18 Piper, on a Form of Slide for Opaque Illumination. 
without necessitating the disturbance of the slides. In addi- 
tion to its portability, it possesses the merit of cheapness, 
durability, and neatness of appearance. 
It may be obtained in its various forms from all the lead- 
ing microscope makers in London. 
On a Form of Slide for Opaque Illumination. 
I would also beg to oiler to your consideration a form of 
slide which meets a want frequently felt in mounting opaque 
objects for the binocular microscope, so that they may be ex- 
amined without the intervention of a glass cover, and, at the 
same time, to have adequate protection against the intrusion 
of dust or other foreign matter when not in use. 
It is especially adapted for botanical or geological speci- 
mens, and for objects of considerable thickness requiring a 
deep cell. 
It consists of the usual mahogany slide, with the addition 
of a thin circular disc of bone or other convenient material, 
which is attached on one side of the central cavity by means 
FIG. 2 
a, Mahogany slide ; b, central cavity ; c, covering disc (turned 
aside), bearing descriptive label; d, pivot on which the cover 
rotates. 
of a split metal rivet, the ends of which are turned outwards, 
on the underside, before the black paper and cardboard 
bottom are applied ; this rivet acts as a pivot, on which the 
cover rotates, so that it can be instantly turned aside for the 
display of the object, and as readily replaced when the slide 
is returned to the cabinet. The cover is also available for 
the application of the label bearing the name and description, 
and can be applied in a few minutes, at an increased cost of 
about twopence per dozen upon the price of the ordinary 
slides. 
By substituting a thin glass instead of the cardboard 
bottom it may be used for Lieberkiihn illumination. 
