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 removalile wooden grating, a copper tank (a) 

 flUed 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 ver;y cold weather this heating tank was supplemented by a pair of 32-candle- 

 power electric lamps (d) with blackened liulbs suspended from the middle of the roof 

 of the chamber and partially enclosed in screens to prevent local and unequal heating 

 of the chamber. Resting on the floor of the chamber above the tank Avas 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 supportirg the eggs. Th? adjustable egg-carrier allows one to regulate 

 the distance between eggs and radium. 



