BALANCES AND WEIGHING MACHINES
Year: 1883

page_text: PROVISIONAL SPECIFICATION left by Charles Henry Bartlett at the Office
of the Commissioners of Patents on the 27th April 1883.
CHARLES HENRY BARTLETT, of the City and County of Bristol
IN BALANCES AND WEIGHING MACHINES
"
"IMPROVEMENTS
My Invention relates first to an improved balance chiefly intended for weighing
letters and parcels for postal purposes, and the like. The balance is of that kind
in which the object to be weighed is counterpoised by a constant weight slid along
a graduated beam on the well known principle of the steelyard and the Invention
has for its object to combine in a balance in which no loose weights are used, a
very clear and open scale for the ounces or other small denomination of weight,
with a wide range of weighing power, so that the balance may be used with the
same facility for weighing letters or parcels of one or more ounces only, as for
parcels of several pounds weight.
The first improvement consists in providing the balance with two independent
graduated arms or steelyards projecting in the same. direction and each having its
own sliding weight the one appropriated for the pounds or other large unit, and
the other for the ounces or other small unit adopted,
These weights may be used either separately or conjointly for counterpoising the
load on the scale pan, and when one alone is in use the other may be so placed as
not to affect the accuracy of the balance. The arm for indicating pounds projects
from a rectangular frame mounted to oscillate on knife edge centres the scale pan
being mounted on knife edges in said frame at the opposite side of the axis of
oscillation to the said arm, all much in the usual way of making balances of this
description. The arm for indicating ounces is attached to the said frame at a
point on the same side of the axis of oscillation as the scale pan, and projects
across the axis of oscillation in the same direction as the other arm the parts being
so proportioned that when both weights are at the inner ends of their respective
arms the unloaded scale pan is exactly balanced. In this initial position of the
ounce" counterpoise and until it is shifted so far along its arm that its centre of
gravity lies at the other side of the axis of oscillation, the counterpoise acts
negatively by adding to the weight on the scale pan side of the balance. Therefore
in shifting it along the arm this negative weight is at first gradually taken off and
after passing a neutral point coincident with the axis of oscillation, the weight is
"
[Price 211

page_text: gradually applied positively on the opposite or steelyard side of the balance. By
this arrangement a much greater range is obtained and consequently a much more
extended and open scale upon which ounces or fractions of an ounce may be easily
read off at a glance.
Another improvement is applicable both to the balance above described and also
to other descriptions of balances and weighing machines in which the horizontality
of the scale pan or platform for receiving the goods or counterweights is maintained
by a vertical tail piece or rod extending downwards beneath the scale pan in the
case of small balances such as Roberval's and upwards in the case of some larger
weighing machines.
T
The object of this improvement is to enable the length of this tail piece or rod
to be adjusted with greater facility than has hitherto been possible and to secure
it after adjustment from any accidental alteration of length. The accuracy of this
adjustment for length is necessary to ensure that the load on the scale shall have
the same effect in whatever part of the scale pan it may be placed as is well
understood.
To enable this adjustment to be made with the desired facility I connect the
tail piece or rod to the scale pan or platform by a screw connection which admits
of regulating the effective length of the tail or rod with the greatest possible nicety
without dismounting or even disturbing the machine and which when once adjusted
may be permanently secured in a ready and effecient manner, For example in
small balances of the kind first described and in balances on the Roberval
principle the tail piece has hitherto been made in two pieces and the adjustment
has been effected from below which is a very tedious operation. I prefer to screw
thread the upper end of the tail piece and connect it to the frame supporting the
scale: pan by nuts or a nut and collar embracing said frame above and below and
contained in a cavity into which molten' lead poured around the nut after the
adjustment is made so as to prevent it being subsequently disturbed