the sheave is called the tackle. The fixed pulley (Fig. 1) gives no mechanical advantage; it merely changes the direction in

Description images/pp0461 1

fig. 1                              fig. 2

which the force is applied; thus W can be raised by merely pulling P down. The single movable pulley gives a mechanical advantage equal to two (Fig. 2) ; for, as the weight W

Description images/pp0461 2

fig. 3               fig. 4             fig. s

is supported by two strings, the strain on each string is half of W; since, the strain on one being supported by the hook A, the power P has to support only the stress of the other string which passes around C. A still greater mechanical advantage is secured by a combination of pulleys, as shown in the second illustration. Theoretically, the larger the number of movable pulleys in any one combination, the greater is the mechanical advantage; but the enormous friction produced and the lack of perfect flexibility in ropes prevent any great increase in the number of pulleys. See Block and Tackle.

Pull'man, George M., an American inventor and business man, was born at Brocton, Chautauqua County, N. Y., March 3, 1831. At 22 he engaged in moving buildings out of the way of the Erie Canal, then in process of widening. He made his home in Chicago in 1859, and in the same year he prepared models of sleeping cars, which became the foundation of his fortune. In 1863 he began building the coaches that are called by his name the world over. A few years later he organized the Pullman Palace Car Company which was. to build them. In 1880 he

founded Pullman, near Chicago, where the coaches were built. In 1887 he added the vestibule to his cars, which greatly increased their comfort. These carshops turn out $15,00 ,000 worth of railway carriages annually. He died in 1897.

Pulque (pul'ka), a favorite beverage of the Mexicans and of the inhabitants of Central America and some parts of South America, made from the fermented juice of the agave plant.

Pulsatilla {pŭTsă-tlVlă) or Pasque Flower is a native of many parts of Europe and of chalky pastures in several parts of England. It has bell-shaped, bluish-purple flowers. It is narcotic, acrid, and poisonous. Pulsatilla is one of the favorite medicines of the homceopathists ; and Easter eggs are sometimes colored purple with the petals of the flower.

Pulse (Latin pulsus, a pushing or beating). The phenomenon known as pulsation is due to the distension of the arteries when blood is sent through them by the contraction of the heart. The pulse is usually examined at the radial artery at the wrist, the advantage of that position being that the artery is easily compressed against the bone. The frequency of the pulse varies with age, ■ from 130 or 140 beats per minute in infancy to 70 or 75 in adult age. It also varies somewhat with sex, adult females having six or eight more beats per minute than males. It is increased by exertion or excitement, and is diminished by lying down or sleeping. In some diseases the pulse may reach 150 to 200 beats per minute; and, on the other hand, in certain organic affections of the heart it may be as slow as 25 or 30. The force of the beats is a measure of the vigor and efficiency of the heart's action, a strong pulse being regarded as a sign of health and vigor and a weak pulse as a sign of debility. The full significance of any changes of pulse in disease can be clearly understood only by considering them in connection with other signs and symptoms in the case.

Puma (pŭ'ma), a member of the cat family inhabiting the Americas from Canada to Patagonia. It goes under a variety of names in different parts of the country, as catamount, panther, American lion etc. It is about 40 inches long, without the tail, tawny in color above and soiled white below. Pumas are good climbers, but are not confined to wooded districts. They prey upon deer, antelope and other animals; near habitations they kill calves, pigs and sheep. See True's Puma or American Lion in the report of the United States National Museum for 1889.

Pum'ice (pum'Ôs), a light mineral, full of pores like a sponge, found near volcanoes. This highly porous and froth-like structure is due to the escape of vapors through the

lava while it was in a state of fusion. It is