Two-thread Machines.—Of these ma chines two subdivisions may be recognized —the lock stitch, and the knotted or double chain stitch, commonly called the Grover & Baker machines. Of these, the lock stitch machines are by far the most common, and for general purposes are in almost universal use. For producing the lock stitch there are two forms of apparatus: (1) the reciprocating shuttle which carries a thread through the loop made by the needle, and (2) the lenticu lar spool or thread case over which the loop is passed by a revolving hook. Of the first kind—shuttle machines—the Howe, the Singer, the Wanzer, and others are familiar forms; the second, or spool and hook appliance, is a peculiarity of the Wheeler & Wilson alone. The needle was originally fixed at the end of a vi brating arm, and, describing the arc of a circle, it required to be curved. Singer first introduced the straight needle car ried by a slide, and it now is in general use. Next to the invention of the eye pointed needle the designing of an efficient feed motion was the most important im provement made in the sewing machine. Singer introduced what is called the wheel feed, but the plan now adopted is one of the many ingenious and beautiful mechanical devices introduced by A. B. Wilson, of Wheeler & Wilson. It is called
the four-motion feed, and consists of a serrated plate to which a forward, down, backward, and upward motion is com municated, the forward and backward motion being varied according to the length of stitch. The tension of the thread in the shuttle is maintained by a small nipping spring which presses against the thread. In the Wheeler & Wilson machine the use of the shuttle is entirely and the lock stitch is formed by carrying the loop from the up per thread over and around the under thread, which is contained within a small lenticular spool, which fits snugly but free in a recess in the side of the revolv ing hook. This exceedingly ingenious de vice, together with the four-motion feed above alluded to, place Mr. Wilson, their inventor, in the front rank of improvers of the sewing machine. The Wheeler & Wilson machine works with great ease and smoothness, and as the machine can be noiselessly worked at a high speed, it is a great favorite for general domestic and light manufacturing uses. The or dinary Grover & Baker machine makes a knotted or double loop chain stitch of a complex character. For general pur poses it is not now in great favor, owing from end to end to the sack seam, draw ing the thread through with it.