NOTES AND CORRESPONDENCE. 
Dr. Beale’s Glass Reflector—I have made several glass 
reflectors of various kinds and different thicknesses of glass, 
for drawing and measuring objects, after the plan of Dr. 
Beale. None of them were made, however, of neutral tint 
or coloured glass. There is a peculiarity attending them, to 
which I wish to direct attention, as I have not seen it noticed 
before. I had made several of glass from +, to + thick, but 
I could not at first get quit of the double reflection from the 
two surfaces of the glass, which rendered it impossible to 
draw or measure objects satisfactorily. I found, however, 
after many trials, that with every piece of glass I used there 
are two positions in which it may be placed distant 180° from 
each other, in which the glass reflects only one image to 
the eye, and in this position, therefore, the glass reflector 
must be placed. This position may easily be found upon 
trial for each piece of glass, as upon looking at the reflected 
image of a window, for instance, by turning the glass round 
in the position it would be placed were it arranged for 
drawing, the two reflected images of the bars of the window 
will be found to converge into each other, and at the proper 
place disappear into one, and this will take place twice in 
one revolution. I understand the difficulty caused by the 
two images or double reflection suggested the use of thin 
glass for the purpose, but the method I have indicated is 
simple, and so perfect as to render it equal to, if not superior, 
to a camera lucida. Iam not aware if any of your readers 
are cognisant of this peculiarity, but, perhaps, some of them 
may inquire into and explain it.—W. Forean, 3, Warriston 
Crescent, Edinburgh. 
_ Growing Slides—The American growing slide described 
in the ‘Annals of Natural History’ for November, and 
mentioned in the discussion at the last meeting of the 
