The Washington times., 1922-06-05
of
Solid or
Liquid
BY Garrett p. Serviss,
Eminent Astronomer and Authority
on Subjects Of Scientific
interest,

Ekuitntnt AbtrOnOfifrT uuo hutnurty
on Subjects Of Scientific
Interest.
Please explain In nonikchni.
cal language what specific gravi.
ty means.-H. OH, Philadel
CTATED in the simplest way.
the specific gravity OF any
~ solid or liquid substance is
its weight as compared with the
weight of an equal volume OF
water. Numerically IL IL the same
thing as density. 1t is a ratio, or
relative value, determined by COM
parison with an arbitrary standard,
the chosen standard being water
except in the Gaze Of gases, when
the standard Is usually air. The
specific gravity Of the human body
is very near unity, i. e., the same
as that of water, which Is the rea'
son why 1t is easy TO swim.
The textbooks on physics will
beautifully mix up your ideas on
the subject. and generally speak
ing the later the text the more in
compr prehensible the presentation
appears TO the unmathematical
reader, though II you get com
mand Of the shibboleth 1t 10 easy
enough.
Most people do not care for the
shibboleth. which, however. 10 NOT
a reason why the matter con
csrned should not be perfectly un'
derstood by them. There 10 un'
questionably too much technicaltty
used n ordinary scientific teach
ing. 1t either repels the student on
narrows his intelligence. II breeds
both master investigators and IN
tellectual priss.
II I have a Cubi" foo CT walcCt
and a cubic foot of lead and throw
them both into q pond OF water,
the wood floats and the lead
plunges to the bottom. because tne
wood weighs less and the lead
more than q cubic foot of water.
Now, the water weights Sky
two and one-half pounds per cubic
foot, and, knowing that fact. l DC
not need anything more 10 tell IN:
how much the upward pressure OF
the water will diminish the weight
OF a body of known volume inst
is suspended in II.
II the lead instead Of being al
lowed to sink to the bottom is sus.
pended underneath the surface OF
the water from a Weighing ma.
chine, II will be found 10 have
sixty-two and one-half pounds sub
tracted from the weight that II
shows when weighed out OF the
water. Since a cubic foot Of lead
weighs 40 pounds, II weighed in
water it's weight will be dimin.
ished to 647h pounds.
A man weighs say, 200 pounds,
but in water. and especially ir pcs
water, which is denser than rure
water, he will float totally i'm
mersed except his nose, because
his specific gravity is about tn
same as that Of the water. and the
pressure OF the latter counterh~d.
ances his weight.
But, that being so, the volume,
1. e., the number OF cubic fesI Tor
inchesl occupied by the mans
body-a thing that II would he DIFF.
ficult to calculate from reaaurr.
ments-is easily ascertatned. SIN.
ply divide his weight out OF water
by the weight OF q cubic foot OF
water. Suppose the water is sea
water weighing $50 pounds PER
cubic foo then divide 700 by $50
and the quo.Ient, 3.l3. shows the
cubic content, or bulk Of the mar.
II some sculptor wanted TO find
out how much lead II would take
to cast a statue OF this man OF eX
actly life size. he would only. have
TO try the experiment Of floating
him in water. The weight OF a
cubic foot Of lead, 10 pounds, mCl.
-
pounds as the required amount ct
lead
But now to return to the lead
and the wood. Since the lead
weighs 7lo pounds out of water,
and loses San pounds wh IN sus.
pended in water, II we divide the
former by the latter we get 1874,
which Is the number Of times that
the lead outweighs it's own volume
OF water, so that, according TO our
definition, 11.34 10 the specific
gravity Of lead.
Then consider the cublc foot of
walnut II weighs less than
cubic foot OF water, as is evideHt
by the fact that II floats without
being totally immersed. In fact.
a cubic foot Of walnut weighs only
thirty.six pounds. 10 ascertain
its specific gravity we divide its
weight out OF water by the weight
of a cubic foot Of water. getting
for answer o.676, which fraction Is
the specific gravity Of walnut.
This fraction also tells us what
proportion Of the cubic foot Of
walnut 10 Immersed whom II floats,
and IL We directly meAsureI that
x,t. yaYld ~.t the anenlftN era NitN