H Y G H Y G 569 no such special preventive is known. Some diseases, such as typhus fever and plague, are successfully combated by scattering the population over a large area and inducing the freest ventilation, and to all diseases this plan may be applied with more or less effect. In those diseases which are known to be communicable, such as scarlet fever, isolation of the patients is an effectual means of arresting the spread ; but the poisons of others, such as measles and hooping-cough, are so subtle that isolation can only be looked upon as a measure of doubtful success. Much stress has been laid upon disinfection as a means of preventing disease, and if properly carried out it has some efficacy. But it is a mistake to place too implicit reliance upon it as ordinarily practised. In dealing with clothing, bedding, &c., the best method is the application of heat, at or above the boiling-point of water, which may be done by means of dry heat, superheated steam, or boiling water. In fumigating places, burning sulphur or the vapour of chlorine or nitrous acid is used, but to be effectual the air must be rendered for the time irrespirable. The solid and liquid disinfectants (so-called) are chloride of lime, the perman ganates, carbolic acid, and a great many similar substances, many of which have been made the subjects of patents. A large number of them are merely deodorants. It may be stated generally that disinfectants are useful as adjuncts to other hygienic measures, but that they cannot replace them, except to a small extent, and in a very imperfect way. 11. Disposal of the Dead. The most frequent plan is interment in the earth, but it may well be a question if this be the best plan ; it has certainly led to much evil when carried out near habitations. Two other plans have been suggested, viz., burial at sea (suggested by the late Dr Parkes) and cremation. The former is hardly likely to be resorted to, but the latter would be effectual in preventing the evil consequences of ordinary interment. At the same time the danger that it might too effectually conceal much secret crime has to be taken into account. Bibliography. E. A. Parkes, Manual of Practical Hygiene, edited by F. de Chaumont; G. Wilson, Handbook of Hygiene; A. Wynter Blytli, Dictionary of Hygiene (after Tardieu); F. de Chau mont, Lectures on State Medicine; A. H. Buck, Hygiene and Public Health, New York ; Michel Levy, Traitt d Hygiene Publique ct Privtc ; Von Pappenheim, Handbuch dcr Sanitats-Polizci ; Roth and Lex, Handbuch dcr Militdrische Gcsundheitspjlege ; and numerous vorksand monographs on special departments. (F. DE C.) HYGINUS, CAIUS JULIUS, a native of Spain, and the freedman of Augustus, by whom he was made chief of the Palatine library. He is said to have fallen into great poverty in his old age, and to have been supported by one C. Licinius. He was a voluminous author, and his works included topographical and biographical treatises, commen taries on Cinna and on Virgil, and disquisitions on agricul ture, bee-keeping, and the military art. All of these are lost. But there have come down under his name two school treatises on mythology, which have produced much discussion. They are entitled (1) Fabularum Liber, con taining 277 mythological legends, and valuable for the use made of the Greek tragedians; and (2) Poeticon Astrono- micon Libri IV., an astronomical treatise of little value. Both are abridgments ; both are by the same hand ; but from the " tyro-like mistakes " in both they have been thought unworthy of the librarian of Augustus. It is not, however, impossible that they are early compositions of his, written before he had gained full command of the Latin language. A suggestion has also been made (Bursian in Fleckeisen s Jahrbuch, xciii. p. 773) that a work of Hy- ginus, named Genealoyiop, was abridged by a grammarian of the latter half of the 2d century, who appended a treatise on the whole mythology arranged according to my thological views. Tins text-book, retaining the name of Hyginus, would be used in the schools, and would be from time to time altered and augmented. But in these, as in the many other opinions that have been advanced, there is nothing beyond conjecture. HYGINUS (surnamed GROMATICUS, from gruma, a sur veyor s measuring rod), a writer on land surveying and castrametation, who nourished in the reign of Trajan (98-117 A.D.). There survive fragments of a comprehen sive treatise De munitionibus castrorum or De castrameta- tione, and of a work J)e limitibus constituendis, which may be found in Lachrnann s edition of the works of the Roman Gromatics (1848), i. 108-134. HYGROMETRY. In the British Islands all are familiar with the arid character of the east winds of spring, and not a few are only too painfully aware of the discomfort experienced while under their influence ; and all are like wise familiar with the opposite state of the atmosphere, most frequently and unmistakably occurring also with east winds, when every object feels damp and clammy to the touch, and horses on the streets are seen each with a steam ing cloud of dense mist around it. In certain other climates, such as are met with in India and South Africa, these effects are greatly intensified, so that on the one hand the ivory scales of thermometers, quill pens, and other objects curl up, articles of furniture open at the joints and split up, and the grass which covers the soil is reduced to a state of tinder ; and on the other hand, everything becomes so permeated with moisture that, even in the interior of houses, furniture, books, and wearing apparel become sodden with wet. These different effects depend on the states of the air as regards the quantity of aqueous vapour diffused through it taken in connexion with the temperature, these varying from the completest possible saturation of the air, which is of occasional occurrence in the rainy season of some tropical climates, to that extreme desiccation of the air which sometimes happens in Great Britain in spring, but more completely and frequently in such dry summer climates as that of the Punjaub. A large number of substances, such as sugar, flour, and bread, possess the property of absorbing moisture, and most gases, as well as air, absorb and retain aqueous vapour. The term liyyrometry is employed to signify the measure ment of the degree of dampness of substances, and to denote the processes by which their humidity is ascertained. The term, however, may be considered as restricted to the humidity of the atmosphere, owing to the paramount im portance of that branch of the subject, and the slight and unsatisfactory knowledge we yet possess of the laws of hygrometry of other substances. All organic substances contain pores for the conveyance of their juices, and are influenced by the accession of mois ture, some of them very markedly so. Every species of wood is liable to these hygrometric changes, the amount of contraction and expansion being much greater across the grain of the wood than lengthways, Hence the panels of doors are fitted into grooves so as to allow of shrinkage, for, if secured at the edges, the panels must inevitably split. The hair of animals is also eminently hygrometric, curling and uncurling as the air becomes drier or moister, and it is because of the peculiar sensations accompanying these hygrometric changes that the cries and behaviour of many of the lower animals furnish valuable prognostications of weather changes. Similarly many manufactured objects, such as paper, cordage, &c., vary in weight, bulk, form, and elasticity with the varying degrees of humidity of the air, and other interesting prognostics have been drawn from these hygrometric changes. In the earlier stages of the investigation of the hygro metry of the air, the hygrometric properties of several sub stances were made use of as instruments of observation. Of these may be named the twisted Indian grass (Oobeena
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