IMPROVEMENTS IN DENTAL CHAIRS
Year: 1877

page_text: LETTERS PATENT to Basil Manly Wilkerson, of Baltimore City, State of Mary-
land, one of the United States of America, Dentist, for the Invention of
"IMPROVEMENTS IN DENTAL CHAIRS."
PROVISIONAL SPECIFICATION left by the said Basil Mauly Wilkerson at
the Office of the Commissioners of Patents on the 8th December 1877.
BASIL MANLY WILKERSON, of Baltimore City, State of Maryland, one of the
United States of America, Dentist. "IMPROVEMENTS IN DENTAL. CHAIRS."
The first part of my Invention relates to the construction of the pedestal or base
upon which the chair body is mounted. The said pedestal consists of a hollow
cylinder, supported upon four legs projecting radially therefrom, three of which are
equidistant from each other, the fourth bisecting the angle between two of the other
legs, and being provided at its foot with a set screw, which may be raised or
lowered to suit irregularities in the floor. A cylindrical liquid reservoir rests and
turns freely within the pedestal, and contains a cylindrical plunger fitted water-
tight within the reservoir by means of a leather cup and washer. A partition is
located in the lower part of the reservoir and is furnished with valves, through
which a liquid within the reservoir will flow when the plunger is raised, the liquid
sustaining the plunger at any point to which it is raised. The elevation of the
plunger is effected by means of a foot lever which carries at its end a pawl, a
corresponding ratchet being formed upon the plunger. The rotation of the reservoir
is prevented when desired by means of a set screw, also operated by a foot lover,
and the plunger may be secured by similar means.
The second part of my Invention relates to the attachment of the frame of the
chair body to the plunger. A bar is secured to the upper end of the plunger, upon
the ends of which bar the chair frame is pivoted, and is capable of being tilted
back. The frame may be secured at any angle by suitable means. The chair seat
is pivoted centrally within the frame, and adjusts itself automatically to the
position of the occupant of the chair.

page_text: The third part of my Invention relates to the construction of the chair framo
and its attachments. The front part of the frame is extended to form foot rests,
one of which may be adjusted to suit the convenience of the patient. The back of
the chair slides within the rear part of the frame, and is adapted to be secured
therein by suitable means. A child's seat is also secured to the chair frame, and
when not in use as a child's seat is folded down, and constitutes a part of the chair
back for use by the adult patient. A spring is arranged to support the child's
seat when folded, so as to bear with a yielding pressure upon the back of the adult
patient.
The fourth part of my Invention relates to the construction of the head rest
The latter consists of a pair of pads connected by means of a slack strap, all of
course properly upholstered. A ball-and-socket joint connects the head rest to one
of a series of links, the connections between which consist of double combs. In
each link a bar is arranged to slide, whereby the tightening of the end link secures
all the joints. The link referred to is secured to the chair back, and is arranged to
be tightened by means of a cam. An arm rest for the operator is attached to the
head rest, being pivoted to an arm which is adapted to be swung to either side of
the head rest, and may be secured in any desired position by means of a button,
which is inserted in the appropriate one of a series of holes in the rear plate of the
head rest.
The fifth part of my Invention relates to the construction of the attachment
bearing the instrument trays, water reservoir, spittoon, &c. To a part of the chair
not affected by the tipping of the body, preferably to the bar which bears the chair
frame, is fimily secured by means of an arm a vertical standard, which latter is
arranged to swivel at its attachment to the arm, which is similarly connected with
the bar referred to. To the vertical standard are secured in the same manner
arms bearing the spittoon and instrument trays. The standard is surmounted by a
water reservoir, and is made tubular, constituting a duct for the water to the
spittoon

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said Basil Manly Wilkerson in the Great Seal Patent Office on the
5th July 1878.
BASIL MANLY WILKERSON, of Baltimore City, State of Maryland, one of the
United States of America, Dentist. "IMPROVEMENTS IN DENTAL CHAIRS."
Figure 1 represents a side elevation of my improved chair; Figure 2, a plan
view of the same, having the chair seat removed.
Figures 3 to 27 inclusive represent enlarged views of various parts of the
chair.
Similar letters of reference indicate similar parts in all the Figures.
This Invention relates, as stated, to dental chairs, and it consists in certain details
of the same and combination of parts not here necessary to enumerate, as they are
herein-after made the subjects of claims based upon the following description
A represents a hollow cylindrical pedestal, supported preferably upon three
legs A projecting radially therefrom, and a fourth leg A", the foot of which
raised slightly above the plane of the remaining three feet, and is provided with a
screw a on the under side, which is raised or lowered, as the case may be, in order
to adjust the chair to suit irregularities in the floor. These legs are arranged as
indicated in the Drawings, the leg A" projecting toward the front, and being
designed to prevent the tilting forward of the chair as the patient steps upon the
foot board, while the adjacent legs A' on either side project forward of the median
line of the chair, in order to be out of the way of the feet of the operator The
back leg A' extends centrally to the rear. By this arrangement of the legs a large
space is left on each side of the central back leg free to be used without obstruction
or hinderance by the operator, who heretofore during his work has frequently been
impeded and annoyed by the legs, which in ordinary chairs extend from the corners
of the chair.
B represents a cylindrical liquid reservoir constructed to rest and turn within
the pedestal A. A cam b, Figures 1 and 3, is inserted through the shell of the
pedestal against the exterior of the cylindrical reservoir, and is provided with a
lever c extending nearly to the floor, and within convenient reach of the foot of the
operator. Upon tuining the lever c the cam b is brought to bear upon the cylinder,
and prevents its revolution. C is a cylinder formed within as a part of the
reservoir B, and C represents a plunger adapted to slide therein. A leather cup
and washer (see Figure 3) secured to the lower end of the plunger serves to fit it
watertight within the cylinder A cap 4 secured on to the lower end of tho
cylinder C serves in connection therewith to form a chamber c", with which the
lower end of the cylinder communicates Two valves d, d, Figures 3 and 4, are
located in the cap 4, and open into the chamber c¹. These valves control the only
means of access from the cylinder below the plunger to the reservoir B, and sub-
serve an end herein-after more particularly described
The plunger C' constitutes the support upon which the chair body rests, and
carries at its upper extremity a bar f, upon which the chair body is pivoted. The
plunger is adapted to be elevated by means of a foot lever D hinged to the upper
part of B, and having upon its inner extremity a spring pawl, which engages
with a series of recessed teeth upon the plunger The lever is caused after each
stroke to assume its normal position through the agency of a spring connecting the
lower end of the pawl with the lower part of the reservoir. At the same time a
projection & on the inner face of the lower part of the pawl strikes the upper edge
or shoulder of a steel key 5 attached to the cylinder, and is thereby thrown out of
engagement. Thus the lifting mechanisın, when in the normal position to which it
is returned by the action of the spring, is entirely disengaged and disconnected
from the plunger.
The reservoir above described contains glycerine, oil, or other suitable liquid
which follows the plunger during its ascent and prevents the descent of the same

page_text: owing to the closure of the valves d, d'. The liquid that thus follows the plunger
is supplied from the reservoir through the larger valve d, which automatically opens
to permit passage of the liquid into the plunger cylinder.
To lower the chair body it is obviously only necessary to open the valve d¹ and
allow the liquid to flow back to the reservoir, which, owing to the comparatively
small size of tho valve d', leaves the plunger cylinder more slowly than it entered
through the large valve d. This arrangement permits of the rapid elevation of the
chair, and at the same time insures that it shall descend gradually and without
shock. The pawl being out of gear, as above described, the plunger freely follows
the liquid.
In order to open the valve any convenient mechanism may be used. The means
I have adopted consists of a rod 2 connecting the valve with a lug e on the set
screw e¹ (see Figures 4 and 7). This set screw carries also a gripping device ell,
and has attached to its outer end a foot lever e111 (sec Figures 1, 2, 4). By
turning the lever in one direction the valve is opened by means of the rod 2 and
lug e. By turning it in the other the plunger is firmly clamped and held in
position A chain connects the lever e¹ with the outer or swinging end of the
foot lever D, and is of such a length that the bringing of the foot lever into position
for elevating the plunger necessarily releases the griping device.
When not in use the lever D is swung around out of the way of the operator.
For this purpose the lever, as shown in Figures 3 and 7, is made in sections (in
this instance two sections) jointed together at D¹, so that the outer section can be
turned on its hinge toward the chair, or rearwardly toward the chair and out of the
way, and when in this position forms a foot rest for the operator. A projection D³
on the outer section brings up against a stop on the inner section, when the lever is
straightened out in position for use.
The chair body is nearly balanced upon the bar f, and hence no especial mechanism
is necessary in order to tilt the chair, but a slight exertion on the part of the
operator sufficing to effect this end.
The mechanism for retaining the chair body firmly in position at any angle is
illustrated in Figures 1, 2, and 19, and consists of a curved perforated bar g secured
to some part of the chair body, and a spring bell crank gl pivoted to the bar f
The short arm of the crank is hinged to a tapering bolt g₁ which slides through
a part of the bar f, and is projected into the perforation in the bar g which falls
opposite.
The object in forming the bolt g¹ tapering is to make a perfectly rigid fastening
and prevent motion or rattling.
The seat or cushion h, Figures 1 and 17, is pivoted within the seat frame and
tilts freely within certain limits, its angle thereby accommodating itself to the
position of the patient. The scat is secured after adjustment by means of the set
screw h¹, Figure 17, or by any other convenient means. The front plate h¹¹ of the
chair frame is inclined inwardly, in order to afford space for the dress of female
patients while seated in the chair.
E, E, Figures 1, 2, 15, 16, represent respectively the upper and lower fixed foot
boards, the intervening space being occupied by the tilting foot board F hinged to
the chair frame. The mechanism for elevating this foot board is illustrated in
Figures 15 and 16, and consists of the following elements:-The inner sides of the
chair frame are furnished with slotted bars i, the upper sides of which are fitted
with ratchet teeth, with which pawls i formed on or rigidly fixed to the ends of a
crank rod i are adapted to engage. A foot piece is attached to the crank rod
outside the chair frame, the rod also carrying one or more arms & loosely attached
to the under side of the tilting foot board.
The pawls are normally in gear with the ratchet, but the motion of the foot
piece in the direction indicated by the arrow, releases them and admits of the
elevation of the foot board. In this operation the footpiece, in practice, is usually
first slightly tilted, so as to take the pawls out of engagement with the ratchets,
and simultaneously with this movement the foot piece, by a direct thrust of the

page_text: oot, is pushed forward, travelling in the line of the slots, and of course carrying
orward with it both the crank pawl rod ill and the connecting rods by which the
oot board is raised. Upon releasing the foot piece, the pawis engage with the
teeth and retain the foot board at the point to which it has been raised. In order
o lower the foot board the pawls are released, as above described, and the
foot board descends by its own weight, the pawls being held out of gear during the
lescent.
The extreme ends of the frame are connected by a foot bar F', which may be
considerably shorter than the width of the chair body, in order to enable the chair
to be revolved in a limited space. The moveable back G of the chair is attached
to the frame by means of tongues and grooves (see Figures 1, 2, 13, 14, 18), and is
held at any desired elevation by means of bolts 1, simultaneously projected outward
by the revolution of a double cain l', operated by incans of a handle upon the
movable back. This handle also serves as a means for elevating and lowering
the movable back, and enables the operator to accomplish this by the use of one
hand.
A supplemental or child's seat G' (see Figures 1, 2, 17, and 18) is pivoted to the
upper ends of the fixed chair frame, and when extended for use is supported by
bars pivoted to its sides. The said bars have pins at their lower ends, which
slide in grooves in the chair frame, as shown, the grooves terminating in slots for
sustaining the seat when extended. The supporting bars are prolonged above the
child's seat, and constitute its arms. When the child's seat is folded it forms a
cushion for the back of the adult patient. The chair frame being provided with a
spring, Figure 17, into contact with which the child's seat comes when folded;
the latter is made to bear with a yielding pressure against the back of the patient
The head rest is secured to the upper end of the extensible back, and is illustrated
in Figures 1, 2, 20, 21, 22, 23, 24, 26, and 27.
A head picce H, formed of a curved dished plate m, is provided with a short
shank extending from its lower edge, and is cushioned and upholstered, as herein-
after described. The shank terminates in a ball m', which is confined in a socket
of like shape in the first of a series of links. The latter consists of an elongated
open link m", Figures 20, 21, 22, in which slides a central block 111, and the
The
socket in which the spherical knob rests is divided equally between the two
other end of this link is provided with a tapering hole situated similarly with
reference to the two blocks, the hole being occupied by the upper cone of the pivot
n, n'. The lower cone n' fits in one end of a second link similar in construction to
the one just described. The other end of this link receives the conical head of a
bar n", and its under side is in contact with a collar on a second barn, through
which collar the bar n¹¹ passes.
The bar n¹¹ has at its lower extremity a V shaped recess, into which a pointed
set screw n¹ is arranged to enter in such a manner as to cause thereby a slight
longitudinal movement when screwed home.
The entire head rest mechanism may be elevated and depressed as desired, and is
secured in position by means of the set screw, as shown in Figure 20.
It is obvious from the conformation of the parts that a single motion of the set
sciew secures all the joints, a highly important feature, as it saves the time necessary
to secure the various thumbscrews heretofore used with lead rests.
The several links that form the variable head rest support are connected together
and to the chair frame by vertical pivots. The devices which connect them are
cones, each of which fits in a tapering socket capable of expansion and contraction.
The locking movement of the set screw n causes a downward movement of
bar n"; this pulls down the cone on the upper end of the bar into its socket, and so,
by expanding the socket, pushes outwardly the moveable block that forms one-half
of the socket; but this block at its opposite end forms a part of the tapering socket
5 of cone n', and its movement consequently causes a contraction of said socket, and
so forces downward the cone n¹, which consequently draws down the upper cone n
into its socket, and the expansion of the socket of cone n has the effect, through the

page_text: medium of sliding block m¹11, of contracting the spherical socket of the ball m';
thus are all these joints stiffened and locked by a slight movement of a single cam.
A reverse movement of the set screw will unlock the joints, and leave the several
links free to move.
A swinging arm rest, Figures 26, 27, is pivoted to the back of the curved plae
m, its pad or arm rest proper swiveling freely at the end of the arm in order to ac-
commodate itself to the motions of the arm of the operator. The swinging arm 12 is
provided with a spring stud 7, which enters one of a number of holes or notches in
the plate 11, and so secures the arm rest at any angle.
The cushion of the head piece consists of two pads o, o, connected by means of a
slack strap o'.
At the back of the chair, Figure 1, an arrangement is shewn for working a foot
power drill. The operator pressing with his foot upon the treadle 20 causes the
crank 21 to revolve, and with it the pulley and fly wheel 22, which in its turn
imparts motion through the vertical spindle 23 to the flexible tube and drill 24 on
the upper end of the same, the treadle being arranged to swivel at x.
The water reservoir, spittoon instrument, trays, &c., are connected to the chair as
follows:-A rod p is secured to the barf by means of a pin p¹, and swings freely,
as shown in dotted lines in Figure 2. A tubular rod p³ is secured to the end of the
rod p, in which tube the rod pill supporting the reservoir is adapted to slide. The
reservoir K is susceptible of a rotary or circumferential motion on the rod p as an
axis in common with its supporting bar, and independent of the swinging bar p
and its vertical tubular extension p¹¹
The reservoir is made vertically adjustable by means of a collar r on the rod pl",
the collar being provided with a thumbscrew 1. The part of the rod p between
the reservoir and the pipe is tubular, and constitutes a duct for the passage
of the water to the annular space around the rim of the bowl g. A valve 8¹
controls the exit from the reservoir, being opened by means of a wire leading to
the top of the latter.
A pipe s leading from the reservoir is used in drawing drinking water, and a
tray for a tumbler is attached to the pipe. The pipe 8 is provided with a
valve operated by means of a sleeve t on the lower end of the pipe connected to the
valve through the medium of a wire.
To a revolving sleeve on the rod p¹¹ is secured an arm t' supporting the standard
t for the instrument trays. A vertically adjustable arm t, extending from the
polygonal notched standard t carries a differentially collared stud u, upon which
the trays west, and are fitted to turn in any direction
Any suitable device may be employed to secure the arm t¹ to the standard. A
convenient means is shown in Figure 11. Upon the standard t are a number of
notches y, y, into which a spring bolt x, working within the arm t¹¹l, is arranged to
enter, and thus secure the same at any required height This bolt is so constructed
that when required it can be drawn out of gear and locked by simply giving it a
slight turn.
The spittoon bowl g is furnished at its lower end or outlet C with a gold trap.
This trap consists principally of a receiver a and a perforated funnel or mouth-
piece d, the latter being so constructed as to fit and so partially close the outlet C;
this mouth-piece d also serves to suspend the body of the trap in its required
position, whence it can readily be lifted and raised out by the ring or handle, as
shewn.
Handles M on either side of the chair are designed for use by the patient during
painful or violent operations. A foot stool N is pivoted to one of the legs A¹ for
the use of the operator
My design has been to furnish a dental chair susceptible of every adjustment
which can possibly be needed, and adjustable also without the necessity of the chair
being vacated, and even while the dentist continues his operations at the mouth of
the patient, resulting in saving much time.
Furthermore, the means I have devised admit of the elevation and lowering of

page_text: the chair and foot board, and the securing of the chair body by means of the foot
of the operator. Heretofore these operations could only be performed by hand,
involving delay and the exercise of considerable muscular effort on the part of the
arm of the operator, causing fatigue and its natural consequences, nervousness, and
unsteadiness of hand.
It will have been observed that the portions of my chair, such as the head rest,
spittoon, instrument trays, &c, are susceptible of adjustments impossible with the
various forms of dental chairs heretofore used, and that these adjustments, while more
varied and complete in my chair, are at the same time accomplished by the means
I have described with greatly increased facility and dispatch.
The plunger I have described may be made hollow, and constitute the fluid
reservoir, and the elevating mechanism may be omitted, and the device raised by
hand.
Having now described and ascertained the nature of my said Invention, and in
what manner the same is or may be performed, what I claim as secured to me by
the herein-before in part recited Letters Patent is,-
1. In a dental chair the combination of these elements, a vertically movable seat
support, a lifting mechanism therefor, which normally is out of engagement with
the support, and mechanism distinct from the lifting mechanism to hold the said
support at any point to which it is raised by the lifting mechanism, and to permit
it, when desired, to pass gradually and without shock from that elevated point to a
lower one, the combination being and acting substantially as set forth.
2. The combination, substantially as set forth, of a vertically movable seat
support, mechanism for elevating said support, and a fluid column for upholding
said support at any elevation to which it may be raised.
3. A dental chair supported upon a plunger adapted to be elevated within a
sheath by suitable means, the said sheath communicating with a fluid supply by
means of a duct or opening provided with an inlet valve, whereby the fluid is
allowed to follow the plunger as the latter is elevated, and to sustain it at any point,
substantially as described.
4. A dental chair mounted upon a plunger adapted to be elevated within a sheath
by means of a ratchet and pawl, the said sheath communicating with a fluid reser-
voir by means of a suitable valve, whereby the fluid is allowed to follow beneath
the plunger as the latter is elevated, and to sustain it at any point, substantially as
described
5 A plunger placed within a sheath, and supporting a dental chair, said plunger
being adapted to be elevated by means of a ratchet and pawl, and sustained at any
point by means of a fluid medium entering said sheath as the plunger rises, as set
forth.
6 The combination in a dental chair of a seat supporting plunger, mechanism for
lifting the same, a fluid column for upholding said plunger at any point, and locking
devices for griping said plunger when so upheld, substantially as herein shewn and
set forth.
7. A foot lever for operating the elevating devices proper, constructed in sections,
hinged or pivoted together, substantially as set forth.
8 In a dental chair elevating mechanism and a locking device connected together,
whereby the latter is released in the act of bringing the elevated mechanism into
position for use, substantially as described.
9. In combination with a swinging end of the jointed foot lever a flexible or
jointed connection between the same, and the mechanism for clamping the plunger,
whereby the latter is released in the act of straightening out the lever, substantially
as described.
10. In combination with a non-rotating pedestal and a vertically moveable seat
support, an intermediate 1otary cylinder, which receives and carries the seat support,
and has its bearing in said pedestal, and elevating mechanism, which is carried by
said cylinder, and is adapted to raise the seat support independently of both the
rotary cylinder and non-rotating pedestal, substantially as herein set forth.

page_text: 11. A chair body mounted upon a plunger, sustained at any desired height by
means of a fluid medium, the said chair body being adapted to tilt, and being
provided with means for securing it at any desired angle, substantially as
described.
12. A seat pivoted centrally or nearly so, and capable of slight oscillations upon
said pivot, in order that the seat may adapt itself to the position assumed by the
occupant of the chair, substantially as described.
13. In a dental chair a seat pivoted centrally, or nearly so, so as to be capable of
slight oscillations for the purpose described, in combination with a locking device for
securing the seat at varying angles as required, substantially as set forth.
14. The front plate of the chair below the seat frame inclined inwardly in com-
bination with the upper fixed foot board and the lower foot board, substantially as
shewn and described, whereby the upper board is carried so far to the rear as not to
interfere with the free use of the lower foot board.
15. In combination with the dental chair, and forming a part thereof, a movable
foot board adapted to be elevated, lowered, and secured by the foot of the operator,
substantially as described.
16 In combination with the fixed foot boards of a dental chair placed in different
planes, an intermediate adjustable foot board, adapted to be operated by the foot of
the operator, substantially as set forth.
17. In a dental chair a movable back sliding in a right line, and provided with
a clamping device, which is attached to the said back, and constitutes a handle for
elevating the same, substantially as described.
.18. In a dental chair a movable back connected to the fixed frame by tongues
and grooves, and provided with a locking device, which constitutes a handle for
elevating it, substantially as described.
19 In a dental chair a supplemental or child's seat, forming an integral part of the
chair, arranged to occupy when in use a position above the main seat, and adapted
when not in use to be folded or turned out of the way of the main seat, substantially
as set forth.
20. In combination with a dental chair a or child's seat adapted to
form an elastic back for the chair when the latter is occupied by an adult patient,
substantially as described.
21. In combination with a dental chair a supplemental or child's seat pivoted to
the back or body of the chair, and adapted, when folded down, to form a supporting
device for the back of the adult patient, substantially as set forth.
22. The supplemental or child's scat, having its supports extended above the seat
when opened, in order to form arms therefor, substantially as set forth.
23. In a dental chair a head rest pivoted twice about parallel axes, and once
about a ball-and-socket joint, as set forth
24. A head rest support formed of links or sections united by conical or tapering
pivots seated in correspondingly shaped sockets capable of expanding and con-
tracting, and bounded in part by movable blocks, which transmit the movement
from one cone and socket to the next throughout the series, whereby the several
joints will be tightened by the operation of a single device, substantially as set
torth.
25. In combination with the head rest of a dental chair an arm support for the
operator, substantially as described.
26. In a dental chair an arm rest adapted to be secured at either side of the bead
rest, substantially as described.
27. In combination with the head rest of a dental chair a swiveling arm rest,
substantially as described.
28. A head rest for a dental chair, consisting of a pair of pads connected by means
of a slack strap, as set forth.
29. In combination with a dental chair a spittoon pivoted twice about vertical
axes, whereby it may be made to occupy any position within the circle described
by the extreme radius of the supporting arms, substantially as described.

page_text: 30. The combination with the spittoon of a dental chair of a water reservoir
connected with and carried by the chair, and adapted to deliver a supply of water
to the spittoon for the purpose of rinsing the same, substantially as set forth.
31. In combination with the spittoon bowl of a dental chair, a water reservoir
adapted to deliver a supply of water through an annular opening near the rim of
the spittoon bowl, substantially as described.
32. A trap suspended within a spittoon by means of wires attached to a
removable ring of greater diameter than the neck of the spittoon, substantially as
described.
33. In combination with a dental chair a footstool for the operator attached
thereto, substantially as described.
34. A support for a dental chair consisting of three legs radiating from a common
centre at equal distances apart, the back leg extending rearward centrally of the
chair, in combination with a fourth radial leg extending directly to the front, and
bisecting the angle formed by two side legs, as set forth.
35. In combination with the water reservoir K a cock consisting of the tube 8",
having at its inner end a valve operated by a sleeve resting over the outer end of
said pipe, and a wire passing within the same and attached to the valve, as
described.
36. The combination of the water reservoir K having a pipe, the opening of which
is controlled by a valve, combined with the bowl g, having the annular opening +!!!
communicating with the supply pipe leading from the reservoir, all substantially as
described and for the purpose set forth
37. The combination, substantially as set forth, with the seat supporting plunger,
its cylinder or sheath, and the elevating mechanism of the fluid reservoir provided
with a large inlet valve, which permits the fluid to follow a rapid ascent of the
plunger, and a smaller outlet valve, which permits the fluid to be displaced by the
descending plunger slowly, so as to insure the gradual and easy descent of the chair
seat.
38. The plunger cylinder arranged within the fluid reservoir, and terminating at
its upper end below the top of said reservoir, so that any fluid that may happen to
be drawn up through the cylinder can pass back therefrom into the reservoir, as
shown and set forth.
39. In combination with a dental chair a dental engine arranged to be carried by
the chair in its rotation, elevation, or rocking adjustment.
40. In combination with a dental chair a foot-power dental engine having a
treadle adapted to be operated at either side of the chair.
41. In combination with a dental chair a dental engine having its shaft attached
at the back of the chair.
In witness whereof, I, the said Basil Manly Wilkerson, have hereunto set my
hand and seal, this Fourteenth day of May, in the year of our Lord One
thousand eight hundred and seventy-eight.
BASIL MANLY WILKERSON
(1.8)