each boom 1 is pivoted , at 31 , to the lower end of a leg 29 which is an integral part of a generally triangular bracket 27 of which the post 7 is one of the side members . pivotal movement of the two booms 1 is obtained by means of a pair of power jacks 33 ( hydraulic or pneumatic ) each extending between one post 7 and one boom 1 , intermediate the ends thereof . in order that the boom and bridge assembly be swung to operative or inoperative position , it is obvious that the two jacks 33 are to be operated in synchronism . the free end of each boom 1 is provided with a levelling jack assembly made up of a telescopic standard 35 and a power jack 37 , the operating rod of the jack 37 and the sliding rod of the standard 35 being of course connected to the same base plate 39 . similar jack assemblies 41 are provided at either end of the support base b mainly for stabilizing the base and , of course , the relevant end of the boom and bridge structure assembly . as to the jack assemblies 35 , 37 , they must of course be adjusted according to the level condition of the lot on which the base plates 39 lie , on the side of the curb 13 or sidewalk 15 opposite the paved road or street on which the jack assemblies 41 are set . in either the case of fig3 or fig4 the intent is to place the booms 1 into a generally horizontal common plane . referring now particularly to fig1 and 5 , the central section 21 of the bridge structure 3 is made up of a series of inverted t cores 43 each having a central stem 45 and a pair of lateral bars 47 , 47 &# 39 ; extending in opposite directions from the stem 45 and making between them an angle which is supplementary to the previously mentioned angle α , particularly shown in fig4 . on the face 17 of the bridge structure 3 , there are provided top and bottom elongated rail members 49 , 49 &# 39 ; secured over the top and bottom surfaces of the lateral bars 47 . in a similar manner , on the second face 19 of the bridge 3 , there are provided a pair of elongated rails 51 , 51 &# 39 ; secured respectively on the top and bottom surfaces of the lateral bars 47 &# 39 ;. the arrangement is such that the outer faces of the rails 49 , 49 &# 39 ; lie in a common first plane and the outer faces of the rails 51 , 51 &# 39 ; lie in a common second plane , the first and second planes making the aforesaid angle α , as best illustrated in fig4 . finally , the ends of the central stems 45 are connected to a longitudinal elongated cylindrical bar 53 , in the case of the central section 21 . on the other hand , the said ends of the central stems 45 are , in the case of the terminal sections 23 , fixed to square hollow bars 55 . corresponding to each end of the central section 21 is a bearing structure for the cylindrical bar 53 . this structure is made up of a pair of channel members 57 , 59 secured together to define an inner housing inside of which there is fixed a square bearing block 61 having a central through bore into which the relevant end of the cylindrical bar 53 journals . as best illustrated in fig6 the cylindrical bar 53 extends beyond the bearing block 61 and its transverse flat radial face is secured to the lower end of an upstanding web 62 which is part of an l - shaped bracket 63 having a pair of spaced lugs 65 of which one is connected to the web 62 by means of a brace 67 . the spaced lugs 65 straddle the square hollow bar 55 of the relevant terminal section 23 of the bridge structure 3 , being connected thereto by a pivot 69 which can be of the bolt and nut type . it should be pointed out here that the square bar 55 is integral part of the terminal section 23 which is identical in construction to the central section 21 except that the top member is a square hollow bar 55 as opposed to the cylindrical bar 53 of the central section 21 . to be noted also is the fact that the said cylindrical bar 53 is secured to the back of the web 62 of the bracket 63 but the square bar 55 is not , so that , by means of a conventional power jack such as 71 in fig5 the terminal section 23 may be angularly displaced with respect to the central section 21 . channel 59 has the web thereof fixedly secured to the bottom of a square sleeve 73 slidably mounted on the relevant boom 1 of likewise square cross - section so as to be freely insertable into the sleeve 73 . note should be taken here that the web 62 of the bracket 63 is not secured to the side of this sleeve 73 , as clearly illustrated in fig6 . one flange 75 of channel 57 extends beyond the sleeve 73 , as best shown in fig5 . to the outer end of this flange 75 is secured an operating lever 77 facing a like lever 79 of which one end is secured to the cylindrical bar 53 of the bridge structure central section 21 . the upward ends of the operating levers 77 , 79 are interconnected by a power jack 81 . whenever power jack 81 is operated , let us say shortened , the operating lever 77 stays stationary as it is ultimately connected to the sleeve 73 of the boom 1 while the lever 79 causes clockwise rotation of the cylindrical bar 53 as well as like rotation of the terminal section 23 since the latter is solid , in this respect , with the central section 21 through its connection to the l - shaped bracket 63 secured to the end of the cylindrical bar 53 . as aforesaid , the advantage of this construction is to place the saw 11 at an angle other than the predetermined angle α between the faces 17 and 19 where the sidewalk is either narrower or wider than conventional sidewalks . also , this possibility of oscillating the bridge structure 3 may be found useful as a final adjustment of the saw 11 where its levelling may not be fully attained by the use of the jack assemblies 35 , 37 in view of the poor level condition of the lot inside the curbstone or sidewalk . referring now to fig2 and 7 , bodily displacement of the bridge structure 3 along the booms 1 is obtained by means of a pair of synchronously operated jacks 83 of which one end is connected to the sleeves 73 and the other ends to pivots 85 on the booms 1 , located adjacent to the pivots 31 of the said booms . referring to fig5 it is pointed out that the operating levers 77 , 79 will normally be held apart by a lock bar 87 having laterally projecting pins 89 at the ends thereof insertable into receiving holes 91 at the outer ends , respectively , of the operating levers 77 , 79 . when the levers 77 , 79 are so set , the faces 17 and 19 of the bridge structure 3 ( fig4 ) will make the aforesaid angle α . when this angle has to be changed , the lock bar 87 is removed and the levers 77 , 79 operated to place the saw 11 at the selected angle at which time the levers 77 , 79 may be locked again in any suitable ways . referring now to fig8 and 9 , the carrier 9 has a generally t - shaped platform 92 over which is mounted a hydraulic or pneumatic motor 93 driving the saw 11 through a gear transmission 95 ( fig9 ) contained in a housing 97 fixed to and depending from beneath the platform 92 . along the edges of the platform 92 , there are provided two pairs of spaced flanges 99 , 99 &# 39 ; defining therebetween passages into which are received two rails 101 over the top of which are provided racks 103 , the rails 101 and their racks 103 being part of the means for mounting the carrier 9 and its equipment on the bridge structure 3 . within the aforesaid passages between the flanges 99 , 99 &# 39 ; are provided a series of pairs of rollers 105 pivotally mounted , in any known manner , on the said flanges 99 , 99 &# 39 ;. these rollers 105 are so located as to ride on the rails 101 , on either side of the racks 103 thereby providing a means of allowing displacement of the carrier 9 and its equipment along a second direction which is perpendicular to the first direction mentioned above corresponding to the longitudinal direction of the bridge structure 3 . means are of course provided to allow the said carrier displacement in the second direction , along arrow c . such means , as shown particularly in fig8 and 9 , comprises a rotary axle 107 supported by a pair of brackets 109 , disposed on either side of the previously mentioned motor 93 , being secured to and upstanding from the central platform 92 of the carrier 9 . rotary pinions 111 are provided at the ends of the axle 107 and are in mesh with the respective racks 103 of the rails 101 . a further motor 113 , mounted on one of the brackets 109 , drives a worm 115 in mesh with a gear ( not shown ) fixed to the axle 107 . it will thus be understood that operation of the motor 113 causes , through the worm and gear arrangement aforesaid , rotation of the axle 107 and pinions 111 thereby causing displacement of the carrier 9 and its equipment along the said second direction . as mentioned above , the rails 101 are part of the means for mounting the carrier 9 on the bridge structure 3 . such means further comprises a channel - shaped bracket 117 having a web 119 , parallel to the first face 17 of the bridge structure 3 , and two flanges 121 , 123 , this bracket 117 thus defining an inner chamber 125 into which the rails 49 , 49 &# 39 ; are disposed . on either side of the latter rails 49 , 49 &# 39 ;, are rollers 127 mounted for free rotation on the flanges 121 and 123 , within the housing 125 . these rollers are mounted so as to ride freely on the opposite faces of the upper and lower rails 49 , 49 &# 39 ;, the latter rails thus constituting means for holding the mounting means on the bridge structure 3 . it will be noted that the rails 101 are secured , at one end , at the lower end of the web 119 of the bracket 117 , being further braced into position by inclined struts 129 connected at one end to the outer ends of the rails 101 and , at the other end , to brackets 131 secured at the upper end of the web 119 . as shown , additional rollers 133 , rotatably mounted on the said brackets 131 are adapted to ride on the top surface of the top rail 49 whereas bottom rollers 135 , similarly mounted at the bottom of the bracket 117 , freely ride on the bottom surface of the lower rail 49 &# 39 ;. the means for driving the aforesaid channel assembly in the first direction along the bridge structure 3 includes a shaft 137 ( fig9 ) mounted for rotation within chamber 125 and on the top and bottom flanges 121 , 123 . on this shaft 137 is fixed a gear 139 ( fig8 ) in mesh with a worm 141 driven by a motor 143 ( hydraulic or pneumatic ) secured outwardly of and on the web 119 . a further gear 140 is mounted on the shaft 137 and at the lower end thereof which meshes with a rack 145 provided on the outer face of the lower rail 49 &# 39 ; ( see fig5 ). when the motor 143 is energized , it drives the shaft 137 into rotation which consequently rotates the lower gear 140 which is in mesh with the rack 145 thereby causing displacement of the bracket 117 and the equipment connected thereto including the carrier 9 and the saw 11 . thus , there has been provided means for displacing the saw in the said first direction , along the bridge structure 3 , and the second direction which is perpendicular to the first direction by having the carrier 9 move along the rails 101 . as pointed out above , the upper and lower rails 49 , 49 &# 39 ; of the bridge structure 3 constitute a holding means for retaining the bracket 117 thereon with its rolling equipment and , as a consequence , the rails 101 and the carrier 9 and the equipment mounted thereon . the same holding means is provided on the face 19 of the bridge structure 3 , opposite the first face 17 , in the form of the previously mentioned upper and lower rails 51 , 51 &# 39 ; ( fig5 ). the said lower face 51 &# 39 ; further has a rack 145 &# 39 ; allowing the displacement of the bracket 117 and its assembly . in order that the carrier 9 and the carrier mounting means can be moved from face 17 to face 19 and vice versa , use is made of the aforementioned turn - table 25 ( fig7 ). this turn - table takes the form of a short half section of bridge structure 3 . it is made up of a pair of horizontal parallel rails 149 and 151 ( fig1 ) of the same cross - section and same vertical spacing as rails 49 , 49 &# 39 ; ( or 51 , 51 &# 39 ;) and integrated together by vertical spacing stems 153 , 155 and 157 . connecting pins 159 project from the terminal faces of the rails 149 , and 151 , at either end thereof . these are intended to fit into receiving bores 160 ( fig5 ) and 161 . as illustrated in fig1 , the turn - table 25 is constructed to fit selectively at the end of the rails 49 , 49 &# 39 ; or 51 , 51 &# 39 ; so that the rails 149 , 151 may constitute continuations thereof , allowing the carrier 9 to be moved on the turn - table 25 . shifting of the turn - table 25 , with carrier 9 thereon , is obtained by the following transfer assembly . the latter is constituted by a cylinder base 163 , secured to the square bar 55 of the terminal section 23 , into which fits the post 165 of a jib 167 having a horizontal arm 169 at the end of which one end of a rope 171 hangs . the other end of the rope 171 is secured to a support bar 173 removably secured by screws 175 on top of the flange 121 of the channel bracket 117 ( fig9 ). normally , the turn - table 25 is secured at the end of terminal portion by a bolt and nut assembly 177 . when the carrier 9 is to be moved from face 17 to face 19 of the bridge structure 3 , the bar 173 is secured on the flange 121 ; the lower end of the cable 171 fixed to the bar 173 ( in any known manner ) the bolt and nut assembly 177 removed and the turn - table 25 , with the carrier 9 thereon , pulled manually to be freed from the terminal section 23 . it is then rotated by 180 , again manually , and the connecting pins 159 inserted in the relevant bores 161 of the face 19 . the bolt and nut assembly 177 is thereafter mounted to secure the turn - table 25 in the extension of face 19 .