140 PNEUMATICS. 



4. Put a wire through the collar of leathers on 

 the top of the receiver, and fix a bit of dry wood 

 on the end of the wire within the receiver ; then 

 exhaust the air, and push the wire down, so as to 

 immerse the wood into a jar of quicksilver on the 

 pump-plate; this done, let in the air; upon taking 

 the wood out of the jar, and splitting it, its pores 

 will be found full of quicksilver, which the force 

 of the air drove into the wood. 



5. Join together the two brass hemispherical 

 cups A and B (Fig. 8.) with a wet leather between 

 them, having a hole in the middle of it ; then 

 bavins; screwed off the handle at C, screw both the 

 hemispheres put together into the pump-plate, and 

 turn the cock E, so that the pipe may be open all 

 the way into the cavity of the hemispheres ; then 

 exhaust the air out of them, and turn the cock; 

 unscrew the hemispheres from the pump, and 

 having put on the handle C, let two strong men 

 try to pull the hemispheres asunder by the rings; 

 this they will find hard 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; and to show that it is the 

 pressure of the air that keeps them together, hang 

 them by either of the rings upon the hook of the 

 wire in the receiver A (Fig. 3.), and, upon ex- 

 hausting the air out of the receiver, they will fall 

 asunder of themselves. 



6. Screw the end A of the brass pipe A B 

 (Fig. 9.) into the pump-plate, and turn the cock e 

 until the pipe be open ; then put a wet leather on 

 the plate c d fixed on the pipe, and cover it with 

 the tall receiver G H, which is close at top; then 

 exhaust the air out of the receiver, and turn the 

 eock e to keep it up ; which done, unscrew the 



