From: Walter Stafford <stafford@bbri.org>
  To  : rasmb@alpha.bbri.org
  Date: Fri, 20 Oct 2000 11:25:35 -0400

Re: "squashed" gaskets as centerpieces

Hi  RASMBers,

	If I remember correctly from my early days: the amount of
deflection of the beam goes as
A x B x dn/dr where A is the optical lever arm, B is the path throught the
solution and dn/dr is the refractive index gradient. So the magnitude of
the bending of the wave front will depend on the path  length as well as
the gradient. Therefore, the smaller optical path through the solution
should result in a decrease in the effect and althouight the skewing is
still there, the error is reduced proportionately by the smaller path
length. Getting the focus in the solution column in the first place would
seem to be the bigger problem especially with the short optical path of the
XL-I which requires much higher precision to position the lenses correctly.

Walter Stafford

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Walter F. Stafford III, Ph.D.
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Analytical Ultracentrifugation Research Laboratory
Boston Biomedical Research Institute
20 Staniford Street
Boston, MA 02114-2500
stafford@bbri.org
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