In  Roller  Pla.  radius  roller,  in. . . .     Pitch  radius  Gears,  No.  I No.  II

COMPARISON  WITH  STANDARD.
Aha.
1
I

Mean  Ordinate.
No.
Inst.  Reading.
0

Difference  from
Mean.
€

1

1  Inst.  Reading.
1             0

Difference  from
Mean.
€

r»

I

j

1

1

1

Mean

I
1

i

Mean  error  of  one  observation,  ±  %/St* -*-  (w  —  x)  in  area in  ordinate. .  .in.
Mean  error  of  result,  ±  tfSe*  -*-  *{m  —  x)  in  area. . .,  in  ordinate. .  .in.
Probable  error  of  one  obs.,  ±  0.67  jfSt* -M»  —  1)  in  area in  ordinate. .  .in.
Probable  error  of  result,       ±0.67  f^r* -*-«(«—  x)  in  area. ....  in  ordinate. .  .in.
39.  Errors  of  Different  Planimeters. — Professor  Lorber,
of  the  Royal  Mining  Academy  of  Loeben,  in  Austria,  made


48


EXPERIMENTAL  ENGINEERING.
[§39-


extensive  experiments  on  various  planimeters,  with  the  results
shown  in  the  following  table :


The  error  in  one  passage  of  the  tracer  amounts  on  an  average  to
the  following  fraction  of  the  area  measured  by —

AXKA  IN—

iThe  ordinary
Polar  Plan-
imeter  Unit
of  Vernier:

to  sq.  mm.  =
.015  sq.  in.
Stark's  Linear
Planimeter
Unit  of  Ver-
nier:
z  sq.  mm.  =
.015  sq.  in.
Suspended
Planimeter
Unit  of  Ver-
nier:

1  sq.  mm.  =
.0015  sq.  in.
Rolling  Planimeter—

Square
cm.
Square
inches.
Unit  of  Ver.
nier:
1  sq.  mm.  =
.00x5  sq.  in.
Unit  of  Ver-
nier:
1 .1  sq.  mm.  =
|  .0001  sq.  in.
