CATALOGUE OF THE MECHANICAL ENGINEERING COLLECTION. 11 



the traces of the oxen were made fast, and, as it was drawn out, the 

 stone rolled on by means of the wheels." The method of the rolling 

 load was adopted by Paeonius in the first century B. C. for trans- 

 porting the new base of the colossal statue of Apollo from the 

 quarry to the temple erected to that god. 



Cat. No. 181,258 U.S.N.M. 



NATURAL FORCES. 



The time came in the course of civilization's advancement when 

 power requirements exceeded those which could be developed by 

 muscular energy, and accordingly man proceeded to utilize the 

 natural forces about him. These included the domesticated animal, 

 the wind and the water, whose potential energy was converted into 

 work through the medium of the horse gin and treadmill, the wind- 

 mill and the water wheel, respectively. Whereas man in turning 

 a crank by hand could do work at the rate of about one-tenth horse- 

 power a minute in an eight-hour day, the ox in the circular-track 

 gin could develop five-tenths and the horse eight-tenths horsepower ; 

 the crude windmill about 4 horsepower; and the crude water wheel 

 about the same amount. 



WINDMILLS. 



Wind for propelling ships was developed at a very early date, but 

 the time of its use for industrial purposes is much later, the exact 

 time being in dispute. Windmills were common beginning about 

 the twelfth century A. D. It is said that the first type adopted 

 to present the vanes or sails toward the wind was to float the mill 

 on water and turn it as required. The next step was to put the 

 mill on a post and turn the building on this as an axis. Follow- 

 ing this the cap or roof only was revolved — a Dutch invention of 

 the sixteenth century. The progressive improvements which fol- 

 lowed consisted mainly in governing, regulating the sail area in 

 accordance with the wind's force, first by reefing and later by 

 altering the angles at which the sails were presented to the wind. 



The windmill, of course, found its greatest application in flat 

 country, and in Holland was probably more universally adopted than 

 in any other country, there being at one time 12,000 mills in opera- 

 tion, averaging 8 horsepower each. 



The modern windmill, used mainly for raising water, is much 

 smaller through the use of steel and lighter metals. Disks, 6 to 30 

 feet in diameter, made up of a number of vanes, take the place of the 

 cloth sail. In one type in particular there are two series of con- 

 centric blades fastened to the purlines of a braced radial frame. 

 The blades are fixed at an angle of about 35° to the plane of the 

 wheel and a peculiarly constructed mechanism turns the wheel 



