720 



PROCEEDINGS OP THE AMERICAN ACADEMY. 



Experimental Method. 



The apparatus finally adopted for the experiments is sketched in Fig- 

 ure 1. For the thermostat a mixture of sodium and potassium nitrates 

 was used, contained in a cylindrical vessel of enamelled iron ("agate 

 ware"), about 30 cm. in diameter and 25 cm. in height, — A in Figure 1. 

 This vessel rested on a tripod, and was heated from below by two Bunsea 

 burners. The heating efficiency and the constancy of the thermostat were 

 surprisingly increased by a sheath of asbestos (B) surrounding the bath 



Fig u UK 1. 



and projecting 10 or 15 cm. below it. This sheath was separated al)out 

 .V cm. from the sid(; of the vessel by a number of corrugated brass strips 

 not shown in the figure. An annular space was tiiiis left between 

 the asbestos and the bath through which the hot gases from the burners 

 could pass freely, and thus heat the thermostat from the sides as well as 

 from below. The careful adjustment of this sheath seemed to be almost 

 essential to the satisfactory operation of the thermostat. 



