APPARATUS NAMED THE SELENOGRAPHIA, TO EXHIBIT THE PHENOMENA OF THE MOON, CONSISTING OF A GLOBE ON WHICH ARE DELINEATED THE SPOTS ON THE MOON'S SURFACE, AFFIXED TO AN INSTRUMENT WHICH IS CONTRIVED TO GIVE IT BUCH MOTIONS AS WILL DESCRIBE THE EFFECTS PRODUCED UPON THE FACE OF THE MOON UNDER ALL CIRCUMSTANCES, WITH CERTAIN APPENDAGES THERETO BELONGING, ILLUSTRATIVE OF THE SAME
Year: 1796

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, JOHN
RUSSELL, of Newman Street, in the Parish of Saint Mary-le-bone, in the
County of Middlesex, Esquire, sends greeting.
WHEREAS the King's most Excellent Majesty, by His Letters Patent
under the Great Seal of Great Britain, bearing date at Westminster, the
Eighth day of November last, gave and granted unto the said John Russell,
his exors, adñiors, and assigns, His especial licence, full power, sole priviledgo
and authority, that he, the said John Russell, his exors; adiñiors, and assigns,
and every of them, by himself or themselves, or by his and their deputy or
leputics, servants or agents, or such others as he, the said John Russell, his
exors, adiñiors, or assigns, should at any time agree with, and no others, from
time to time and at all times thereafter during the term of fourteen years
therein expressed, should and lawfully might make, use, exercise, and vend his
new invented "APPARATUS NAMED THE SELENOGRAPHIA, TO EXHIBIT THE PHENOMENA
OF THE MOON, CONSISTING OF A GLOBE ON WHICH ARE DELINEATED THE SPOTS ON THE
MOON'S SURFACE, AFFIXED TO AN INSTRUMENT WHICH IS CONTRIVED TO GIVE IT
BUCH MOTIONS AS WILL DESCRIBE THE EFFECTS PRODUCED UPON THE FACE OF THE
MOON UNDER ALL CIRCUMSTANCES, WITH CERTAIN APPENDAGES THERETO BELONGING,
ILLUSTRATIVE OF THE SAME;" in which said Letters Patent is contained a
proviso that if the said John Russell should not particularly describe and
ascertain the nature of the said Invention, and in what manner the same is to
be performed, by an instrument in writing under his hand and seal, and causo

page_text: the same to be inrolled in Ilis Majesty's High Court of Chancery within one
calendar month next and immediately after the date of the said Letters Patent,
that then the said Letters Patent, and all liberties and advantages whatsoever
thereby granted, should coase, determine, and become void, as in and by the
said Royal Letters Patent, relation being thereunto had, will more fully and at
large appear.
NOW KNOW YE, that in pursuance of and in compliance with the said
proviso in the said Letters Patent contained, I, the said John Russell, do
hereby disclose, discover, and describe my said Invention, as in the Plan and
Drawings of the same hereunto annexed, and herein-after particularly men-
tioned, in manner following (that is to say):-
This apparatus is designed to exhibit the phenomena of the moon. It
consists of a globe on which are expressed the spots on the visible part of the
surface of the moon, accurately taken by a micrometer from the moon itself
and transferred to a globe, being carefully engraved from the original drawings
made by actual and very minute observation, the lunar mountains being attended
to and expressed with great exactness. This globe is fixed to an instrument
which is contrived to give it such motions as will describe the effects produced to
the inhabitants of the earth upon the face of the moon, in its different degrees
of elongation from the sun under all states of libration, in longitude and
latitude, the inclination of the moon's equator to the plane of the ecliptic, the
first meridian of the moon with the plane of the illuminated hemisphere, the
apparent motion of the polar axis of the moon, and the motion of the moon's
incan centre while performing her periodical circuit round the earth, and revo-
lution on her axis during the whole cycle. Upon this globe, when required, are
inodeled or cast from such models the mountains or elevations on the surface of
the moon, which will contain most properly all the effects together. As an
appendage to the lunar globe, which has not the mountains elevated, a spherical
segment is invented to be cast in a mould from the original model, and upon
this are elevated the various mountains seen on the surface of the moon, and so
coloured that those spots of the moon are properly represented which owo
their respectivo luminous or dark appearance, not to elevation, but to other
causes which render them conspicious. The lunar globes are made like
the common terrestial globes, covered with prints representing the moon
in the same manner as those represent the earth.
The instrument to move this globe is made of metal or wood, or both united.
The parts of each consist (with some necessary exceptions) of circles, semi-
circles, and segments of spheres or circles so placed that the radius of each would
unite in one common centre, which is that of the lunar globe itself. Some of the

page_text: globes are fixed to an instrument which admits only of part of the motions, as
may be required by different persons-more simple, but upon the same prin-
ciple of motion; and some are supported by stands without movements.
What has been said of the engraved lunar globe in the preceding general
description of the selenographic apparatus, will give a sufficient idea of that
part of the work, the globe being covered with printed gores, which not only
represent those spots on the moon produced by the light or the dark colour of
its substance, but those spots also which, being clevated above the general level
of the moon's surface, are rendered conspicious by the light they receive in
consequence of their clevation, and the shadows they cast upon the adjoining
plains, &c. In those lunar globes which have elevated models of the mountains;
it is not necessary to give any other shade but that of the dark or sad colour of
the local tint, as in the different parts of the moon itself, because those elevated
parts will in the model or cast produce their proper shadows according to the situ-
ation of the lamp which is to give the lunar globe its requisite illumination. As the
models, &c. of the lunar mountains will not only afford much pleasure, but will
also tend to illustrate the subject of selenography, when properly coloured, and
as they will be expensive, and sometimes may not be so convenient to the
possessor to have them upon the lunar globe, when the light and shadow or
local colour are not the particular object of consideration, the spherical
segments which have been noticed will be an agreeable substitute for the
illustration of the light, shadow, and colour of the particular parts of the
moon, and one of them should therefore accompany each globe which has not
the mountains elevated upon it. A diameter of twelve inches is recommended
as a convenient size for the lunar globe, and also for the spherical segment, but
any other may be adopted for both. That degree of convexity may be given to
the segment which is adapted to the surface of a sphere whose radius is about
two feet. Its general form will be explained by Figure 1, a section where «.
is the convex surface, 6 the base, c, c, c, c, little indentations which represent the.
sections of the mountains modelled or cast upon the convex part of it..
to which when a lamp is applied they will catch the light and project a
shadow. These segments may be framed to hang up, or may be fixed to.
stands.
It has been already observed "that the machinery which is to move the lunar.
globe consists in-general of circles, semicircles, segments of spheres, and arches
of circles, so placed together that the radius of each would unite in one common
centre, which is that of the lunar globe itself," by which means all its motions are
performed, while the centre of that globe is at all times stationary. This may
be the more clearly comprehended by the Drawing, which represents the less

page_text: complicated instrument of which two views are annexed, with the globe fixed
to it. Figure 2 exhibits the back view, and Figure 3 the profile of the same,
with some necessary parts placed by themselvos, marked by the same letters
to avoid confusion. This instrument consists chiefly of threo segments of
hollow spheres made to fit in and move each other. One is screwed to the
globe, the next is fixed to a staid supporting the whole, and the last is divided
and partly fixed to the second, and partly moved by the cylinder or handle,
one point of which pierces the globe, and is united to the first of these segments,
which cylinder passes through a slit made in the outside hollow segment.
Figures and 5 are the plan and section of the first segment, drawn separate
because in Figures 2 and 3 it is in a great measure hid from the sight by the
parts which cover it. a, a, is the convex or outward surface; b, the concave.
This is fixed to the lunar globe, with screws at d, d, d, d. e represents the
point of the cylinder within the concave surface, and which enters the globe
diametrically opposite to the point where the prime meridian unites with or
intersects the equator of the lunar globe, of which more will be said hereafter.
f, in Figures 3, 4, and 5, is the solid cylindrical bar cast with and of one pieco
with the spherical segment a, b, Fig. 4 and 5. By the means of this cylinder
or handle all the motion is given to the lunar globe, its length being in pro-
portion with the rest in the Drawing. This cylinder passes through the
external and divided segment, is made fast by a collar or any other means,
and to its end a large mill-headed screw of any shape may be fixed for the
conveniency of moving in the manner requisite. h, h, h, in Fig. 2, 3, and
6, is the second segment, having a large hole, seen in Figure 6 at i, which is
hid in the other Drawings and here exposed to view, that segment being
drawn by itself for that purpose. The concave part of receives that
convexity of a, Fig. 4 and 5, and is screwed to the stand at k, by which it is
supported. It has the outward segment, which is divided, either fixed to it or
noving upon it, as 7, 7, or m. Figures 2 and 3, or in Figure 7, where that
Eegment is divided. The external segment 1, 1, m, must have its internal or
concave surface exactly to fit the convexity of the former. The picces 7, 7,
are to be separated by a parting tool from m at n, n, m, n, Figures 2 and 3,
and they are to be fastened by screws to h, as in Figures 2 and 3, so
that m may slide backward and forward with ease. mis to have a vertical
slit opened in it, o, o, Figures 2 and 7, capable of receiving the cylin
drical handle f, Figures 3, 4, and 5, with whatever sliding pieco the
workman may think necessary, which is to move upwards and downwards in
the slit o, o, through which the handle must be brought, and there fixed by a
collar g, Figure 3, by screws to the bar, tight enough to hold it together while

page_text: it freely admits the proper motion of the spherical segments. To the end
of the cylinder the nut screw before mentioned is to be added.
The prime meridian of the lunar globe q, q, being brought to a mark in the
most vertical part of h, Figures 2, 3, and 6, an hole must be bored through the
collar and centre of the cylinder f, parallel to the equator of the globe, pro-
jecting outwards, to be seen beyond the nut screw, as s, Figuro 2, which is
to be used as an index to the graduations upon m at t; or the index may be
fixed to a collar round the cylinder above the other collar, capable of being
adjusted horizontally when the lunar globe's axis presents itself oblique, or it
may be fixed to the sliding piece. The sides of h, at u, u, are to be graduated
also, and the sides of m squared off, that it may do the office of an index, the
better to point to the degrees at u, u; or the pieces 1, 1, have graduations with
à mark on m, as w, w, expressed in the Drawing. The hole in h, Figure 6,
should be large enough for the centre of the cylinder to move fifteen degrees
at least. The graduations must be made on each piece according to the radius
of their different segments. When the instrument is made of wood, it is not
thought necessary to divide the part 1, l, m, and instead of a cylindrical bar a
square one is used for an handle, and a square opening instead of the slit o.
The hole in i of the middle picce, being made large enough, will admit of the
libratory motion. If this instrument is most approved, it may be made, of
brass. If the preceding description is well considered, it will be perceived by
those who understand the motions of the moon, that as the cylindrical bar is
moved backwards and forwards by m sliding over h, Figures 2 and 3, the
graduations u, u, or, will express the degree of libration in longitude; and as
the same cylinder is moved upwards and downwards in o, the graduations t
will point out by the index s the libration in latitude. Moreover, by a small
degree of rotation of that cylinder, an inclination of the polar axis of the lunar
globe may be given that will express the theory of libration either simple or
compound. If a quadrant be fixed to the part in Figures 2 and 3, with the
furniture for the moon's polar libration, which is occasioned by the obliquity
of its axis, if the segment of the sphere be continued until it becomes a
compleat hemisphere, if the lunar globe has a brass meridian applied to its
front, with semicircles representing part of the ecliptic, and a moveable termi-
nator, all graduated with a small terrestial globe, for the diurnal and menstrual
libration (all of which will be described); then will the instrument be
complete for the use of those who may apply it to more curious investigation.
However, that which has been already described may be sufficient to give the
general idea of the apparent motion of the moon's surface, and to this
any part of the succeeding description of the more complete instrument

page_text: may be applied, or parts to produce similar effect upon the same principle.
Figures 8, 9, and 10 represent the back, the profile, and the front view of the
complete instrument. A, the lunar globe, with all the parts which give it
motion, is supported by a brass hemisphere B, and fixed citler within or upon
it ; the hemisphere has its concave part turned inwards, and its convex part
turned outwards, and is strong enough to bear the parts attached to it, and of
sufficient size to admit the globe with its brass meridian C. It has likewise a
square hole in its back D large enough for the necessary libration, with other
void places made to take off the needless weight of metal. E. E, E, E, aro
four ribs of the hemisphere, connecting the rim F, which has the brass meri-
dian let into it. On the ribs of the hemisphere are four stops, with adjusting
screws G, G, in contact with four spherical plates of brass fixed to the globe,
that its weight may not hang entirely upon the cylindrical bar fixed to that
globe. On account of the brass meridian C, the lunar globe is in this case more
distant from the hemisphere than it was in the former instance from the cen-
tral spherical segment, which in its measure produces the same effects upon the
motion of the lunar globe. That space is to be supplied by a thick spherical
segment I, Figures 8 and 11, whose concave part is to be turned towards that
which is fixed to the globe, and whose convex part is to be in contact with the
square II, which is there to be made concave to receive it; and part of the
spherical parallelogram K is also to come in contact with I. It is to be cylin
drical where it enters the circular hole made in the square, to which it is to bo
firmly secured with the cap of square brass L by screws; the slit M is to be
opened sufficiently wide to admit the cylinder Y with such a slide as the work-
man may think most proper, and it must be of sufficient length to permit that
cylinder or bar to move upwards and downwards as much as the degree of the
libration requires in the lunar globe; at the least five degrees of motion must
be allowed to result from the inclination of the polar axis. The part in which
the slit is opened. being within the square II, must be turned convex, and it
must coincide with the centre of the globe when all the parts are put together.
that the works may move with regularity. In other respects it is not necessary
that the exact form of this thick spherical segment be preserved by the
workman; but this has been adopted, and answers the end for which it was
designed.
'
Any form may be used in this and other parts of the instrument which will
effect the purposes intended, namely, that of permitting or assisting the peri-
phery of the lunar globe to move in the required directions, whilst the centre of
that globe keeps its place in respect to the brass hemisphere, and this will be
effected by the methods here recommended.

page_text: The square part H should have upon its back and upper edge a strong qua-
drant of brass, as N, to support the furniture which moves and guides the polar
libration. On each side of H, and fixed to it, are arches of brass to keep
the motion steady; of one is formed a rack O, the other is used to receive
the pressure of the stop P. The pinion, &c., to the rack and stop no intel-
ligent workman need to have described, as it is believed the Drawing will be
understood. Any other that will do the same office may be used. They are.
either to move the square H horizontally backwards and forwards in the spherical
parallelogram by the rack, or the stop is to detain it when that is required.
The part K is named the spherical parallelogram, because it is partly con-
fomable to each, not that it is strictly of any true mathematical figure, but
the terms are used for the sake of distinction. It is spherically concave beneath
that it may slide upon the convexity of the hemisphere, and convex on the
outside that the other parts may slide upon and move over it; as it is to move
upwards and downwards over the square hole in the hemisphere, picces of
brass should there be screwed on each side of that hole to keep the motion:
steady; or arches of brass should be screwed underneath on the short sides of
the parallelogram in contact with the sides of the hole in the hemisphere,
which will perform the same office; and that method may be adopted which to
the workman may appear the most eligible; the inner edges of the longer sides:
of the parallelogram must be parallel to each other like the parallels of tho
equator if cut into an hollow sphere, and not like the gores of the globe, whose
planes would unite at the centre or intersect each other. These parallels must
likewise be just so far from each other as to admit of the square part H to move
freely backward and forwards within it, by the rack and pinion O, but without
too much liberty. The arches fixed upon the square moving over it, with the
other parts which have been noticed, will help to preserve this steady while it
slides upwards and downwards to express the libration in latitude. The bottoni
of the parallelogram at R has a rack united to it with the pinion S and stop T';
fixed upon the lower rib of the hemisphere, which will be sufficiently evident
in the Drawings. To describe more particularly the brass meridian C, which
with the lunar globe should be received or let into the brass hemisphere, that
the outward edge of the meridian may come out no farther than the edge of
the hemisphere:-For a globe of twelve inches in diameter its breadth may be
nearly that of half an inch, and in most respects similar to the meridians of
common globes; but this should have a groove made in its edge to which four
screws are applied through the rim of the hemisphere, that it may be made
firm to one point or slackened to admit of the necessary motion. yet so as to keep
it from slipping from the hemisphere until it is required to be taken out. When

page_text: the lunar globe is fixed, the hemisphere and outward edge of the meridian
must exactly divide it. Crossing the plane of this meridian at a right angle in the
front of the lunar globe, and fixed by screws to that meridian from behind, the
strong semicircular bar Q, Figures 9 and 10, must be placed with its upper
edge chamfered off. This edge is to represent the celiptic, and it must exactly
divide the plane of the brass meridian and the lunar globe horizontally. In a
right angle to this, another but thinner semicircle is to be screwed with proper
hinges to the brass meridian, with a notch in its centre to let in the former.
This part R is named the terminator, representing the boundary of light
and shadow, and it is to move by the hinges backwards and forwards
over the globe. C. Q, and R, are all to be graduated; the degrees
upon the chamfered edge of Q and the semicircle R begin in the mikilo
of cach, and the graduations on both meet the brass meridian at the
90th degree. The graduations on the brass meridian begin at the edge
of the ecliptic, and ascend and descend on each side till they meet on the top
and bottom at 90 degrees; and these parts of the meridian at the mark of
separation are, in general use, to be placed under those points of the hemi-
sphere which are at Sa, Sa; an imaginary line passing through these marks
represents the axis or pole of the ecliptic. The arches which form the racks O
and R. on each side of the pinions, are also to be graduated, that it may be
known how many degrees they move the parts horizontally or vertically, which
the graduated semicircles in the front will not so perfectly express, in some
situations into which the lunar globe must be moved. It has been mentioned
that the square part H has, fixed to its upper edge and back, a strong quadrant
of brass N, so called because it is in length about the quarter of a circle; it is
to bear the furniture which is to move and guide the polar libration, now to
he considered and described. Upon this quadrant, at 90 degrees from the
centre of the circle II, is to be fixed the axis of the wheel U, which governs
the polar libration of the lunar globe, described in Figures 8, 9, and 10, nearly
in their just proportion; some of these parts, the wheel especially, are made of
double the size of the other Drawings, and fit for a globe of twelve inches in
diameter, that the component parts may be distinctly seen. The wheel U lins
an indented edge, moved by the pinion W; upon it are two moveable circles
u, w. On that marked u is engraved the signs, &c., of the zodine; and it has
an index which, when that circle is properly adjusted, will point to the sign
which the moon is in, agreeable to the state of polar libration, the degrees of
which are more or less according to the apparent obliquity. Upon the circle
marked wo are engraved also divisions representing the periodical revolution of
the moon, to shew when the moon's revolution, with respect to the ecliptic, as

page_text: seen from the earth's centre, is accomplished. On the same circle are likewise
engraved the divisions of the moon's synodical revolution, by a continuation of
the divisions, marking the days and hours, &c., in a spiral direction, under the
former, to fill up the interval which is wanting betwixt the accomplishment of
the periodical and synodical revolutions. One index, as a, fixed upon the qua-
drant N, points to both, by which means such changes upon the face of the moon
may be noticed as then take place, from the libration in latitude and longitude;
&c., during that interval. At the distance of two degrees and an half from the
centre of this wheel, a steel pin, as y, is to be firmly secured by screws, capable
of an adjustment, should it be required, by means of a sliding plate of brass =;
this steel pin, being placed out of the centre of the wheel, is the cause of all
the libration, which results from the obliquity of the axis of the lunar globe.
There is this provision made for experiments; for though it be allowed
that the obliquity of the moon's polar axis is two degrees and an half,
yet men of science lo not seem absolutely certain that it is not a little
more or a little less. In this, and in all other not absolutely (leter-
mined circumstances, the instrument should not be so fixed but that
it can be otherwise adjusted, when it is requisite. Upon this steel pin y
should be placed a strong bar X, named the polar guide, into the smaller
end of which the steel pin must enter.; at the other end of it should be an
hollow but strong cylinder, of a calibre just sufficient to receive the end of tho
solid cylinder or bar Y, which that must enter. The holes in the bar or guide
X, made for the pin and the cylinder must have their middle points exactly 90
degrees distant from each other. This circumstance must be strictly attended
to. If it should be found difficult to make the hole in the strong quadrant N
in the right place, that hole may be made in a slide of brass moving upon the
quadrant, which may be secured by a capstan-headed screw v, when its truc
place is known. The trial of this movement in the libration of the polar axis
of the globe may be made by turning the pinion W; if the north pole of that
globe moves round the centre of the wheel which that pinion turns, at the distance
of two degrees and a half regularly, then it may be presumed that it is placed
right and of a just proportion, especially if the opposite pole moves with the
same degree of regularity. Upon the head of the pinion W a dart should be
engraved with its point directed in the same way as in the Drawing, to shew
which way it must be turned, a circumstance of no small importance, in order
to give the globe its proper motion. Concerning this instrument in its less
complicated state, it is mentioned that the solid cylinder or bar is of one piece,
and cast with that segment of a sphere which is screwed to the globe. To this
more compleat instrument it is the same by which all the motion of the lunar

page_text: globe is communicated; but in respect to the length of the cylinder, and the
means by which it is properly screwed to its place, it is a little different. In
the Drawing, Fig. 12, the parts will be seen. Z is the spherical segment; p is
the point which enters the globe diametrically opposite to the point where the
prime meridian of the globe intersects the equator; t, t, t, t, are holes for the
screws which fasten it to the lunar globe; Y is the cylinder or bar; u, the collar
pressing upon the slide which moves upwards and downwards in the slit M,
Figs. 8 and 9. The cylindrical bar Y should. be of such a length, that when
it enters the hollow cylinder of X it should come nearly, but not flush, to the
outside of that hollow cylinder. In the end of the bar Y-an hole should be
made, where a strong mill-headed screw should be applied, the shoulder of which
must press against the edges of the hollow cylinder X, which will drive the
collar & upon the part underneath, straining the works together, but not so
tight as to obstruct the motion of the parts improperly; and then an hole must
be drilled through the hollow cylinder X, and the solid cylinder or bar Y, and
a steel pin exactly fitting the hole drilled, must be pressed into it, which is to
remain, firmly securing them together. As the truth of the motion of the
instrument greatly depends upon the proper union of X and Y, the
following direction in this circumstance must be carefully attended to:-
Upon the most vertical part of the rim of the hemisphere S, a, it has
been premised that there should be a mark, and opposite upon its lower
edge another; a line supposed to run through these marks is the pole or
axis of the ecliptic. Upon the lunar globe, Figure 10, is a line drawn nearly
horisontally round the globe, which is its equator. In a right angle to this is
another, which is named the prime meridian; this is placed upon the lunar
globe, in the middle point ou its equator, when that globe. is in a mean state of
the libration in longitude. This line appears central in the moon itself, and its
plane fronts the centre of the earth when the moon is seen in the line of apsides.
The workman should understand these lines before he drills the hole now under
consideration, then he may proceed, attending to the following directions:-The
pinions which move the librations should be turned until the globe is in a
perfectly mean state of libration, which may be known before the graduations
are made upon those arches of brass which are upon the back of the instrument,
thus: the centre of the wheel U should be moved exactly over those marks
upon the hemisphere, representing the pole of the ecliptic of the lunar globe, and
the point where the prime meridian intersects the equator will be directly level
with the brass ecliptic at 0° degrees. The lunar globe then represents the moon
in the line of the nodes, and her poles in the plane of her then visible
hemisphere, and those lines the equator and meridian will be each degrees

page_text: and an half distant from tho pole and plane of the ecliptic. When that part of
the machine is moved which depends upon the pinion W being turned, those
points upon the prime meridian at 90 degrees of distance from the equator,
which are the points of the axis or poles of the lunar globe, if they circulate
round the pole of the brass ecliptic at the distance of two degrees and an half, it is
so far good. If the equator of the globe riscs and falls in the samo space on each
side of the upper edge of the brass ecliptic, the line of the prime meridian
remaining always situated at 0° degrees upon the brass ecliptic, which it should
lo, though the equator rises and falls, except when the pinion which moves the
libration in longitude of the lunar globe be turned; when all these effects,
I say, are produced upon the lunar globe by the instrument, the whole of that
work is properly executed, and the pin should be made very secure in the
cylinder, as in the former instance. If the graduations which must be made
upon the arches of brass have not been previously made, perhaps they may
be now executed with more truth, directed by the graduations upon the
semicircles seen in the front, if the equator and prime meridian are brought
to every separate division, and then the spaces marked on the arches behind.
N.B. The equator and prime meridian are both faintly marked on the
lunar globe, as also the plane of the moon's visible hemisphere, corresponding
to that time when the moon is in a mean state of her libration; and where this
line of the visible hemisphere intersects the prime meridian, which is at
90 degrees from the equator, the intersections represent the poles or points of
the moon's polar axis. As it is of great importance that the line of the equator
should be properly drawn, it may be needful to say, that it should be
placed on the spot named Censorinus, and should run within three degrees
north latitude of Grimaldus, which information respecting its place is ascribed
to the abilities of Cassini and of Tobias Mayer, vid. De la Lande's Astronomy.
In the centres of the spots which are most known, and to which names are
given by selenographists, little crosses may be engraved; and when measure-
ments are made such will be useful, and may prevent the globe from
being injured by the application of compasses. If the screws which fix the
brass meridian in the hemisphere be a little loosened, the semicircles, especially
that named the terminator, may be brought to any part, and the whole surface
of the lunar globe may be formed into triangles, or any spot pointed out which
is without a name, by its distance being noticed from three separate and
well-known spots in its vicinity. Those parts of the instrument are now
described which give a libratory motion to the lunar globe, and which are
intended to solve some problems not required to be particularly noticed in this
Specification, as such do not respect the formation of the apparatus.

page_text: We now proceed in other parts of the machine, which though they move not the
Innar globe, yet exhibit sonic circumstances that cause an apparent libration in
tho moon itself, occasioned by the motion of the earth on its axis, and its situn-
tion in respect to the ecliptic. A strong arch of brass, Figs. 9 and 10, No. 1 (in
proportion to the. Drawings), is to be occasionally screwed to the bottom of the
hemisphere rising in the front of the lunar globe with a shelf supporting a
small terrestial globe, with its wheel, and the pinion by which it is turned,
working in the indented edge of that wheel; on this wheel the pole of its little
globe is fixed in the place and in that degree of obliquity which the axis of
the earth has to the plane of the ecliptic; the signs of the zodiac, &c., are to be
engraved on the wheel; an index is to be placed on that part of the shelf, Fig.
9, No. 2, the most distant from the lunar globe. This index will point to that
sign, &c., engraved on the wheel which the earth would be seen to bo
in from the moon; the small terrestial globe is to be placed on the oblique
wire just mentioned, capable of being turned agreeably.to the earth's rotation.
and at such an height upon the wire that the centre of the little globe shall ba
equal with that of the upper edge of the brass celiptic and the centre of the lunar
globe. Upon the small globe an hour circle must be fixed, and on the firm axis
or wire, round which it has its rotation a moveable index is to be placed, to
shew the time when any place fixed upon on that globe comes in view of the
Junar globe, representing the moon's rising. A small wire is to be fixed as the
pole of the horizon of that place where the selenographic instrument is to
be used; if in London, at that point where it is situated. Upon the upper
edge of the strong arch a plate of brass, as represented in the Drawing, is to bo
placed, Figures 9 and 10, No. 3 and 4, flat on the top, with an hollow at one
end large enough for the reception of the small globe; as this flat brass
plate is to be smaller at the end next the lunar globe, that may be chamfered
off underneath, that it may be close upon the chamfered edge of the brass
ecliptic. A line must be drawn upon the centre of this plate, No. 4, Figure 9,
pointing to the centres of both globes. As the earth when seen from the
moon subtends an angle of about two degrees of the moon's surface, that size
would be two small for observation and the purposes for which it is intended.
One of several degrees of the moon's periphery is therefore to be used with
two lines, one on each side of that in the centre of the brass plate, both
tangents to the small globe, and continued on converging until they meet the
Iar globe at the end of the plate at two degrees. The use of this part of the
instrument is to shew the diurnal libration of the moon, which is equal to the
horizontal parallax, by turning the small globe by the hour circle, and also
the menstrual libration of the moon' by turning the pinion which moves the

page_text: wheel on which the globe is fixed in the way as directed by a dart on the
pinion, Figure 13, with some other changes which take place from the different
inclinations of the terrestial and lunar axis, and the planes of their equators.
It is not thought necessary to be more particular concerning this part of the
machine, as all are so delineated as to be, with the remarks already made,
sufficient. But it may be proper to observe that mill-headed screws are the
most approved to fasten this supporting arch, which may be readily taken out,
and the whole removed, when it is necessary. The inclination of the horns of
the moon changing with the horizon of places can be represented by an hinge
joint in tho stand of the globe, with a rack and pinion for those who may
require it; but its necessity is prevented in the use of the small terrestial
globe, which will describe it.
In witness whereof, I, the said John Russell, have hereunto set my hand
and scal, this Seventh day of December, in the thirty-seventh year
of the reign of our Sovereign Lord George the Third, by the grace of
God of Great Britain, France, and Ireland King, Defender of the
Faith, &c., and in the year of our Lord One thousand seven hundred
and ninety-six.