204 BKNJ. PIKE'S, JR., DESCRIPTIVE CATALOGUE. 



Fig. 197. the C ock ; unscrew the hemispheres from the 

 pump, and having put on the handle, let two 

 strong men try to pull the hemispheres asunder 

 by the rings, which they will find it difficult to 

 do ; for if the diameter of the hemispheres be 

 four inches, they will be pressed together by the 

 external air with a force equal to 190 pounds. 



We have recently improved this article by 

 manufacturing them of iron, which is not so 

 liable as brass to be bent by an accidental 

 blow. 



Price, 3^ in. brass, $4.00 ; 4| in. brass, $6.00. 

 " 3^ in. iron, $4.00 ; 4 in. iron, $5.00. 



Lever and Stand for weighing a column of air. Fig. 198 

 consists of a strong base, having a short pillar serving as the 

 fulcrum of a lever fixed therein ; on the short end of the 

 lever the handles of the hemispheres are supported, the 

 stop-cock being screwed to the base. This arrangement is 



Fig 198. 



designed to prove the pressure of the air on the hemispheres 

 to be about fifteen pounds on every square inch. If the 

 diameter of the hemispheres be four inches, the area is 

 twelve and a half inches, which multiplied by fifteen gives 

 187 Ibs. ; the power requisite to separate them when ex- 

 hausted, as shown by the lever. The exhausted hemispheres 

 will of themselves come asunder under an exhausted receiver. 



Price, $5.00. 



Spouting Tube. Fig. 199 consists of a long glass tube, 

 having a brass cup and stop-cock. To use, exhaust the air 

 by the air-pump, and turn the stop-cock ; then plunge the 

 end of the cock in water, and open the cock, when the water 

 will violently rush in, and nearly fill the tube. 



Price, $2.50. 



