THE INCUBATOR. 127 



for showing the level of the water between the walls. 

 The object of the water chamber, which is formed by 

 the double wall arrangement, is to insure, by means of 

 the warmed water, an equable temperature at all parts 

 of the apparatus — ^at the top as well as at the sides, 

 back, and bottom — and the apparatus should be kept 

 filled with water, otherwise the purpose for which it is 

 constructed will not be accomplished. When the cham- 

 l>er between the walls Ls filled with water heat is suj)- 

 plied from a gas-flame placed beneath it. 



Fig. 31. 



Koch's safety bamer. 



The burner employed in heating the incubator was 

 originally devised by Koch, and is known as '' Koch's 

 safety burner" (Fig. 31). . It is a Bunsen burner pro- 

 vided with an arrangement for automatically turning 



