12 



MECHANICS. 



Fig. 20 



C' 



(29.) The weighing -machine is formed 

 of a composition of levers. This ma- 

 chine may be used in any case where 

 considerable weights are to be deter- 

 mined, and is commonly used at turn- 

 pikes in weighing wagons, to ascertain 

 that they are not loaded beyond what is 

 allowed by law to the breadth of their 

 wheels. 



A system of levers is placed in a 

 horizontal position in a box about 

 a foot deep, so that a platform sup- 

 ported by the levers shall be on a level 

 with the road ; 1 he wagon to be weighed 

 being rolled upon the platform, the 

 power which, through the intervention 

 of the combination of levers, is capable 

 of sustaining it, becomes an indication 

 of its weight. The advantage of this is, 

 that a very small weight becomes the 

 measure of a very great one, and the 

 practical process of weighing is thereby 

 expedited. 



Fig. 21 is a ground plan of the sys- 

 tem of levers in such a machine as 

 this*. In the middle of the box is a 

 fulcrum-pin, / k, formed like the nail of 



a balance, which rests with its edge on 

 arches of hardened steel firmly fa stened 



* For a more detailed account of this machine, see 

 GaEQOHY's Mechanics, vol. ii. p. 553. 



to the bottom of the box. This lever 

 goes through one side of the box, and 

 is furnished at its extremity with a hard 

 steel pin m n, also formed to an edge 

 below. In the centre of the box a nail 

 of hard steel ij passes through the 

 lever just mentioned at P, and presents 

 a hard edge upwards. In the four 

 corners L M N O of the box are 

 firmly fixed small blocks of hard steel, 

 having hollow hemispherical cavities or 

 cups in their upper surfaces. BCD 

 E F represent the upper edge of a 

 strong iron bar, having hard steel studs 

 on its lower surface at" B and F, which 

 rest in the cups or cavities of the steel 

 blocks just mentioned. There is also 

 a hard edge immediately under D which 

 rests on the edge of i j and at right 

 angles to it. At C E are fixed studs 

 of pointed steel presented upwards. On 

 the other side of the lever is a similar 

 arrangement marked by the same letters 

 accented. 



We have, then, four pointed studs pre- 

 sented upwards, and which are so ad- 

 justed as to be in the same horizontal 

 plane. On these studs the platform 

 rests on which the body to be weighed 

 is placed. 



Now, suppose that a wire or rod be 

 connected with the end mn of the lever 

 F P, and be carried upwards perpendi- 

 cularly to the plane of the box L M O N, 

 and finally, be connected with the end 

 of another lever, from the other arm of 

 which the counterpoise or power is 

 suspended; the amount of that power 

 or counterpoise will be the indication of 

 the weight upon the platform. To de- 

 termine the proportion of this counter- 

 poise to the weight on the platform, let 

 the arms B C, F P, and the arm of the 

 final lever with which Im is connected 

 be w, w' and w" respectively, and let 

 B D, Ym and the arm of the final lever 

 on which the power acts be p,p', and p" 

 respectively. The four levers B' D', B D, 



