the first embodiment of the mechanism according to the invention is illustrated in fig1 to 3 ; it essentially comprises , arranged on a frame ( not shown ) and which supports bearings designed to allow pivoting of the mobile parts : a gear 10 , mounted pivoting on the frame , a power source made up of a barrel 12 , a speed regulator 14 primarily made up of a flywheel connected to the barrel 12 by the gear 10 for which it ensures regulation of the rotational movement , and a speed adjuster 16 integrated to the gear 10 . the barrel 12 comprises ( fig2 ) a drum 12 a , an arbor 12 b mounted pivoting on the frame and on which the drum 12 a can turn , and a spring 12 c housed inside the drum 12 a and connected thereto by its outer end and to the arbor by its inner end . the arbor 12 b supports , integral in rotation , a wheel 18 provided with wolf teeth . a wheel 20 is mounted idle on the arbor 12 b . it supports a spring pawl 22 engaged in the toothing of the wheel 18 . it is provided with an outer toothing 20 a , forming the first wheel of the gear 10 and designed to cooperate with the device 16 , as will be explained later . the adjuster 16 comprises a wheel assembly 24 mounted pivoting on the frame and a lever 26 integral with the arbor of the wheel assembly 24 and which can go from one to the other of the two positions illustrated in fig1 and 3 . the lever 26 also supports two wheel assemblies 28 and 30 each comprising a wheel and a pinion . these wheel assemblies mesh continuously via their wheel with the wheel assembly 24 , while the pinions of the wheel assemblies 28 and 30 mesh respectively with the wheel 20 depending on whether the lever 26 occupies the positions illustrated in fig1 and 3 . the number of teeth comprised by the wheels of the wheel assemblies 28 and 30 are different . in the example illustrated in the drawing , the wheel of the wheel assembly 28 comprises twenty - four teeth , that of the wheel assembly 30 , twenty - seven . as all of the other components of the kinematic chain between the barrel 12 and the speed adjuster 14 do not change , the gear ratio between the configurations illustrated in fig1 and 3 , respectively , is 9 / 8 . the gear 10 also comprises three wheel assemblies 32 , 34 , 36 . the pinion of the wheel assembly 32 is driven by the wheel of the wheel assembly 24 , while the wheel of the wheel assembly 36 drives the flywheel . the gear 10 also comprises at least one wheel assembly ( not shown ) meshing with the wheel 20 and connected to a control device actuating a hammer designed to strike on a gong , at given moments . this part of the mechanism is well known by those skilled in the art . it is in particular described in the work previously mentioned . the frame supports two banking elements 38 cooperating with a positioning member 40 to allow the lever 26 to be able to occupy two stable positions , illustrated in fig1 and 3 , respectively . without there being a need to describe them further , one skilled in the art will be able to choose the technically suitable solution to produce the banking elements and the positioning organ . thus , for an average winding of the barrel spring , the ringing has a duration of approximately 18 seconds when the gear 28 is engaged with the wheel 20 , and 20 seconds , when the gear 30 meshes with the wheel 20 , or a gap of approximately two seconds between the two positions . fig4 to 6 show another type of adjuster 42 , with ball bearing , designed to replace the adjuster 16 previously described . the mechanism of fig1 to 3 equipped with an organ of this type corresponds to a second embodiment . this adjuster is , as shown in fig5 , adjusted such that the flywheel constituting the speed adjuster 14 , has a maximal speed , and in fig4 a minimal speed . an arbor 44 mounted pivoting on the frame , defining an axis aa and provided with a collar 44 a at one of its ends , an output wheel 46 engaged with the gear 32 , fixed rigidly on the arbor 44 and provided with a first cylindrical portion 46 a whereof the free end is truncated to form a first conical surface 46 b , an input wheel 48 engaged with the wheel 20 , mounted pivoting and sliding on the arbor 44 , provided with a second cylindrical portion 48 a oriented toward the wheel 46 and with the same outer dimension as the cylindrical portion 46 a , and forming a second conical surface 48 b , an intermediate stone 50 , bearing against the collar 44 a , a socket 52 mounted pivoting on the arbor 4 , bearing against the stone 50 , a spring 54 arranged between the socket 52 and the turning - arbor 48 a , and tending to push the wheel 48 toward the wheel 46 , a ball bearing 56 comprising balls 58 , a frame 60 provided with a third conical surface 60 a , and a ring 62 in which are engaged the turning - arbor 48 a and the cylindrical portion 46 a , the balls 58 being arranged so as to be in contact with the conical surfaces 46 b , 48 b and 60 a , and positioned by the ring 62 , a control carriage 64 connected to the arbor 60 and mounted on the frame so as to be able to move along a direction parallel to the axis aa , a control organ arranged so as to allow the movement of the carriage 64 between first and second extreme positions , defined by bankings , respectively , and corresponding to the maximum and minimum run times of the ringing . as one can see more particularly in fig4 and 5 , the ring 62 is mounted pivoting and sliding on the cylindrical portions 46 a and 48 a . it angularly positions the balls 58 in relation to each other , while allowing them to roll and move radially . the conical surface 46 b has an apex angle different from that of the conical surface 48 b . in the example , the apex angle defined by the surface 46 b is smaller than that defined by the surface 48 b . the conical surfaces 46 b , 48 b and 60 a respectively form first , second and third rolling surfaces for the balls 58 . unlike a conventional ball bearing , one will note that the conditions for friction between the balls and the rolling surfaces must allow the balls to roll and not slide on the surfaces 46 b , 48 b and 60 a . in this way , the input wheel drives the output wheel . because the angles of the conical surfaces are different , the points of contact of the balls with the conical surfaces 46 b and 48 b are located at different distances from the axis aa ; the rolling paths of these balls therefore are not the same length . this causes a speed differential between the input wheel and the output wheel , variable according to the position of the respective contact points of the balls with the conical surfaces 46 b and 48 b and also according to the apex angles defined by these surfaces . by acting on the control organ so that the wheel reaches its maximal speed and therefore , the duration of the ringing is minimal , the frame 60 is moved along a direction parallel to the axis of the arbor 44 , in the direction of the wheel 48 . the wheel 48 is then pushed back , the spring 54 being compressed . this situation is illustrated in fig5 . for an average winding of the barrel spring , the ringing then lasts approximately 15 seconds . by acting on the control organ so that the wheel reaches its minimal speed and therefore , the duration of the ringing is maximal , the spring 54 causes the cylindrical portion 48 a to penetrate the cylindrical portion 46 a , pushing the balls 58 radially outward , which increases the ratio between the speed of the input wheel 58 and the output wheel 46 . this situation is illustrated in fig4 . for an average winding of the barrel spring , the ringing then lasts approximately 17 seconds , or 2 seconds longer than in the position of fig5 . advantageously , the control organ can be stabilized at each position between the first and second extreme positions . in this way , the duration of the ringing can be adjusted continuously , between the maximum and minimum durations . the control organ can , for example , be a worm screw accessible from the inside of the watch case , so as to be able , using a screwdriver , to adjust the duration and frequency of the hour ringing . one will note that the control organ could also act on the position of one of the input or output wheels , an elastic organ maintaining the conical surface of the frame 60 in contact with the balls . fig7 diagrammatically illustrates the manner in which the speed adjuster can be integrated into the gear 10 , in a watch equipped with a speed regulator , of the flywheel type for example . in this diagram , one can see the power source 12 , the speed regulator 14 and the ringing device 68 diagrammatically illustrated by rectangles . they are connected to each other by the gear 10 , which comprises three branches 10 a , 10 b and 10 c , connected to the power source 12 , the speed regulator 14 and the ringing mechanism 68 , respectively . in this mechanism , the speed adjuster 16 can be placed in one or the other of the three locations , identified 16 a , 16 b and 16 c , or on the branch 10 a , the branch 10 c and at the intersection of the three branches . if the mechanism according to the invention was provided with a substantially isochronous speed regulator , it would then be possible to place the adjuster at positions 16 b or 16 c , or on the branch 10 b . fig8 to 10 show a third embodiment of a speed adjuster according to the invention . the essential device of this variation is the flywheel ending the striking gear and constituting the speed regulator 14 . the rest of the ringing gear connecting the barrel to the flywheel is conventional . the flywheel comprises an arbor 70 , pivoting on elements of the frame and kinematically connected to the ringing barrel 12 . this arbor serves as a pivot axis bb for a plate 72 on which arms 74 ending by rubbing organs 76 , for example stones , are pivoted . light springs 78 slightly stress the arms by pushing them toward the center of the plate 72 . an annulus 80 mounted on the frame is arranged concentrically to the arbor 70 . it surrounds the arms 74 and is located in the plane of the rubbing organs 76 . like a traditional flywheel , when the ringing mechanism is in operation , the arbor 70 is driven in rotation and with it , the plate 72 . under the effect of the centrifugal force , the arms 74 oscillate around their pivot point and the rubbing organs 76 come into contact with the ring and rub against it . by reaction and under the effect of the springs , the arms 74 pivot and the frictional organs 76 move toward the arbor 70 , before coming back , under the effect of the centrifugal force , into contact again with the ring 80 and so on . the arms thus describe an oscillating movement in a plane perpendicular to the axis bb , which causes the inertia of the wheel to vary . moreover , the rubbing organs intermittently come into contact with the ring . this makes it possible to adjust the unwinding speed of the ringing barrel and therefore the frequency with which the blows to the ringing mechanism are struck . the ring 80 defines an inner wall 80 a which , according to the invention , has a variable diameter . preferably , the variation of the diameter is continuous such that this inner wall 80 a is tapered . the relative position of the rubbing organs 76 and the ring 80 along the axis bb is adjustable . thus , the rubbing organs can come into contact with the ring at different levels in reference to the axis bb . the contact point between the organs and the ring can therefore be located at different distances in relation to the center of the ring 80 . in order to vary the relative position of the rubbing organs 76 and the ring 80 along the axis bb , the embodiment illustrated in the drawing proposes the ability to move the ring along the axis bb . to do this , the ring is placed on a support formed by a positioning lever 82 , particularly illustrated in fig1 . pins 84 are positioned in the frame so as to vertically guide the ring 80 and ensure its position in relation to the axis bb . at least one spring organ ( not shown ) exerts a force on the ring tending to push it against the lever . the positioning lever is in contact with the ring in two areas , defining a chord in relation to the circle formed by the ring 80 . the lever comprises a first pair of surfaces 82 a , located in a first plane and separated from each other by a distance equal to the cord defined above . thus , when the ring is pushed on the first pair of surfaces 82 a , the rubbing organs 76 can come into contact with the inner wall 80 a of the ring at a first level , in points located at a first distance in relation to the center of the ring . the lever comprises a second pair of surfaces 82 b , located in a second plane different from the first in reference to the ring and also separated from each other by a distance equal to the chord . thus , when the ring 80 is pressed on the second pair of surfaces 82 b , the frictional organs 76 can come into contact with the inner wall of the ring at a second level , in points located at a second distance in relation to the center of the ring . the lever 82 is mounted mobile in relation to the ring and can move between first and second positions , in which the latter part is pushed on the first or the second pair of surfaces , respectively . the lever can be actuated from the outside of the watch by its wearer . advantageously , the lever 82 is arranged such that its first and second positions are marked and stabilized by a notch . to do this and according to the illustrated example , the lever 82 comprises an elastic portion 82 c provided with two housings 82 d , capable of cooperating with a fixed element , such as a pin 83 , fixed on the frame . preferably , the elastic portion 82 c can be formed such that the pin can only be positioned in the zone defined by the two housings . to this end , the edge of each of the housings 82 d , located opposite the other housing , is high enough that , despite the elasticity of the zone , the fixed pin 83 cannot cross it . the elastic zone 82 c is formed such that , if the pin is bearing between the two housings , it returns into position in one or the other of the housings . one thus obtains a jumper spring function , i . e . the lever 82 can only be in its first or second positions . one therefore has , side by side on the lever , a surface which is part of the first pair 82 a and a surface which is part of the second pair 82 b , a threshold being formed between these two surfaces . in order to promote the passage of the support of the ring between the first pair and the second , the threshold is not at a right angle , but rather is tilted . guide organs can be provided in order to optimize the translation of the lever 82 . the surfaces of the lever are thus perfectly positioned in relation to the ring 80 . thus , depending on the position of the lever 82 chosen by the user , the rubbing organs 76 , mounted on the arms 74 , have a more or less large distance to travel before coming into contact with the inner wall 80 a of the ring 80 . the movements of the arms 74 , at a given angular speed , are determined by their masses , the elastic characteristics of the springs 78 , the mass of the rubbing organs 76 and their positioning in relation to the pivot center . the obvious result of this is that the angular speed necessary for the rubbing organs to come into contact with the ring varies according to the parameters cited above . adjusting the pre - winding of the springs 78 makes it possible , for example , to adjust the average duration of the ringing , and changing the distance to be traveled by the rubbing organs 76 makes it possible to go from slow speed to high speed . one will note that additional positions can be provided , in order to offer more adjustments of the frequency . the ring could also be moved by first and second surfaces arranged in different planes in reference to the ring and only acting on one zone of the ring . the surfaces therefore would not be arranged in pairs . the pins 84 provided for vertical guiding of the ring ensure that the latter part translates without putting itself at an angle . the lever can also have slanted planes such that the position of the ring can be adjusted continuously . the lever surfaces could also not comprise moreover , other solutions can be considered by one skilled in the art to modify the relative level of the ring and of the rubbing organs . for example , the ring could be raised via a screw , also offering the possibility of continuously varying the frequency of the ringing . the plate could also be moved , even if such a solution is less simple a priori , in order to preserve the kinematic connection with the ringing gear . thus are proposed embodiments making it possible to vary the speed of a watch ringing mechanism . of course , the description above was provided solely as a non - limiting example of the invention and one skilled in the art will be able to provide for various variations without going beyond the scope of the invention , particularly concerning the speed or gear ratios . in the second embodiment , the bearing surfaces for the balls can also not be perfectly conical , but have a certain concavity or convexity .