16 THE VIVARIUM. 
covered with felt. A door made of perforated zinc, (see D) is 
useful for both ventilation and the regulation of heat. The backs 
and sides (within) of the cases a and c, are covered with paper of 
a suitable tint, or painted. The outsides of the cases, the backs, 
top, and sides are protected with felt of some pleasing colour. 
And a curtain of the same material is arranged to fall over the 
front of the cases on very cold nights. Strips of felt ought also 
to be nailed on the edges of the cases (£) to prevent the escape of 
heat between them and the glass. 
The glass fronts of these Vivaria are made to slide to and fro. 
The glass will not jam in the grooves if 
the gravel which covers the bottom of the 
cases be of the size of peas. If sand or 
unsifted gravel be used, some of it is sure 
to get into the lower grooves and cause 
the glass occasionally to stick. To pre- 
vent this, the grooves at the bottoms of 
the cases ought to be so formed that any 
sand or gravel which may be thrown into 
them will drop away from the glass. This 
can be done by making each groove of two 
laths of about tin. thick. The laths are 
kept at the right distance apart by means 
of little strips of wood which run perpen- 
dicularly from the bottom of each lath to 
8. — INTERIOR OF 
THE BOILER CASE. 4, 
Fic. 
Larger Boiler; B, Saw- 
dust to prevent un- 
necessary loss of Heat; 
Cc, Opening through 
which the Heat can both 
Ascend and Descend; D, 
Small Boiler; £, Filling 
Pipe. 
within a 4in. of the top of each. To these 
strips the laths are nailed. The ends of 
the strips of wood over which the glass 
sides run should be slightly rounded at 
the corners to prevent unnecessary friction. 
These strips may be placed about every 
4in. The bottom of the groove being open, all sand, gravel, and 
moisture will drop through or down; and the glass sides always 
run freely and easily. The upper grooves may, of course, be 
formed in the ordinary way. 
These cases (Fig. 6) are made to stand on a table or some 
similar support, and face a sunny window. When the water in 
the boiler becomes quite hot, a very little flame is sufficient to 
