212 COALFIELDS AND COLLIERIES OF AUSTRALIA. 



platform will produce a presure of Icwt. at (B). The lever 

 (FBX) produced to a point outside the macliine is used to further 

 reduce this pressure, which can then be measured by means 

 of a steelyard. The proportion of the two levers being- the 

 same, whatever point on the platform the load is placed, the 

 effect is the same; for the part that is not taken up by one 

 lever, is taken up by the other. If the proportion of (FA) 

 to (FB) was 1 to 4 and (fa) to (fb) 1 to 4, then the pressure 

 at (A) will be equal to quarter of itself at B, likewise with 

 the other lever. The instrument will therefore act as if a 

 weight equal to a quarter of the thing weighed was suspended 

 at (B). Pooley's platform weighing machine, which is 

 largely used at collieries, is constructed as shown in Figs. 

 134 and 135. The short lever is first placed in position at 



PLATFORM WEIGHING MACHINE-SECTIONAL VIEV 



Fig. 135. 



the end of the box nearest the pillar. It is suspended from 

 its fulcrum links (A), which must be hung as shown, the 

 hooks facing inwards. Knife-edge bearings are used so as to 

 diminish the friction as much as possible. The long lever is 

 now passed over the back rail of the short lever into the neck 

 of the box, its end centre (D) being the point of suspension. The 

 long and short levers are connected together at each side by 

 coupling rings (B), and the stool with its bearings is made 

 to rest on the centres (E). The check links (C) are used to 

 prevent the stool bearings from binding against the jaws of 

 the levers. The pillar, is next bolted to the neck of the box, 

 and the steelyard hung as shown in Fig. 136. The levers and 

 steelyard are then connected by means of a suspension rod. 

 Finally, the platform is placed on the box so that the planed 

 snugs rest dead upon the frame, and the machine is adjusted 

 as follows, and should be tested every morning. The weights 

 are removed from the plate of the counterpoise (C). The 

 poise (P) is put back to zero on the steelyard, anil th platform 



