656 PROCEEDINGS OF THE AMERICAN ACADEMY. 



what smaller above, so as to leave an air-space between it and the walls 

 of the pot. 



In order that the holder might be easily rotated, a pin soldered to a 

 thin diametral web F which ran across the bottom of the holder was 

 inserted in U, and a vertical brass rod soldered to a similar web, E, at 

 the top of the holder passed through a hole in the cover of the pot which 

 it fitted closely. An ebonite thimble fitting tightly on the rod and turn- 

 ing with it, permitted the slow entrance of ice-cold air into the pot with- 

 out allowing any water to leak in. The rod could be clamped at pleasure 

 to a brass yoke which is turned slowly by the electric motor. In order 

 to prevent the introduction of heat into the pot by conduction down the 

 rod, the exposed portion was buried in cracked ice. When the holder was 

 filled with ice and turned by the motor, the web at the bottom compelled 

 the ice to rub over the floor of the casting, since the holder itself had no 

 bottom ; and as a result of this, the lower surface of the ice quickly 

 acquired and kept a mirror-like surface. The drip from the pot came 

 out of the edge of the casting Z through a straight hole about 26 cm. 

 long and 6 cm. in diameter drilled horizontally in the plate and ending 

 just inside the pot. The whole apparatus was very slightly tipped to 

 insure the steady outflow of the drip. 



A large cylinder K, 35 cm. high, made of rolled brass 4 mm. thick 

 and open at the top and bottom, was mounted on brass ball-bearings 

 placed on the outside of the hard rubber jacket of the pot, P, by means 

 of six vanes, one of which, X, is shown in Figure 2. K weighed about 

 twenty kilograms when empty, and rested u^iou 144 brass balls each 12 

 mm. in diameter. When set in motion by a slight push ^continued to 

 rotate for about a minute before coming to rest ; it was so truly hung 

 that the outside could be used as a pulley and the whole rotated by 

 means of the belt shown in Figure 1. The vanes reached to within 

 about 2 mm. of the floor of the casting, and when the whole was filled 

 with cracked ice and then rotated, the ice at the bottom which rubbed 

 on Z soon got and held a very smooth surface. 



A hole in the bottom of Z carried away the drip and prevented any 

 accumulation of water on the floor of the ice-box. To prevent irregu- 

 larities arising from honeycombing of the ice in the box, a suitably loaded 

 brass tripod was used to pack the ice by light blows delivered at inter- 

 vals of about twenty-one seconds by aid of the lever L. A train of wheels 

 was necessary to reduce the speed of K t,o one revolution in twenty sec- 

 onds, though only two wheels are showti in the drawing. The tripod 

 slid in guides which revolved with K, and a swivel at the top prevented 

 the cord from twisting. 



