524 



MACHINES, WORK, AND ENERGY 



the broken thread? Can the lock stitch seam be ripped in this 

 manner? 



POINT OF SHUTTLE. 



BOBBIN OF 

 VNDEQ THFtEAD 



1. Point of shuttle entering loop of 

 needle thread. 



2. Shuttle in loop of needle 

 thread. 



BOBBIN OF / 

 \JJNDEK THT&AD 



3. Shuttle thread enclosed by needle 

 thread. 



4. Stitch completed. 

 FIG. 325. How a vibrating-shuttle machine forms the knot. 



619. Classes of Lock-stitch Machines. Lock-stitch ma- 

 chines are classified according to the way in which the stitch 



