Historical Development of the Windmill - Wind Turbine Technology: Fundamental Concepts of Wind Turbine Engineering - page 14

The horizontal-axis windmill was a considerably more complex mechanism than the
Persian vertical-axis type, but its adoption is readily explained by the fact that it was so
much more eficient. The puzzle lies in the origin of its invention and its sudden
appearance in a region that seems to have had no knowledge of vertical-axis windmills.
Was it a completely separate invention, or was it a question of diffusion of knowledge
about wind power from the East, perhaps with a prototype to copy of which no record
remains? Or was it a natural development from the horizontal-axis water wheel? There is
no irm consensus, but the opinion among authorities seems to be that this new mill
developed naturally from the water wheel. In his discussion of Vowles' paper, “An Inquiry
into Origins of the Windmill” [1930], Wailes declares that
“he considered the step from the Roman watermill with its horizontal wheelshaft
to the ordinary windmill to be easier than from the horizontal windmill with a
vertical shaft to the ordinary windmill with a horizontal shaft. All the essentials
of a windmill were ready to hand except the sails which replace the blades and
rim on the water wheel.”
Even more latly, Wailes declares in his book The English Windmill that
“the mechanism of the early postmill is like that of an early watermill turned
upside-down, the watermill drive being from below upwards and the windmill
drive from above downwards; and it is my opinion, in spite of absence of proof,
that the origin of the (horizontal-axis) windmill considered from the mechanical
standpoint is just that and no more” [1954].
The diffusion theory of origin from the East has some support from those who can-
not accept the notion of a single lash of invention. It takes two different forms; one is by
virtue of trade routes from East to West, and the other is by virtue of returning Crusaders.
Both have credence, but there is no positive evidence for either. Vowles details the spread
of the Greek inheritance and the establishment of schools of learning throughout the Near
East and eventually the whole Islamic empire [1930]. Many of the centers of learning were
distributed along a great trade route, the old Royal Road, so that a large volume of ideas
was spread far and wide, along with the merchandise, from the Baltic to the Far East. He
believes that the European windmill was irst established in Holland, and that because of
the omnidirectional wind, as opposed to the S¯st¯n environment, “a new form would
therefore be evolved to suit the conditions.” Arguments against this notion hold that
Holland's irst attested mill came 70 years after those in France and England, and that the
S¯st¯n mills were actually far from a major trade route.
The other diffusion theory holds that between the First Crusade in 1096 and the irst
known appearance of the horizontal-axis windmill some 50 years later, a large number of
people who recognized the potential of the windmill moved to and fro between Northwest
Europe and the Middle East, and that many of them then pursued the mill's potential in their
homelands. This is a feasible theory, but it too lacks positive evidence; the verse quoted
earlier about the German soldiers also indicates that the horizontal-axis mill was unknown
in the Levant. So it seems that the irst solid records we have of European windmills are
those from the time of the peevish Abbot Samson of Bury St. Edmunds in 1191, with
perhaps the possibility of some of those analyzed by Kealey being of earlier standing if
additional evidence could be found.