40 PROCEEDINGS OP THE AMERICAN ACADEMY. 



wooden disk turned to fit it, and a central pin inserted in H, and was 

 then soldered firmly to Z. This was accomplished, after many trials of 

 other materials, by the use of white pitch as a flux, and the result left 

 nothing to be desired. The walls of the pot tlius formed were jacketed 

 on the outside, except for a height of about 2 millimeters at the bottom, 

 by an inch thick casting of hard rubber made for the purpose in the 

 form of a cylindrical shell. This casting, which was cut off square at 

 the tO}:) of the pot, tapered to nothing near the bottom, but did not rest 

 upon the floor. (Figure 10.) Upon the top of this jacket was fastened 

 a hard rubber cover shaped somewhat like a cylindrical hat. This had 

 an opening at the top which could be closed by an accurately fitting 

 rubber plug. In the box P, thus made, is placed a thin-walled ice 

 holder, ^>, open at top and bottom, of the same outside diameter below 

 as the inside of the brass pot, but somewhat smaller above, so as to leave 

 an air space between it and the walls of the pot. 



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

 thin diametral web, F^ which runs across the bottom of the holder, is 

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

 the top of the holder passes through a hole in the corner of the pot 

 which it fits closely. A hard rubber thimble fitting tightly on the rod 

 and turning with it permits the slow entrance of cold air into the pot 

 without allowing any water to leak in. The rod can be clamped at 

 pleasure to a brass yoke which is turned l)y the motor. In order to pre- 

 vent the introduction of heat into the pot by conduction down the rod, 

 the exposed ])ortion is buried in cracked ice held in a thin m(!tallic cup 

 carried by the yoke and resting on it. When the holder is filled with 

 ice and is turned by the motor, the web at the bottom compels the ice 

 to rub over the floor of the casting, since the holder itself has no bottom, 

 and as a result of this, the lower surface of the ice ipiickly acfjuires and 

 keeps a mirror-like surface. The drip from the pot comes out of the 

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

 0.6 cm. in diameter drilled in the plate afld ending just inside the pot. 

 The whole apparatus is very slightly tilted so as 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, is 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 9. K weighs about 20 kilo- 

 grams when empty, and rests upon 144 brass balls each about 12 mm. in 

 diameter. When set in motion by a slight push, it continues to rotate 



