542 H Y D H Y D In the above table for Sikes s hydrometer two densities are given corresponding to each of the degrees 20, 30, 40, 50, 60, 70, 80, and 90, indicating that the successive weights belonging to the particular instrument for which the table has been calculated do not quite agree. The discrepancy, however, does not produce any sensible error in the strength of the corresponding spirit. A table which indicates the weight per gallon of spirituous liquors for every degree of Sikes s hydrometer is printed in 23 and 24 Viet. c. 114, schedule B. This table differs slightly from that given above, which has been abridged from the table given in Keene s Handbook of Hydromctry , apparently from the equal divisions on Sikes s scale having been taken as corresponding to equal increments of density. Sikes s hydrometer was established for the purpose of collecting the revenue of the United Kingdom by Act of Parliament, 56 Geo. III. c. 140, by which it was enacted that "all spirits shall be deemed and taken to be of the degree of strength which the said hydrometers called Sikes s hydrometers shall, upon trial by any officer or officers of the customs or excise, denote such spirits to be." This Act came into force on January 5, 181 7, and was to have remained in force until August 1, 1818, but was repealed by 58 Geo. III. c. 28, which established Sikes s hydrometer on a permanent footing. By 3 and 4 Will. IV. c. 52, 123, it was further enacted that the same instruments and methods should be employed in determining the duty upon imported spirits as should in virtue of any Act of Parliament be employed in the determination of the duty upon spirits distilled at home. It is the practice of the officers of the inland revenue to adjust Sikes s hydrometer at 62 F., that being the temperature at which the imperial gallon is denned as contain ing 10 Ib avoirdupois of distilled water. The specific gravity of any sample of spirits thus determined, when multiplied by ten, gives the weight in pounds per imperial gallon, and the weight of any bulk of spirits divided by this number gives its volume at once in imperial gallons. Mr J. B. Keene of the Hydrometer Office, London, has constructed an instrument after the model of Sikes s, but provided with twelve weights of different masses but equal volumes, and the instrument is never used without having one of these attached. When loaded with either of the lightest two weights the instrument is specifically lighter than Sikes s hydrometer when unloaded, and it may thus be used for specific gravities as low as that of absolute alcohol. The volume of each weight being the same, the whole volume immersed is always the same when it lloats at the same mark whatever weight may be attached. Besides the above, many hydrometers have been employed for special purposes. Twaddell s hydrometer is adapted for densities greater than that of water. The scale is so arranged that the read ing multiplied by 5 and added to 1000 gives the specific , r gravity with reference to water as 1000. To avoid an inconveniently long stem, different instruments are employed for different parts of the scale as mentioned above. The lactometer co nstructed by Dicas of Liverpool is adapted for the determination of the quality of milk. It resembles Sikes s hydrometer in other respects, but is provided with eight weights. It is also provided with a thermometer and slide rule, to reduce the readings to the standard temperature of 55 F. The marine hydrometers, as supplied by the British Government to the royal navy and the merchant marine, are glass instruments with slender stems, and generally serve to indicate specific gravities from 1 000 to 1 040. Before being issued they are compared with a standard instrument, and their errors determined. They are employed for taking observations of the density of sea-water. The salinometer is a hydrometer intended to indi cate the strength of the brine in marine boilers in which sea-water is employed. Saunders s salinometer consists of an hydrometer which floats in a chamber through which the water from the boiler is allowed to flow in a gentle stream, at a temperature of 200 F. The peculiarity of the instrument consists in the stream of water, as it enters the hydrometer chamber, being made to impinge ngainst a disk of metal, by which it is broken into drops, thus liberating the steam, which would otherwise disturb the instrument. Say s stereometer is an instrument for the deter mination of the volumes, and hence of the densities, -p ,* of bodies which cannot be conveniently measured by Q the ordinary hydrometer, as, for example, soluble r,, ^ , and porous bodies, powders, &c. The instrument consists of a glass tube PC (fig. 10), of uniform bore, terminating in a cup PE, the mouth of which can be rendered air-tight by the plate of glass E. The substance whose volume is to be determined is placed in the cup PE, and the tube PC is immersed in the vessel of mercury D, until the mercury reaches the mark P. The plate E is then placed on the cup, and the tube PC raised until the surface of the mercury in the tube stands at M, that in the vessel D being at C, and the height MC is measured. Let k denote this height, and let PM be denoted by I. Let u represent the volume of air in the cup before the body was inserted, v the volume of the body, a the area of the horizontal section of the tube PC, and h the height of the mercurial barometer. Then, by Boyle s law, ,h-k . . v = u~al , k The volume u may be determined by repeating the experiment when only air is in the cup. In this case v = 0, and the equation becomes (u, + al )(h - k ) = uh, h ~ V whence u = ai p Substituting this value in the expression for v, the volume of the body inserted in the cup becomes known, and if m represents its mass its density is . (W. G.) HYDROPATHY is the treatment of disease by water, used outwardly and inwardly. Like many descriptive names, the word " hydropathy " is defective and even misleading, the active agents in the treatment being heat and cold, of which water is little more than the vehicle, and not the only one. Thermo-therapeutics (or thermo- therapy) is a term less open to objection. The name " hydropathy," however, as being itself an advance on an earlier and less happy designation, " the water cure," as having obtained general currency, is here employed. Hydropathy, as a system, or mode of treatment complete in itself, dates from about 1829, when Vincenz Priessnitz (1801-51), a farmer of Grafenberg in Silesia, Austria, be gan his public career in the paternal homestead, extended so as to accommodate the increasing numbers attracted by the fame of his cures. Two English works, however, on the medical uses of water had been translated into German in the century preceding the rise of the move ment under Priessnitz. One of these was by Sir John Floyer, a physician of Lichfield, who, struck by the reme dial use of certain springs by the neighbouring peasantry, investigated the history of cold bathing, and published in 1702 his " tyvxpoXovaLa, or the History of Cold Bathing, both Ancient and Modern" The book ran through six editions within a few years, and the translation was largely drawn upon by Dr J. S. Hahn of Silesia, in a work pub lished in 1738, On the Healing Virtues of Cold Water, Inwardly and Oultvardly applied, as proved by Experience, The other work was that of Dr Currie of Liverpool, entitled Medical Reports on the Effects of Water, Cold and Warm, as a Remedy in Fevers and other Diseases, published in 1797, and soon after translated into German by Michaelis (1801) and Hegewisch (1807). It was highly popular, and first placed the subject on a scientific basis. Hahn s writings had meanwhile created much enthusiasm among his countrymen, societies having been everywhere formed to promote the medicinal and dietetic use of water ; and in 1804 Professor Oertel of Ansbach republished them and quickened the popular movement by unqualified commen dation of water drinking as a remedy for all diseases. In him the rising Priessnitz found a zealous advocate, and doubtless an instructor also. The origin of hydropathy is thus to be traced to an English source and to the medical profession. The broad conception that water had curative relations to the whole realm of disease seems to have been first grasped by a Capuchin monk of Sicily, Father Bernardo, who, at Malta, in 1724, obtained results by iced water alone, which, according to Hahn, caused a great stir through out Europe ; but, owing to the excesses of his imitators, it was of no long duration. With this exception there is,
as regards the remedial use of water, nothing in the history
