New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1873-10-29

ideal number Of pairs ia three for the entire body
eleven Probably the ary@ OF the dlnerene n,c
segment Certainly at least on evolution prlneiples
from the indications In existing caterpars we are per
haps warranted in concluding he ancestral type OF
lepidopterous larv0 was provided Win TWO pairs vi
thOraclc spiracles.
MEASUREMENT OF yoLUME-By PROP. ,. p. HIIGARD.
The determination of the weightof given volume OF
water Is still problem remaining TO be solved with tue
extreme precision now looked for In fundamental
physical constant. The hiogramme was originally &c
termined TO be the weight OF a cubic dcclneter OF
water, but subsequent experiments nave gwen results
which Indicate an uncertainty OF perhaps 100 mill-
grammes IN the 'hcoretc yauc OF tnI ko te
experiments agreeing closely with the Ffeueh, while the
English Swedish ana Austrian results diner consdeia
bly, The International Metric Commissions at thelr met
ing IN Paris last Autumn, resolved 10 make reuetrf-
legal standard As n member OF the Executive Com
mtee OF that body, nave considered th2 mrans OF az
tanning the greatest precision IN the results TIC most
difficult part OF the problem is the admeasurenent OF lhe
volume, which should be ascertaned 10 one ten,inl
llOnth part. Tie cylndrtc form has generally bcen
considered the best for the body which for the
displacement OF equal volume OF water because
Since "a whole meter can ne accurately measured "a
its tenth part, aud hence with greater pTopotohate
accuracy, is advantageous TO employ the large dn
sion in the experiment. limited however, by the facilities
temperature Oi maximum density OF water propose
to use cylinder having hight Of quarter meier ana
circumference OF meter The weight oi water III
placed by 10 viii be nearly % kDs, Which can De
weighed 10 10 mill NEUTRALITY-SUSPICIOUS. 10 half MILL
gramme IN a kilO, very sufficient precision.
But Il is in the way Of measuring the circumference
that the novelty OF plan resides. This Will TIC done
pairing It's length with that OF meter TIC parallel
positions OF the vertical diameter before and ait
revolution are known by delicate spIri'-ievei At
tached To the base OF the cylinder.
The two microscopes OF a comparatOr are hxed upon
next referred to a standard meter Tie two rails are
itte farther apart than half the length OF the cylinder
which may be rolled great number Of circumference
along ITS entire length, the degree OF accordance deter
miuing the frequency of the points OF measurement.
of at "A -
be- determined by reelection, as well as Its deviation
from paraiielsm during revolution. go
The steel centers on which the cylinder is turned Will
for cticcfin mo roIiin, in sfeadv mnuncr They ,iI
Likewise serve for the guidance OF coutactlevcr aud
rejecting apparatus by which the length OF the cynnder
along cOuceUc Ui distances between the bases
will he asccrtaaed.
Mr.. Lane proposes ascertain the exact volume Of
hollow sphere whose external aud internal suria es are
nearly aud coGceutrc by tho method OF determining
IT, moments ofrotaon three different da meters. aud
comparing them with those Of two cylindrical misses
disposed al equal distances from the axis OF Ylbr ion
OF the tOrsOG balance, the measure OF their distance
when they have nearly the same moment Of rotation ~
the sphere, anu tie tsuse OF Inc curve, beng the
elements OF pr cs0n, which can DC obtained Win very
great accuracy.
DISCUSSION on PROF HmGAFDs PAPER.
Mr.. Fhrman Rogers asked OF whag material Prot. III
gard proposed make the cylinder and the track or
would the width Of the track be in to ayod
great danger Of angular Displacement
Prof Higard replied that it would he quite difficult To
roll the cylinder ouJ OF position direct rolling motion
j: 80 much easl e than any siding mo'lGn. .,..,.
Mr. RDlcrs tnOugIt that there would be nothing 20 in
dcite whether the cylinder was truly cyliuducll or
partly clipic9l. The dancer in lathe tlgays OF
getting aH ellipse Instead OF cylinder.
l,J cor.iers N 90 f,r as IN courlud, INN no dril
ton from q crrular would be OF a small order
that the circumference would stlil be exact lie hoped
40 overcome tuai Objection. -,- -
Prpr Wqlcou Giops VI Harvard College asked "
sphere could not be constructed with more accurl
than cylinder. Every upucun knows that 10 construct
cylindrical lens iS ono OF the most dhcuit things &c
PROT Hilgard did not know the mechanical means by
winch an accurate whole sphere QUA possibly DC made
IlpI' CIV. 9uAI's' 'liI tn u1'iu Va ~ ~
spheres might be shifted continually on tue lathe lie
supposed that tine way IN when me japanese sue
coed IN giving such beautiful appearance ANA accuracy
to the quartz spaeres they tdrn.
Prof. Hi!Gard said that they could turn on each
diameter only single CHIP ~ II we're Ihoy wohH
have take thousand dlamcters 10 make The Sphero
Prot. Gibbs aso suggested that the tracks On wAch
the cylinder rolls must be ground TO perf CITY true
edge otherwise there would be variations IN tie 'esh
Pro-. Hlgard replied that thc variations woulf be
small and ~ee9naa Thy ~ a., yu en6ot
see light when they are put together, -, -
PROT Young don'iod II plane surface w'- really any
harder 10 uaGe than eynaIic.l or spherical one lis
suggested thata plane surface might ~ tested easlf
than cylindrical one lie Vcntured TO suggest tetra-
Prof MAYER thought that Tue difficulty would be to
Pro- Gibbs said that whenever you have solid
bounded by plane surfaces you hal hot ohy the d'l
Guilty OF making those surfaces perfectly plane Oit also
! of making the ANGLES absolutely true. 49,
Prof. Tman was called upOn for his opinion lie
confessed iLar Inc wag not practically acqu Inted with
this subject. He under the impression thai tic
cylindrical form wOull Do the best. lie could not sec
! how 4 true sphere could be made. -
/ Wr Rogers Thought there was difference between
making a true sphere aud truly spherical surface III
must mind that the lcuSnak docs not care
much about the thickness o has aus. What ne wants Is
"A spherical Surface. He thought th1t al eNp'fi.Iec
would go % that II piece OF metal j. moved rom
It's position In lathe almost Impossible u get on
tue center back again. In some o oht Dcsl ali"
shops they have got into the habit OF balancing pull y,
| which arc shafiing at a very ngh sPeed, "
turning them Of, not according to thrit hSaic nut
according their weight. II Is conferred IN the it"e ia
such manner that II II Is the least bt heavier on one
side than another II is easily seen lhe OJi't l. ~
get tie center OF gyratOn, on winch Tue pulcy
without and scrYccani tith on lhc h'IhS-
! NAUTICAL center Of lines from the circumference
Tue session then Adjourned % mee' to-norFo" al - ~