350 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
Fig, 3. 
Fig. 4. 
Fig. 3. Interior view of constant-temperature chamber with double walls, the 
double-glazed glass door open. This cubical chamber measured about twenty inches 
to the side, and contained, below a removable wooden grating, a copper tank (a) 
filled with water heated by an electric coil regulated by an automatic device (6) depend- 
ing on the expansion of a curved metal strip for making and breaking the circuit. 
In very cold weather this heating tank was supplemented by a pair of 32-candle- 
power electric lamps (d) with blackened bulbs suspended from the middle of the roof 
of the chamber and partially enclosed in screens to prevent local and unequal heating 
of the chamber. Kesting on the floor of the chamber above the tank was a thermo- 
graph (c), and the support (e) for radium, eggs, and a small reservoir for moistening 
the eggs. 
Fig. 4. Enlarged view of the support (e, Figure 3), showing the base (a), on which 
rests the lead cell (b) containing the radium, the two cylindrical posts supporting the 
movable carrier for the eggs (c), and a movable glass-tube water reservoir (d) termi- 
nating at one end in a fine nozzle, from which a plug of fine threads leads to the moist 
filter paper supporting the eggs. The adjustable egg-carrier allows one to regulate 
the distance between eggs and radium. 
