Litchfield enquirer. [volume] (Litchfield, Conn.) 1829-current, 1880-12-09

The metric system has been much discussed
but never, perhaps. from quite the point of
view of Mr.. Coleman Sellers, of Philadelphia,
who is the author. of paper read before the
American Society of Mechanical Engineers
and printed in the Journal of the Franklin In
stitute. He is not q closet theorist, but
maker OF machinists' tools on a large scale.
aud as his establishment has for twenty years
used both the French and the English systems
OF measurement, he is not the advocate of
either. He speaks therefore, from abundant
information, and almost judicialy, and what
he says deserves attention. In practice, saws
MIR. Sellers, the unit of the metric system is
not the metre but the millimetre, for precise
ly the same reason that the inch and not the
yard is the unit of the English system ;; that's.
the yard and the metre are too unwieldy for
the large majority of usual measut ement.
Moreover, by the use of millimetres, decimals
and multiplicity of figures are largely avoided
Eight millimetres is written simply in the
millimetre scale, but is written OOS i'm the
metre scale. 1t is easy to see what constant
and minute care is necessary to avoid errors IN
the use of the letter form = The inch aud the
millinletre-0ne 25.4 times larger than 1.
other-are, then, the units to be compared.
Either, of course, uiay be divided by tenths,
but the milliaieter must be so divided, and on
repeated processof' halvmg il as can the inch
One, consequence of this-at first apparently
slight distinction is that the u,illi,netre is not
nearly so well ad 4pted as the inch to the purl
poses of the. draughtsMan. The millmetre
furnishes only useful scales as against IL
furnished by the inch, to which may be added
of course, the decimal Subdivisions. An the
inch scales may be mead from any good rule,
but below the one tenth nillimetre scale spec
ial scales must be constructed and.x besides,
drawings on the. nillinetre scales are not SC
readily raised and reduced as on the one-half,
one quarter, and one-eighth incn scales, on
which radius and diameter dimensions may be
interchanged. Again, the millimetre does No,
lend itself to the system of ship and merchant
| sizes-that is the system of sizes by which
| goods are made and sold-nearly so readily as
| the inch. The system of. sizes lies at the bot
tom of all modern facture by machine Thus
all the screws, bolts, drills, nuts, SC, among
| increase in size, say by sixteenths of an inch
up to ipch, by eighths up to Q inches, by
| quarters up to inches, &C., or the series may
be varied, as may be convenient. Nothing
could be more easily memorized or used but q
similar series is impossible under the metric
system. German bar iron, for instance, &C
Vances by millinietre up to 40 milimeters
by millimetres to 90, by 5'millimetres above
~. The system must be memorlzed by 4(
and 80, by l, Q, and s. German drills, again
advance in size thus; TO- 70, 10, 1S, 90 %
%, %, 80, &c. The system must be memo
rized entire: there is no step for the memory
MIR. Sellers touches upon the subject ,solel,
from the point of view of mechanical engin
eer, profession which as it now exists, ha.
been born since the metric system, and, with
no hostility to it, he declared against it on tn.
merits. 8