New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1894-09-24
A NEW MEASURE FOR ELECTRICITY.
DR. CREHoRE's METHOD OF GETTING RECORD
WITH POLARIZED LIGHT.

DR. CREHoRE's METHOD OF GETTING A RECORD
WITH roLARIzED LIGHT.
Most Of the Instruments in actual for measur.
Ing the exact amount OF electric current flowing in
a conductor give indications at any instant when
certain connection is made. which may be done every
few minutes This method yields fairly satisfactory
results. but is precise as might be and does
not afford continuous record. Al, Of the inven-
tons for securing the latter object until very
Gently have required that some small object having
weight, Ike a mirror or diaphragm. shall be moved.
Such a pan. for an alternating current especially.
has its advantages But the last general meeting
OF the American Institute OF Electrical Engineers
DR.. Albert II. Crehore proposed a method which IL
free from the latter objection, and while not de-
veloped completely. looks II It might possess
practical value.
The underlying principle OF this plan is an OLD
one: the application is new. When beam OF
light ha: been "polarized" by passing through /
Nicol prism 1t will readily go through another such
PRISM provided that the latter Is held in pre-
scribed position. To secure the utmost brlancy 1t
is necessary that certain plane in the second
crystal Ohe analyzer; be exactly parallel with the
corresponding plane In the first CHE polarizer):
but II the analyzer be turned on its axis quarter
way around in either direction the ray will be
tnguished. Faraday discovered. however. that II
the medium through which the light passed after
polarization be magnetzed In certain particular
manner the beam would oe affected just II the
analyzer had been rotated. Thus. II the two in
struments placed short distance apart, and
the analyzer were set so that the polarized ray
would come through and appear on q screen with
the highest intensity which 1t was capable Of
hibting magnetization Of the transparent medium
between pair would diminish the brightness OF
the light. II 4 andlyzer were turned so as 10
obliterate the BEAM magnetism would render IL
NOR" or less visible. DR.. Crehore took for his ex-
pertinent glass tube twenty seven inches long and
filled with bi-sulphice OF carbon a fluid not only
exceedingly clear. but also possessing some other
desirable properties The tube mad i Nlcol prism
a each end. and was wound for about two feet Of
length with six layers Of insulated copper wire.
When the currer; was 'ent through this coil. the
bi-suphiie magnetized ond the lines OF mag
the direction OF the beam to be experimental with.
Now II white light be sent through such apparatus
before the current Is turned on that which would
appear the screen. and which would fade and
be white. But when e.ectpcity Is sent through the
coli, its rotatonal influence Is different for each
OF the constituent co.ors. Hence. II the light be
projected through a small slit. rainbow may then
be produced; and dark streak across H. represent
ing the total extinction OF some color or shade
OF color, may be produced by setting the analyzer
developed about midway between the extreme red
and vioet. Alterations OF the current then caused
the dark streak 10 osci.lae regularly from one end
OF the spectrum TO the other. Its position always
ment has been found to be approximately proper
tona, to the current.
The vibrating signal has not as sharp edges. Dr.
Crehore says, might be desired. and Photographic
Plates which would register its fluctuations would
need TO be very sensitive. Besides, the method 10
better adapted TO showing the direction Of any
variations in the current than the amount OF the
current. But h. has gotten rid OF the element Of
weight and provides for continuous register. and
when certain details are perfected. the plan may
prove highly ssrviceab.e .....- 49,