24 



Prof. B. Osgood Peirce on the 



the pot, tapered to nothing near the bottom, but did not rest 

 upon the floor (fig. 4). Upon the top of this jacket was 

 fastened a hard rubber^ cover shaped Fio . 4 



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, Q, open at top and bottom, 

 of the same outside diameter below as 

 the inside of the brass pot, but some- 

 what 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 

 cover 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 by the motor. In order to 

 prevent the introduction of heat into the pot by conduction 

 down the rod, the exposed portion is buried in cracked ice 

 held in a thin metallic 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 quickly 

 acquires 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 centim. long and 0*6 centim. in diameter drilled 

 in the plate and ending just inside the pot. The whole appa- 

 ratus is very slightly tilted so as to ensure the steady outflow 

 of the drip. 



A large cylinder, K, 35 centim. high, made of rolled brass 

 4 millim. 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 fig. 2. K weighs about 20 kilograms when 

 empty, and rests upon 144 brass balls each about 12 millim. 



