COMPRESSED-AIR LOCOMOTIVE. 241 COMPROMISE MEASX7RES. experiments have been conducted in New York City, on some of the railway lines crossing the city from east to west. In all of thesc o.vpcri- ments a locomotive car has been cmployetl carry- ing the tanks underneath the seats or under the floor of the car. In Europe the Mekarski sys- tem of compressed-air street-car locomotion has been used api)arently with considerable success in Paris, France, and Berne, Switzerland. A special feature of the ilekarski system is the heating of the air. to maintain it at a constant temperature, by passing it through superheated water at 330° F. The air thus becomes saturated with steam, which subsequently partly con- denses, its latent heat being absorbed by the expanding air. The pressure used at Berne in the car reservoirs is 440 pounds per square inch. The engine is constructed like an ordinary steam tramway locomotive, and drives two coupled axles spaced .5.2 feet apart. It has a pair of outside horizontal cylinders, 5.1 by 8.0 inches: four coupled wheels. 2"io inches in diameter. The total weight of the car, including compressed air, is 7 '4 tons. The storage-tanks consist of ten sheet-iron cylinders with an aggregate capa- city of 6414 feet of compressed air. The cars will run for four miles without refilling the reservoirs. On the Paris lines the pressure used is 54" pounds, and the cars make trips of seven miles without refilling the reservoirs. Mining Locojiotives. As generally con- structed, the air for mining locomotives is stored in one or two steel tanks having a cubic capacity designed for the length of run, weight of ti'ain, grades, etc. These tanks usually occupy the space that the boiler does on an ordinary steam- locomotive. The air from the main tank or tanks is conducted through copper-i)ipe connec- tions to an auxiliary reservoir of suitable diam- eter. The pressure in this auxiliary tank can be regulated (usually 150 pounds) anywhere from 30 pounds U]) to 300 pounds, as required. The air is reduced and controlled from the main tank by a reducing-valve and stop-valve, and can be regulated to any jiressure at a moment's notice ; when once set, a constant pressure is maintained in the auxiliary reservoir. The air is fed to the engine cylinders from the auxiliary reservoir. Cora])ressed-air locomotives for in- dustrial uses are built substantially the same as mining locomotives. From the preceding it will be seen that the two types of compressed-air locomotives are. the compressed-air motor car for street-railway propulsion and the compressed - air locomotive proper for mine, plantation, and factory haul- age. In both forms the prime motive power is steam, whose energy as it conies from the boiler is emploved first to drive the air compressors: and. second, as stored in the compressed air. to propel the car motor or locomotive proper. See Air CoiiPRESsoR.s and CoMTRESSEn-AiR Engine. COMPRESSED - AIR TREATMENT. A term applied to the ii-^e of air under pressure for therapeutic purposes. The treatment is admin- istered in one of the following two ways : ( 1 ) by causing the patient to enter an air-tight chamber, in which air is forced under pressure till the desired density is obtained: (2) by causing the patient to enter a cabinet in which he is seated in such a position as to receive into his mouth the end of a tube which, passing through the front of the cabinet, connects the cavity of his lungs with the outside atmosphere, while an apparatus on the roof of the cabinet i^ so ar- ranged as to jiump air out of tiio cabinet. In the airtiglit room, the pressure upon all parts of the patient's body, including the lung-cavity, is the same. In the cabinet, the pressure within the lung-cavity is many times greater than on the rest of the body, tlius causing great exj)an- sion of the lungs and cliest. The latter treatment relieves collapse of pulmonary vesicles and con- solidations, in many cases ; the former treatment is said to cause increased absorption of o.vvgen and an improved function of the nuicous mem- brane of tile respiratory tract. Both methods of treatment are used in cases of tuberculosis, and the former also in elironic bronchitis and asthma, at certain water-cures. See Tubebcu- LO-sLS ; t^Ai.s.soN Disease. COMPRESSIBILITY {from Lat. cotnprcs- siis, p.p. of compriinere, to compress, from com-, together +' premere, to press). That property of bodies by 'which they admit of being pressed into less space than they otiierwise occupy. It is measured by the relative change of volume produced by the ajiplication of unit pressure. The particles composing bodies are in all cases at greater or less distance from one another: and whatever brings the particles closer together diminishes the volume or bulk of the body. This mav be effected by various agencies, as, for ex- ample, by the withdrawal of lieat. but the eft'ect is called compression only when it Is caused by mechanical force, as by pressure or by percus- sion. All bodies are compressible, but in dif- ferent degrees. Solids and liquids wei'e at one time believed to be incomjiressible ; more accu- rate experiments, however, have proved that this is not the case; water, f<u' instance, subjected to a pressure of 15,000 pounds to the square inch, loses one-twentieth of its volume. Gases, on the other hand, are strikingly compressible, and by means of a common air-pump a very large amount of air can be forced into the space of one cubic inch. The variation of the volume of a gas with the pressure is expressed by the law of Boyle and Mariotte. See Gasqs; IMoLECULES — Molecular Weights. COMPRESSOR. An instrument used on ship- board for temporarily cheeking the running of the anchor-chain. It consists usually of a curved arm pivoted at one end and arranged to be swiuig across the under side of the chain-pipe through the deck and grip the chain by pressing it against the lip of the pipe. The term was also applied to an attachment to old-type guns for checking the recoil by squeezing two or more surfaces together and tluis increasing the friction. COMPRESSOR. Air. See Air C'ompre.ssor. COMPROMISE MEASURES OF 1850. or Omxiui-.s Bill. A name popularly given to a series of measures passed by the United States Congress in 1850, directed to a general .settle- ment of certain questions arising out of the struggle over slavery. The aflirmance of Ameri- can rights in the Oregon territory, by the Treaty of 1840 with England, and the acquisition of still larger territories from IWexico by the Treaty of Guadalupe-Hidalgo (q.v). made urgent the prob- lem of providing suitable governments for this territory, and at the same time made acute the controversy between North and South over the securing of acceptable provisions concerning
