Powell] TECHNOLOGY, OR THE SCIENCE OF INDUSTRIES 333
It now remains for us to set forth the classes of powers which are used by men to promote their welfare. These are muscular power, wind-power, water-power, heat-power, and electric power.
Muscular power — This power is the primordial force used by mankind, first as human power, but in the second stage of human culture animals were domesticated and used as beasts of burden. Especially is one animal used for this purpose, namely, the horse, and the power of a horse for a definite period of time, established conventionally, has come to be used as the standard of measure- ment for powers. Animals are used not only for carrying and hauling burdens, but they are used also for impelling machinery.
Wind-power — Wind-power is used to propel machinery and especially in the navigation of water to propel vessels, and the machinery devised for the latter purpose consists of masts and sails. In the early history of civilization the propulsion of ves- sels and the running of mills were relatively much more common than at present, and yet this power is widely used. Since air has been liquefied it seems likely that this substance is to play a still more important role in mechanics, and air is to become a commodity.
Water-power — Water-power is used chiefly for the running of mills. The tides as they rise and fall are utilized in their onward rush to impel mills by the construction of the necessary machin- ery, and the fall of water in running streams is utilized for the same purpose. Water is used also as steam to connect heat- power with machinery.
Heat-power — This power is obtained from the combustion of plants and animals and the hydrocarbon products derived from them. Steam is but a medium through which heat-power is applied.
Electric power — Electric power is also a medium for transmit- ting wind-power, water-power, and heat-power ; but it also seems to be an independent power itself. Not being a physicist I am not competent to properly discuss this subject.
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