Jan 27, 2009
        Measurements of the magnetic field at the center of the solenoid
with a Hall probe give a field 2% larger than the field given in the
lab writeup.  Med Webster recommends that you use this correction
factor and assign a 1% error to the magnetic field times effective length.
Work on the calibration of the Hall probe continues.

        The windows previously used have been found to have a small amount
of optical activity.  New fused quartz windows have been purchased, but the
mounting method had to be changed.  The windows are now on the outer surface
of a notch turned into the end caps.  The machine shop length measurements
are thus no longer applicable.  You will need to measure the length.  The
thickness of the new windows is 1/8 inch with an error negligible for your
purposes.
   The effective length in the magnetic field has been integrated for
a range of lengths of the liquid and the results are shown in the table:
       liquid length   effective (magnetic) length
         0.2440 m   0.21507 m
         0.2450     0.21546
         0.2460     0.21584
         0.2470     0.21622
         0.2480     0.21658
         0.2490     0.21694
         0.2500     0.21728


     Is it useful to measure the rotation for both field directions?
Explain.


The Verdet constant is slightly temperature dependent:
   V=V_20 ( 1. - [153*(T-20) + 3.06*(T-20)**2]*10^-6)
where V is the constant at temperature T and V_20 is the value at 20
deg C.  V_20 is 0.0131 min/G-cm.  I have taken the temperature
dependence from the International Critical Tables, Vol 6 p435.in the
section on MAGNETO-OPTICS, by A. Cotton, A. Lucas, and M.Cau.  It is
on the web at:
http://www.knovel.com/web/portal/basic_search/display?_EXT_KNOVEL_DISPLAY_bookid=735
    (Note added Jan 16, 2009 - This web site has been rearranged and I cannot
find this reference there now.)

    Be sure to measure the temperature of the water after completing the
measurements so you can see if temperature correction is necessary for
your work.

The measurement of V_20 was done by Francis Slack and is reported in the
Physical Review, Vol 46, p 945. (1934).  It was measured as part of
the effort to study the difference between heavy water and water.  Slack
was a Professor of Physics at Vanderbilt and Chair of the department here.
He endowed the Slack Lecture held here annually.