Beck, on an Improved Growing CelL 
35 
the old principle of the bird fountain. As the water evaporates 
from under the cover^ more is supplied through the hole^ 
and from time to time an air bubble ecters at b ; thus a con- 
stant circulation is maintained/^ 
This arrangement has^ I think^ one or two disadvantages. 
When the water sinks as low as the position of the object, 
the water line may become a considerable annoyance in 
viewing the object, and in those cases when it is necessary to 
use impure water there must be a considerable obstacle to 
the best illumination. I also think there will be a difficulty 
under some circumstances in cleaning the trough thoroughly. 
The plan I now propose is as follows : — An annular glass cell 
(fig. 1), formed by cementing two glass rings (a and b) upon a 
circular piece of glass [c), with, a central aperture (d) the size 
Fig. 2. 
of the smaller ring, is securely fastened into a brass plate 
(fig. 2, e)y which has a projecting ring, on which a screw is cut ; 
upon this a cap (g) screws and fastens down an upper circular 
glass plate, which is provided with the two necessary holes, 
and a ledge (h) for the thin glass. By this arrangement there is 
no more than the ordinary obstruction to the illumination. 
The supply water can never come across the field of view, and 
the piece of apparatus can be taken to pieces in a minute, 
either for adding fresh water or for thoroughly cleaning the 
cell. 
Mr. Smith only mentions the suitability of the growing 
trough for small objects such as can be retained under the 
ordinary thin glass, but by employing a cell of between one 
and two-tenths of an inch in thickness, or more, upon the 
upper plate, a considerable quantity of water may be pre- 
served ; his contrivance is therefore equally well adapted to 
comparatively large objects, and it is impossible to tell at 
once how far its sphere of usefulness may extend. 
