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LEFT VACUUM CLEANEB 149 VAIL extension; that, in other words, mat- ter was indistinguishable from space. Such inquiries, however, can lead to nothing definite. The experimental phil- osopher is obliged to recognize the prac- tical impossibility of obtaining a per- fect vacuum. The so-called Torricellian vacuum, which exists above the mer- cury column of a barometer, is really filled with mercury vapor probably mixed with a small percentage of air. The very action by means of which the air pump produces its vacuum shows that there can never be an absolute void — a little air always remaining behind. Andrews, fol- lowing up a suggestion of Davy, ob- tained remarkable vacua by first pump- ing in carbonic acid so as to expel as far as possible the air, and then after ordinary exhaustion leaving the carbonic acid to be taken up by moistened caustic potash which has been previously placed in the receiver. In this way Andrews removed all but s^o.W of the gas originally present, whereas by ordinary air pump action only Hi of the gas can be removed. Frankland, Gassiott, Crookes, Dewar, and others, have de- vised various improvements. Dewar takes advantage of the property of the gases to condense on the surface of solids in a remarkably ingenious way. A piece of carbon, placed in the vacuum ves- sel, is kept heated while the vessel is being exhausted. After the exhaustion is completed as far as possible, the car- bon is allowed to cool so as to permit the small quantity of gas present to con- dense in its pores. A gentle heating of the carbon at once releases a quantity of the gas, so that this method is inval- uable in the study of electric discharges through rarefied gases, since the rarefac- tion can be so easily altered at will. VACUUM CLEANER, a mechanical device for getting rid, by means of air suction, of dirt and dust from the floors and other parts of a house. It consists in the main of a nozzle which is run over the area that needs cleaning, a pipe con- necting the nozzle with a separator where the dust and dirt are removed from the air, and an exhausting apparatus for producing a vacuum. The nozzles are in such shapes and sizes as the work may require. Some vacuum cleaners are operated by current which is derived from connection with a lamp socket. An- other of a more extensive kind, mounted on a carriage and driven by an internal combustion engine, is stationed outside the building to be cleaned and the hose passed through the window. The third type is located as a rule in the basement of a building and is connected by per- manent pipes with outlets to which noz- zles and hoses may be attached in dif- ferent parts of the buildings. VAGINA, the membranous canal lead- ing from the uterus or womb to the ex- ternal genitalia. The vagina in lower mammals, such as the Oy^iitliorhynchus, opens into cloaca, while in the kangaroos and other Marsupialia it opens into a canal named the uro-genital canal, which receives the efferent ducts of the urinary organs. In higher quadrupeds the va- gina is distinct both from the rectum and the urinary ducts. In the human subject it attains a length of about four inches measured along its anterior wall and six inches measured on its posterior surface. It lies between the bladder and rectum; constricted at its commencement it becomes dilated toward its uterine end. The coats of the vagina number three — an external or muscular layer, a layer of erectile tissue, and an inner or mucous layer. The mucous layer is thrown into folds or rugae, which permit the distension of the canal in the process of parturition. VAIL, ALFRED, an American in- ventor; born in Morristown, N. J., Sept. 25, 1807; was graduated at the Univer- sity of the City of New York in 1836, and in 1837 became associated with Sam- uel F. B. Morse in his experiments for the purpose of perfecting a scheme of telegraphy. His mechanical knowledge applied to the experimental apparatus resulted in the first available Morse ma- chine. He invented the combination of the horizontal-lever motion to actuate the style; devised the alphabet of dots, spaces and dashes which it necessitated; and in 1844 constructed the automatic lever and grooved roller which embossed on paper the characters which he origi- nated. He was appointed assistant su- perintendent of the telegraph line con- structed between Baltimore and Wash- ington in 1843, and on the completion of the system, in 1844, was stationed at Baltimore, where he invented the finger key and received the first message from Washington. He died in Morristown, N. J., Jan. 18, 1859. VAIL, CHARLES H., an American clergyman; born in Tully, N. Y., April 28, 1866; was graduated at St. Law- rence University in 1892; studied theol- ogy and was ordained in the Universalist Church; was pastor of All Souls' Church, Albany, N. Y., in 1893-1894. In the latter year he accepted the pastorate of the First Universalist Church in Jer- sey City. In 1901 he was an unsuccess- ful candidate for governor of New Jer- sey on the Social Democratic ticket. His publications include: "Modern Social-