42 



PROCEEDINGS OF THE AJVIERICAN ACADEMY. 



for about a minute before coming to rest. This, like most of our other 

 apparatus, was constructed by Mr. G. W. Thompson, the mechanician 

 of the Jefferson Laboratory, and we have been much indebted to his skill 

 and patience at every stage of our work. A' is so truly hung that the 

 outside can be used as a pulley and the whole can be rotated by the use 

 of the belt shown in Figure 8. The vanes reach to about 2 millimeters 



Figure 11. 



of the floor of the box, and when the whole is filled with cracked ice and 

 then rotated, the ice at the bottom which rubs on Z soon gets and holds 

 a very smooth surface. A hole in the bottom of Z carries away the drip 

 and prevents any accumulation of water on the floor of the ice box. We 

 were at first troubled by irregularities arising from honeycombing of the 

 ice in the ice box, and to remedy this a suitably loaded brass tripod is used 

 to pack the ice by light blows delivered at intervals of 21 seconds, by the 

 aid of th-. lever L. A train of four wheels is necessary to reduce the 



