referring more particularly to the drawings , there is provided a base 10 which may be a metal casting . two rods 12 and 14 extend laterally from the base 10 . the free ends of the rods 12 and 14 are threaded . the opposite ends of the rods may be swaged as shown at 16 ( fig2 ) in countersunk holes 18 in the base 10 through which the rods 12 and 14 extend . the rods enable a cover 20 to be held against the base 10 by z - shaped overlapping strips 22 and 24 which are screwed onto the threaded ends of the rods 12 and 14 . the rods 12 and 14 are preferably metal tubes . the swage 16 at the end of the rods 12 and 14 in the casting prevents them from turning as the strips 22 and 24 are screwed on to hold the cover 20 in place . the cover is a box , rectangular in cross - section and open at the end thereof , which meets the base 10 along the edge of its open end . the cover 20 is preferably made of clear plastic material so that the switch mechanism 26 is visable for inspection . holes 29 in the overlapping portions of the strips 22 and 24 may receive a wire strand which is sealed with lead so as to secure the switch mechanism 26 against tampering . the switch mechanism is made up of a pendulum assembly 28 and an assembly of two groups 30 and 32 of sets of contacts . the group 30 has a set of normally closed contacts 34 and a set of normally open contacts 36 . the lower , normally closed contact set 34 may be referred to as the front contact set of the group 30 , while the upper , normally open contact set 36 may be referred to as the back contact set thereof . the group 32 has a set of front contacts 38 and a set of back contacts 40 . the mechanism is illustrated in the drawings in the position where the pendulum is vertical with no acceleration or deceleration forces applied to the mechanism . the envelope of the base 10 and cover 20 is preferably the same as that of a vital relay used in train control systems sold by the general railway signal company of rochester , n . y . the base is received and mounted in a receptacle for such relays and thus can be conveniently accommodated in the onboard control system of the train . the receptacle is known as a plug board . the mechanism is mounted in line with the direction of acceleration or deceleration of the train on the plug board , such that the pendulum is vertical in the absence of deceleration or acceleration forces . gravity is used as a reference in the operation of the switch mechanism and misalignments must be compensated either in the mounting or in the means for adjusting the actuation of the contact sets 34 to 40 which are provided on the pendulum and which will be described in detail hereinafter . the pendulum assembly 28 has base and stem sections 42 and 44 . weights 46 and 48 are attached to opposite sides of the base section 42 at the bottom of the pendulum . an axle 50 ( see fig4 ) is secured along the vertical bi - sector of the pendulum in the stem section 44 by a pin 52 which extends laterally through the stem section 44 and through the axle 50 . a pair of brackets 54 and 56 are attached , as by brazing , to a back plate 58 . nuts and bolts 60 attach the back plate to the base 10 . the brackets 54 and 56 extend laterally from the base 10 parallel to each other . bearing assemblies ( not shown ) within threaded rods 62 and 64 support reduced diameter ends of the axle 50 therein . one of these reduced diameter ends 66 is shown in fig4 . the bearing assemblies within the threaded rods 62 and 64 preferably contain jewel bearings biased toward the axle 50 by springs which are in the bearing assembly . the rods 62 and 64 with their bearing assemblies are held on the free ends of the brackets 54 and 56 by nuts 68 and 70 threaded onto the threaded rods 62 and 64 . the free ends of the brackets 54 and 56 , below the threaded rods 62 and 64 and their bearing assemblies , are maintained separated by a bolt and nut assembly 72 . the shank 74 of the bolt 72 has a sleeve 76 thereon ( see fig3 ) which maintains the free ends of the brackets 54 and 56 separated . the shank 74 and sleeve 76 extend through a hole 78 ( see fig2 ) in the base section 42 of the pendulum , and act as a stop to prevent excessive swings of the pendulum , which might cause damage to the switch contacts in the groups 30 and 32 under extreme acceleration or deceleration . the axle 50 has its axis horizontal and perpendicular of the pendulum . assuming that the forward direction of movement of the train is the direction in which the closed end of the cover 20 is facing ( to the left as shown in the drawings ), the pendulum will swing in a clockwise direction when the train decelerates . the pendulum swings in opposite directions , clockwise and counter - clockwise , in response to deceleration and acceleration of the train . if the train is for example a subway train , which is not turned around at each end of its route , the pendulum will swing counter - clockwise when the train is decelerating and is moving from right to left . the pendulum will swing counter - clockwise when the subway train decelerates during its movement in the opposite direction , i . e . from left to right as shown in the drawing . it is a feature of this invention to provide a single integral switch mechanism which senses when such acceleration and deceleration or deceleration in opposite directions exceeds a predetermined level . a single device in accordance with the invention rather than two devices is all that is necessary to sense opposite directions of acceleration and deceleration . consider next the contact groups 30 and 32 . each set of contacts , of which the normally closed contacts 34 of the group 30 are typical , is made up of a fixed contact 79 and a moveable contact 80 . these contacts move between make position and break position . in the case of the contact group 30 the contact set 34 is shown in make position and the contact set 36 is shown in break position . the contacts are vital in that they are of material which does not weld or stick when current flows through the contact . the fixed contacts 79 are preferably made of a silver impregnated carbon . the moveable contacts 80 are silver . these are vital contacts of the same type that are used in vital relays of railway signalling system and are recognized as vital in the industry . the contact groups 30 and 32 themselves may be the same construction as used in vital b - relays of railway signalling systems . each group has room for three sets of contacts . only two sets are used . the contacts are all mounted on the ends of leaf spring fingers which are molded into insulating blocks 82 . it will be noted from fig1 that there is room in the block 82 for three side by side contact groups . only two groups are used ; the center group being omitted . contactor prongs 84 and 86 may be part of or conductively attached to the spring fingers . these connectors for each contact set are received between the prongs 84 and 86 . by way of example , the moveable contact 80 of the normally closed contact set 34 is mounted at the end of a spring finger 87 . the fixed contact 79 is fixed in position by a clip 90 of stiff material which extends laterally outward from the block 82 on top and bottom sides of its spring finger 88 . the moveable spring finger 87 is formed with a permanent set so that the moveable contact 80 is biased to make contact with the fixed contact 79 . the normally open contact set 36 similarly has its moveable contact on a spring finger which is biased in the same direction as the spring finger 87 of the front contact set 34 . the normally open contact set 36 will then be biased apart or to break contact there between . each of the spring fingers in the contact groups have slots 92 and 94 ( see fig1 ). pushers 96 and 98 extend vertically through these slots . the slots in each of the moveable spring fingers have rollers 100 therein which are received in notches in the pushers . bands 104 around moveable spring fingers keep the pushers in place against the rollers 100 . the pushers 96 and 98 have feet 106 and 108 at bottoms thereof . the foot 106 has its end or sole facing downwardly . the instep or top of the foot 108 faces upwardly . the sole surface of the foot 106 and the instep surface of the foot 108 present themselves for abuttment with means for actuating the contact sets 34 to 40 in the contact groups 30 and 32 from the position shown in the drawings to their opposite positions , i . e . with the normally closed contacts 34 and 40 broken and with the normally open contacts 38 and 36 making contact with each other . such actuation occurs only when a predetermined level of deceleration is obtained in one direction in the case of the contact group 30 and in the opposite direction in the case of the contact group 32 . the means for actuating the contact groups 30 and 32 is provided by the pendulum . mounted on opposite sides of the pendulum are bracket plates 110 and 112 . each of these bracket plates is pivotally mounted about the axle 50 by reason of holes therein through which the axle 50 extends . slots 114 and 116 in the bracket plates 110 and 112 respectively are located above the axle 50 . screws 117 and 120 extend to these slots and are threaded into the opposite sides of the stem section 44 of the pendulum . these screws , like other nuts and bolts in the mechanism may be equipped with washers of the lock or shake proof type to provide firm connections . by pivoting the bracket plates 110 and 112 about the axle 50 , these plates can be set at different angles of inclination with respect to the vertical . the screws 117 and 120 are then tightened to maintain the bracket plates 110 and 112 at the preset inclinations . extending outwardly in opposite directions from the inside of each of the bracket plates 110 and 112 are shoes 122 and 124 . arms 126 and 128 are fixedly attached to the plates 110 and 112 by brackets 130 and 132 which are riveted to the shoes 122 and 124 and sandwich the end of the arms 126 and 128 therebetween . the free end of the arm 126 moves together with the pendulum into abutting relationship with the sole of the foot 106 of the pusher 96 when the pendulum swings in the counter - clockwise direction . this occurs only when the pendulum swings in the counter - clockwise direction a predetermined distance corresponding to a predetermined level of deceleration or acceleration depending upon the direction of forward travel of the train . the arm 126 does not make contact with the pusher 96 when the pendulum swings in the clockwise direction , since the foot is clear of the arm when it swings in the clockwise direction . similarly the arm 128 moves into abutting relationship with the instep of the foot 108 of the pusher 98 only when the pendulum swings in the clockwise direction , and only when such a swing is over a predetermined distance . the distance of the swing corresponds to the predetermined level of acceleration or deceleration at which actuation of the switch contacts is desired . for swings in the counter - clockwise direction , the arm 128 is clear of the pusher so that the contact sets 38 and 40 in the contact group 32 remain in the position in which they are maintained by the bias of the spring fingers attached to the moveable contacts thereof . it will be observed that the bias of the spring fingers of the moveable contact of the sets 38 and 40 is in the opposite direction to the bias of the spring fingers of the moveable contacts of the contact sets 34 and 36 . accordingly when and only when acceleration or deceleration is in one direction , which produces counter - clockwise swinging of the pendulum can actuate the contacts 34 and 36 of the group 30 be actuated . conversely only acceleration or deceleration which produces swinging in the clockwise sense can actuate the contacts 38 and 40 of the group 32 . the level of acceleration or deceleration which will produce actuation of the contacts is readily adjusted by setting the inclination of the brackets 110 and 112 with respect to the vertical . this setting also sets the inclination of the arms 126 and 128 with respect to the vertical . the top of the stem section 44 of the pendulum is preferably calibrated in terms of deceleration rates corresponding to different inclinations from the vertical . these calibrations are indicated on a scale of from zero to four miles per hour per second ( see fig2 and 4 ). the tops of the plates 110 and 112 are also calibrated with a vernier scale which provides a visual indication of the deceleration rates to 0 . 2 miles per hour per second . the pointer is set at a position between 1 and 2 mph / sec . in fig2 ; the vernier indicating an additional 0 . 2 mph / sec . or a total of 1 . 2 mph / sec . the inclination of the arm 126 and its bracket plate 110 is then set such that the contacts in the group 30 are actuated for decelerations of 1 . 2 miles per hour per second . the arm 128 and its bracket plate 112 may be set at the same or such other deceleration level as may be desired . the actuation of the contact groups 30 and 32 is independent , one from the other , by virtue of the different settings and the clearance provided between the path of the arms 126 and 128 and the feet 106 and 108 of the pushers 96 and 98 . the arms 126 and 128 are leaf springs similar to the spring fingers which hold the contacts 34 to 40 and will provide some deflection to relieve forces on the contacts in case of accelerations or decelerations greater than the present rate . the entire switch mechanism may be placed on a calibrating table and the scale inscribed on the plates 110 and 112 and on the stem section 44 of the pendulum . the weights 46 are selected so that pendulum assembly 28 has a natural frequency preferably between 2 hz and 2 . 5 hz so that the switch mechanism is not responsive to vibration accelerations . further isolation from such vibration accelerations may be provided by electrical means , such capacitors connected across the switch contacts , if desired . from the foregoing description it will be apparent that there has been provided an improved switch mechanism which senses acceleration and deceleration events which exceed predetermined levels , which mechanism is especially suitable for use in train speed control systems for brake assurance purposes . variations and modifications within the scope of the invention will undoubtedly suggest themselves to those skilled in the art . for example , where additional contact sets are required they may be provided outboard of the contact groups 30 and 32 or by additional contacts in the groups . accordingly the foregoing description should be taken as illustrative and not in a limiting sense .