apparent. History does not reveal the
earliest forms of any primitive machines nor does it reveal much about
the various early stages in evolution toward more complex types. At best
we have discovered and dated certain developments as existing in
particular areas. Whether these forms were new at the time they were
first found or how widely dispersed such forms may have been is unknown.
Surviving evidence is in the form of pictures or drawings, such as the
little-known screw-cutting lathe of 1483 (fig. 1) shown in _Das
mittelalterliche Hausbuch_.

This lathe shows that its builder had a keen perception of the necessary
elements, reduced to bare essentials, required to accomplish the object.
Present are the coordinate slides often credited to Henry Maudslay. His
slides are not, of course, associated with the spindle; neither is there
any natural law which compels them to guide the tool exactly parallel
with the axis of revolution. In this sense the screw-cutting lathe in
the _Hausbuch_ is superior because it is in harmony with natural law and
can generate a true cylinder, whereas Maudslay's lathe can only transfer
to the work whatever accuracy is built into it.

In principle this machine shown in the _Hausbuch_ is very advanced as we
see when we follow the design through to the present time. The artist,
whose drawings give us our only knowledge of the machine, himself was
obviously not very familiar with the details of its function. Reference
to figure 1 shows that the threads on the lead screw and on the work,
wind in opposite directions. This must be an error in delineation since
the two are closely coupled together without any intervening mechanism
so that the only possible result on the work must be a thread winding in
the same direction as on the original screw. The work also is shown
threaded for its entire length; this cannot be accomplished with any one
location of the cross-slide. We are left with the question of whether
this slide was used in two locations or whether the artist, possibly
working from notes or an earlier rough sketch, failed to show an
unthreaded portion on one end or the other of the work.

[Illustration: Figure 1.--EARLIEST REPRESENTATION FOUND OF A
MASTER-SCREW TYPE of thread-cutting machine. From the inconsistencies,
such as right- and left-hand threads on master and work, it appears that
the artist had scant insight into actual function. From plate 62 of _Das
mittelalterliche Hausbuch, nac