66 Scientific Proceedings, Royal Dublin Society. 
As it is obviously an advantage that the oculist should retain 
a record of the obscurities delineated from time to time by the 
patient, and photographic printing of the drawing on ground glass 
involves a little trouble, a direct tracing on paper can be made 
by the patient.1 For this purpose the ground glass G, Plate III., 
fig. 2, is lifted out of its clips, and a piece of clear plate-glass of 
the same size is substituted. On this a piece of tracing-paper 
cut to the exact size is held by the spring-clips S, S. The tracing 
paper is ruled as shown in fig. 5; the object of this is to enable 
the image of the pupil to be drawn more easily, by making the 
intersection of the cross-lines the centre of the projected image 
of the right or left pupil. 
Fig. 4. 
It is convenient to know the exact retinal area shadowed 
by the obscurities at any given time, so that the rate of progress, 
or amendment, of the defect can be determined. This is accom- 
plished by having the tracing-paper printed in very faintly-ruled 
5 mm. squares, such as are shown in part on the right hand of 
fig. 5. Upon counting the squares covered by the drawing of 
1 There is also a disadvantage in a photographic print of the tracing on ground 
glass, that it Jaterally inverts the shadows that are drawn, unless the print be taken 
through the glass, when it is of course less sharp; moreover the tracing-paper can be at. 
once named and dated, and stuck in the practitioner’s case-book for future reference. 
