12. The power plant at the Pikes Peak Hydro-electric Company utilizes a head of 2150 ft., which is equal to a pressure of 935 lbs. per square inch, to run a Pelton wheel. If the area of the nozzle is 1 sq. in. and the jet has a velocity of 22,300 ft. per minute, what is the horse-power developed if the efficiency is 80 per cent.? 13. A test made in 1909 of the turbines at the Centerville power house of the California Gas and Electric Corporation showed a maximum horse-power of 9700, speed 400 r.p.m. under a head of 550 ft. The efficiency was 86.25 per cent. How many cubic feet of water passed through the turbines each second? 14. The turbine in the City of Tacoma Power Plant (see Fig. 120) uses a head of 415 ft. 145 cu. ft. a second pass through the turbine. Calculate the horse-power. 15. In problem 14, what is the water pressure per square inch at the turbine? 16. The power plant mentioned in problem 13 develops 6000 kw. What is the efficiency? Review Outline: Work and Energy Work; how measured, units, foot-pound, kilogram meter, erg. Energy; how measured, units, potential, _P.E._ = _w × h_, or _f × s_. Kinetic = _(wv²)/(2g)_. Power; how measured, units, horse power, watt, 5 forms of energy, conservation. H.p. = (lbs. × ft.)/(550 × sec.). Machines; 6 simple forms, 2 groups, advantages, uses, Law: _W × D_{w}_ = _F × D_{f}_. Lever; moments, mechanical advantage, uses and applications. Wheel and Axle and Pulley; common applications, mechanical advantage. Inclined Plane, Wedge, and Screw; mechanical advantage and efficiency. Friction; uses, how reduced, coefficient of, laws (3). Water Wheels; types, efficiency, uses. CHAPTER VII HEAT, ITS PRODUCTION AND TRANSMISSION (1) SOURCES AND EFFECTS OF HEAT =138. Importance of the Study of Heat.=--Heat is brought to our attention through the sensations of heat and cold. In winter, we warm our houses and prevent the escape of heat from them as much as possible. In summer we endeavor to keep our living rooms cool and our bodies from being overheated. A clear understanding of the several _sources_, _effects_, and _modes of transferring_ heat is of importance to everyone living in our complex civilization, especially when we consider the multitudes of objects that have as their principal use the _production, transfer or utilization_ of heat. =139. Principal Sources of Heat.=--_First_ and most important is the _Sun_, which is continually sending to us _radiant energy_ in the form of light and heat waves. These warm the earth, make plants grow, evaporate water, besides producing many other important effects.