WINDMILLS 



313 



than steel when new, but owing to the variation in wind 

 velocity and direction it is only a short time before the 

 continual vibration has worked the .tower loose at all 

 joints and splices. At every joint in the wood tower 

 there is a chance for the rain to run in and cause decay. 

 Therefore as an offset to the greater rigidity of the wood 

 tower one must consider the time for tightening bolts, 

 labor for painting, and money for replacing the tower 

 every few years. 



Steel towers, as a rule, are not as rigid when new as 

 the wood, but they do not present as great a surface to 

 the wind as the latter, and since all parts are metal 

 there is no chance for a loosening of the joints. The 

 steel tower not only saves all of the labor and expense 

 required to keep the wooden tower in repair, but it is 

 practically indestructible. 



In a cyclone the steel tower will often become twisted 

 before the wooden one will be broken. However, the 

 latter will generally become so racked and splintered that 

 it cannot be repaired. 



433. Anchor posts can be made by setting strong fence 

 posts in the ground their full length and nailing some 

 strips across them to hold beneath the earth ; but a bet- 

 ter method is to insert an angle iron in a concrete base, 

 which will support the tower posts. The dimensions of 

 the base should be about 18 X 18 inches X 4 feet for 

 small mills, and proportionally larger for large mills. 



434. Erecting mills. Windmills over 60 feet high 

 should be assembled piece by piece, but low towers can 

 be assembled on the ground, including windmill head, 

 sails, and vanes, then raised in a manner similar to Fig. 

 211. After the tower has been raised it should be exam- 

 ined and all braces and stays given the same tension 

 and all nuts tightened. It is also well before the pump 



