.3200350

.519

.2923207

.559

.3066436

.599

.3203714

.520

.2926864

.560

.3069938

.600

.3207074

TABLE III. (See Articles 90, 100.)

17

x or z

i

C

x or z

g

£

0.000

0.0000000

0.0000000

0.040

0.0000936

0.0000894

.001

.0000001

.0000001

.041

.0000984

.0000938

.002

.0000002

.0000002

.042

.0001033

.0000984

.003

.0000005

.0000005

.043

-.0001084

.0001031

.004

.0000009

.0000009

.044

.0001135

.0001079

0.005

0.0000014

0.0000014

0.045

0.0001188

0.0001128

.006

.0000021

.0000020

.046

.0001242

.0001178

.007

.0000028

.0000028

.047

.0001298

.0001229

.008

.0000037

.0000036

.048

.0001354

.0001281

.009

.0000047

.0000046

.049

.0001412

.0001334

0.010

0.0000058

0.0000057

0.050

0.0001471

0.0001389

.011

.0000070

.0000069

.051

.0001532

.0001444

.012

.0000083

.0000082

.052

.0001593

.0001500

.013

.0000097

.0000096

.053

.0001656

.0001558

.014

.0000113

.0000111

.054

.0001720

.0001616

0.015

0.0000130

0.0000127

0.055

0.0001785

0.0001675

.016

.0000148

.0000145

.056

.0001852

.0001736

.017

.0000167

.0000164

.057

.0001920

.0001798

.018

.0000187

.0000183

.058

.0001989

.0001860

.019

.0000209

.0000204

.059

.0002060

.0001924

0.020

0.0000231

0.0000226

0.060

0.0002131

0.0001988

.021

.0000255

.0000249

.061

.0002204

.0002054

.022

.0000280

.0000273

.062

.0002278

.0002121

.023

.0000306

.0000298

.063

.0002354

.0002189

.024

.0000334

.0000325

.064

.0002431

.0002257

0.025

0.0000362

0.0000352

0.065

0.0002509

0.0002327

.026

.0000392

.0000381

.066

.0002588

.0002398

.027

.0000423

.0000410

.067

.0002669

.0002470

.028

.0000455

.0000441

.068

.0002751

.0002543

.029

.0000489

.0000473

.069

.0002834

.0002617

0.030

0.0000523

0.0000506

0.070

0.0002918

0.0002691

.031

.0000559

.0000539

.071

.0003004

.0002767

.032

.0000596

.0000575

.072

.0003091

.0002844

.033

.0000634

.0000611

.073

.0003180

.0002922

.034

.0000674

.0000648

.074

.0003269

.0003001

0.035

0.0000714

0.0000686

0.075

0.0003360

0.0003081

.036

.0000756

.0000726

.076

.0003453

.0003162

.037

.0000799

.0000706

.077

.0003546

.0003244

.038

.0000844

.0000807

.078

.0003641

.0003327

.039

.0000889

.0000850

.079

.0003738

.0003411

.040

.0000936

.0000894

.080

.0003835

.0003496

18

TABLE III.

x or i

f

f

x or z

f

f

1

0.080

0.0003835

0.0003496

0.120

0.0008845

0.0007698

.081

.0003934

.0003582

.121

.0008999

.0007822

.082

.0004034

.0003669

.122

.0009154

.0007948

.083

.0004136

.0003757

.123

.0009311

.0008074

.084

.0004239

.0003846

.124

.0009469

.0008202

0.085

0.0004343

0.0003936

0.125

0.0009628

0.0008330

.086

.0004448

.0004027

.126

.0009789

.0008459

.087

.0004555

.0004119

.127

.0009951

.0008590

.088

.0004603

.0004212

.128

.0010115

.0008721

.089

.0004773

.0004306

.129

.0010280

.0008853

0.090

0.0004884

0.0004401

0.130

0.0010447

0.0008986

.091

.0004996

.0004496

.131

.0010615

.0009120

.092

.0005109

.0004593

.132

.0010784

.0009255

.093

.0005224

.0004691

.133

.0010955

.0009390

.094

.0005341

.0004790

.134

.0011128

.0009527

0.095

0.0005458

0.0004890

0.135

0.0011301

0.0009665

.096

.0005577

.0004991

.136

.0011477

.0009803

.097

.0005697

.0005092

.137

.0011654

.0009943

.098

.0005819

.0005195

.138

.0011832

.0010083

.099

.0005942

.0005299

.139

.0012012

.0010224

0.100

0.0006066

0.0005403

0.140

0.0012193

0.00 103 6 G

.101

.0006192

.0005509

.141

.0012376

.0010509

.102

.0006319

.0005616

.142

.0012560

.0010653

.103

.0006448

.0005723

.143

.0012745

.0010798

.104

.0006578

.0005832

.144

.0012933

.0010944

0.105

0.0006709

0.0005941

0.145

0.0013121

0.0011091

.106

.0006842

.0006052

.146

.0013311

.0011238

.107

.0006976

.0006163

.147

.0013503

.0011387

.108

.0007111

.0006275

.148

.0013696

.0011536

.109

.0007248

.0006389

.149

.0013891

.0011686

0.110

0.0007386

0.0006503

0.150

0.0014087

0.0011838

.111

.0007526

.0006018

.151

.0014285

.0011990

.112

.0007667

.0006734

.152

.0014484

.0012143

.113

.0007809

.0006851

.153

.0014684

.0012296

.114

.0007953

.0006969

.154

.0014886

.0012451

0.115

0.0008098

0.0007088

0.155

0.0015090

0.0012607

.116

.0008245

.0007208

.156

.0015295

.0012763

.117

.0008393

.0007329

.157

.0015502

.0012921

.118

.0008542

.0007451

.158

.0015710

.0013079

.119

.0008693

.0007574

.159

.0015920

.0013288

.120

.0008845

.0007698

.160

.0016131

.0013398

TABLE III.

19

x or z

{

£

x or z

k

f

0.160

0.0016131

0.0013398

0.200

0.0025877

0.0020507

.161

.0016344

.0013559

.201

.0026154

.0020702

.162

.0016559

.0013721

.202

.0026433

.0020897

.163

.0016775

.0013883

.203

.0026713

.0021094

.164

.0016992

.0014047

.204

.0026995

.0021292

0.165

0.0017211

0.0014211

0.205

0.0027278

0.0021490

.166

.0017432

.0014377

.206

.0027564

.0021689

.167

.0017654

.0014543

.207

.0027851

.0021889

.168

.0017878

.0014710

.208

.0028139

.0022090

.169

.0018103

.0014878

.209

.0028429

.0022291

0.170

0.0018330

0.0015047

0.210

0.0028722

0.0022494

.171

.0018558

.0015216

.211

.0029015

.0022697

.172

.0018788

.0015387

.212

.0029311

.0022901

.173

.0019020

.0015558

.213

.0029608

.0023106

.174

.0019253

.0015730

.214

.0029907

.0023311

0.175

0.0019487

0.0015903

0.215

0.0030207

0.0023518

.176

.0019724

.0016077

.216

.0030509

.0023725

.177

.0019961

.0016252

.217

.0030814

.0023932

.178

.0020201

.0016428

.218

.0031119

.0024142

.179

.0020442

.0016604

.219

.0031427

.0024352

0.180

0.0020685

0.0016782

0.220

0.0031736

0.0024562

.181

.0020929

.0016960

.221

.0032047

.0024774

.182

.0021175

.0017139

.222

.0032359

.0024986

.183

.0021422

.0017319

.223

.0032674

.0025199

.184

.0021671

.0017500

.224

.0032990

.0025412

0.185

0.0021922

0.0017681

0.225

0.0033308

0.0025627

.186

.0022174

.00178G4

.226

.0033627

.0025842

.187

.0022428

.0018047

.227

.0033949

.0026058

.188

.0022683

.0018231

.228

.0034272

.0026275

.189

.0022941

.0018416

.229

.0034597

.0026493

0.190

0.0023199

0.0018602

0.230

0.0034924

. 0.0026711

.191

.0023460

.0018789

.231

.0035252

.0026931

.192

.0023722

.0018976

.232

.0035582

.0027151

.193

.0023985

.0019165

.233

.0035914

.0027371

.194

.0024251

.0019354

.234

.0036248

.0027593

0.195

0.0024518

0.0019544

0.235

0.0036584

0.0027816

.196

.0024786

.0019735

.236

.0036921

.0028039

.197

.0025056

.0019926

.237

.0037260

.0028263

.198

.0025328

.0020119

.238

.0037601

.0028487

.199

.0025602

.0020312

.239

.0037944

.0028713

.200

.0025877

.0020507

.240

.0038289

.0028939

20

TABLE III.

1
x or z

f

f

x or z

f

f

0.240

0.0038289

0.0028939

0.270

0.0049485

0.0036087

.241

.0038635

.0029166

.271

.004i»888

.0036337

.242

.0038983

.0029394

• .272

.0050292

.0036587

.243

.0039333

.0029623

.273

.0050699

.0036839

.244

.0039685

.0029852

.274

..0051107

.0037091

0.245

0.0040039

0.0030083

0.275

0.0051517

0.0037344

.246

.0040394

.0030314

.276

.0051930

.0037598

.247

.0040752

.0030545-

.277

.0052344

.0037852

.248

.0041111

.0030778

.278

.0052760

.0038107

.249

.0041472

.0031011

.279

.0053118

.0038363

0.250

0.0041835

0.0031245

0.280

0.0053598

0.0038620

.251

.0042199

.0031480

.281

.0054020

.0038877

.252

.0042566

.0031716

.282

.0054444

.0039135

.253

.0042934

.0031952

.283

.0054870

.0039394

.254

.0043305

.0032189

.284

.0055298

.0039654

0.255

0.0043677

0.0032427

0.285

0.0055728

0.0039914

.256

.0044051

.0032666

.286

.0056160

.0040175

.257

.0044427

.0032905

.287

.0056594

.0040437

.258

.0044804

.0033146

.288

.0057030

.0040700

.259

.0045184

.0033387

.289

.0057468

.0040963

0.260

0.0045566

0.0033628

0.290

0.0057908

0.0041227

.261

.0045949

.0033871

.291

.0058350

.0041491

.262

.0046334

.0034114

.292

.0058795

.0041757

.263

.0046721

.0034358

.293

.0059241

.0042023

.264

.0047111

.0034603

.294

.0059689

.0042290

0.265

0.0047502

0.0034848

0.295

0.0060139

0.0042557

.266

.0047894

.0035094

.296

.0060591

.0042826

.267

.0048289

.0035341

.297

.0061045

.0043095

.268

.0048686

.0035589

.298

.0061502

.0043364

.269

.0049085

.0035838

.299

.0061960

.0043635

.270

.0049485

.0036087

.300

.0062421

.0043906

TABLE la.

21

E L L H> S E .

PYPERBOLA.

A

Log £„

Log diff.

LogEr

Log diff.

Log Er

Log diff.

Log E,.

Log dilf.

0.000

0.0000000

9.2401

0.0000000

9.6378

0.0000000

9.2398

0.0000000

9.6378

.001

.0001738

.2403

9.9995656

.6381

9.9998263

.2395

.0004341

.6375

.002

.0003477

.2406

.9991309

.6384

.9996528

.2392

.0008680

.6372

.003

.0005217

.2408

.9986959

.6386

.9994794

.2389

.0013017

.6370

.004

.0006958

.2413

.9982607

.6389

.9993061

.2386

.0017350

.6367

0.005

0.0008701

9.2416

9.9978252

9.6391

9.9991329

9.2383

0.0021682

9.6365

.006

.0010445

.2418

.9973895

.6394

.9989598

.2381

.0026010

.6362

.007

.0012190

.2420

.9969535

.6396

.9987869

.2378

.0030337

.6360

.008

.0013936

.2423

.9965173

.6399

.9986141

.2375

.0034660

.6357

.009

.0015683

.2428

.9960807

.6402

.9984414

.2372

.0038981

.6354

0.010

0.0017432

9.2430

9.9956439

9.6405

9.9982688

9.2369

0.0043299

9.6352

.011

.0019182

.2433

.9952068

.6407

.9980963

.2366

.0047615

.6349

.012

.0020933

.2435

.9947695

.6410

.9979240

.2363

.0051928

.6347

.013

.0022685

.2438

.9943319

.6412

.9977517

.2360

.0056239

.6344

.014

.0024438

.2443

.9938941

.6414

.9975796

.2357

.0060547

.6342

0.015

0.0026193

9.2445

9.9934560

9.6417

9.9974076

9.2354

0.0064853

9.6339

.016

.0027949

.2448

.9930176

.6420

.9972357

.2351

.0069156

.6336

.017

.0029706

.2453

.9925789

.6423

.9970639

.2348

.0073456

.6334

.018

.0031465

.2455

.9921^00

.6425

.9968923

.2345

.0077754

.6331

.019

.0033225

.2458

.9917008

.6428

.9967207

.2342

.0082049

.6329

0.020

0.0034986

9.2460

9.9912614

9.6430

9.9965493

9.2339

0.0086342

9.6326

.021

.0036748

.2460

.9908217

.6433

.9963780

.2336

.0090632

.6323

.022

.0038510

.2465

.9903817

.6436

.9962068

.2333

.0094920

.6321

.023

.0040274

.2470

.9899415

.6438

.9960357

.2330

.0099205

.6318

.024

.0042040

.2472

.9895010

.6441

.9958648

.2328

.0103487

.6316

0.025

0.0043807

9.2475

9.9890602

9.6444

9.9956939

9.2325

0.0107767

9.6313

.026

.0045575

.2477

.9886192

.6446

.9955232

.2322

.0112045

.6311

.027

.0047344

.2480

.9881779

.6449

.9953526

.2319

.0116320

.6308

.028

.0049114

.2485

.9877363

.6452

.9951821

.2316

.0120592

.6306

.029

.0050886

.2487

.9872945

.6454

.9950117

.2313

.0124862

.6303

0.030

0.0052659

9.2490

9.9868524

9.6457

9.9948414

9.2310

0.0129130

9.6301

.031

.0054433

.2494

.9864100

.6459

.9946712

.2307

.0133395

.6298

.032

.0056209

.2497

.9859674

.6462

.9945012

.2304

.0137657

.6295

.033

.0057986

.2499

.9855245

.6465

.9943313

.2301

.0141917

.6293

.034

.0059764

.2502

.9850813

.6468

.9941615

.2298

.0146175

.6290

0.035

0.0061543

9.2504

9.9846378

9.6471

9.9939918

9.2295

0.0150430

9.6288

.036

.0063323

.2509

.9841940

.6474

.9938222

.2292

.0154683

.6285

.037

.0065105

.2512

.9837499

.6476

.9936528

.2290

.0158933

.6283

.038

.0066888

.2514

.9833056

.6478

.9934834

.2287

.0163180

.6280

.039

.0068672

.2516

.9828610

.6481

.9933142

.2284

.0167426

.6278

.040

.0070457

.2519

.9824161

.6484

.9931450

.2281

.0171668

.6275

22

TABLE la.

1

ELLIPSE.

HYPERBOLA.

A

Log Ke

Log cliff.

LogEr

Log diff.

Log Er

Log diff.

Log E,.

Log Diff.

0.040

0.0070457

9.2519

9.9824161

9.6484

9.9931450

9.2281

0.0171668

9.6275

.041

.0072243

.2524

.9819709

.6487

.9929760

.2278

.0175908

.6273

.042

.0074031

.2526

.9815255

.6489

.992807 1

.2275

.0180146

.6270

.043

.0075820

.2531

.9810798

.6492

.9926383

.2272

.0184381

.6267

.044

.0077611

.2533

.980G339

.6494

.9924696

.2269

.0188614

.6265

0.045

0.0079403

9.2536

9.9801877

9.6497

9.9923010

9.2266

0.0192844

9.6262

.046

.0081196

.2538

.9797412

.6500

.9921325

.2263

.0197072

.6260

.047

.0082990

.2543

.9792944

.6502

.9919642

.2260

.0201297

.6257

.048

.0084786

.2546

.9788474

.6505

.9917960

.2258

.0205520

.6255

.049

.0086583

.2548

.9784001

.6508

.9916279

.2255

.0209740

.6252

0.050

0.0088381

9.2550

9.9779525

9.6511

9.9914599

9.2252

0.0213958

9.6250

.051

.0090180

.2555

.9775046

.6514

.9912920

.2249

.0218174

.6247

.052

.0091981

.2558

.9770564

.6516

.99-11242

.2246

.0222387

.6245

.053

.0093783

.2560

.9766079

.6519

.9909565

.2243

.0226597

.6242

.054

.0095586

.2565

.9761592

.6521

.9907890

.2240

.0230805

.6240

0.055

0.0097391

9.2567

9.9757102

9.6524

9.9906215

9.2237

0.0235011

9.6237

.056

.0099197

.2570

.9752609

.6527

.9904542

.2235

.0239214

.6235

.057

.0101004

.2572

.9748113

.6529

.9902869

.2232

.0243415

.6232

.058

.0102812

.2577

.9743615

.6532

.9901198

.2229

.0247614

.6230

.059

.0104622

.2579

.9739114

.6535

.9899528

.2226

.0251810

.6227

0.060

0.0106433

9.2582

9.9734611

9.6538

9.9897859

9.2223

0.0256003

9.6225

.061

.0108245

.2584

.9730103

.6541

.9896191

.2220

.0260194

.6222

.062

.0110058

.2589

.9725593

.6543

.9894525

.2217

.0264383

.6220

.063

.0111873

.2591

.9721080

.6546

.9892859

.2214

.0268570

.6217

.064

.0113689

.2594

.9716565

.6548

.9891195

.2211

.0272753

.6215

0.065

0.0115506

9.2598

9.9712047

9.6551

9.9889531

9.2208

0.0276935

9.6212

.066

.0117325

.2601

.9707526

.6554

.9887869

.2206

.0281114

.6210

.067

.0119145

.2603

.9703002

.6557

.9886208

.2203

.0285291

.6207

.068

.0120966

.2606

.9698475

.6560

.9884548

.2200

.0289465

.6205

.069

.0122788

.2610

.9693945

.6562

.9882889

.2197

.0293637

.6202

0.070

0.0124612

9.2613

'.1.9689413

9.6565

9.9881231

9.2194

0.0297807

9.6200

.071

.0126437

.2617

.9684878

.6567

.9879574

.2191

.0301974

.6197

.072

.0128264

.2620

.9680340

.6570

.9877918

.2189

.0306139

.6195

.073

.0130092

.2622

.9675799

.6573

.9876263

.2186

.0310301

.6192

.074

.0131921

.2625

.9671255

.6576

.9874610

.2183

.0314461

.6190

0.075

0.0133751

9.2629

9.9666708

9.6578

9.9872957

9.2180

0.0318618

9.6187

.076

.0135583

.2632

.9662159

.6581

.9871306

.2177

.0322773

.6185

.077

.0137416

.2634

.9657606

.6584

.9869655

.2174

.0326926

.6182

.078

.0139250

.2638

.9653051

.6587

.9868006

.2172

.0331076

.6180

.079

.0141086

.2641

.9648492

.6590

.9866358

.2169

.0335224

.6177

.080

.0142923

.2648

.9643931

.6592

.9864711

.2166

.0339370

.6175

i

TABLE la.

23

ELLIPSE.

HYPERBOLA.

A

I

LogE,,

Log diff.

LogEr

Log diff.

LogE0

Log diff.

Log Er.

Log Diff.

0.080

0.0142923

9.2643

9.9643931

9.6592

9.9864711

9.2166

0.0339370

9.6175

.081

.0144761

.2646

.9639367

.6595

.9863065

.2163

.0343513

.6172

.082

.0146601

.2649

.9634800

.6598

.9861420

.2160

.0347654

.6170

.083

.0148442

.2652

.9630230

.6600

.9859776

.2157

.0351793

.6167

.084

.0150284

.2655

.9625657

.6603

.9858133

.2155

.0355930

.6165

0.085

0.0152128

9.2659

9.9621081

9.6606

9.9856491

9.2152

0.0360064

9.6163

.086

.0153973

.2662

.9616503

.6609

.9854850

.2149

.0364196

.6160

.087

.0155819

.2665

.9611922

.6611

.9853210

.2146

.0368325

.6158

.088

.0157667

.2668

.9607337

.6614

.9851572

.2143

.0372452

.6155

.089

.0159516

.2671

.9602749

.6617

.9849934

.2140

.0376577

.6153

0.090

0.0161367

9.2674

9.9598159

9.6620

9.9848298

9.2138

0.0380699

9.6150

.091

.0163218

.2677

.9593566

.6623

.9846663

.2135

.0384819

.6148

.092

.0165071

.2680

.9588970

.6625

.9845028

.2132

.0388937

.6145

.093

.0166925

.2684

.9584371

.6628

.9843395

.2129

.0393052

.6143

.094

.0168781

.2687

.9579769

.'6631

.9841763

.2126

.0397165

.6141

0.095

0.0170638

9.2690

9.9575164

9.6634

9.9840132

9.2123

0.0401276

9.6138

.096

.0172497

.2693

.9570556

.6636

.9838502

.2121

.0405385

.6136

.097

.0174357

.2696

.9565945

.6639

.9836873

.2118

.0409491

.6133

.098

.0.176218

.2700

.9561331

.6642

.9835245

.2115

.0413595

.6131

.099

.0178081

.2703

.9556714

.6645

.9833618

.2112

.0417696

.6128

0.100

0.0179945

'9.2706

9.9552095

9.6648

9.9831992

9.2109

0.0421796

9.6126

.101

.0181810

.2708

.9547472

.6650

.9830367

.2107

.0425893

.6123

.102

.0183677

.2712

.9542847

.6653

.9828743

.2104

.0429988

.6121

.103

.0185545

.2715

.9538218

.6656

.9827121

.2101

.0434080

.6118

.104

.0187414

.2718

.9533586

.6659

.9825499

.2098

.0438170

.6116

0.105

0.0189285

9.2722

9.9528951

9.6662

9.9823879

9.2095

0.0442258

9.6114

.106

.0191157

.2725

.9524314

.6664

.9822259

.2093

.0446343

.6111

.107

.0193030

.2728

.9519673

.6666

.9820641

.2090

.0450426

.6109

.108

.0194905

.2731

.9515030

.6670

.9819023

.2087

.0454507

.6106

.109

.0196781

.2734

.9510383

.6673

.9817407

.2084

.0458585

.6104

0.110

0.0198659

9.2738

9.9505734

9.6676

9.9815791

9.2081

0.0462661

9.6101

.111

.0200538

.2741

.9501081

.6678

.9814177

.2079

.0466735

.6099

'.112

.0202418

.2744

.9496425

.6681

.9812563

.2076

.0470807

.6096

.113

.0204300

.2747

.9491766

.6684

.9810951

.2073

.0474876

.6094

.114

.02Q6183

.2750

.9487105

.6687

.9809340

.2070

.0478943

.6092

0.115

0.0208067

9.2754

9.9482440

9.6690

9.9807730

9.2067

0.0483008

9.6089

.116

.0209953

.2757

.9477772

.6692

.9806121

.2065

.0487071

.6087

.117

.0211840

.2760

.9473101

.6695

.9804513

.2062

.0491131

.6084

.118

.0213729

.2763

.9468428

.6698

.9802905

.2059

.0495189

.6082 •

.119

.0215619

.2767

.9463751

.6701

.9801299

.2056

.0499245

.6080

.120

.0217511

.2770

.9459071

.6704

.9799694

.2054

.0503298

.6077

24

TABLE la.

ELLIPSE.

HYPERBOLA.

A

LogE,,

Log diff.

LogEr

Log diff.

LogE,,

Log diff.

Log Er.

Log Diff.

0.120

0.0217511

9.2770

9.9459071

9.6704

9.9799694

9.2054

0.0503298

9.6077

.121

.0219404

.2773

.9454388

.6707

.9798090

.2051

.0507349

.6075

.122

.0221298

.2776

.9449702

.6709

.9796487

.2048

.0511399

.6072

.123

.0223193

.2779

.9445013

.6712

.9794885

.2045

.0515446

.6070

.124

.0225091

.2783

.9440321

.6715

.9793284

.2043

.0519490

.6068

0.125

0.0226990

9.2786

9.9435626

9.6718

9.9791684

9.2040

0.0523533

9.6065

.126

.0228889

.2789

.9430927

.6721

.9790085

.2037

.0527573

.6063

.127

.0230791

. .2792

.9426226

.6724

.9788487

.2034

.0531611

.6061

.128

.0232693

.2795

.9421521

.6727

.9786890

.2032

.0535647

.6058

.129

.0234597

.2799

.9416813

.6729

.9785294

.2029

.0539681

.6056

0.130

0.0236503

9.2802

9.9412103

9.6732

9.9783699

9.2026

0.0543712

9.6053

.131

.0238410

.2805

.9407389

.6735

.9782105

.2023

.0547741

.6051

.132

.0240318

.2808

.9402672

.6738

.9780512

.2021

.0551768

.6049

.133

.0242228

.2812

.9397952

.6741

.9778920

.2018

.0555793

.6046

.134

.0244139

.2815

.9393229

.6744

.9777329

.2015

.0559816

.6044

0.135

0.0246052

9.2818

9.9388503

9.6747

9.9775739

9.2012

0.0563836

9.6041

.136

.0247966

.2822

.9383773

.6749

.9774150

.2010

.0567854

.6039

.137

.0249882

.2825

.9379041

.6752

.9772562

.2007

.0571870

.6037

.138

.0251799

.2828

.9374305

.6755

.9770975

.2004

.0575884

.6034

.139

.0253717

.2831

.9369567

.6758

.9769390

.2001

.0579895

.6032

0.140

0.0255637

9.2834

9.9364824

9.6761

9.9767805

9.1998

0.0583904

9.6029

.141

.0257558

.2838

.9360079

.6764

.9766221

.1-996

.0587911

.6027

.142

.0259481

.2841

.9355331

.6767

.9764638

.1993

.0591916

.6025

.143

.0261405

.2844

.9350580

.6770

.9763057

.1990

.0595919

.6022

.144

.0263331

.2848

.9345825

.6773

.9761476

.1988

.0599919

.6020

0.145

0.0265258

9.2851

9.9341067

9.6775

9.9759896

9.1985

0.0603917

9.6018

.146

.0267187

.2854

.9336307

.6778

.9758317

.1982

.0607913

.6015

.147

.0269117

.2857

.9331543

.6781

.9756739

.1979

.0611907

.6013

.148

.0271048

.2861

.9326775

.6784

.9755162

.1977

.0615899

.6010

.149

.0272981

.2864

.9322005

.6787

.9753586

.1974

.0619888

.6008

0.150

0.0274915

9.2867

9.9317231

9.6790

9.9752011

9.1971

0.0623876

9.6006

.151

.0276851

.2871

.9312455

.6793

.9750437

.1969

.0627861

.6003

.152

.0278789

.2874

.9307675

.6796

.9748864

.1966

.0631844

.6001

.153

.0280728

.2877

.9302892

.6798

.9747292

.1963

.0635825

.5999

.154

.0282668

.2880

.9298106

.6801

.9745721

.1960

.0639804

.5996

0.155

0.0284610

9.2884

9.9293317

9.6804

9.9744151

9.1958

0.0643780

9.5994

.156

.0286553

.2887

.9288524

.6807

. .9742582

J955

.0647755

.5992

.157

.0288498

.2890

.9283728

.6810

.9741014

.1952 .0651727

.5989

.158

.0290444

.2893

.9278929

.6813

.9739447

.1949 .0655697

.5987

.159

.0292392

.2897

.9274127

.6816

.9737881

.1946 .0659665

.5985

.160

.0294341

.2900

.9269321

.6819

.9736316

.1944

.0(163 631

.5982

TABLE la.

25

ELLIPSE.

HYPERBOLA.

A

LogEB

Log diff.

LogEr

Log diff.

Log Et,

Log diff.

Log E

Log diff.

0.160

0.0294341

9.2900

9.9269321

9.68.19

9.9736316

9.1944

0.0663631

9.5982

.161

.0296292

.2903

.9264512

.6822

.9734752

.1941

.0667595

.5980

.162

.0298243

.2906

.9259700

.6825

.9733189 .1938

.0671556

.5978

.163

.0300197

.2910

.9254885

.6828

.9731627 .1936

.0675516

.5975

.164

.0302152

.2913

.9250067

.6831

.9730066

.1933

.0679473

.5973

0.165

0.0304109

9.2916

9.9245245

9.6833

9.9728506

9.1930

0.0683428

9.5971

.166

.0306067

.2920

.9240421

.6836

.9726947

.1928

.0687381

.5968

.167

.0308026

.2923

.9235592

.6839

.9725389 .1925

.0691332

.5966

.168

.0309987

.2926

.9230761

.6842

.9723831

.1922

.0695281

.5963

.169

.0311949

.2930

.9225926

.6845

.9722275

.1920

.0699228

.5961

0.170

0.0313913

9.2933

9.9221089

9.6848 "

9.9720719

9.1917

0.0703172

9.5959

.171

.0315879

.2936

.9216247

.6851

.9719165

.1914

.0707114

.5956

.172

.0317846

.2940

.9211403

.6854

.9717611

.1912

.0711055

.5954

.173

.0319815

.2943

.9206555

.6857

.9716059

.1909

.0714993

.5952

.174

.0321784

.2946

.9201704

.6860

.9714507

.1906

.0718929

.5949

0.175

0.0323756

9.2950

9.9196850

9.6863

9.9712957

9.1904

0.0722863

9.5947

.176

.0325729

.2953

.9191992

.6866

.9711407

.1901

.0726795

.5945

.177

.0327704

.2956

.9187131

.6869

.9709859

.1898

.0730724

.5942

.178

.0329680

.2960

.9182266

.6872

.9708311

.1895

.0734652

.5940

.179

.0331657

.2963

.9177399

.6875

.9706764

.1893

.0738578

.5938

0.180

0.0333636

9.2966

9.9172528

9.6878

9.9705218

9.1890

0.0742501

9.5935

.181

.0335617

.2970

.9167654

.6881

.9703673

.1887

.0746422

.5933

.182

.0337599

.2973

.9162776

.6884

.9702129

.1885

.0750341

.5931

.183

.0339582

.2977

.9157895

.6886

.9700587

.1882

.0754259

.5928

.184

.0341568

.2980

.9153011

.6889

.9699045

.1879

.0758173

.5926

0.185

0.0343555

9.2983

9.9148123

9.6892

9.9697504

9.1877

0.0762086

9.5924

.186

.0345543

.2987

.9143232

.6895

.9695964

.1874

.0765997

.5922

.187

.0347533

.2990

.9138338

.6898

.9694425

.1871

.0769906

.5919

.188

.0349524

.2993

.9133441

.6901

.9692887

.1869

.0773812

.5917

.189

.0351517

.2997

.9128540

.6904

.9691350

.1866

.0777717

.5915

0.190

0.0353511

9.3000

9.9123635

9.6907

9.9689813

9.1863

0.0781619

9.5912

.191

.0355507

.3003

.9118727

.6910

.9688278

.1861

.0785520

.5910

.192

.0357505

.3007

.9113816

.6913

.9686743

.1858

.0789418

.5908

.193

.0359504

.3010

.9108901

.6916

.9685210

.1855

.0793315

.5906

.194

.0361505

.3014

.9103983

.6919

.9683678

.1853

.0797209

.5903

0.195

0.0363507

9.3017

9.9099062

9.6922

9.9682146

9.1850

0.0801102

9.5901

.196

.0365511

.3020

.9094138

.6925

.9680615

.1847

.0804992

.5899

.197

.0367516

.3024

.9089210

.6928

.9679086

.1845

.0808881

.5896

.198

.0369523

.3027

.9084278

.6931

.9677557

.1842

.0812767 i -5894

.199

.0371532

.3031

.9079343

.6934

.9676029

.1839

.0816651 .5892

.200

.0373542

.3034

.9074405

.6937

.9674502

.1837

.0820533

.5889

TABLE la.

ELLIPSE.

HYPERBOLA.

•

A

Lo- Et.

Log cliff.

T.og Er

Log cliff.

Log Et.

Log diff.

Log Er.

Log Diff.

0.200

0.0373542

9.3034

1

9.9074405 ! 9.6937

9.9674502

9.1837

0.0820533

9.5889

.201

.0375554

.3037

.9069463 .6940

.9672976

.1834

.0824413

.5887

.-20-2

.0377567

.3041

.9064518

.6943

.9671451

.1831

.0828291

.5885

.203

.0379582

.3044

.9059569

.6946

.9669927

.1829

.0832166

.5882

.204

.0381598

.3047

.9054617

.6949

.9668404

.1826

.0836040

.5880

0.205

0.0383616

9.3051

9.9049662

9.6952

9.9666882

9.1823

0.0839911

9.5878

.206

.0385635

.3054

.9044703

.6955

.9665361

.1821

.0843781

.5876

.207

.0387656

.3058

.9039741

.6958

.9663841

.1818

.0847649

.5873

.208

.0389679

.3061

.9034775

.6961

.9662321

.1815

.0851514

.5871

.209

.0391703

.3065

.9029806

.6964

.9660803

.1813

.0855377

.5869

0.210

0.0393729

9.3068

9.9024833

9.6967

9.9659285

9.1810

0.0859239

9.5867

.211

.0395757

.3071

.9019857

.6970

.9657768

.1808

.0863099

.5864

.212

.0397786

.3075

.9014877

.6974

.9656253

.1805

.0866956

.5862

.218

.0399817

.3078

.9009894

.6977

.9654738

.1802

.0870812

.5860

.214

.0401849

.3081

.9004907

.6980

.9653224

.1800

.0874665

.5858

0.216

0.0403883

9.3085

9.8999917

9.6983

9.9651711

9.1797

0.0878517

9.5855

.216

.0405918

.3088

.8994924

.6986

.9650199

.1795

.0882367

.5853

.217

.0407955

.3092

.8989927

.6989

.9648687

.1792

.0886214

.5851

.218

.0409994

.3095

.8984927

.6992

.9647177

.1789

.0890060

.5849

.219

.0412034

.3099

.8979923

.6995

.9645667

.1787

.0893903

.5846

0.220

0.0414076

9.3102

9.8974915

9.6998

9.9644159

9.1784

0.0897745

9.5844

.221

.0416120

.3106

.8969904

.7001

.9642651

.1782

.0901585

.5842

.222

.0418165

.3109

.8964889

.7004

.9641145

.1779

.0905422

.5839

.228

.0420211

.3112

.8959881

.7007

.9639639

.1776

.0909258

.5837

.224

.0422260

.3116

.8954849

.7010

.9638134

.1774

.0913091

.5835

0.225

0.0424310

9.3119

9.8949824

9.7013

9.9636630

9.1771

0.0916923

9.5833

.226

.0426362

.3123

.8944795

.7016

.9635127

.1768

.0920753

.5830

.227

.0428415

.3127

.8939762

.7019

.9633625

.1766

.0924580

.5828

.228

.0430470

.3130

.8934726

.7022

.9632123

.1763

.0928405

.5826

.229

.0432527

.3133

.8929687

.7025

.9630623

.1760

.0932229

.5823

0.230

0.0434585

9.3137

9.8924644

9.7028

9.9629124

9.1758

0.0936050

9.5821

.231

.0436645

.3140

.8919597

.7031

.9627625

.1755

.0939870

.5819

.232

.0438707

.3144

.8914547

.7035

.9626128

.1752

.0943687

.5817

.233

.0440770

.3147

.8909493

.7038

.9624631

.1750

.0947503

.5814

.234

.0442835

.3151

.8904436

.7041

.9623136

.1747

.0951317

.5812

0.235

0.0444902

9.3154

9.8899375

9.7044

9.9621641

9.1745

0.0955128

9.5810

.236

.0446970

.3158

4894310

.7047

.9620147

.1742

.0958938

.5808

.237

.0449040

.3161

.8889242

.7050

.9618654

.1740

.0962745

.5806

.238

.0451111

.3165

.8884170

.7053

.9617162

.1737

.0966551

.5803

.239

.0453184

.3168

.8879094

.7056

.9615670

.1734

.0970355

.5801

.240

.0455259

.3171

.8874015

.7059

.9614180

.1732

.0974157

.5799

TABLE la.

27

ELLIPSE.

HYPERBOLA.

A

J-"g Eo

Log diff.

Log Er

Log diff.

L"g E,,

Log diff.

Log Er.

Log Diff.

0.240

0.0455259

9.3171

9.8874015

9.7059

9.9614180

9.1732

0.0974157

9.5799

.241

.0457335

.3175

.8868932

.7063

.9612690

.1729

.0977957

.5797

.242

.0459413

.3179

.8863846

.7066

.9611202

.1727

.0981755

.5794

.243

.0461493

.3182

.8858756

.7069

.9609714

.1724

.0985551

.5792

.244

.0463575

.3186

.8853663

.7072

.9608227

.1722

.0989345

.5790

0.245

0.0465658

9.3189

9.8848566

9.7075

9.9606741

9.1719

0.0993137

9.5788

.246

.0467743

.3193

.8843465

.7078

.9605256

.1716

.0996927

.5786 •

.247

.0469830

.3196

.8838360

.7081

.9603771 .1714

.1000716

.5783

.248

.0471918

.3200

.8833252

.7084 '

.9602288

.1711

.1004502

.5781 '

.249

.0474008

.3203

.8828140

.7087

.9600805

.1709

.1008287

.5779

0.250

0.0476099

9.3207

9.8823025

9.7090

9.9499824

9.1706

0.1012069

9.5777

.251

.0478193

.3210

.8817906

.7094

.9597843

.1704

.1015850

.5775

.252

.0480288

.3214

.8812783

.7097

.9596363

.1701

.1019628

.5772

.25:3

.0482385

.3217

.8807657

.7100

.9594884

.1698

.1023405

.5770

.254

.0484483

.3221

.8802526

.7103

.9593406

.1696

.1027180

.5768

0.255

0.0486583

9.3224

9.8797392

9.7106

9.9591929

9.1693

0,1030953

9.5766

.256

.0488685

.3226

.8792254

.7109

.9590453

.1691

.1034724

.5763

.257

.0490788

.3231

.8787113

.7112

.9588977

.1688

.1038493

.5761

.258

.0492893

.3235

.8781968

.7116

.9587502

.1685

.1042259

.5759

.259

.0495000

.3238

.8776819

.7119

.9586029

.1683

.1046024

.5756

0.260

0.0497109

9.3242

9.8771666

9.7122

9.9584556

9.1680

0.1049787

9.5754

.261

.0499219

.3245

.8766510

.7125

.9583084

.1678

.1053548

.5752

.262

.0501331

.3249

.8761350

.7128

.9581613

.1675

.1057308 .5750

.263

.0503445

.3252

.8756186

.7131

.9580143

.1673

.1061065

.5748

.264

.0505560

.3256

.8751019

.7134

.9578673

.1670

.1064821

.5746

0.265

0.0507677

9.3260

9.8745848

9.7137

9.9577205

9.1668

0.1068574

9.5743

.266

.0509796

.3263

.8740673

.7141

.9575737

.1665

.1072326

.5741

.267

.0511917

.3267

.8735495

.7144

.9574270

.1662

.1076076

.5739

.268

.0514040

.3270

.8730312

.7147

.9572804

.1660

.1079824

.5737

.269

.0516164

.3274

.8725126

.7150

.9571339

.1657

.1083570

.5735

0.270

0.0518290

9.3277

9.8719936

9.7153

9.9569875

9.1655

0.1087314

9.5733

.271

.0520418

.3281

.8714742

.7157

.9568412

.1652

.1091056

.5730

.272

.0522547

.3284

.8709544

.7160

.9566949

.1650

.1094797

.5728

.273

.0524678

.3288

.8704343

.7163

.9565487

.1647

.1098536

.5726

.274

.0526811

.3292

.8699137

.7166

.9564027

.1644

.1102272

.5724

0.275

0.0528946

9.3295

9.8693928

9.7169

9.9562567

9.1642

0.1106007

9.5722

.276

.0531082

.3299

.8688715

.7173

.9561108

.1639

.1109740

.5719

.277

.0533220

.3303

.8683498

.7176

.9559650

.1637

.1113471

.5717

.278

.0535360

.3306

.8678278

.7179

.9558193

.1634

.1117200

.5715

.279

.0537502

.3310

.8673053

.7182

.9556736

.1632

.1120927

.5713

.280

.0539646

.3313

.8667825

.7185

.9555281

.1629

.1124652

.5710

28

TABLE la.

ELLIPSE.

HYPERBOLA.

A

LogE0

Log diff.

Log Er

Log diff.

Log EB

Log diff.

LogEr.

Log Diff.

0.280

0.0539G46

9.3313

9.8667825

9.7185

9.9555281

9.1629

0.1124652

9.5710

.281

.0541791

.331,7

.8662593

.7188

.9553826

.1627

.1128375

.5708

.282

.0543939

.3320

.8657357

.7192

.9552372

.1624

.1132097

.5707

.2*3

.0546087

.3324

.8652117

.7195

.9550919

.1622

.1135817

.5704

.284

.0548238

.3327

.8646873

.7198

.9549467

.1619

.1139534

.5701

0.285

0.0550390

9.3331

9.8641625

9.7201

9.9548015

9.1617

0.1143250

9.5699

.286

.0552546

.3335

.8636374

• .7204

.9546564

.1614

.1146964

.5698

.287

.0554700

.3338

.8631118

.7208

.9545115

.1612

.1150677

.5695

.288

.05568.38

.3342

.8625859

.7211

.9543666

.1609

.115'4387

.5693

.289

.0559018

.3345

.8620596

.7214

.9542218

.1606

.1158096

.5691

0.290

0.0561179

9.3349

9.8615329

9.7217

9.9540771

9.1604

0.1161803

9.5689

.291

.0563342

.3353

.8610058

.7221

.9539325

.1601

.1165508

.5687

.292

.0565507

.3356

.8604783

.7224

.9537879

.1599

.1169211

.5685

.293

.0567674

.3360

.8599504

.7227

.9536435

.1596

.1172913

.5683

.294

.0569842

.3364

.8594221

.7230

.9534991

.1594

.1176612

.5680

0.295

0.0572013

9.3367

9.8588935

9.7233

9.9533548

9.1591

0.1180310

9.5678

.296

.0574185

.3371

.8583644

.7236

.9532106

.1589

.1184006

.5675

.297

.0576359

.3375

.8578349

.7240

.9530665

.1586

.1187699

.5673

.298

.0578535

.3379

.8573051

.7243

.9529224

.1584

.1191391

.5671

.299

.0580713

.3383

.8567748

.7246

.9527785

.1581

.1195081

.5668

.300

.0582893

.3387

.8562442

.7249

.9526346

.1578

0.1198768

9.5666

TABLE Ha.

29

TO-

»„.

Log AI .

Log Aj.

Log Aj.

0
2

<5 o o.oo

2 47 11.83

+3.7005216
3.7000079

—0.00000
0.47160

—9.695
9.691

4

5 34 0.00

3.6984710

0.76930

9.681

6

8 20 1.19

3.6959236

0.93987

9.664

8

11 4 52.82

3.6923863

1.05702

9.641

10
12

13 48 13.31
16 29 42.39

+3.6878872
3.6824613

—1.14430
1.21171

—9.610
9.571

14

19 9 1.36

3.6761493

1.26497

9.525

16

21 45 53.23

3.6689972

1.30744

9.470

18

24 20 2.89

3.6610547

1.34135

9.405

20
22

26 51 17.15
29 19 24.78

+3.6523748
3.6430121

—1.36825
1.38929

—9.329
9.239

24

31 44 16.52

3.6330224

1.40535

9.130

26

34 5 44.97

3.6224621

1.41714

8.994

28

36 23 44.51

3.6113863

1.42520

8.814

30
32

38 38 11.23
40 49 2.74

4-3.5998496
3.5879044

—1.43003
1.43201

—8.538

—7.847

34
36

42 56 18.02
44 59 57.33

3.5756011

3.5629877

1.43149
1.42877

+8.237

8.585

38

47 0 2.00

3.5501091

1.42410

8.753

40
42

48 56 34.33
50 49 37.39

4-3.5370077
3.5237227

—1.41772
1.40983

4-8.857
8.928

44

52 39 14.95

3.5102905

1.40060

8.978

46

54 25 31.32

3.4967444

1.39020

9.013

48

56 8 31.24

3.4831149

1.37878

9.038

50
52

57 48 19.82
59 25 2.41

4-3.4694297
3.4557140

—1.36645
1.35333

4-9.056
9.067

54

60 58 44.53

3.4419903

1.33952

9.073

56

62 29 31.82

3.4282790

1.32512

9.076

58

63 57 29.99

3.4145981

1.31021

9.075

60
64

65 22 44.74
68 5 26.60

4-3.4009637
3.3738900

—1.29486
1.26308

4-9.071
9.056

68

70 38 21.86

3.3471520

1.23025

9.035

72

73 2 13.17

3.3208214

1.19672

9.008

76

75 17 40.91

3.2949510

1.16277

8.978

80
84

77 25 22.94
79 25 54.44

4-3.2695785
3.2447291

—1.12863
1.09447

+8.945
8.910

88

81 19 47.97

3.2204185

1.06044

8.874

92

83 7 33.52

3.196ti546

1.02665

8.837

96

84 49 38.62

3.1734393

0.99319

8.798

100
104

86 26 28.52
87 58 26.32

4-3.1507694
3.1286388

—0.96012
0.92749

4-8.760
8.721

108

89 25 53.18

3.1070382

0.89534

8.682

112

90 49 8.43

3.0859565

0.86370

8.643

116

92 8 29.76

3.0653811

0.83257

8.605

30

TABLE Ha.

TO-

iV

Log AI •

Log Aa-

Log As-

116

9°2 8 29.76

+3.0653811

—0.83257

+8.605

120

93 24 13.33

3.0452984

0.80199

8.567

124

94 36 33.98

3.0256943

0.77194

8.529

128

95 45 45.25

3.0065544

0.74244

8.491

132

96 51 59.60

2.9878638

0.71347

8.454

136

97 55 28.43

+2.9696079

—0.68505

+8.418

140

98 56 22.24

2.9517723

0.65716

8.382

144

99 54 50.68

2.9343427

0.62979

8.346

148

100 51 2.62

2.9173052

0.60293

8.311

152

101 45 6.25

2.9006462

0.57658

8.276

156

102 37 9.12

+2.8843526

—0.55071

+8.242

160

103 27 18.23

2.8684116

0.52534

8.209

164

104 15 40.03

2.8528110

0.50043

8.176

168

105 2 20.49

2.8375388

0.47598

8.143

172

105 47 25.18

2.8225838

0.45198

8.111

176

106 30 59.23

+2.8079349

—0.42841

+8.080

180

107 13 7.45

2.7935817

0.40526

8.049

184

107 53 54.28

2.7795141

0.38253

8.018

188

108 33 23.87

2.7657223

0.36020

7.988

192

109 11 40.10

2.7521971

0.33826

7.959

196

109 48 46.58

+2.7389297

-0.31670

+7.930

200

110 24 46.69

2.7259114

0.29551

7.901

210

111 50 16.87

2.6944032

0.24407

7.831

220

113 9 55.67

2.6642838

0.19472

7.764

230

114 24 20.89

2.6354467

0.14732

7.700

240

115 34 4.97

+2.6077961

—0.10174

+7.637

250

116 39 35.94

' 2.5812455

0.05786

7.577

260

117 41 18.16

2.5557170

0.01556

7.519

270

118 39 32.86

2.5311401

9.97476

7.463

280

ll'J 34 38.67

2.5074507

9.93535

7.409

290

120 26 51.98

+2.4845910

—9.89725

+7.356

300

121 16 27.30

2.4625078

9.86038

7.305

310

122 3 37.49

2.4411532

9.82467

7.256

320

122 48 34.01

2.4204831

9.79006

7.208

330

123 31 27.11

2.4004569

9.75648

7.161

340

124 12 25.97

+2.3810379

—9.72387

+7.116

350

124 51 38.87

2.3621918

9.69219

7.072

360

125 29 13.25

2.3438873

9.66139

7.029

370

126 5 15.87

2.3260956

9.63142

6.987

380

126 39 52.85

2.3087898

9.60224

6.947

390

127 13. 9.75

+2.2919450

—9.57381

+6.907

400

127 45 11.66

2.2755384

9.54610

6.868

420

128 45 48.63

2.2439555

9.49269

6.794

440

129 42 16.43

2.2138871

9.44176

6.723

460

130 35 2.66

2.1851991

9.39310

6.655

TABLE

31

T0.

t>0.

Log AI .

Log A2-

Log Ay-

460

130 35' 2.66

+2.1851991

—9.39310

+96.655

480

131 24 30.82

2.1577741

9.34654

6.589

500

132 11 1.09

2.1315086

9.30188

6.527

520

132 54 50.84

2.1063114

9.25901

6.467

540

133 36 15.19

2.0821011

9.21777

6.409

560

134 15 27.33

+2.0588051

—9.17805

+96.353

580

134 52 38.80

2.0363588

9.13976

6.299

600

135 27 59.81

2.0147037

9.10278

6.247

640

136 33 45.52

1.9735615

9.03246

6.148

680

137 33 45.39

1.9350140

8.96649

6.055

720

138 28 48.27

+1.8987593

—8.90438

+95.968

760

139 19 33.81

1.8645446

8.84571

5.885

800

140 6 34.57

1.8321564

8.79012

5.807

850

J41 0 45.22

1.7939648

8.72451

5.714

900

141 50 30.05

1.7580440

8.66275

5.627

950

142 36 24.37

+1.7241428

—8.60441

+95.544

1000

143 18 57.20

1.6920492

8.54915

5.466

1050

143 58 32.66

1.6615826

8.49665

5.392

1100

144 35 30.95

1.6325881

8.44666

5.321

1150

145 10 9.20

1.6049315

8.39896

5.254

1200

145 42 41.98

+1.5784963

—8.35333

+95.189

1250

146 13 21.82

1.5531804

8.30962

5.127

1300

146 42 19.55

1.5288937

8.26767

5.068

1350

147 9 44.57

1.5055568

8.22735

5.011

1400 .

147 35 45.11

1.4830989

8.18853

4.956

1450

148 0 2'8.40

+1.4614567

— 8.15110

+94.903

1500

148 24 0.83

1.4405738

8.11498

4.851

1600

149 7 55.10

1.4008865

8.04631

4.754

1700

149 48 6.25

1.3636849

7.98190

4.663

1800

150 25 5.10

1.3286785

7.92126

4.576

1900

150 59 16.75

+1.2956243

—7.86398

+94.495

2000

151 31 1.89

1.2643177

7.80971

4.418

2100

152 0 37.76

1.2345845

7.75814

4.345

2200

152 28 18.85

1.2062750

7.70903

4.275

2300

152 54 17.45

1.1792601

7.66216

4.208

2400

153 18 44.05

+1.1534272

—7.61732

+94.145

2500

153 41 47.70

1.1286779

7.57435

4.084

2600

154 3' 36.21

1.1049254

7.53310

4.025

2700

154 24 16.39

1.0820930

7.49344

3.969

2800

154 43 54.21

1.0601125

7.45526

3.914

2900

155 2 .'54.93

+1.0389230

—7.41844

+93.862

3000

155 20 23.19

1.0184698

7.38289

3.811

3200

155 53 38.39

0.9795803

7.31529

3.715

3400

156 24 7.80

0.9431040

7.25186

3.625

3600

156 52 14.00

0.9087603

7.19213

3.540

32

TABLE IIa.

la-

«v

Log AI •

Log A2-

Log AS.

8600

3800

15°6 52 14.00
157 18 15.42

+0.9087603
0.8763145

—97.19213
7.13568

+93.540
3.459

4000

157 42 27.29

0.8455688

7.08218

3.383

4200

158 5 2.33

0.8163545

7.03133

3.311

4400

158 26 11.25

0.7885269

6.98289

3.242

4600
4800

158 46 3.15
159 4 45.83

+0.7619607
0.7365469

— 96.93664
6.89238

+93.176
3.113

5000

159 22 25.99

0.7121902

6.84996

3.053

5200

159 39 9.45

0.6888063

6.80923

2.995

5600

160 10 6.00

0.6446674

6.73234

2.885

6000
6400

160 38 9.17
161 3 45.36

+0.6036264
0.5652780

—96.66082
6.59398

+92.783

2.688

6800

161 27 15.57

0.5292915

6.53125

2.599

7200

161 48 56.78

0.4953934

6.47215

2.514

7600

162 9 2.89

0.4633554

6.41629

2.435

8000
8400

162 27 45.39
162 45 13.90

+0.4329843
0.4041157

—96.36332
6.31297 •

f92.359

2.287

8800

163 1 36.52

0.3766081

6.26499

2.219

9200

163 17 0.16

0.3503393

6.21916

2.154

9600

163 31 30.72

0.3252029

6.17531

2.091

10000
10500

163 45 13.32
164 1 20.80

+0.3011054
0.2723199

—96.13326
6.08303

+92.031
1.959

11000

164 16 27.66

0.244H894

6.03516

1.891

11500

164 30 40.23

0.2186921

5.98944

1.826

12000

1'64 44 3.94

0.1936223

5.94568

1.764

13000
14000

165 8 42.90
165 30 55.26

+0.1465042
0.1029147

—95.86343
5.78733

+91.646
1.538

15000

165 51 4.63

0.0623627

5.71652

1.437

16000

166 9 29.58

0.0244528

5.65032

1.342

17000

166 26 24.88

9.9888624

5.58817

1.254

18000
19200

166 42 2.53

166 59 18.90

+9.9553241
9.9174751

—95.52959
5.46348

+91.170
1.076

20400

167 15 11.32

9.8819393

5.40141

90.987

21600

167 29 51.00

9.8484507

5.34290

90.904

22800

167 43 27.11

9.8167866

5.28758

90.825

24000
26000

167 56 7.28
168 15 26.77

+9.7867585
9.7399215

—95.23512
5.15328

+90.750
90.633

28000

168 32 51.95

9.6965794

5.07755

90.525

30000

168 48 41.17

9.6562474

5.00706

90.424

32000

169 3 8.84

9.6185347

4.94116

90.330

34000
36000

169 16 26.46
169 28 43.36

+9.5831221
9.5497452

—94.87926
4.82093

+90.242
90.159

38000

169 40 7.19

9.5181828

4.76576

90.080

40000

169 50 44.28

9.4882481

4.71343

90.005

TABLE Ilia.

33

^

Log /t.

Log Diff.

9

Log /i.

Log Diff.

•n

Log //.

Log Diff.

0.00
.01
.02

0.00000 00
.00000 18
.00000 72

1.556
1.857

0.30
.31
.32

0.00167 33
.00179 01
.00191 12

3.0594
.0754
.0910

0.60
.61
.62

0.00735 26
.00763 61
.00792 74

3.4468

.4585
.4703

0.03
.04
.05

0.00001 62
.00002 89
.00004 52

2.0354
.1614
.2589

0.33
.34
.35

0.00203 67
.00216 66
.00230 10

31062
.1211
.1356

0.63
.64
.65

0.00822 68
.008.J3 45
.00885 08

3.4H22
.4941
.5061

0.06

.07
.08

.00006 52
.00008 88
.00011 61

2.3385
.4057
.4639

0.36
.37
.38

0.00243 99
.00258 34
.00273 15

3.1498
.1638
.1774

0.66

.67
.68

0.00917 59
.00951 03
.00985 42

3.5 1S2
.5304
5427

0.09
| .10
.11

0.00014 70
.00018 16
.00021 99

2.5152
.5617
.6031

0.39
.40
.41

0.00288 43
.00304 20
.00320 45

3.1911

.2044
.2175

0.69
.70
.71

0.01020 81
.01057 23
.01094 73

3.5551
.5677
.5805

0.12
.13
.14

0.00026 18
.00030 74
.00035 68

2.6410
.6767

.7097

0.42
.43
.44

0.00337 20
.00354 45
.00372 22

3.2304
.2433
.2557

0.72
.73
.74

0.01133 35
.01173 15
.01214 19

3.5934
.6066
.6200

0.15
.16
.17

0.00040 99
.00046 68
.00052 75

2.7404
.7694
.7966

0.45
.46
.47

0.00390 50
.00409 31
.00428 67

3.2681
.2807
.2930

0.75
.76

.77

0.01256 52
.01300 22
.01345 36

3.6336
.6476
.6618

0.18
.19

.20

0.00059 20
.00066 03
.00073 25

2.8222
.8466
.8701

0.48
.49
.50

0.00448 58
.00469 06
.00490 11

3.3053
•3173
.3293

0.78

.79
.80

0.01392 02
.01440 31
.01490 32

3.6765
.6915
.7070

0.21
.22

.23

0.00080 86
.00088 86
.00097 25

2.8924
.9135
.9340

0.51
.52
.53

0.00511 75
.00533 98
.00556 83

3.3411
.3529
.3647

0.81
.82'
.83

0.01542 18
.01596 03
.01652 02

3.7231
.7397
.7570

0.24
.25
.26

0.00106 04
.00115 23
.00124 83

2.9538
.972!)
.9914

0.54
.55
.56

0.00580 30
.00604 41
.00629 19

3.3764

.3882
.4000

0.84
.85
.86

0.01710 33
.01771 19
.01834 86

3.7751
.7942
.8144

0.27
.28

.29

.00134 84
.00145 25
.00156 08

3.0090
.0261
.0430

0.57

.58
.59

0.00654 65
.00680 80
.00707 66

3.4117
.4233
.4350

0.87
.88

.89

0.01901 65
.01971 95
.02046 29

3.8360
.8593
.8846

0.30
.31
.32

0.00167 33
.00179 01
.00191 12

3.0594
.0754
.0910

0.60
.61
.62

0.00735 26
.00763 61
.00792 74

3.4468
.4585
.4703

0.90
.91
.92

0.02125 29
.02209 92
.02301 60

3.9128
.9452

!

5

34

TABLE IVo.

m sin 2* = sin (z — q). m and q positive.

"g

fc"

a

0'

z"

z™

z"

1

1°

j>

m"

m'

m'

m"

m"

m'

m

m"

O

1

4.2976

9.9999

0 ,

1 0

O /

1 20

O /

1 20

O 1

89 40

0 /

89 40

o /

177 37

180 55

181 0

2

3.3950

9.9996

2 0

2 40

2 40

89 20

89 20

175 14

181 51

182 0 j

3

2.8675

9.9992

3 0

4 0

4 0

89 0

89 0

172 52

182 46

183 0

4

2.4938

9.9986

4 0

5 20

5 20

88 40

88 40

170 28

183 42

184 0 1

5

2.2044

9.9978

5 0

6 41

6 41

88 19

88 19

168 5

184 37

185 0 j

6

1.9686

9.9968

6 0

8 1

8 1

87 59

87 59

165 41

185 32

186 0

7

1.7698

9.9957

7 1

9 22

9 22

87 38

87 38

163 18

186 28

186 59

8

1.5981

9.9943

8 1

10 42

10 42

87 18

87 18

160 52

187 23

187 59

9

1.4473

9.9928

9 2

12 3

12 3

86 57

86 57

158 28

188 18

188 58

10

1.3130

9.9911

10 3

13 25

13 25

86 35

86 35

156 3

189 13

189 57

11

1.1922

9.9892

11 5

14 46

14 46

86 14

86 14

153 37

190 9

190 56

12

1.0824

9.9871

12 7

16 8

16 8

85 52

85 52

151 10

191 4

191 54

18

0.9821

9.9848

13 9

17 31

17 31

85 29

85 29

148 43

191 59

192 52

14

0.8898

9.9823

14 12

18 53

18 53

85 7

85 7

146 14

192 54

193 49

15

0.8045

9.9796

15 16

20 17

20 17

84 43

84 43

143 45

193 49

194 46

16

0.7254

9.9767

16 20

21 40

21 40

84 20

84 20

141 14

194 44

195 42

17

0.6518

9.9736

17 26

23 5

23 5

83 55

83 55

138 42

195 39

196 38

18

0.5830

9.9702

18 33

24 30

24 30

83 30

83 30

136 9

196 33

197 33

19

0.5185

9.9667

19 41

25 56

25 56

83 4

83 4

133 34

197 28

198 28

20

0.4581

9.9629

20 51

27 23

27 2:!

82 37

82 37

130 58

198 23

199 22

21

0.4013

9.9588

22 2

28 50

28 50

82 10

82 10

128 19

199 17

200 15

22

0.3479

9.9545

23 15

30 19

30 V.)

81 41

81 41

125 38

200 11

201 8

23

0.2976

9.9499

24 31

31 49

31 49

81 11

81 11

122 55

201 6

202 0

24

0.2501

9.9451

25 49

33 20

33 20

80 40

80 40

120 9

202 0

202 51

25

0.2053

9.9400

27 10

34 53

34 53

80 7

80 7

117 20

202 54

203 42

26

0.1631

9.9345

28 35

36 28

36 28

79 32

79 32

114 27

203 47

204 32

27

0.1232

9.9287

30 4

38 5

38 5

78 55

78 55

111 30

204 41

205 22

28

0.0857

9.9226

31 38

39 45

39 45

78 15

78 15

108 27

205 35

206 1 1

29

0.0503

9.9161

33 18

41 27

41 27

77 33

77 33

105 19

206 28

207 0

30

0.0170

9.9092

35 5

43 13

43 13

76 47

76 47

102 3

207 21

207 48

31

9.9857

9.9019

37 1

45 4

45 4

75 56

75 56

98 37

208 14

208 36

32

9.9565

9.8940

39 9

47 1

47 1

74 59

74 59

95 0

209 6

209 24

33

9.9292

9.8856

41 33

49 6

49 6

73 54

73 54

91 6

209 58

210 1 1

34

9.9040

9.8765

44 21

51 22

51 22

72 38

72 38

86 49

210 50

210 58

35

9.8808

9.8665

47 47

53 58

53 58

71 2

71 2

81 53

211 41

211 46

36

9.8600

9.8555

52 31

57 13

57 13

68 47

68 47

75 40

212 32

212 33

q'

9.8443

9.8443

63 26

63 26

63 26

63 26

63 26

63 26

213 15

213 15

q' = 36° 52' 11.64" sin q' = 0.6

TABLE IVa.

35

m sin z4 = sin (z -4- <?). nz and g positive.

'i

trj

zl

2*1

zm

0"

7

!

M

m'

m"

m"

m'

m'

m"

m"

m

O

O /

O /

O /

O /

O /

O t

O /

O /

1

4.2976

9.9999

2 23

90 20

90 20

178 40

178 40

179 0

359 0

359 5

2

3.3950

9.9996

4 46

90 40

90 40

177 20

177 20

178 0

358 0

358 9

3

2.8675

9.9992

7 8

91 0

91 0

175 0

175 0

177 0

357 0

357 14

4

2.4938

9.9986

9 32

91 20

91 20

174 40

174 40

176 0

356 0

356 18

5

2.2044

9.9978

11 55

91 41

91 41

173 19

173 19

175 0

355 0

355 23

6

1.9686

9.9968

14 19

92 1

92 1

171 59

171 59

174 0

354 0

354 28

7

1.7698

9.9957

16 42

92 22

92 22

170 38

170 38

172 59

353 1

353 32

8

1.5981

9.9943

19 7

92 42

92 42

169 18

169 18

171 59

352 1

352 37

9

1.4473

9.9928

21 32

93 3

93 3

167 57

167 57

170 58

351 2

351 42

10

1.3130

9.9911

23 57

93 25

93 25

166 35

166 35

169 57

350 3

350 47

11

1.1922

9.9892

26 23

93 46

93 46

165 14

165 14

168 55

349 4

349 51

12

1.0824

9.9871

28 50

94 8

94 8

163 52

163 52

167 54

348 6

348 56

13

0.9821

9.9848

31 17

94 31

94 31

162 29

162 29

166 51

347 8

348 1

14

0.8898

9.9823

33 46

94 53

94 53

161 7

161 7

165 48

346 11

347 6

15

0.8045

9.9796

36 15

95 17

95 17

159 43

159 43

164 44

345 14

346 11

16

0.7254

9.9767

38 46

95 40

95 40

158 20

158 20

163 40

344 18

345 16

17

0.6518

9.9736

41 18

96 5

96 5

156 55

156 55

162 34

343 22

344 21

18

0.5830

9.9702

43 51

96 30

96 30

155 30

155 30

161 27

342 27

343 27

19

0.5185

9.9667

46 26

96 56

96 56

154 4

154 4

160 19

341 32

342 32

20

0.4581

9.9629

49 2

97 23

97 23

152 37

152 37

159 9

340 38

341 37

21

0.4013

9.9588

51 41

97 50

97 50

151 10

151 10

157 58

339 45

340 43

22

0.3479

9.9545

54 22

98 19

98 19

149 41

149 41

156 45

338 52

339 49

23

0.2976

9.9499

57 5

98 49

98 49

148 11

148 11

155 29

338 0

338 54

24

0.2501

9.9451

59 51

99 20

99 20

146 40

146 40

154 11

337 9

338 0

25

0.2053

9.9400

62 40

99 53

99 53

145 7

145 7

152 50

336 18

337 6

26

0.1631

9.9345

65 33

100 28

100 28

143 32

143 32

151 25

335 28

336 13

27

0.1232

9.9287

68 30

101 5

101 5

141 55

141 55

149 56

334 38

335 19

28

0.0857

9.9226

71 33

101 45

101 45

140 15

140 15

148 22

333 49

334 25

29

0.0503

9.9161

74 41

102 27

102 27

138 33

138 33

146 42

333 0

333 32

30

0.0170

9.9092

77 57

103 13

103 13

136 46

136 46

144 55

332 12

332 39

31

9.9857

9.9019

81 23

104 4

104 4

134 56

134 56

142 59

331 24

331 46

32

9.9565

9.8940

85 0

105 1

105 1

132 59

132 59

140 51

330 36

330 54

33

9.9292

9.8856

'88 54

106 6

106 6

130 54

130 54

138 27

329 49

330 2

34

9.9040

9.8765

93 11

107 22

107 22

128 38

128 38

135 38

329 2

329 10

35

9.8808

9.8665

98 7

108 58

108 58

126 2

126 2

132 13

328 14

328 19

36

9.8600

9.8555

104 20

111 13

111 13

122 47

122 47

127 29

327 27

327 28

<t

9.8443

9.8443

116 34

116 34

116 34

116 34

116 34

116 34

326 45

326 45

q' = 36° 52' 11.64" sin/ = 0.6

\

36

TABLE Va.

X.

A. Diff.

B.

Diff.

B'.

Diff.

0

0

- 0.00

—9.60

— o'.ooo

—11

_ 6'.ooo

—34

1

9.00

9.00

0.011

11

0.034

34

2

17.99

8.98

0.023

12

0.067

33

3

26.95

8.95

0.034

11

0.101

34

4

35.88

8.91

0.045

11

0.134

33

5

— 44.77

—8.87

—0.057

—12

—0.167

—33

6

53.61

8.80

0.068

11

0.200

33

7

62.37

8.73

0.080

12

0.232

32

8

71.07

8.65

0.092

12

0.263

31

9

79.67

8.56

0.104

12

0.294

31

10

— 88.18

—8.46

—0.117

—13

—0.324

—30

11

96.58

8.34

0.129

12

0.353

29

12

104.86

8.22

0.142

13

0.382

29

13

113.01

8.08

0.156

14

0.409

27

14

121.02

7.94

0.169

13

0.436

27

15

—128.88

—7.79

—0.183

—14

—0.461

—25

16

136.59

7.62

0.197

14

0.486

25

17

144.12

7.43

0.211

14

0.509

23

18

151.47

7.27

0.226

15

0.531

22

19

158.63

7.08

0.241

15

0.552

21

20

—165.60

—6.86

—0.256

—15

—0.571

—19

21

172.35

6.65

0.271

15

0.590

19

22

178.89

6.43

0.287

16

0.606

16

23

185.20

6.20

0.303

16

0.622

16

24

191.28

5.96

0.319

16

0.636

14

25

—197.11

—5.71

—0.336

—17

—0.648

—12

26

202.69

5.45

0.352

16

0.659

10

27

208.00

5.18

0.369

17

0.668

9

28

213.05

4.91

0.386

17

0.676

7

29

217.81

4.63

0.403

17

0.682

6

30

—222.30

—4.34

—0.419

—16

—0.687

— 4

31

226.48

4.04

0.436

17

0.690

3

32

230.37

3.74

0.453

17

0.692

1

33

233.95

3.42

0.470

17

0.692

0

34

237.21

3.10

0.486

16

0.691

+ 2

35

—240.15

—2.78

—0.502

—16

—0.688

+ 4

36

242.76

2.45

0.518

16

0.683

5

37

245.04

2.11

0.534

16

0.677

6

38

246.98

1.77

0.549

15

0.670

8

39

248.57

1.41

0.564

15

0.661

9

40

—249.80

—1.06

—0.578

—14

—0.651

+11

41

250.68

0.70

0.591

13

0.639

12

42

251.20

0.33

0.604

12

0.627

13

TABLE Va,

37

X.

A.

Diff.

B.

Diff.

B'.

Diff.

42

— 25L20

— 0.33

— 6'.604

— 12

— 6'.627

+13

43

251.34

+ 0.04

O.G15

11

0.613

15

44

251.11

0.42

0.626

11

0.597

16

45

250.50

0.80

0.636

10

0.580

17

46

249.51

1.18

0.645

8

0.563

18

47

—248.13

+ 1.57

—0.652

— 7

—0.544

+19

48

246.36

1.96

0.659

6

0.524

20

49

244.20

2.36

0.664

4

0.503

21

50

241.64

2.76

0.667

3

0.482

22

51

238.68

3.16

0.669

1

0.459

23

52

—235.31

+ 3.57

—0.669

+ 1

—0.436

+23

53

231.54

3.98

0.667

2

0.412

24

54

227.35

4.39

0.664

4

0.387

25

55

222.76

4.80

0.659

6

0.361

26

56

217.75

5.22

0.651

9

0.335

26

57

—212.32

+ 5.64

—0.641

+ 11

—0.309

+26

58

206.47

6.06

0.629

13

0.282

27

59

200.20

6.47

0.615

15

0.255

27

60

193.52

6.90

0.598

18

0.227

28

61

186.40

7.32

0.579

20

0.200

27

62

—178.87

+ 7.74

—0.557

+ 23

—0.172

+28

63

170.91

8.17

0.532

26

0.144

28

64

1 62.52

8.60

0.504

29

0.116

28

65

153.70

9.03

0.474

32

0.088

28

66

144.46

9.45

0.440

35

0.061

27

67

—134.79

+ 9.88

—0.403

+ 38

—0.033

+28

68

124.69

10.31

0.363

41

—0.006

27

69

114.16

10.74

0.320

45

+0.021

27

70

103.20

11.17

0.273

49

0.048

27

71

91.81

11.60

0.222

52

0.074

26

72

— 80.00

+ 12.03

—0.168

+ 56

+0.099

+25

73

67.75

12.46

0.110

59

0.124

25

74

55.07

12.H9

0.049

63

0.148

24

75

41.97

13.32

+0.016

67

0.172

24

76

28.43

13.72

0.086

71

0.195

22

77

— 14.47

+14.18

+0.159

+ 75

+0.216

+21

78

0.07

14.61

0.237

80

0.237

21

79

+ 14.76

15.04

0.319

84

0.257

20

80

30.02

15.47

0.405

88

0.276

19

81

45.70

15.89

0.496

93

0.294

18

82

+ 61.80

f 16.32

+0.591

+ 97

+0.311

+16

83

78.84

16.76

0.691

102

0.326

15

84

95.32

17.19

0.795

106

0.340

13

1

38

TABLE Va.

X.

A.

Diff.

B.

Diff.

B'.

Diff.

84

//
+ 95.32

+17.19

+ 0.795

+106

+6/.340

+ 13

85

112.72

17.62

0.904

111

0.352

12

86

130.56

18.06

1.018

116

0.363

10

87

148.84

18.49

1.137

121

0.373

9

88

167.54

18.92

1.261

126

0.381

7

89

+ 186.69

+19.36

+ 1.390

+132

+0.386

+ 5

90

206.27

19.80

1.525

137

0.390

3

91

226.29

20.24

1.665

142

0.392

1

92

246.75

20.68

1.810

148

0.392

— 1

93

267.65

21.13

1.961

154

0.390

3

94

+ 289.01

+21.58

+ 2.118

+159

+0.385

— 6

95

310.82

22.03

2.280

165

0.378

8

96

333.08

22.49

2.449

171

0.368

11

97

355.80

22.95

2.623

178

0.355

14

98

378.99

•23.42

2.805

184

0.339

17

99

+ 402.65

+23.89

+ 2.992

+191

+0.320

— 21

100

426.78

24.37

3.187

198

0.297

25

101

451.40

24.86

3.388

204

0.270

28

102

476.51

25.36

3.596

212

0.240

32

103

502.12

25.86

3.812

220

0.205

37

104

-4- 528.24

+26.38

+ 4.036

+227

+0.165

— 42

105

554.88

26.90

4.267

235

0.121

47

106

582.04

27.43

4.506

240

0.071

53

107

609.75

27.99

4.755

250

+0.015

59

108

638.02

28.55

5.012

261

—0.048

66

109

+ 666.85

+29.11

+ 5.278

+271

—0.117

— 72

110

696.27

29.72

5.554

281

0.193

80

111

726.29

30.33

5.841

292

0.278

89

112

756.93

30.96

6.138

302

0.371

98

113

788.21

31.61

6.446

314

0.474

108

114

+ 820.15

+32.28

+ 6.766

+326

—0.587

—119

115

852.77

32.98

7.099

339

0.712

131

116

886.11

33.70

7.445

353

0.849

144

117

920.18

34.45

8.806

368

1.000

158

118

955.02

35.22

8.181

383

1.166

174

119

+ 990.65

+36.05

+ 8.572

+399

—1.348

—191

120

1027.13

36.91

8.980

417

1.548

209

121

1064.47

37.79

9.407

436

1.767

230

122

1102.71

38.73

9.853

456

2.009

253

123

1141.93

39.71

10.320

478

2.274

278

124

+1182.14

+40.74

+10.809

+501

—2.566

—306

125

1223.41

41.82

11.323

527

2.886

336

126

1265.78

42.96

11.863

554

3.239

370

TABLE Va.

39

X.

A.

Diff.

B.

Diff.

B'.

Diff.

126

127

+126o.78
1309.33

+ 42.96
44.16

+ 1L863
12.431

+ 0.554

0.584

— 3^239

3.627

— 0.370
0.408

128

1354.11

45.43

13.031

0.616

4.055

0.449

129

1400.20

46.78

13.663

0.651

4.526

0.496 ;

130

1447.67

48.20

14.333

0.690

5.047

0.547

131
132

+1496.61
1547.11

+ 49.72
51.33

+ 15.043
15.796

+ 0.731
0.777

— 5.621
6.257

— 0.605
0.669

133

1599.28

53.04

16.597

0.827

6.960

0.741

134

1653.20

54.87

17.451

0.883

7.739

0.821

135

1709.02

56.82

18.363

0.945

8.603

0.912

136
137

+1766.84
1826.84

+ 58.91
61.15

+ 19.341
20.389

+ 1.013
1.088

— 9.563
10.631

— 1.014
1.128

138

1889.15

63.55

21.517

1.171

11.820

1.258

139

J 953.95

66.14

22.732

1.265

13.148

1.406

140

2021.43

68.92

24.047

1.371

14.633

1.573

141
142

+2091.79
2165.28

+ 71.90
75.15

+ 25.475
27.027

+ 1.490
1.623

— 16.295
18.163

— 1.765
1.984

143

2242.15

78.65

28.722

1.774

20.263

2.234

144

2322.68

82.47

30.576

1.946

22.631

2.523

145

2407.20

80.58

32.615

2.143

25.309

2.856

146
147

+2496.06
2589.66

+ 91.16
96.11

+ 34.862
37.351

+ 2.368
2.626

— 28.344
31.794

— 3.242
3.713

148

2688.45

101.56

40.115

2.924

35.730

4.224

149

2792.96

107.54

43.199

3.272

40.233

4.836

150

2903.74

114.13

46.659

3.677

45.403

5.566

151
152

+3021.46
3146.88

+121.43
129.53

+ 50.553
54.966

+ 4.153
4.717

— 51.366
58.267

— 6.437
7.469

153

3280.84

138.56

59.987

5.385

66.295

8.705

154

3424.37

148.67

65.737

6.185

75.677

10.202

155

3578.59

160.01

72.357

7.155

86.700

12.024

156
157

+3744.88
3924.79

+172.81
187.33

+ 80.042
89.014

+ 8.328
9.767

— 99.726
115.221

— 14.260
17.023

158

4120.22

203.89

99.577

11.548

133.773

20.471

159

4333.38

222.87

112.111

13.777

156.174

24.815

160

4566.94

244.78

127.132

16.603

183.404

30.348

161
162

+4824.14
5108.93

+244.78
270.26

+145.317
167.550

+20.209
24.869

—216.860
258.371 .

— 37.483
46.802

163

5426.19

300.11

195.056

31.062

310.464

59.156

164

5782.01

335.39

229.674

39.353

376.683

75.318

165

6184.14 377.50

273.762

50.636

462.100

98.618

166
167

+6642.49 +428.33
7170.07 490.43

+330.946
406.573

+66.405
88.993

—574.089
723.733

—130.816
177.025

168

7784.18 567.43

508.933

122.256

928.140

246.403

169

8508.45

651.086

1214.530

CONSTANTS.

Log.

Attractive force of the Sun, Jc in terms of radius, 0 .0172021 8.2355814

Jc in seconds, 3548".18761 3.5500066

Length of the Sidereal Year (HANSEN and OLUFSEN), 365d.2563582 2.5625978

•Length of the Tropical Year, 1850, 365d.2422008 2.5625809

Horizontal equatorial parallax of the Sun (ENCKE),* 8".5776 0.9333658

Constant of Aberration (STRUVE), 20".4451 1.3105892
Time required for light to pass from the S«tn to

the Earth, 4978.827 2.6970785

Radius of Circle in Seconds of arc, 206264".806 5.3144251

in Seconds of time, 13750S.987 4.1383339

Sin 1" 0.000004848137 4.6855749

Circumference of Circle in Seconds of arc, 1296000" 6.1126050

in Seconds of time, 86400' 4.9365137

in terms of diameter, n 3.14159265 0.4971499
General Precession (STRUVE) 50".2411 -f- 0".0002268if
Obliquity of the ecliptic (STRUVE and PETERS), 23° 27'54".22 — 0.4645 1— .0000014;!2

in which t is the number of years after 1800

Daily precession, 1850, 0".1375837 9.1385669

Modulus of Common Logarithms, M 0.4342945 9.6377843

' The Constants of Parallax, Aberration, etc., are those used in the American Ephemeris, and
the authority for them may be found by reference to the volume for 1855.
(40)

Fig. 2.

fit/. • 7 .

Fiy. 7.

Fig. 8.

Fiy.M

I

te

YE 03715

84350:2

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