This balance is subject to the inconvenience of the divisions becoming
much shorter as the weight increases. The distance between the
divisions indicating one and two pounds being, in the example we have
given, about seven tenths of an inch, whilst that between 20 and 21
pounds is only one tenth of an inch; consequently a very small error
in the place of the divisions indicating the larger weights would
occasion very inaccurate results. The Danish balance is represented at
_fig. 194._
_The Bent Lever Balance._
This instrument is represented at _fig. 195._ The weight at C, is
fixed at the end of the bent lever A B C, which is supported
by its axis B on the pillar I H. A scale-pan E, is suspended from
the other end of the lever at A. Through the centre of motion B draw
the horizontal line K B G, upon which, from A and C let fall
the perpendiculars A K and C D. Then if B K and B D
are reciprocally proportional to the weights at A and C, they will be
in equilibrio, but if not, the weight C will move upwards or downwards
along the arc F G till that ratio is obtained. If the lever be so
bent that when A coincides with the line G K, C coincides with
the vertical B H, then as C moves from F to G, its momentum will
increase while that of the weight in the scale-pan E will decrease.
Hence the weight in E, corresponding to different positions of the
balance, may be expressed on the graduated arc F G.
_Brady’s Balance, or Weighing Apparatus._
This partakes of the properties both of the bent lever balance and of
the steelyard. It is represented, at _fig. 196._ A B C
is a frame of cast iron having a great part of its weight towards A. F
is a fulcrum, and E a moveable suspender, having a scale and hook
at its lower extremity. E K G are three distinct places, to
which the suspender E may be applied, and to which belong respectively
the three graduated scales of division expressing weights, _f_ C,
_c d_, and _a b_. When the scale and suspender are applied at
G, the apparatus is in equilibrio, with the edge A B horizontal,
and the suspender cuts the zero on the scale _a b_. Now, any
substance, the weight of which is to be ascertained, being put into
the scale, the whole apparatus turns about F, and the part towards B
descends till the equilibrium is again established, when the weight
of the body is read off from the scale _a b_, which registers to
ounces and extends to two pounds. If the weight of the body exceed two
pounds, and be less than eleven pounds, the suspender is placed at K;
and when the scale is empty, the number 2 is found to the right of the
index of the suspender. If now weights exceeding two pounds be placed
in the scale, the whole again turns about F, and the weight of the
body is shown on the graduated arc _c d_, which extends to eleven
pounds, and registers to every two ounces.
Public-domain text, read in full here on John Shaqi.
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