(11 



WEIOHING-MACHI.NI:. 



WEIGHING-MACHINE. 



is to be ascertained ; but sometimes a oale-plate or dish suspended by 

 bain* u idd. The moveable weight U commonly attached to a ring, 

 the iWui of which enable* it to rait in notuhet cut on the upper edge 

 of the uteulyanl, corresponding with the graduation* engraved on iU 

 tide. A ring or hook U also attached to the fulcrum, *o that the 

 instrument may be conveniently hung upon a fixed support, or if amall, 

 held in the baud ; and a vertical index or pointer, timilar to that 

 ittai-hrrt to the beam cf common soules, u sometime* added. The 

 fulcrum, and the axu from which the weight is suspended, should, 

 when much nicety u required, be provided with knife edge* or bear- 

 ing* resembling those uaed in other lever-balances. Many steelyard* 

 are supplied with a second fulcrum ; the two being placed at different 

 dintanom from the point to which the hook or Male it attached, and 

 having their respective pointer* and suspeuding-hooks on opposite side! 

 of the lever, or rather, when held in the position for use, one above 

 and the other below it, a* shown in the following cut of an ancient 

 Boman steelyard. In using a steelyard of this kind, capable of weigh- 

 ing from one to sixty pounds, the fulcrum which u nearest to the 

 middle is used if the article be under fifteen pounds; while if it 

 exceed that weight, the Instrument must be inverted, and suspended 

 from the fulcrum which divides the lever most unequally. 



Several ingenious bent-lever balance* have been contrived, some of 

 which, from the circumstance of the levers being of unequal arms, 

 resemble the steelyard in principle ; and various modifications of the 

 steelyard have been invented for delicate scientific purposes, or for 

 adapting it to the purpose of weighing very heavy bodies. Of the 

 latter class is that which is employed usually at the toll-gate* on 

 roads for the purpose of determining the weights of laden carriages. 

 In order to prevent the roads from being too much cut up, the burdens 

 allowed to be conveyed along them by carts or waggons are made to 

 depend on the breadth of the wheels ; and a fine is imposed for any 



2 feet deep, the side* and bottom being lined with brickwork or 

 and 1. 1 11 s us represent a longitudinal section ><i tl..- pit p> n>.-ndicu- 

 larly to the ground : abed, u'ti'c'd' are two trapezoidal frames oi 

 acting as levers; and eauu of tlio aid* ban, as ac or bd, ha>, in th 



excess above the regulated quantity. 

 The usual weighing-machine ma 

 platform sunk on a level with the road, and made to rest at four 



. 

 The usual weighing-machine may be described, in a general way, as 



pointa on a double lever of the second kind. The extremities of the 

 arms of these levers rest upon a third lever, which may be of the first 

 or second kind ; and this last lever may cither serve as a steelyard, or 



tMljrud, found at Pompeii, with part of the bom and 

 inscription on a larger teals. 



may b connected with one arm of an ordinary balance, or with the 

 extremity of a steelyard. 



But to bo more particular, let A B c D be the plan of a rectangular pit 

 sunk In the ground, from 8 to 12 feet long, feet broad, and about 



vertical position, the form which ia represented by at, a'<? in the sco- 

 tiou. At each extremity a, 6, a', V, in the plan, the frames have * 

 conical steel point, which appears at a, a' in the section ; this rests in 

 a hemispherical cavity made in a die or cylinder of the same metal, 

 which is either attached to the iron-work forming the sides of the pit, 

 or U supported on a block of stone mink in the ground at each of the 

 four interior angles; and under the shorter side, cd or tfd", of each 

 frame there is a wedge-like prism of tempered steel, having its edge 

 parallel to that aide. The ends of these prisms appear at c and c' in 

 the section. 



The bar PQ is an iron lever, which in the above diagram is of the 

 second kind, having at P a pin, mn, like that of a balance, turning in 

 two steel rings on a pillar of stone sunk in the ground, or of iron 

 resting on the bottom of the box ; a steel pin, pq, formed also like that 

 of a balance, with its edge upwards, passes through tho bar PQ; and 

 upon this rest the edges of the prisms at cd ami c'cf , as shown in the 

 section. 



The platform supporting the carriage which is to be weighed, and 

 which is represented at M in the section, has below it four iron feet, 

 of which two appear at X and v ; and the under surfaces of these feet 

 are formed with hemispherical cavities which reat on the points of four 

 conical steel pins at t, u, f, u', on the two lever-frames ; consequently 

 tip- weight on the platform pressing at those four points, the prisms at 

 cd, ift are forced down upon the fiapq ; and this lost then presses 

 down the extremity Q of the lever v Q. This lever itself may be made 

 to act as a steelyard ; or, by a rod or chain, tho extremity q may be 

 connected with one arm of a balance or steelyard above the machine ; 

 in either case the weight of the carriage may be ascertained. 



It is evident, from the nature of the lever, the pressure of the plat- 

 form itself being balanced by a constant weight at Q, that if w represent 



the weight of the carriage, w. 2_ . will express the pressure at <J, 



ac PQ 



or the weight by which that of the carriage is determined ; and this in 

 independent of the power obtained by a steelyard which may be con- 

 nected with Q. If = -1- and - , a weight equal to 10 pounds 



ac . 14 i'j 16 

 at q' will balance a weight equal to 1 ton upon the platform. 



The Spring Balance is a machine in which the elasticity of a spring 

 of tempered steel is employed as a means of measuring weight or force. 

 The name is most commonly applied to machines for the former pur- 

 pose ; those employed to ascertain the muscular strength of men and 

 animals, the amount of power required to move a carriage or a boat, 

 or any other force applied in the form of a pull, being called dyna- 

 mometers. [DYNAMOMETER.] 



One of the simplest kinds of spring-balance is that which, when 

 employed as a weighing-machine, is known as the spring or pocket 

 steelyard. It consists of a helical spring formed by bending a Hteel 

 wire spirally round a cylindrical mandril or axis, so as to 'form an 

 extensive series of convolutions. This spring is placed in the interior 

 of a tube of bras* or iron, closed at both ends : one end of the spring 

 abutting against the plate which closes the lower end of the tube. A 

 rod, having a hook or loop at its lower extremity, to hold the article 

 to be weighed, passes through a hole in the bottom of the tube. 

 and up the inside of the spring. At the upper end of thU rod 

 is a small plate, which slides up and down like a piston in the 

 tube, and rests upon the upper or free end of the spring ; thereby 

 causing it to collapse when a heavy body is attached to the hook at 

 tho bottom of the sliding-rod. The machine is supported l>y means of 





