4 BECK, ON ILLUSIVE APPEARANCES. 
Having removed some scales from the imsect on a glass 
slide as already described, cover them with a piece of thin 
glass, which may be prevented from moving by a little paste 
at each corner. Fig. III may then be taken as an exaggerated 
section of the various parts. 
A B is the glass slide with a supposed scale, C, closely 
adherent to it, and D, the thin glass cover, secured to A B 
by avery little paste at the corners, The object thus prepared 
should then be placed under a high power, the + and No. 3 
eye-piece, with the achromatic condenser illumination, an- 
swering well. 
If under these circumstances a very small drop of water 
Fie, IIL 
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(E) be placed at the edge of the thin glass, it will ran under 
by capillary attraction, but when it reaches the scale (C), it 
will run first between it and the glass slide A B, because the 
attraction there will be greater, and consequently the 
markings on that side of the scale which is in contact with 
the glass slide will be obliterated, while those on the other 
side will for some time at least remain unaltered ; when such 
is the case the strongly marked vertical lines disappear, and 
the radiating ones become continuous (see fig. I, the lower 
left hand portion). 
To try the same experiment with the other or mner 
surface of the scales, it is only requisite to transfer them, by 
pressing the first piece of glass by which they are taken from 
the insect, upon another piece of glass, to which a few scales 
will adhere, and then the same process as that already 
described may be repeated with them, when the radiating 
lines will disappear, and the vertical ones will become 
continuous (see fig. II, left portion). 
These results therefore show that the interrupted appear- 
ance is produced by two sets of uninterrupted lmes on 
different surfaces; the lines in each instance being caused 
by corrugations or folds on the external surfaces of the ~ 
scales. 
Whilst some may like to try this experiment for themselves, 
others will be satisfied with the appearance which a few scales 
are almost sure to present in every slide that is mounted. 
Figs. I and II already referred to are parts of a camera lucida 
drawing of a scale which happened to have the opposite 
