HOSPODAR 63 HOTCHKISS GUN assimilated to hospitals on shore and are under the supervision of the Bureau of Medicine and Surgery of the U. S. navy. Surgeons are usually in command, and they are supported by assistant surgeons and nurses, in addition to the personnel necessary for navigation and other pur- poses. An ordinary ship has about 200 beds, to which vi^ould be attached a hos- pital staff of 10 officers and 40 men. Hospital ships used for civilian pur- poses are permanent institutions. These are of two classes: those that work in conjunction with the merchant marine, and those used as floating hospitals for the poor and for the purpose of giving children in the cities the benefit of sea air during the summer. During the World War charges and counter charges with respect to the im- proper use of hospital ships arose con- stantly. The German Government re- peatedly accused the British of using the ships for the transport of unwounded soldiers and military supplies, and, as a result, treated some of them as ordinary vessels of war. HOSPODAR (hos-po-dar), a Slavonic title once commonly given to the gover- nors of Moldavia and Wallachia. Lithu- anian princes and Polish kings also bore the title. HOST, the consecrated bread or wafer used by the Roman Catholic Church in her celebration of the eucharist. It is unleavened, thin, flat, and of circular form, and has certain mystic signs im- pressed on its surface. The host is sup- posed after being blessed to be no longer bread and wine, but to be transformed into the real body and blood of Christ. HOSTAGE, a person given in pledge or security for the performance of cer- tain conditions, or for the safety of others. HOT AIR ENGINES, a type of prime mover in which air, which has been heated to a high temperature and pres- sure, acts upon a piston and thus con- verts thermal energy into mechanical energy. Air, under high temperature and pressure, is admitted into a cylinder where it expands and moves a well fitted piston, supplied with nearly airtight piston rings. Consequently its temper- ature and pressui'e are decreased. The air is then exhausted either into the atmosphere, or carried through a system of pipes and again heated and injected into the engine. When the same charge of air is reheated, and new air used only to replace leakage, the engine is said to be of the closed cycle type, while those of the open cycle type are the ones in which a fresh charge of air is used for each stroke of the piston. Some engines are designed to have the tem- perature change take place at constant volume, others at constant pressure. In some engines a device is used to absorb the heat from the exhaust air and use it to heat the new air. If the engine is fitted with such apparatus, it is said to be regenerative, if it has no such device it is non-regenerative. The theo- retical economy of the hot air engine has often been urged, but there has been no large successful commercial application of the principle, for in the larger sizes steam is much more economical, while the smaller sizes cannot compete with the internal combustion engine. The Rev. Robert Stirling built a comparatively successful engine about 1816, which was used commercially in Dundee, Scotland, after 1827. In 1833 John Ericsson de- signed a hot air engine of large size for use in his boat, but after much experi- mentation it was pronounced a complete failure. Napier and Rankins did early experimental work in this field, and Stephen Wilcox, Philander Shaw, and S. H. Roper, Americans, separately built and sold a number of the engines. HOT BED, a bed or stratum of stable- litter, tan, dead leaves, etc., in a state of fermentation, and therefore emitting heat, covered with a layer of earth, the whole having a glazed box surmounting it. A hot bed is used for the growth of , melons, cucumbers, etc., or to afford tem- porary protection to seeds unlikely to germinate vigorously in the open air. HOT BLAST, a stream of air forced through a furnace and heated to 500" or 600°. The combustible gases from the stack are generally used to heat the air. For this purpose a kind of oven is built near the top of the stack, sur- mounted by a kind of chimney which draws off a portion of the inflamed gas. In this oven is a series of pipes through which the air is forced before it enters the stack. The hot blast effects a saving of heat, and accomplishes the reduction of the most refractory ores in less tir^.e and with a less expenditure of fuel than the cold blast. HOTCHKISS, BENJAMIN BERKE- LEY, an American inventor; born iu Watertown, Conn,, Oct. 1, 1826; was ia early life a machinist and turned his attention to the invention of deadly weapons, most notable of which is the HoTCHKiss Gun (q. v.). He died in Paris, Feb. 14, 1885. HOTCHKISS GUN, a gun consisting of an inner tube over which is shrunk
