POWELL. 332 POWER. POWELL, ilAi D ilSGS— ). An American violinist, born in Peru, 111. .She studied music (18S1-S3) in Leipzig, Paris, and Berlin, where she was a pupil of Joachim. She was solo- ist with the orchestras of Thomas, Seidl, Nikisch, and Danirosch, accompanied the New York Arion Club on its European tour in 1892, and played in England and on the Continent in 1898-99. Her jjlaying was marked by intelligent interpretation, an unusual purity of tone, and adequate technique. POWER (OF. povoir, poucii; poer, Ft. pou- voir. It. poterc, power, from ML. potere, for Lat. posse, to he able). In the English and American law of real property, an authority vested in one or more persons enabling them to make valid conveyances of land, irrespective of their having any interest therein themselves. Such a power may be created by any instrument capable of transferring real estate, but it is most fre- quently conferred by will. It may be general, authorizing the person in whom the power is vested (known as the donee of the power) to convey to any person whatsoever, including him- self, or special, where the exercise of the power is restricted to certain persons or classes of per- sons. The latter is its more usual form. The will of the person creating the power (known as the donor) must be strictly observed, not only as to the persons in whose favor it may be exercised, but also as to the time and mode of its execution, whether during the life- time of the donee, by deed, or at his death, by last will and testament. The power when duly executed is operative to divest the estate of the person by whom the land is then held and to vest it in one or more others according to its terms. But the deed or will by which this re- sult is produced is regarded not as that of the donee executing the power, but as that of the donor by whom it was created, and it derives its efficacy from the instrument by which the power was created. Its operation, therefore, is to invalidate (or, more properly, to 'revoke') the previously existing title and to substitute the title of the new 'appointee' in its stead. Accordingly, where, as in the ordinary case, the real projjerty is vested in one person and the power of appointment, as it is more fully de- scribed, in another, the legal title of the former is held in strict subordination to the power held by the latter, and the due execution of the power vill invalidate any conveyance or incumbrance of the property by such owner. Powers are described as owing their efficacy to the Statute of Uses, which had the effect of transforming into legal estates the equitable in- terests in land, which, under the former practice of conveying property to one person to the use of another, might have been created by parol appointment. Thus the owner of land might give to .another the use thereof, reserving to him- self or giving to another the right or power of revoking such use or trust and appointing an- other in lieu thereof. It will be seen that it needed only the touch of the statute, converting these uses into legal estates, to put into efTect the elaborate system of powers above described. This .system forms an important and intricate chapter in the law of real property. It has, how- ever, been greatly modified by statute in many of the United States. See Sugden, on Powers; Leake, Law of Property in Land; Tiffany, on Peal Propcrtij ; Williams, Real Property. POWER (in physics). The work done by a machine or any agency in a unit of time. In the C. G. S. system the unit of power is one erg per second. Other units are, however, in practical use. Such are the 'watt,' or 10' ergs per second, and the 'horse-power,' or 33,000 foot-pounds per minute (this equals 746 watts approximately). POWER (in mathematics). See Expoxext. POWER, Transmi.ssiox of. The processes and methods of transmitting the power gener- ated by prime motors to the machines and mech- anisms operated in performing useful functions is one of the most important problems of mod- ern engineering. In practically all cases the power generated by a prime motor (steam-en- gine, water-wheel, or windmill) has to be trans- mitted through an appreciable distance to be applied to the machine which utilizes it in per- forming «ork. The means by which this is ac-, complished are various and may be classed as-l gears or gearing, belts and ropes, compressed air,} hydraulic pressure, and electricity. Ge.eing is one of the oldest and most exten- sively used methods of power transmission for, | short distances. If two cylinders with parallel ' axes are pressed together and one of them is ro- tated on its axis, it will drive the other by means of the friction between the surfaces. If actual teeth are formed upon the two cylinders, we have a pair of gear wheels which drive each other by pressure upon the faces of the teeth if the teeth are properly shajied. If the driving gear and the | driven gear are of equal diameter, they have the same speed of rotation ; if the driven wheel is smaller than the driving gear, it rotates faster, and if it is larger it rotates slower. Intermedi- ate gear w'heels are commonly introduced between i the driving gear wheel and the driven gear wheel, which may be of the same or ditlerent diameters. By the suitable arrangement of gear wheels and ] proper variations of their relative size and form, the motor shaft speed may be either increased or I diminished and the direction of rotation may be changed to any angle with the driving shaft. See . illustration of typical gear wheels, in article Gearing. Belts. Next to gear wheels the most familiar I means of power transmission are hclts. (Seej Belt.) If two cylinders mounted on parallel I shafts are set so far away from each other that | their surfaces do not touch, one may be drivenj from the other by encircling both with an endles3«| flat belt of flexible material. The driving power] from the motor shaft is transmitted to the driven f shaft b}' means of the friction between the sur- face of the belt and that of the two pulleys. Change of speed is accomplished by increasing or I decreasing the diameter of the driven i)ulley as j compared with the driving pulley. Change in the 1 direction of i-otation is accomplished by twisting! the belt ; thus a horizontal or an oblique pulley | can be driven from a vertical pulley. Belt tran.s- mission is particularly an American development! and is more extensively used in this country than elsewhere. In Englisb jiractice for many years gearing was preferred to belts, and at present rope drivers are used in England in preference to belts. Rope transmission is similar to belt transmission in principle and operation, but in place of flat belts, embracing smooth-faced pulleys, one or
