APPARATUS, MATERIAL, AND REAGENTS. 35 



removed, and the water-chamber filled completely with 

 distilled or rain water at the temperature required. The 

 caoutchouc plug is replaced and the tube placed in position. 

 Gas enters through d (Fig. 17), and passes through the 

 opening at its extremity into the chamber of the box. 

 Thence it passes through the vertical exit which is connected 

 with the gas burners. As the temperature rises the water 

 rises in the tube, and at the same time exercises a pressure 

 on every part of the walls of the incubator, and hence on 

 the diaphragm. In consequence of this, the diaphragm 

 bulging outwards approaches the end of the tube d, and 

 gradually diminishes the gas supply. As a result the 

 temperature falls, the water contracts and sinks in the 

 tube, and the diaphragm receding from </, the gas supply 

 is again increased. By adjusting the position of the tube 

 d to the diaphragm, any required temperature within the 

 limits of the working of the apparatus can be regulated to 

 the tenth of a degree ; provided, (i) that the gas supply is 

 rendered independent of fluctua- 

 tions of pressure, by means of a 

 gas-pressure regulator, (2) that the 

 height of the water in the tube 

 is controlled daily by the with- 

 drawal or addition of a few drops 

 of distilled water, and (3) that 

 the apparatus is kept in a place 

 with as even a temperature as pos- 

 sible, and sheltered from currents 

 of air. 



The burners in Fig. 16 are pro- 

 tected with mica cylinders similar 

 to the burner represented in Fig. 18. 

 The flames of these burners can be turned down to 

 the smallest length without danger of extinction, and the 

 temperature may be regulated very satisfactorily without 

 using the heat regulator just described, if the gas first 



FIG. 18. 



GAS BURNER PROTECTED 

 WITH MICA CYLINDER. 



