22 THE REALITIES OF MODERN SCIENCE 



for sailing boats or for operations where continuity is 

 not essential, wind is not a satisfactory source of energy. 

 Horses, it is true, were available, but it is doubt- 

 ful if they were much used for such purposes as these. 

 They were not the property of the poorer classes, and 

 were used for hunting and for warfare. For these 

 buildings the energy was derived from men. Beside 

 one of the large pyramids of Gizeh stand the quarters 

 of the workmen, long chambers, capable of housing 

 4000 men. When we are told that the roof over the 

 chamber in one of the pyramids was formed by three 

 layers of cut stones, each piece weighing about 30 

 tons, we realize more fully the large amount of human 

 energy which must have been expended in such a con- 

 struction. The laborers who supplied this energy 

 were slaves, usually members of subject races, who 

 performed such tasks much as the Hebrews once made 

 brick for the Egyptians. 



It would be of interest to follow the development of 

 slavery to its peak in the Roman Empire, its transi- 

 tion into feudalism, and the organization of society in 

 medieval Europe. Through all the centuries from the 

 earliest Egyptian records to the present time, under 

 one form or another of slavery, men have supplied the 

 energy for the monuments of dynasties. When man's 

 development along scientific lines was yet too small 

 to allow him to utilize the enormous stores of energy 

 in the world about him, the main source of energy was 

 in food, for the conversion of which into mechanical 

 energy the human body is an efficient engine. But 

 to-day man's growing scientific abilities are making 

 possible grandeurs of buildings and comfort of builders 



