In comparing this standard, a method was employed very similar to that used
in marking it. The bar, properly supported, was placed upon a box that
rested upon rolls, and on this same box was placed the government standard
with which the Brown & Sharpe standard was to be compared. The standard was
placed in position under the microscope, and after being properly set to
the standard, the bar to be measured was placed under the microscope, and
by the micrometer screw of the microscope the variation was measured. Three
comparisons were made by each of the attendants on each end before
determining the reading of the microscope, and after such comparisons and
many repetitions of it, the value of the standard No. 2 was found to be
36.00061 inches for the yard, and 1.0000147 meter for the meter.
After this work had been done, Mr. Beale prepared a second standard which
he called No. 3, and after examining, as shown above, the error was found
to be 0.00002 inch for the yard, and 0.000005 meter for the meter.
Observing these variations as compared with the standards originally made,
we find they are very close, and it is doubtful if many repeated trials
would furnish more accurate work, when we remember that out of forty
original standards made, but two are correct at 62 degrees Fahrenheit.
After establishing a yard, the problem of obtaining an inch comes next, and
this was made by subdividing the yard into two equal parts, these into
three, and the three further subdivided into six parts. It should be
particularly noted that no mention has been made of a standard inch, as
there is none, the standard yard only existing, the subdivision of which
falls upon those undertaking standard work. There is a remarkable agreement
between at least three leading gage makers of this country and abroad, and
each came to the result by its own method of subdividing the standard yard.
Kinds of Measurements and Measuring Tools
The measurements in the shop may, in general, be divided into measurements
of length and measurements of angles. The length measurements in turn may
be divided into line measurements and end measurements, the former being
made by placing a rule or similar instrument against the object being
measured, and comparing its length with the graduations on the measuring
instruments; the latter are made by comparing the object being measured
with the measuring instrument, by bringing the object measured into actual
contact with the measuring surfaces of the instrument. Examples of line
measurements are the ordinary measurements made with the machinist's rule,
and examples of end measurement are those made by the micrometer, measuring
machines, and snap gages. Angular measurements can also be divided into two
classes; those measured directly by graduations on the instrument, and
those measured by comparison with a given angle of the instrument.
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