ing great pressures. In pneumatic transmission the power is transmitted by compressed air in pipes to pneumatic engines and tools. It is a system used largely in mining where pneumatic drills are used, and within a few years its use in connection with many machine-tools has greatly extended. Pneumatic tools, as riveting-machines, drills, presses etc. usually are very convenient in operation, and although the mechanical efficiency of the whole system is low, owing to the thermal losses in compressing the air, the use of pnuematic transmission for short distances is increasing, owing to convenience of operation, flexibility and portability of tools. In mining and tunneling it has the great additional advantage of furnishing necessary ventilation along with power. For efficiency, flexibility, economy of operation and cost of operation no system of power-transmission can compete with electrical transmission for longer distances. For longer distances, as 25 to 100 miles, it is the only system by which power-transmission is possible, and even for short distances, as in machine-shops, it is competing with belts and shafts. Many shops and factories are to-day putting in motors for each machine, and thus doing away with belts and shafting. Long distance power-transmission by electricity is the most notable engineering achievement of recent years. It began in the experimental plant of Marcel Deprez at the Munich Exposition of 1882. The line was from Miesbach to Munich, a distance of 37 miles, the power transmitted was ½ H. P., and the pressure was 1,350 volts. The dynamos and generators were similar Gramme machines. This plant was of small magnitude, but it established the possibility of long-distance transmission. During the next few years power-transmission was developed largely in the way of stationary motors operated on central-station lines and especially in electric railways. (See Electric Railways.) Economical transmission of electric energy for long distances requires high voltages, and high voltages cannot be handled easily except in alternating-current apparatus (see Transformer), so that long-distance transmission was not fully developed until the invention of the successful A. C. motor, the polyphase induction-motor. (See Electric Motor.) In 1891 an experimental line from Lauffen to Frankfort-on-the-Main was shown at the Frankfort Electrical Exhibition, in which over 100 H. P. was efficiently transmitted 110 miles at 20,000 volts by the use of three-phase A. C. apparatus. Since then numbers of large commercial plants have been installed, transmitting thousands of H. P. from three to 35 miles. The Fresno, Cal., Folsom-Sacramento and Niagara Falls plants probably are as notable as any of these plants; but the plants at Lachine Rapids, Montreal, at Portland, Ore., of the Standard Electric Company of California and several plants in Switzerland and Italy are equally interesting to the engineer. In the Fresno plant 1,000 H. P. is transmitted 35 miles by a three-phase system from a water-plant in the Sierras to Fresno. Sacramento, Cal., is supplied by a similar system, with about 4,000 H. P. from the falls at Folsom, 23 miles away. At Niagara Falls 50,000 H. P. is generated by ten dynamos, run by turbines, and the power is distributed as far as Buffalo, 27 miles away. The Standard Electric Company's lines bring electric power into San Francisco and San José from a point in the Sierra Nevada. The electric cars and lighting of San José are supplied by electric currents generated 83 miles away. All these long-distance lines have been built to transmit the power from water-power, but it is one of the plans of the future to establish generating-plants at the mouth of coal-mines and transmit the power instead of the coal to cities within a radius of from two or three hundred miles. See Niagara Falls City and Niagara Power-Plant.
Tran′spira′tion (in plants), the loss of water by evaporation from a plant. Since 50 to 98 per cent. of the plant-body is water, it loses water whenever the air contains less moisture in proportion to its capacity than the plant. Transpiration therefore is unavoidable under the conditions of most land-plants. To reduce this unavoidable loss, the larger land-plants make the outer tissues of the aërial parts nearly waterproof. But the air-passages (see Aëration) permit evaporation from the cells bounding them; hence the moisture diffuses through the stomata (q. v.) to the outer air. Were evaporation prevented by waterproofing these cells also, the absorption of gases for food-making and respiration would be nearly impossible. The amount of transpiration varies greatly in different plants according to their structure and contents; in the same plant it varies with age and the varying external conditions, as temperature, light, moisture etc. Therefore, only a very general idea can be given of the amount of water transpired. On a hot summer-day a plant with five square meters (about six square yards) of foliage (such as a thrifty sunflower as high as a man might have) will evaporate about 1.2 liters (2.5 pints) of water. A birch 40 feet high, with perhaps 200,000 leaves, will give off on a hot day 300 to 400 liters of water (about 2.5 barrels). But these rates would not be kept up as an average through the growing-season. The evaporation from a leaf-surface is 2 to 7 times less than that from an equal area of water.
Transplanting, a horticultural process, the transference of plants, as trees, from a nursery or from their native habitat or of
