in that form of the present invention chosen for purposes of illustration in fig1 an accelerometer is shown , indicated generally at 2 , comprising a pair of transparent plates 4 and 6 , formed of glass or the like with a layer of liquid crystal material 8 interposed therebetween . the liquid crystal material 8 may be any suitable nematic liquid crystal material , such as a eutectic mixture of 45 parts by weight of 4 - methoxybenzylidene - 4 &# 39 ;- n - butylaniline with 55 parts by weight of 4 - ethoxybenzylidene - 4 &# 39 ;- n - butylaniline or a eutectic mixture of 15 parts by weight of 4 - n - butoxybenzylidene - 4 &# 39 ;- cyanoaniline with 85 parts by weight of 4 - methoxybenzylidene - 4 &# 39 ;- n - butyaniline . any flexible means , such as cellophane tape , not shown , may be employed to retain the liquid crystal material 8 between the plates 4 and 6 . the facing surfaces 10 and 12 of the plates 4 and 6 are coated with coatings 13 and 15 of an electrically conductive lubricant or aligning agent , such as lecithin , to achieve homotropic alignment of the molecules of the liquid crystal material 8 . in addition , the outer surfaces of the plates 4 and 6 are coated with a layer of light polarizing material , as seen at 14 and 16 . a voltage source 18 is connected , as by conductors 20 and 22 , to the lubricant coatings 13 and 15 to apply a suitable voltage , approximately 25 volts , across the liquid crystal material 8 to assure that the molecules of the liquid crystal material 8 are aligned perpendicular to the planes of the plates 4 and 6 , as indicated at 24 . one of the plates , plate 4 , for example , is fixedly mounted , as by cementing the plate 4 to a suitable flange 26 which projects from a suitable object 28 . the second plate , plate 6 , has one side thereof rigidly attached to a movable inertial mass member 30 and a suitable resilient means 32 is coupled between the opposite side of plate 4 and the object 28 . finally , a light source 34 provides a beam of light , indicated by dashed lines 36 , which is collimated by a suitable optical system 38 , traverses plates 4 and 6 and the liquid crystal material 8 is focused by a suitable lens 40 and is sensed by a suitable optical analyzer and photodetector 42 . in use , at rest or in equilibrium , the various parts of the accelerometer 2 are in the position shown in fig1 and the output of the photodetector 42 is constant . however , if any acceleration should occur , there will be relative movement between the movable mass 30 and the object 28 , causing plate 4 to shift with respect to plate 6 , as indicated by arrow 44 . this shifting of plate 4 , with respect to plate 6 , will cause a shearing action to occur within the liquid crystal material 8 which will disturb the molecular alignment and , hence , the optical properties of the liquid crystal material 8 . this , in turn , will alter the light transmission of the liquid crystal material 8 and consequently , will vary the signal output of the photodetector 42 . since only very slight movement is required to cause shearing of the molecules of the liquid crystal material 8 , the accelerometer 2 will be extremely sensitive . moreover , the variation in the output of the photodetector 42 will be functionally related to the rate of acceleration over a significant range . consequently , the accelerometer 2 will be extremely accurate , as well as sensitive . it will also be apparent that the accelerometer 2 may be very compact and light in weight . in addition , it will be obvious that the light beam 36 may be of any desired length . thus , the light source 34 and photodetector 42 may be located at a considerable distance from the plates 4 and 6 . accordingly , the plates 4 and 6 may be located in a position which is remote or otherwise inaccessible . fig2 illustrates an alternative form of the accelerometer 2 of fig1 . in this form of the invention , the facing surfaces 10 and 12 of the plates 4 and 6 are covered with reflective coatings 46 and 48 and the light source 34 and photodetector 42 are located on a common side of the accelerometer 2 . the light source 34 is positioned to direct a beam of polarized light , represented by dashed line 50 , past one edge of the reflective coating 46 of plate 4 onto the reflective coating 48 of plate 6 . the light beam 50 undergoes multiple reflection at the reflective coatings 46 and 48 until it passes beyond the opposite end of reflective coating 46 of plate 4 , as seen at 52 , and is detected after passage through an analyzer by photodetector 42 . obviously , each time that the light beam 50 is reflected from reflective coating 44 , it travels through the liquid crystal material 8 to the reflective coating 46 and vice versa . thus , as with the device of fig1 any movement of plate 4 , with respect to plate 6 , in the direction indicated by arrow 44 , will cause shearing within the liquid crystal material 8 which will disturb the optical properties of the liquid crystal material 8 and , hence , will alter the passage of light beam 50 . this will be sensed by photodetector 42 . fig3 illustrates a further alternative form of the present invention . this form of the invention is similar to that of fig2 . however , in this form of the invention , the mass 30 has been mounted directly on plate 4 and the resilient means 32 has been omitted . with the apparatus of fig3 vertical motion of plate 4 relative to plate 6 , as indicated by arrow 52 , will cause stretching or compression of the crystals within the liquid crystal material 8 . this , in turn , will alter the optical properties of the liquid crystal material 8 , causing changes in the light beam 50 which will be sensed by the photodetector 42 . obviously , numerous other variations and modifications may be made without departing from the present invention such as utilizing a laser for the light source . accordingly , it should be clearly understood that the forms of the present invention described above and shown in the accompanying drawing are illustrative only and are not intended to limit the scope of the present invention .