This is the first of a series of notes to be published by the officers
in order to keep the members informed of the activities of the society and of
the different members.  These notes will also contain a summary of some useful
techniques which can be applied to many of the microscopical specialties.  The
technique chosen for this note is the Rheinberg Differential Color Illumin-
ation.

     The officers are very much concerned about the very poor attendance at
some of the monthly meetings.  It is expected that the attendance will vary
from season to season and that the meetings must compete with other interests
of a busy person, but the attendance of only ten people to a carefully prepar-
ed program by a well known expert is a serious matter.  The problem of getting
members to serve as officers, particularly in the more unpopular posts of sec-
retary and treasurer is not fair as the work involved in these posts dilutes
the pleasure that the appointed member gets from belonging to the society.  At
the present time the office of treasurer is vacant; are there any volunteers?

     The officers are trying to reorganize the activities of the society to
give more to the members at less work to themselves.  The new style meeting
announcement is one step and this series of notes is another.

     Those members who saw the very fine film on the Phase Contrast Microscope
that was all too briefly shown in the area by Mr. W. H. Hartmann, 1508 Divisa-
dero Street, are still remarking on the simple pictorial explanation of phase
contrast.  The film was produced by the English firm of microscope builders,
Cooke, Troughton and Simms, Ltd. x x x x x x Mr. Arthur T. Brice tells us that
he is finally ready to make lapse-time motion pictures under the name of Phase
Films x x x x x x Silge and Kuhne have now moved into their new quarters at
375 Sutter Street and they are very pleased with themselves about how well
their plans turned out x x x x x x There are a few members who regularly take
stereo-photomicrographs and their experiences would make an interesting future
note if enough members are interested.

THE RHEINBERG DIFFERENTIAL COLOR ILLUMINATION

     The Rheinberg method of illumination is similar to that of dark-field ex-
cept that in the Rheinberg method the dark-field stop has been changed so that
the central opaque disk stop is substituted by a colored filter disk and the
peripheral ring around the disk stop is a filter of contrasting color.  When a
colorless object is put into a microscope field illuminated by the Rheinberg
method it will stand out brightly against the background with an intensity de-
pendent on its refractive index, reflecting power, size and quantity of light
incident upon it.  The result is known as optical staining and it gives effects
of extraordinary beauty.  The sketch shows the method of obtaining this illum-
ination with a microscope equipped with an ordinary Abbe condenser.

     The Rheinberg method is especially recommended for the examination of
mineral and chemical crystal fragments, diatoms and small living organisms such
as rotifers, water fleas and unstained plant sections.  The method is also a
good method of regulating contrast in photomicrography.

     The Rheinberg stops are easily made from colored gelatine filters used in
photography and the pieces of gelatine can be cemented on a dark-field stop
with a hole punched in the blank central disk or cardboard disks cut to fit the
condenser ring.

     It is recommended that the first collection of Rheinberg stops include the
following color combinations, a blue center stop with a red peripheral ring, a
green center stop with a red peripheral ring, a blue central stop with a white
peripheral ring, and an opaque center with alternate red and blue sectors in
peripheral ring.  The sector stop is useful in illuminating striae and ridges
against a dark background.  It is recommended that the gelatine be of the deep
colors so that they will give enough color contrast with the intense illumin-
ation usually used with the microscope.