286 JOURNAL OF THE WASHINGTON ACADEMY OF SCIENCES VOL. 13, No. 13 
is tinted yellow. In this examination the pearl is supported on a wire 
extending into the hole to the center of the pearl. The wire is held be- 
tween the thumb and first finger in an upright position and the hole is 
examined with the aid either of a magnifying glass, a microscope, or a 
binocular microscope. The work of Galibourg and Ryziger® has 
demonstrated that with the aid of a microscope and a suitable mirror 
it is possible to detect differences in homogeneity of the material ex- 
posed along the hole drilled through the pearl. The mirror, which they 
employ, is the top of a mercury column, like that in a thermometer 
tube. The mercury is forced up through the hole in the pearl by a 
delicately adjusted apparatus and the reflections from the top of the 
mercury column are observed through a strong magnifying system 
(microscope or binocular). \ This‘method-is said to be very successful. 
The pear] is illuminated by a strong light from the side. The difference 
between the darker center and the enclosing pearl shell, especially at 
the boundary between the two, is clearly shown in the curved mirror. 
In applying this method, the writer has had difficulty in obtaining a 
uniform movement of the mercury column because of the capillary 
dimension of the hole and the tendency for slight obstructons to bar 
temporarily the passage of the mercury; in passing an obstruction, the 
mercury tends to flow rapidly and to advance by jumps rather than 
smoothly. The apparatus moreover is complicated and for purposes 
of this sort the handling of mercury is rarely satisfactory. ; 
The following simpler and equally efficient method may serve the 
same purpose. In place of the mercury column a small bead fused on 
the end of a pure gold wire is used. A short piece of fine gold wire 
(0.2 mm. diameter and about 1 em. long) is satisfactory; the bead is 
produced by holding the end of the wire in a Bunsen flame for a time 
sufficient to melt down the tip and formasmallbead. The gold bead 
thus produced is much smoother and presents a more perfect reflecting 
surface than does a silver or platinum wire bead, or the surface which 
can be formed by grinding and burnishing the end of a fine steel needle 
in a lathe. The gold bead can be silver plated if desired. In the 
writer’s experience, however, this is unnecessary. ‘The wire is held 
stationary in a vertical position with the bead uppermost between the 
thumb and forefinger, the pearl to be examined is held by the other 
hand and slid over the stationary wire so that the wire passes through 
the drilled hole. If desired, the wire and also the pearl can be held by 
mechanical device and the pearl moved up or down by a screw. ‘The 
pearl is illuminated by a strong light from the side. During this 
> The Watchmaker, Jeweler, Silversmith and Optician, pp. 1821-1823. 1922. 
