Mr Tait on a Portable Diorama. 143 
I shall now describe the apparatus in detail. 
1. The Box.—Stretching frames are to be prepared for re- 
ceiving the paper or linen on which the pictures are to be exe- 
cuted; and as these are confined within the inner edges of 
them, the frames ought to be made thick and narrow, so as 
not unnecessarily to increase the width of the box, and should 
be bevelled off to allow access to the brush in painting the 
back. Those frames are inserted in succession through a slit 
in the top of the box, about two-thirds distant from the front, 
and are received into a groove projecting from the top, sides, 
and bottom of the box, of such a breadth as fully to cover 
the front of them. 
Two openings, one above in front and the other behind, 
admit the light ; and both should be as large as possible. The 
front opening ought to be of the form seen in the figure, in 
order to admit the light gradually ; an erect right angled tri- 
angle, with its base across the breadth of the box, being 
placed immediately behind the front-opening to aid this ob- 
ject. The openings have a ply of fine tissue-paper, Persian 
silk, or other appropriate material, placed over them, to dif- 
fuse the light. This is moveable, and is usually white, but 
may be of an orange, purple, blue, or other tint for particular 
purposes; and one or two plies may be used according to cir- 
cumstances. The shades for the openings may be made to 
open and close in any manner found conyenient, but so as to 
exclude all light when closed. 
The small opening in the front, through which the pictures 
are to be viewed, ought to be opposite to the ordinary height 
of the horizon of pictures, perhaps about a third or a fourth 
part of their whole height. A small tube of about two inches 
in length, is fixed before that opening. The outer end is to 
be about an inch and a quarter in length, and about an inch 
in height, and is to be made to fit the eye, so as to screen it 
from extraneous light; while its inner end must expand into 
an oblong opening, so as to allow the spectator to view the 
entire picture. The tube may be made to receive lenses to 
magnify the pictures if desired. The internal end of this tube 
must be so constructed as to prevent light from above shining 
into it. 
The inside of the tube, and every part of the box seen 
