CERTAIN IMPROVEMENTS IN CHRONO- METERS AND OTHER TIMEKEEPERS
Year: 1842

page_text: TO ALL TO WHOM THESE PRESENTS SHALL COME, I, EDWARD
JOHN DENT, of 82, Strand, and 33, Cockspur Street, in the County of Middlesex,
Chronometer Maker, send greeting.
WHEREAS Her present most Excellent Majesty Queen Victoria, by Her
Letters Patent under the Great Seal of Great Britain, bearing date at West-
minster, the Twenty-first day of March, in the fifth year of Her reign, did,
for Himself, His heirs and successors, give and grant unto me, the said
Edward John Dent, Her especial licence, full power, sole privilege and
authority, that I, the said Edward John Dent, my exors, adññors, and assigns,
or such others as I, the said Edward John Dent, my exors, adiñors, or
assigns, should at any time agree with, and no others, from time to time and
at all times during the term of years therein expressed, should and lawfully
might make, use, exercise, and vend, within England, Wales, and the Town
of Berwick-upon-Tweed, my Invention of "CERTAIN IMPROVEMENTS IN CHRONO-
METERS AND OTHER TIMEKEEPERS;" in which said Letters Patent is contained
a proviso, that I, the said Edward John Dent, shall cause a particular
description of the nature of my said Invention, and in what manner the same
is to be performed, to be inrolled in Her said Majesty's High Court of
Chancery within six calendar months next and immediately after the date
of the said in part recited Letters Patent, as in and by the same; reference
being thereunto had, will more fully and at large appear.

page_text: NOW KNOW YE, that in compliance with the said proviso, I, the said
Edward John Dent, hereby declare that the objects of the Invention are,-
Firstly, to obviate by a continous correction the errors arising from the
tension of the balance spring not following the same law of increase and
decrease at different temperatures with the law that governs the corresponding
increase and decrease in the inertia of the balance; hence, the ratio which
should invariably exist between the tension and the inertia is not maintained
throughout; whereas a correspondence between theso two is a condition
absolutely necessary to the correct performance of a chronometer at different
temperatures. By the neglect of this important condition, it has been
observed that, with the exception of two opposite extremes of temperature,
the rates of chronometers, as hitherto generally constructed, have been
between these temperatures accelerated or the rate on each side of a menn
temperature has been retariled.
The Invention which I have now succeeded in bringing to maturity has
occupied my unceasing attention since the year One thousand eight hundred
and twenty-nine, when I received the first premium prize given by Govern-
ment for the hitherto unrivalled performance of my chronometer ("Dent,
No. 114"). From previous and subsequent comparison of the rates of the
chronometers tried and published by order of Government, I came to the con
clusion that there was some decided defect in the principle of their construc-
tion, as the rates of the best chronometers showed a losing rate at the two
extremes of temperature. I published, under the signature of my late firm,
in the Nautical Magazine for April, One thousand eight hundred and thirty-
three, page 222, a notico of this anomaly, calling the attention of the scientific
chronometer maker to the subject, and this, I have no doubt, was the first
public notice of the apparently inherent defect; although, subsequently to the
date of this announcement until now, many attempts have been made by
different artists to correct the losing at extremes of temperature, none appear
to have entirely succeeded, as the real cause of the defect was not traced to
its true source, which is, as I now state it to be, a want of uniformity between
the tension and the inertia. The defect is explicable when it is considered
that the compensation weights of the balance in the ordinary chronometer do
not sufficiently approach the centre of motion on an increase of temperature,
and hence causing the rato to bo a losing one; and, on the other hand, that s
they are brought out too far from the centre of motion by a decrease of tem-
perature, hence occasioning the same error (namely, a losing rate.) in the
opposite extreme. The nature of this defect may be elucidated by the
following experiments:-.

page_text: From laborious experiments which I have prosecuted on a tempered steel
balance spring, in order to determine not only the amount of variation in rate
between thirty-two degrees and one hundred degrees in the thermometer
(Fahrenheit), but also by what law certain increments or decrements of heat
between those points affect thic times of vibration, I havo ascertained the
fact to be that the times of vibration vary nearly equally for equal increments
and decrements of heat. The law producing the error in the balance spring
being thus determined, if we advert to the mathematical law that the times of
vibration vary as the square of the distance from the centre of motion, we
discover the cause of the disproportionate action in the compensation weights;
that is to say, their going out too far from the centre in the one case, and not
sufficiently approaching it in the other. My present Invention is designed to
rectify the above-mentioned defect, by applying to the ordinary compensation,
which may be termed primary compensation, the addition of a secondary
continuous compensation, which will move the compensation weights over ariy
required space, so that the times of vibration will be in accordance with the
varying tension of the balance spring.
In the Drawings annexed are magnified representations of different modifi
cations of my Invention, given as exemplifications of the principles upon which
my improvements are effected.
Figure 1 represents the plan of a compensation balance, in which the two
compensation weights are each carried by a primary and a secondary com
pensation piece, which pieces are shewn straight in order to facilitate the
clear understanding of the principles of my Invention, although in practice
I frequently use a curved figure for the picces, or make the primary and
secondary compensations in one curved piece. a is a simple balance bar,
made of brass or other non-magnetic metal or metallic compound; b, two
primary compensation pieces of brass and steel, or other suitable metals, which
pieces are firmly fixed on the balance bar a, nearly at the extremities, and run
parallel with it towards the centre; c, two secondary compensation pieces
attached to the free ends of the primary pieces b, and proceeding in a direction
from the centre; the brass of these pieces is, in both cases, at the inside of
the angle, and the steel at the outside. d, the compensation weights; e, the
timing weights. The pieces I term the primary compensation, because
their action is to vary the inertia by bringing the compensation weights d
nearer to the centre of motion for an increase of temperature, and the reverse
for a decrease. And it is to be distinctly understood that this may be fairly
considered, as the only adjustment which the ordinary chronometer possesses

page_text: to correct the errors of the balance spring. I have before remarked that the
compensation weights in the usual construction do not go sufficiently in
towards the centre of motion on an increase of temperature, while they come
out too far on a decrease. I will now explain how the correction of this fault
is to be accomplished by my Invention:-The compensation pieces c move
the compensation weights d, on a change of temperature, in a direction nearly
concentric with the centre of motion, and thus produce little or no variation,
as regards the times of vibration.
These pieces I denominato the "continuous secondary compensation pieces,"
and their action is confined to the placing the compensation weights & in a
position calculated to vary the inertia in a geometrical proportion when moved
by the primary compensation pieces. For example, on an increase of tempern-
turo the weight d is moved further from the junction of the primary compen
sation piece 6 with the bar, and as the length of the dotted line f, drawn from
the centre of gravity of the compensation weight d to the junction with the bar
-as the length of this line, I say, is augmented by increase of temperature, the
compensation weight d makes a quicker and nearer approach to the centre of
motion; whereas, on a decrease of temperature the length of the same line fis
shortened and the leverage is decreased, so that the compensation weight dis
not taken out so far or so rapidly from the centre of motion.
Figure 2 shews the plan of a balance in which the primary and secondary
compensation is obtained on each side of the balance from one curved piece.
9, the balance, made of brass or other non-magnetic metal; h, two blocks or studs
raised above the face of the balance to form the supports of the compensation;
k, l, m, two lamine, each curved in such a manner as to combine the joint
effect produced by the primary and secondary compensation pieces shown at 6
and c of Figure 1; the part from k to corresponding to the primary compen-
sation piece, and that from to m corresponding to the secondary continuous
compensation pioce of Figure 1; n, two prolongations from the ends of the
compensation pieces of steel only; p, two compensation weights screwed to the
prolongations n; q, four timing weights. Figuro 3, a perspectivo view of tho
same balance.
Having thus fully explained the principle of my primary and secondary con-
tinuous compensation, I would remark that my Invention embraces every modi-
fication of this principle, by which the compensation shall increase the distanco
from the centre of gravity of the compensation weight to the junction of the
compensating lamina with the bar, on an increase of temperature, and shorten
that distance on a decrease. In order to adjust this balance as regards the

page_text: econdary compensation, if the chronometer gains at the extremes of tempera-
ure compared with the mean, the secondary compensation piece must be
hortened, and the time restored by adding to the nuts at the ends of the bar;
f the chronometer loses at the extremes of temperature, the reverse operations
must be resorted to; the ordinary adjustments for temperature are made by
sliding the weights p along the prolongations n.
in
In Figures 1, 2, and 3 the compensation weights are represented as moving
a plane at right angles to the axes of motion. But I produce a similar
effect by causing the compensation weights to move in a plane, passing through
the axis of motion, the mode of accomplishing which I now proceed to explain.
Figure 4 represents a balance formed according to this mode. r, a compen-
sation diameter bar fixed on the balance axis; it is composed of brass and steel,
the brass being underneath; this is the only compensating power possessed by
the ordinary chronometer, whereas, in my Invention, it performs the action of
the primary compensation merely. s, two blocks attached on the ends of the bar
to receive the secondary compensation pieces; t, two secondary compensation
pieces, each constituted of two pair of lamina bent into the form of staples
and rivetted together, with the bows lying in opposite directions, one end of
the lamina being fixed upon the block s, the brass being in the insides of the
staples, and the steel on the outsides. u, two pillars fixed on the end of the
upper piece of these lamina to carry the weights; these pillars are furnished
with screws, on which the weights turn for adjusting their heights; v, the two
adjustable weights. By this arrangement the weight always moves in a line
perpendicular to the centre of the block on the end of the bar. On elevation
of temperature the distance between each staple is increased in height, and by
this means the compensation weight is raised from the balance bar; under these
circumstances, the augmentation thus effected by my continuous secondary
compensation enables the primary compensation to carry the weight over a
greater space with accelerated speed towards the centre of motion; the revorso
effect, of course, taking place on a decrease of temperature. This variation of
speed and distance to and from the centre of motion could not possibly be
brought about if the weight was placed on a rigid immoveable support
secured in the balance bar, as is usually done in the ordinary balances of this
construction.
It may be remarked, that the bows of the secondary compensation pieces
may stand across the length of the bar r obliquely, or at any angle, without
varying the perpendicularity of the motion of the weights.
Figure 5 is a perspective view of a balance of the same kind as Figure.t;

page_text: but having, in this case, the secondary compensation pieces, each made in the
form of ono staple only, standing across the primary compensation bar at right
anglos, which is an essential condition of this construction, because, a single
staple compensation will not raise the weight perpendicularly from the end
of the bar, therefore the bow of the staple should be placed in that position
which will raise the weight so as to cause as trifling a variation in the inertin
as possible.
In order to adjust the secondary compensation of the balances shown in
Figures 4 and 5, if in excess, the staples must be shortened or thickened, and
the reverse if in defect; the primary compensation is adjusted by varying the
height of the weight on the serow it, according to the usual practice.
And I hereby further declare, that the second part of my Invention consists
in the introduction of a remontoire escapement into a chronometer or other
portable timekeeper. The remontoire spring being wound up at regular inter-
vals by the mainspring, through the train of wheels, gives an invariable impulse
to the balance by means of the impulse escape wheel. The principle of this
escapement. now introduced into a chronometer, may be considered the same
as that lately invented by G. B. Airy, Esquire, Astronomer Royal, who fur-
uished me with the Drawings from which I recently constructed the first astro-
nomical clock containing his escapement. Mr. Airy having generously given his
Invention to the public, I have adopted those parts of it which were applicable
to a chronometer, and have succeeded in preserving the ordinary detached
escapement (which has so long and so deservedly maintained.its undisputed pro-
eminence), and uniting in conjunction with it such adaptatious as to convert it
into a remontoiro escapement.
The result of this combination is, that a constaut impulse is given to tho
balance by the impulse escape wheel, without its receiving any lateral pressure
(unless that of the remontoire spring may be so called).
G
In order to accomplish this object, a second escape wheel is introduced,
which I term the train escape wheel, and which revolves concentrically with
the impulse escape wheel; each of these wheols having its separate axis in the
samo straight line. The mode of construction is shown in the magnified
Drawings, where Figure 6 reprosents an elevation of a chronometer litted with
my modification of Mr. Airy's escapement; Figure 7, section through the
line of the axis of the two escape wheels; Figure 8, plan of the two asenpo
wheels, showing a detached escapement and part of a lover escapement;
Figure 9, plan of the two escape wheels, with part of a duplex escapement;
Figure 10, plau of part of an escapo wheel of a detached escapement, with the

page_text: locking spring and Mr. Airy's checking pallet. In Figures 6, 7, 8, and 9, and 10,
the train escape wheel is drawn with red lines, as is also the lever pallet. The
letters of reference signify the same parts in Figures 6, 7, 8, 9, and 10. a, the
pinion of the train escape wheel; this is shown in Figure 6 as a solid pinion
turning in a cock, but in Figure 7 as a hollow pinion turning free on a fixed
arbor pin or stud. b, (see Figure 7,) the fixed stud, upon which the pinion a
turns; c, (in Figures 6 and 7,) the train escape wheel fixed upon the upper
end of the pinion a; d, (see Figure 7,) a nut head firmly placed upon the top
of the stud b, in the centre of which nut head is fixed the jewel hole to admit
the lower pivot of the impulse escape wheel, the upper pivot acting in the plate
as usual; e, the impulse escape wheel; f, a spiral remontoire spring, connecting
the train escape wheel and the impulse escape wheel together, to give an
invariable impulso to the balance; g, the ordinary locking spring, having the
locking pallet passing through the spring to receive the teeth of the train escape
wheel c at each vibration of the balance; h, the locking pallet, projecting on
cach side of the locking spring, so as to act in both escape wheels simul-
taneously.
I would here remark, that the mode of unlocking of the escapement-by-the
balance is the same as in the ordinary detached escapement, with the exception
that, instead of one escape wheel, two are simultaneously unlocked at each
vibration; namely, the wheels c and e; k (see Figure 10) a checking pallet
fixed in the locking spring to prevent the passing by of more than one-tooth of
the wheel c at each unlocking; 1, cogs projecting upwards from the face of the
train escape wheel c, similar to those of the duplex escapement. They are
situated as near as possible to the outer circumference of the wheel, only
leaving sufficient room for the pallet k to escape between the upright cogs and
the teeth of the escape wheel c.. This mode was invented by Mr. Airy, and
suggested by him to me. m, part of the ordinary lever escapement to lock
and unlock the train escape wheel c.
And I hereby further declare that, I lay no claim to the balance bar
shewn in Figure 1, nor the timing screws attached to it; and I lay no claim
to the ordinary brass balances shown in Figures 2 and 3, neither to the
timing screws attached to them, nor to the lamina in either of those Figures,
independently of their form, nor to the weights, independently of their
position.
But what I claim in respect to Figures 1, 2, and 3, is the combination of a
primary compensation with my continuous secondary compensation, in all forms
and positions, which shall augment the distance between the centre of gravity

page_text: of the compensation weights and the junction of the primary compensation
pieces with the bar, by an increase of temperature, and which shall diminish
that distance by a decrease, as herein-before described and exemplified.
And further declare that, I lay no claim to the compensation diameter bar
shown in Figures 4 and 5, neither to the form of the curved compensation
pieces, nor to weights standing upon rigid supports from the ends of a diameter
compensation bar.
But I claim the application of secondary compensation pieces, erected upon
the ends of a diameter compensation bar, by this addition the compensation
weights are raised by menus of heat from their point of junction with the ends
of the compensation bar, and depressed by cold, whereby, on an encrease of tem-
perature, a curvaturo upwards takes place in the diameter compensation bar;
the weights being simultaneously raised by the introduction of my secondary
compensation, are taken by the curvature quicker and over a greater spaco
towards the centre of motion, and the roverso on a decrease of temperature,
which could not be effected by the curvature of the diameter bar alone, as
herein-before described and exemplified.
And I further declare that, I lay no claim to the ordinary parts of a chrono-
meter, neither to the detached escapement, nor to the parts of the lever or the
duplex escapements shown in the Drawings; these being introduced merely to
facilitate the explication of my improvements. I lay no claim to the connecting
of a train escape wheel and an impulse escape wheel, as invented by Mr. Airy
for his escapement in an astronomical clock. And I lay no claim to the pallet
shewn in Figure 10, which acts as a guard to prevent the train escape wheel
from passing more than one tooth at each unlocking.
But I claim the simultaneous locking of two escape wheels by one locking
spring in a chronometer, or other portable timekeeper. And I claim for the
same purpose, the combination of parts of a lever, or a duplex escapement, in
conjunction with the ordinary detached escapement. And I claim in a chrono-
'meter, or other portable timekeeper, that arrangement of the impulso escape
wheel in which there is no lateral pressure on the pivots beyond the pressure
of the connecting remontoire spring, as herein-before described and exemplified.
In witness whereof, I, the said Edward John Dent, havo hereunto set
my hand and seal, this Twenty-first day of September, in the year of
our Lord One thousand eight hundred and forty-two.

page_text: AND BE IT REMEMBERED, that on the Twenty-first day of September,
in the year of our Lord 1842, the aforesaid Edward John Dent came before
our said Lady the Queen in Her Chancery, and acknowledged the Specification
aforesaid, and all and every thing therein contained and specified, in form
above written. And also the Specification aforesaid was stamped according
to the tenor of the Statute made for that provided.
Inrolled the Twenty-first day of September, in the year of our Lord One
thousand eight hundred and forty-two.