This improved class of hooks are provided with a much deeper cavity than those first introduced, an arrangement permitting of the employment of a more commodious bobbin, which is generally covered by a cap, as in the revolving shuttle, but free to revolve.  In some cases the cap carries a tension plate preventing its revolution with the hook.  But beyond these improvements on Wilson’s original device, the utility of the hook mainly depends upon two things quite apart from the hook itself.  These are the dispensing with the old fashioned check brush and the use of a positive take-up.

Thus, in the original machine, the stitch was pulled up by the succeeding revolution of the hook.  For while one revolution sufficed to cast it over the spool, a second turn was requisite to complete the stitch.  In this way, to make a first stitch with such an apparatus required two turns of the rotating hook.  The improvements mentioned enable the machine to complete a stitch with one turn of the hook—­an important step in advance, when we consider that by the old method each length of slack thread must be tightened up solely through the fabric and the needle eye.  But this particular arrangement bears so much upon the introduction of the positive take-up itself that further reference to it must be reserved until that device has been described.

Simple Thread Hooks.—­The best known of these is Willcox & Gibbs.  It has been so often described, that no further reference to it may be made.  It continues to make the same excellent twisted stitch as it produced twenty-five years ago.

Of Vibrating Shuttles.—­These are shuttles of the long description, moving in a segment of a circle.  There are several varieties.  The most novel machine of this kind is the vibrating shuttle machine just produced by the Singer Manufacturing Company.  In this case the shuttle itself consists of a steel tube, into the open end of which the wound reel is dropped, and is free to revolve quite loosely.  Variation of tension is thus obviated in a very simple manner.  The chief point of interest in the machine is undoubtedly the means employed in transferring the motion from the main shaft to the underneath parts, an arrangement as ingenious and effective as any device ever introduced into stitching mechanism.  It is the invention of Mr. Robert Whitehall, and consists of a vertical rocking shaft situated in the arm of the machine Motion is imparted to it by means of an elbow formed upon the main shaft acting upon two arms, called wipers, projecting from the rocking shaft, the angle formed by the arms exactly coinciding with that of the elbow in its revolution.  This admirable motion will no doubt attract much attention from mechanists and engineers.

The Lock Stitch from Two Reels.—­In the early days of the sewing machine, the makers of it often met with the question, “Why do you use a shuttle at all?  Can you not invent a method of working from a reel direct?” The questioner generally means a reel placed upon a pin, just as the upper reel is placed.  The reply to such a query is, of course, that to produce the lock stitch in that way is impossible—­as indeed it is.