ngth, width, and
thickness. They are also arranged so that in each arm may be clasped one
piece each of Figs. 370, 371, and 372. The three central arms may, of
course, be set up in a different order, and here we have merely chosen
the way that is the most simple to describe and illustrate.

[Illustration: Fig. 377.--Beginning to place on the Cross Pieces.]

[Illustration: Fig. 378.--Placing the Key Piece to overlap end projection
of Central Bar.]

SECOND STAGE.--In the remaining part of the work the chief difficulty is
to keep the puzzle from falling to pieces before the key finally locks
it. Take the longer cross parts, Fig. 370, and clasp one to each arm. The
six need not all be put on meanwhile, but only those which are most
easily handled. The next size (Fig. 371) may then be put on.

In the ordinary course each arm could be completed with its three cross
pieces till the sixth was attempted, and here the reader would find that,
at the last moment, his attempt was frustrated. He could not get the
last small piece in, as other bars lock the puzzle. Here it is that the
"key" comes in.

THE KEY PIECE.--When the writer fits up the puzzle he finds that three of
the arms may straight away be fitted complete with their three cross
parts. These are the ones where the longer cross piece (Fig. 370) _lies
flush with the back of the central bar_ (see Fig. 377). This is easily
found out when at work on the puzzle. In the case of the other three arms
there is, of course, a gap caused by the long slots of the central bars.
Adjust the parts on the first-named three arms, and then deal with the
fourth arm, putting in all three cross parts. For the little one here,
use the "key."

By placing the "key" so that it _overlaps the end projection_ of the arm
(see Fig. 378) a space is left at the centre, and means is thus afforded
for getting in the three cross parts on the remaining two arms.

This practically ends the puzzle. While the "key" is in its overlapping
position the parts may be separated, but if it is _turned round on its
narrow neck_, so that it is in exactly the same position as the other
five small cross parts, it locks the whole thing so tightly that nothing
but sheer force could loosen the twenty-one pieces.

So far as the order of putting together is concerned, there are many
equally satisfactory ways, these being determined by the ease or
difficulty that one experiences in holding the half-finished puzzle. It
all