CATALOG OP THE MECHANICAL COLLECTIONS 9 



without adding to the bulk or weight of the portion that had to be 

 faced about. The final development in this direction was the tower, 

 or "smock", mill familiarly known as the Holland windmill, which 

 was a Flemish invention of the early sixteenth century. In this the 

 roof portion or cap carrying the sails and main shaft is the only part 

 turned (see below). 



The earliest post mills were provided with a long sweep or beam 

 by which the miller walking on the ground and pushing upon the 

 beam could turn the mill about. This method was employed in turn- 

 ing the movable parts of the turret and tower mills and was for 

 many years the feature that limited the height to which mills 

 could be built. In the tower mills balconies were provided around 

 the tower so that it was not necessary to extend the beam to the 

 ground, but the first real improvement was the "pulley-winder", con- 

 sisting of a cogwheel fastened to the cap and meshed with a ring 

 gear that ran around the upper rim of the tower. The cogwheel 

 was turned by a pulley and endless rope that hung around the 

 pulley and down outside the tower so that the miller pulling on the 

 rope turned the cogwheel, causing it to travel in the gear around the 

 tower, pulling the cap with it. The final improvement in this direc- 

 tion was the automatic winder, which consists of a small set of sails 

 placed at right angles to the main sails of the mill so that when the 

 wind was directly into the main sails the small set was edgewise 

 to the wind and at rest, but should the direction of the wind change 

 it would cause the small set to revolve and turn a cogwheel that acted 

 as in the pulley winder to bring the main sails into the wind. Auto- 

 matic winders came into use early in the eighteenth century. 



None of the early windmills had means of governing the speed 

 other than by turning the sails away from the wind or by applying 

 the brake. Later the large sails Avere made up of swiveled slats 

 connected to a bar as in Venetian blinds, so that the angle of the 

 slats could be varied, opening or closing the surface of the sail to 

 present more or less surface to the wind. They were also made up 

 of small fabric elements wound on separate rollers so that the fabric 

 might be rolled up to present less surface. These operated against 

 the pull of springs that served to unroll the elements. These arrange- 

 ments permitted the governing of the speed of the mill without turn- 

 ing the heavy cap, and before the end of the eighteenth century they 

 were being used in connection with centrifugal ball governors to 

 efi'ect full automatic regulation of the mill. 



American types of whidmiU. — Many windmills of the Dutch, or 

 tower, type have been erected in the United States, some at very early 

 dates. The stone tower at Newport, R. I. (the Viking tower of tradi- 

 tion), is believed to be the ruin of a "stone-built windmill" mentioned 



49970—39 2 



