A MICROSCOPE-STAGE INCUBATOR. 327 



which, although imperceptible, is yet capable of demonstration ; 

 for by holding the bulb of a delicate thermometer in the various 

 parts of the incubator the different degrees of temperature are 

 clearly indicated. I have found it advisable to immerse only 

 about a half or two thirds of the incandescent lamp, for in this 

 way the circulation of the water is greatly facilitated. 



In constructing the tank, a small pipe {p-p') was soldered 

 into the side of C, so that in case the water did not cool here 

 with sufficient rapidity, a cold stream from a tap or reservoir 

 could be run through the pipe, thus insuring a constant current 

 throughout the three apartments. This precaution was later 

 found unnecessary, at least for temperatures at which the bird's 

 egg incubates. 



When the incubator is arranged as described above the tem- 

 perature of the water in the region of the egg-cell does not vary 

 over 0.2 C, a variation practically negligible for all ordinary 

 purposes. However, if it be desired to maintain a temperature 

 even more constant than this, it could easily be done by making 

 the regulator more sensitive in the ways suggested by Mast, and 

 by constructing the tank so as to prevent the loss of heat, by 

 radiation. 



This, tank, which measures thirteen inches long, seven wide, 

 and six and a quarter high, can be made by any good tinsmith, 

 and the apparatus with all its fixtures can be had at a cost not 

 to exceed five or six dollars. 

 University of Chicago. 



