A NEW AND IMPROVED ASTRONOMICAL INSTRUMENT BY MEANS OF WHICH IS OBTAINED THE TRUE TIME AT MID-DAY OR ANY OTHER MOMENT OF THE DAY, THE LATITUDE, THE LONGITUDE, AND THE MERIDIAN LINE
Year: 1870

page_text: ETTERS PATENT to Henri Adrien Bonneville, of the British and
Foreign Patent Offices, 18, Chaussée d'Antin, Paris, in the Empire
of France, and 10, Sackville Street, Piccadilly, in the County of
Middlesex, Patent Agent, for the Invention of "A NEW AND IMPROVED
ASTRONOMICAL INSTRUMENT BY MEANS OF WHICH IS OBTAINED THE TRUE
TIME AT MID-DAY OR ANY OTHER MOMENT OF THE DAY, THE LATITUDE,
THE LONGITUDE, AND THE MERIDIAN LINE."-A communication from
François Martin Pannetrat, residing at Rue St. Dominique, St.
Germain, in Paris, aforesaid.
Sealed the 12th August 1870, and dated the 7th April 1870.
COMPLETE SPECIFICATION filed by the said Henri Adrien Bonneville
at the Office of the Commissioners of Patents, with his Petition
and Declaration, on the 7th April 1870, pursuant to the 9th Section
of the Patent Law Amendment Act, 1852.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, HENRI
ADRIEN BONNEVILLE, of the British and Foreign Patent Offices, 18,
Chaussée d'Antin, Paris, in the Empire of France, and 10, Sackville
Street, Piccadilly, in the County of Middlesex, Fatent Agent, send
greeting.

page_text: WHEREAS I am in possession of an Invention for "A NEW AND
IMPROVED ASTRONOMICAL INSTRUMENT DY MEANS OF WHICH IS OBTAINED THE TRUE
TIME AT MID-DAY OR ANY OTHER MOMENT OF THE DAY, THE LATITUDE, THE
LONGITUDE, AND THE HERIDIAN LINE," a communication to me from François
Martin Pannetrat, a person resident at Rue St. Dominique, St. Germain, 5
in Paris, aforesaid, and have petitioned Her Majesty to grant unto me,
my executors, administrators, and assigns, Her Royal Letters Patent for
the same, and made solemn Declaration that it is a communication.
NOW KNOW YE, that I, the said Henri Adrien Bonneville, do hereby,
declare that the following Complete Specification, under my hand and 1
seal, fully describes and ascertains the nature of the Invention, and
the manner in which the same is to be performed, reference being had
to the accompanying Drawings, and to the figures and letters marked
thereon, that is to say :-
The Invention communicated to me relates to an instrument intended 1
to measure, with the help of the sun, in all places in the world, on land
or on sea; 1st, the true time of mid-day or, in other words, the moment
of the passage of the sun over the meridian; 2nd, the latitude at all
times of the day as long as the sun is above the horizon, the true time
being known; 3rd, the true time of the place where one may be, at 2
every instant of the day, the latitude being known approximatively;
4th, the longitude of the place where one may be; 5th, the meridian
line or true north and south line and, consequently, the declination of
the compass or "variation." If this instrument does not lead to the
complete suppression of the sextant and other reflecting instruments, of 2
the chronometer, and of the compass, at least it will be found indis-
pensable for controling and regulating with nicety these different
instruments and the operations effected with them. It dispenses almost
entirely with all calculations and reduces the observations to a great
simplicity, and at the same time ensures an exactitude almost me- 3
clanical. It does not consequently demand any deep theoretical study.
It is independent of atmospheric influence. It has finally the advantage
of being capable if necessary of replacing alone all the other instru-
ments, viz., sextant, chronometer, and compass. The size of this
instrument is variable, it may be reduced to the size of a large snuff box, 3
and thus carried in the pocket, or, if great exactitude and precision is
required, this size may be increased.

page_text: :
It is important before entering into the explanation to give an idea
of the probleme to be solved, this will be done by referring to Fig. 1 of
the accompanying Drawings, which also sets forth the relations between
the instrument and the terrestial globe.
Suppose D the place whose position is to be determined on the sphere
represented by the circumference E, 9', E', g, and whose axis from onc
pole to the other is shown by the line 7, g³, and the line E, E¹, indicates
the equatorial plan. It is required to find what distance separates the
point D from the point E or in other words from the equatorial line,
that which is effected by astronomically measuring the distance from the
point Z, zenith of the observer to the point Z equatorial zenith. By
drawing from the points Z and 7', the lines Z, E, E¹, and Z', D, D',
which meet at the point P the centre of the sphere, we have the two
angles E, P, D, and D', P, E', equal to one another as also the arcs E, D,
and D', E', both similar to the arc Z, Z. Consequently if a method of
any description enables one to measure the arc D', E', the measure of
the arc Z, Z, will be obtained also, and therefore that of the arc E, D.
It is precisely this that this instrument is intended to effect.
This instrument consists of a rectangular box A (see Fig. V., which
represents a front view of the instrument, and Fig. VI. which is a side
view of the same) hung so as to turn on two pins b, b', and whose axis
passes through the centre of the volume of the box in the direction of
its length. The axis of the two standards c, c¹, is perpendicular to the
base D, D', which pivots horizontally at T on a support, whose
legs d, d, d, are composed of screws, by means of which the base may
be maintained in a perfectly horizontal position, which forms an essential
condition for the exactitude of the observations. This true horizontal
position is ascertained by means of two water levels n, n', fixed at right
angles on the base. A screw nut S. (see Figs. V. and VI.) serves to
arrest the pivoting movement when the box is in the desired position.
Inside the box are two hollow demi-cylinders with their concave parts
standing back to back at the centre of the volume of the box (sce
Fig. VII.). Their bases form exact half circles. These demi-cylinders
are graduated in their concave part, by means of lines parallel with the
hemicycle of the base, and of others perpendicular to the first and
parallel with the generating line of the cylinder; Fig. 2 represents these
graduations developped in a plan.

page_text: Thus arranged, these two demi-cylinders represent exactly, each of
them, the section of a part of one of the hemispheres included between
the two tropics (see Fig. III.) graduated in its concave instead of in its
convex part. The line E, E', (Fig. II. III. and VII.) which divides
the longitudinal lines into equal parts, represents the equator, the others
above and beneath, marked 0 to 24, represent the degrees of borcal and
austral declination of the sun from one tropic to the other. The
distance intervening between said lines increases gradually from the
first (the nearest to E, E', which is marked zero) to the last, according
to the principle demonstrated, Fig. IV. Thus, by taking the line g, g',
as the axis of the earth, the point P as the centre of the sphere, the
arc g, O, g¹, as a meridian, the point O as one of the points of the
equatorial line, the points a, b, c, as degrees of intertropical latitude, and
then if from the centre P two radii are drawn, which after cutting the
circumference at the points a, b, c, extend far enough to meet the
tangent M, M, it is clear that the divisions 8, 16, and 24 increase in
proportion as they depart from 0, in a progression of which it is
important to take account for the greater precision of the observations.
The other lines perpendicular to the former and equidistant from one
another are the meridians, the middle one M, M', marked 12 (see
Fig. II.), being the generating line of the cylinder, represents the mid-
day of the place, and the others to the right and to the left, marked
1 to 6 and 6 to 11, the horary lines of the diurnal arc with subdivisions
by fractions of 2° 30', say, ten minutes of time.
A thread 9", g, (Fig. VII.,) perpendicular to the long sides of the
box and corresponding exactly to the line M, M³, serves as axis to each
of the demi-cylinders. At the centre of this thread is a knot P¹, which
should correspond with the point 0 or of the line M, M'. In order
to obtain this precision the thread is retained in 9", "", by screws which
enable one to bring back the knot to the centre, which is determined by
placing a second thread in the length of the box from E to E', the
extreme points of the equatorial line; the place where this second
thread will cut the first will be the precise centre sought for. The
thread g", g, thus represents the axis of the earth of which the knot is
the true centre (see Fig. III. and IV.).
• On a board N (see Fig. V. and VI.), attached by hinges to one of the
large sides of the box so as to remain applied or to be withdrawn at

page_text: will, exists a compass card whose north and south line is precisely in
the plan of the thread g", "", and of the line M, M'. This board may
be equally well placed on either side of the box, provided that whatever
be the slope of this latter the said board be held horizontally, it could
also be so arranged as to act at the same time as cover or lid to the box.
The upper demi-cylinder serves for the observations from 6 a.m. to
6 p.m., the lower one before 0a.m. and after 6 p.m. in high latitudes,
or when the sun is continually at the edge of the horizon, that is to say,
in the polar regions. And as this latter is very rarely used, it could,
with a view of simplification and economy, be suppressed in the con-
struction of some of these instruments (see Fig. XIV., which shows a
model of an instrument constructed on this latter principle).
At the foot of one of the vertical standards is fitted a quarter circle B
(Fig. VIII.), graduated from 0 to 90. An alhidade G is fixed to rest
at the axis of the box, which axis is the centre of the circle of which
the dial B is an arc, so that by running the allidade on the dial, a
rotating motion is imparted to the box which slopes (see Fig. VIII.),
and describes on the plan E', P, E, O, (see Fig. III. and Fig. VII.,) an arc
exactly similar to that described by the alhidade on the dial. This dial
could rigourously suffice if the alhidade were furnished, like those of
sextants with a vernier or nonius giving the minutes and the seconds,
and according to the size of the instruments and the degree of precision
required this observation may be arrested here. Nevertheless, to obtain a
higher degree of exactitude it will be better to apply the following
improvement to the instrument.
At the top of the albidade G (Fig. VIII.) a second dial 9 will be seen.
A second alidade H (Fig. IX.) is attached by a pin on to the first at
the point p, which is the centre of the circle of which the dial 7 is an
arc; this latter alhidade plays in the contrary direction to the first G.
At the head of this second one, that is to say, on the prolongation of
the radius under the centre p and forming with it a broken line,
exists a little hand, which exactly covers the indicating stroke of the
alhidade G. The indicator of the albidade II is then at the extreme
left of the dial y destined to give the fractions of degrees in minutes.
To divide this dial, the alhidade II is first placed in this position and in
front of the indicating stroke on the alhidade on the dial is traced a
line, which is the prolongation of said stroke, and marked 0 (zero). The
indicator G being then placed in front of any degree line but zero, on the
I

page_text: dial B, the alhidade H is run out until its head hand, changing
from right to left, has measured backwards on the dial B the space of
a degree, that is to say, until its point is found exactly in front of
The
the division which preceeds that marked by the indicator G.
indicator has then passed to the extreme right of the dial g, on
which is traced a stroke marked 60, which is the prolongation of the
stroke of the indicator of the alhidade and the arc intercepted by
the two points 0 and 60 similar to the arc described by the hand, is
divided into 60 sections, equivalent to as many minutes.
In order to obtain the complement of fractions, a third dial and
alhidade are required. This third dial is on the pin of the alhidade H
(see Fig. IX. and X.) upon which the third albidade L is fixed by a pin
at m this latter is the radius of the circumference of which the dial
is an arc.
Its head has a hand, which fulfils in relation to the divisions
of the dial the same functions as the one placed at the head of the
albidade H in relation to the divisions of the dial B, to the extreme left of
the dial, the line 0 is traced, being a prolongation of the stroke of the
indicator L, and the same proceeding is effected as before, dividing into
60 parts, which will represent seconds, the space run over by this indicator
on the dial, whilst its hand will have measured backwards one of the
divisions of the dial 9. By this means, if it is judged necessary,
fractions of one-third may be taken into account (see Fig. XVI., which
represents an instrument measuring thirds of seconds; here a fourth
alhidade M will be remarked, being pinned to the end of the alhidade L,
indicator of seconds, and running the indicating stroke of its point on
a fourth dial placed on the pin of the alhidade L, which dial has been
divided into sixty parts which are thirds of seconds, in the same way as
the others by means of the hand at the head of the alhidade M).
It will be understood that a number of combinations could be
included in the construction of an instrument on this principle, cach
of which would be preferable according to the requirements of the
accompanying circumstances, that is to say, according to the importance,
more or less considerable, of the questions of weight, volume, and delicate
nature of such an instrument.
Fig. XV. represents an instrument constructed as just explained.
Fig. XIII. represents the same with a double play of alhidades and dials,
one on each side of the box, an improvement which not only affords greater

page_text: convenience but is also an extra guarantee for eveness and for precise
solutions.
Fig. XIV. represents an instrument with but one demi-cylinder, viz.,
the upper one. In this case the axis of suspension and rotation of the
box instead of passing through the centre of the volume is lowered so as
to pass continually through the point 0 (see Figs. III. IV. and VII.),
which in this case lies directly on the bottom, being intended specially
to realize a reduction in the general proportions of the instrument,
principally in the height, and thus necessitates certain modifications in
the measuring apparatus. Consequently a single dial g is fixed not to
the foot of one of the standards but to the right hand corner of one
of the small sides of the box itself, so that the first stroke of this dial,
to the left, marked zero, is entirely included in the supposed plan
E, P, E, O, Fig. III. and VII. A single alhidade G prolongation
immoveable and vertical of the corresponding standard in the axis of the
pin & serves to mark the divisions of the dial, which are only degrees.
To trace these divisions the box is caused to turn in such a way that
the sides a, b, a', ', change the vertical position they occupy for a
perfectly horizontal one; this results in the supposed plan E, P, E', O,
also changing from vertical to horizontal after having run over an arc
of 90°, which the indicator of the alhidade will have duly registered on
the dial. In coincidence with this indicator another line is then traced
to the right of the dial, which is marked 90, and the space included
between these two extreme lines is divided into 90 fractions, each
representing one degree. To effect an operation, that is to say, an
observation, all the indicators should be brought on to the zeros, com-
mencing with the indicator of the thirds, if the instrument has one,
otherwise by the one denoting seconds, then the minutes, and, finally,
the degree. For this purpose the box should be perfectly perpendicular,
in other words, the supposed plan which passes in E, O, E', P (Fig. III.
D'
and Fig. VII.), ought to be quite vertical. The line Z', D, P,
(Fig. 1), that is to say, the terrestial ray in its prolongation as far as
the zenith of the observer, passes infallibly through the points O, P, of
the Figs. III., IV., and VII., inasmuch as the graduated demi-cylinder
represents the lower hemisphere 9, E', ' (Fig. 1) of the planet. This
condition of verticalness is simply a question of level. To find the
exact time of mid-day with this instrument (this problem being in
relation and essential for the solution of all others) and without
the aid of any other, the observations should commence at the moment
"

page_text: that the sun is approximatively judged to be on the point of reaching
its greatest height, that is to say, of passing over the meridian, the
operation is then pursued as follows:-The base being perpendicular and
the indicators on the zeros, the instrument is so placed that the box in
turning on the axis b, b', slopes towards the sun (see Fig. X.), that is
to say, towards the south if the observer is in the boreal hemisphere,
and towards the north if in the austral hemisphere.
We shall only speak of the observations made in the borcal hemi-
spero and of those with the upper demi-cylinder, as all the other
observations are identical.
samc.
The instrument is then set by turning the base horizontally from right
to left or from left to right on the point T (Fig. V. and VI.), until the
shadow of the thread ", g¹¹, exactly covers the line of the meridian
M, M, (Fig. II. and VII.,) then still maintaining it thus, the box is turned
vertically by pushing the alhidade G on the dial B, until the shadow of
the knot reaches the intersection of the line M, M', and of the longi-
tudinal line which represents the declination of the sun calculated for
the day (for this a knowledge of the time tables, or at least of ephemeris,
giving the equation of time and the declination of the sun, is required.)
It is evident that if the declination is borcal, the observer being in the
boreal hemisphere, the shadow of the knot will fall below the line E, E',
if on the other hand the declination is austral, it will fall above the
Suppose the first hypothesis, the shadow of the knot is thus
below the line E, E', as long as the sun rises this shadow will incline to
descend, which will necessitate the prolongation of the vertical move-
ment of the box so as to maintain this shadow on the desired line. A
fugitive but appreciable moment will at last arrive when the shadow
will become stationary before inclining to reascend; it is this passing
but appreciable moment that must be arrested, to rapidly fix the box
by the screw of the alhidade G, which will be the precise time of mid-
day, in other words, the precise instant the sun passes over the meridian
and inclines to re-descend. Observation being then taken of the figure
of the divisions marked by the alhidade G on the dial B, the exact
latitude of the place is obtained; this alhidade, which, as previously
mentioned, pivots on the same axis and at the same time as the box,
having described on this dial an arc similar to that described by the box
in its evolution towards the sun. Under this new condition the line
E', P, E, Z, (Fig. 1,) that is to say, the terrestial radius in its prolonga-

page_text: tion to the equatorial zenith passes through the points O, P, (Fig. III.,
IV., and VII.,) instead of the line D', P, D, Z', and the are Z, Z', is
measured. It is now that the lines of declination present their great
importance. If the terrestial axis were unchangeably perpendicular to
the plan of the ecliptic, the sun would be continually at Z at mid-day
with regard to the observer D, but it is not so, and for example, if
it be supposed at any other point S of the intertropical zone (Fig. 1),
it is evident that by inclining the box (representing the lower hemi-
sphere g, E', g¹,) so that the shadow of the knot may fall on the central
point the arc Z', S, will alone have been really measured and to the
measure found it will be necessary to add the measure known of the
arc S, Z. (If the sun were in the other hemisphere it would have to be
deducted.) This work is avoided by this instrument which itself takes
account of the declination. Nevertheless a small calculation of this
3 nature will become necessary whenever the calculated declination
presents fractions. As in consequence of the size of the instrument the
divisions representing the degrees of declination are always too near to
one another to admit of subdivisions the fractions must at first be
neglected, that is to say, the shadow of the knot must be made to
coincide with the line to which it is nearest, which will of necessity give
a few minutes and seconds more or less. Suppose, for example, the
declination of the day to be 19° 16' the shadow of the knot must be
made to coincide with the line 19 save to add the 16' to the figure read
on the dial after the operation. Let this figure be 15° 44′ the latitude
of the place will be 46°. If the declination had been 19° 41' the shadow
of the knot would have been made to coincide with the line 20 and 10'
would have to be deducted from 45° 41' which leaves 45° 28'. If the
indicator does not correspond exactly to a degree line on the dial B but
gives a fraction, for example, 48° and a fraction, in order to know what
this fraction represents in minutes and seconds the following operation
must be observed :—The alhidade I must be moved so as to bring the
hand on its head round on to the line 48 of the dial B and the space run
over in the contrary direction by the indicator on the dial will
determine the number of minutes. This number may itself have a
fraction, suppose this number to be 34+X. To determine this fraction
the same proceeding must be executed with the allidade L, the hand on
the head being brought round on to the line 31 of the dial its indicator -
will then mark the complement of seconds on the dial h, suppose these
seconds to be 25 the latitude found will be at % a second near
"

page_text: 4S 31 25. To find the latitude at any other time of the day not mid-
day the true time must be known, being obtained by the ordinary
observations and instruments, the box is placed in such a position that
the shadow of the thread covers the horary line corresponding to the
known time, and it is inclined at the same time until the shadow of the
knot falls on the line of the declination as calculated. The are run over
by the indicator to arrive at these coincidences measures necessarily the
latitude of the place. To find the true time at any other time of the day
than at mid-day it is requisite to know at least approximatively the latitude
of the place where the observation is to be made. (The morning and the
evening; a slight difference in latitude is of little importance.) The indi-
cators are arranged so as to mark the latitude, say for example 48° 34′ 25″.
To begin, the indicator of seconds is placed on 25 of the dial h, it is then
observed that the hand at its head has measured in the contrary direction
backward from the zero of the dial 9 a fraction necessarily equivalent to
these 25", consequently the alhidade H has only to be run out until this
hand be on the division 34 of the dial 9 for the indicator H to measure
thereon forwards the 25" In this movement the albidade's hand H
measures downwards backwards from the zero of the dial B, the
fraction equivalent to 34′ 25," and the alhidade G has only to be pushed
until this hand arrives at 48 for the indicator to be in advance between
48 and 49 in the exact proportion of these 34′ 25." The box will thus
have the inclination necessary to measure the horary angle. The base
is then made to pivot horizontally so that the shadow of the knot falls
on the line of declination of the day and remains on this line. During
this time the shadow of the thread is projected parallel with the horary
lines, to the right and left of the line M, M', (Fig. II. and VII.,)
according to whether it is before or after noon, and it passes successively
from one to the other every ten minutes. As soon as it covers one of
the lines the true time is obtained. At whatever time of the day the
observation is made the true time has only to be reduced to the mean
time (by the equation of time furnished in any little work on ephemeris),
and this mean time to be compared with that of the first meridian, to
have the exact longitude of the place.

page_text: To obtain on board a ship a stability sufficient to assure the constant
horizontal position of the base of the instrument, in short to neutralize
the effect of the movement of the ship recourse has been had to the
double balance multiplied and combined (see Fig. XI.)
A is a board with tail piece and tolerably heavy (Fig. XII. represents
a section of the same). a is a pin upon which the instrument can be
fixed at will by means of a hole pierced in the base for this purpose at
the centre of gravity of the instrument; b, b', are pins upon which rests
and pivots the board; B is a circle of metal which surrounds the
board; inside it is provided at b, b', with two fixed notches to receive
the pins of the board, outside with two pins c, c', whose axis cuts the
axis of suspension b, b', of the board at right angles. C, D, E, F, G, are
circles fitting into one another; their suspension play is in opposition,
like the first mentioned, only that the axis of the circles D and E cutting
one another at right angles, cut the others at angles of 45°, they are
intended to neutralize the effects of the diagonal movements combined
from side to side or from head to stern.
Having thus described the said Invention, and the manner of per-
forming the same, I would have it understood I do not confine
myself to the precise details herein indicated and represented in tho
Drawings as these may obviously be modified without departing from
the principle of the said Invention; but what I claim and desire to
secure by the said Letters Patent is, a new and improved astronomical
instrument resulting from the combination of certain organs above
specified, some new and some already know, and by means of which can
be obtained the true time at mid-day or at any other part of the day,
the latitude, the longitude, and the meridian line, said instrument being
constructed and working substantially as described and shown in the
Drawings.
In witness whereof, I, the said Henri Adrien Bonneville, have
hereto set my hand and seal, this Second day of April, in the
H. BONNEVILLE. (L.S.)