OF ARTS AND SCIENCES. 95 



cosity of water. It would therefore require 1,000 atmospheres to force 

 this sample of marine glue through a capillary tube .01 cm. in diame- 

 ter and 1 cm. long, at the small rate of .05 cm. per hour, supposing 

 (an unfavorable supposition) that its viscosity does not increase under 

 pressure. Pressure moreover tends to close capillary interstices be- 

 tween nut and screw, thus making the apparatus even more efficient 

 at high pressures than at low pressures. At high pressures, finally, a 

 single turn of the screw has a much larger pressure equivalent, for 

 the compressibility of the oil has materially decreased. 



4. Steel Screw. — To rotate the screw ^^^^^(Figs. 1, 2, 3), it is 

 provided with a lever and ratchet, LDR. The ratchet wheel is shown 

 at RR (Figs. 1, 3), and is square-cut to correspond with the right and 

 left click, D. A pin, E, sliding in a socket of the lever, Z, and actu- 

 ated by a spring (Fig. 1), enables the observer to adjust the ratchet 

 either for forward or retrograde motion of the screw ST. The figure 

 gives a full account of the manner in which the parts of lever and 

 ratchet are put together, and I need only add that the (steel) ratchet 

 wheel RR is forged to the shaft T of the screw. 



The screw .S-S is one inch in diameter with twelve threads to the inch. 

 The shaft TT is held in position by a journal, HHH, fixed between 

 slides (see Fig. 2), and bolted securely down to the bedplate FG. 



5. Barrel. Head. — The planed front end of the cast iron bedplate 

 FG, the part FF of which is hollowed out to catch drippings, carries 

 the barrel BBB. It is seen in cross-section in Figure 4, and its flat 

 side IS firmly secured between the guides of the bedplate, by two bolts 

 (Figs. 1 and 4). 



KK is the stuffing screw, being essentially a hollow steel nut of the 

 form shown, and provided with a large flange for screwing it forcibly 

 in place. Both the inner and the outer cylindrical surface of A'A' 

 are threaded with twelve turns to the inch. Moreover the inner 

 thread, bbbb, of A'A" is a continuation of the thread aaaa in the walls of 

 the barrel. Inasmuch as the thread cccc also has twelve turns to the 

 inch, it is clear that the nut A'A' can be forced in or out, no matter 

 what the position of the screw SS may be. In practice cccc is cut 

 first, and the nut screwed in place. After this the whole thread 

 hbaaaabb is cut at one time. The gasket of marine glue (§ 3) is 

 shown at mm. It is compressed by A'A'. At high pressures, the 

 friction is sufficient to hold the nut A'A' in place without the need of 

 a lock-nut. 



It is seen that after the screw ST enters the barrel BB, the chief 

 strain is borne by the thread aaaa. 



