Page:Encyclopædia Britannica, Ninth Edition, v. 15.djvu/520

M A N - M A N FIG. 4. Desgoffe s Manometer. with the vessel continuing the fluid whose pressure is to be mea sured. The compressed fluid acting upon T depresses the piston D and causes the mercury to rise in AB. Let p be the pressure of the lluid per unit of area, s the area of T, and S the area of D ; also let P be the pressure per unit of area as recorded by the height of the mercury in AB. Thus evidently we have S ps = PS , or p = P . Hence by making S very great and s very small a very great pressure can be measured by a comparatively short column of mercury in AB. As part of the pressure p is em ployed to stretch the india-rubber mem brane, the ratio S : s should be made very great, so that D will only sink a very short distance. Caille- tet, who employed this manometer in his experiments on the compressibility of fluids, had it so arranged that (ne glecting the stretch ing of the india- rubber) the mercury * IG - 5> Section of Desgofle Manometer. in AB rose 4 - 3 metres while the piston in D sunk only one-eighth of a millimetre. Metallic manometers depend on the principle exemplified in the aneroid barometer. Suppose a long tube, preferably of elliptic section, and having thin walls of elastic material, to be closed at one end and either bent or coiled up in the form of a spiral. Let the open end be attached to an apparatus whereby the pressure in side the tube can be either increased or diminished. If the pressure inside the tube be made greater than that outside, the tube has a tendency to straighten or uncoil itself, but if the pressure outside be greater than that inside the tube has a tendency to bend or coil itself up farther. Fig. 6 represents an early form of metallic mano meter made on this principle by Bourdon, the first to construct such instruments. A metallic tube a6,closed at b, is coiled in a spiral and rigidly at tached at the open end a to a tube with stop-cock m, whereby it can communicate with the compression apparatus. A light index e is attached to b and moves over a graduated scale. The scale is graduated by applying known pres sures inside the tube. This form of mano meter is very conveni ent for rough practical work, but has no pre tensions to scientific FlG> 6 - Bourdon s Metallic Manometer, accuracy, as changes of temperature affect the elasticity of the tube in a way which is difficult to discover and allow for. Various forms of metallic manometers have been recently invented, the best-known of which are perhaps those of Bourdon and Schafer, in which the index is moved by a train of wheels actuated by the free end of the elastic tube. Air-pump Manometer. For measuring pressures less than that of the atmosphere, as in the receiver of an air-pump, a special form of mercury manometer is employed, consisting of a glass U tube with each leg over 30 inches long and half filled with mercury. One leg communicates by an air-tight communication with the re ceiver of the air-pump, and the other is left open. As the exhaustion proceeds, the mercury falls in the open leg and rises in the other. When only considerable degrees of exhaustion are to be measured, the instrument takes the form of a short U tube closed at one end and open at the other, and has its closed leg completely filled with mercury, the mercury being held up by the atmospheric pressure. The whole is enclosed in a wide glass tube closed at the top and hermetically fixed at the lower end to a brass piece, provided with a stop-cock, whereby it can be screwed on to the sole plate of the air-pump. The diil erence of level in the two legs gives the degree of exhaustion obtained. See Ganot s Physics ; Wiillner s Lehrbuch der Experimentalphysik; Amagat in Annales do Chemie et de Physique, March 1880; Report of H. M.S. C/iallenger, in regard to pressure corrections supplied by thermometers, by Professor Tait. (J. BL. ) MANOR, in English law, is an estate in land, to which is incident the right to hold certain courts called courts baron. It might be described as the unit of tenure under the feudal system, and it is historically connected with the territorial divisions of the mark and the parish or township. 1 The legal theory of the origin of manors refers them to u grant from the crown, as stated in the following extract from Perkins s Treatise on the laws of England : " The beginning of a manor was when the king gave a thousand acres of land, or a greater or lesser parcel of land, unto one of his subjects and his heirs, which tenure is knight s service at the least. And the donor did perhaps build a mansion house upon parcel of the same land, and of 20 acres, parcel of that which remained, or of a greater or lesser parcel before the statute of Quia Emptores did enfeoff a stranger to hold of him and his heirs to plow 10 acres of land, parcel of that which remained in his posses sion, and did enfeoff another of another parcel thereof to go to war with him against the Scots, &c., and so by continu ance of time made a manor." It is still, as Mr Joshua Williams terms it, a "fundamental rule" that all lands were originally derived from the crown, and that the queen is lady paramount mediate or immediate of all the land in the realm. A manor then arises where the owner of a parcel so granted or supposed to have been granted by the crown (arid who is called in relation thereto the lord) has in turn granted portions thereof to others who stand to him in the relation of tenants. Of the portion reserved by the lord for his own use (his demesne) part was occupied by villeins, with the duty of cultivating the rest for the lord s use. These were originally tenants at will, and in a state of semi-serfdom, but they became in course of time the copyhold tenants of the later law. (See COPYHOLD.) It is of the essence of copyhold that it should be regulated by the custom of the manor ; and that, according to some authorities, is one reason why a manor cannot be created at the present day. " Length of time being of the very essence of a manor, such things as receive their perfection by the continuance of time come not within the compass of a king s prerogative" (Scriven, Copyholds, chap. i.). But the effect of the statute of Quia Emptores was to make the creation of manors henceforward impossible, inasmuch as it enacted " that upon all sales or feoffments of land, the feoffee shall hold the same, not of his immediate feoffor, but of the chief lord of the fee of whom such feoffor him self held it." The statute did not apply to the king s tenants in capite, who might have aliened their land under a licence. Accordingly it is assumed that all existing manors are " of a date prior to the statute of Quia Emptores, except perhaps some which may have been created by the king s tenants in capite with licence from the crown " (Williams, Real Property, chap. iv. ; see also Scriven, Copy holds, chap. i.). When a great baron had granted out smaller 1 Laveleye (Primitive Property, chap, xviii.) observes that in the 10th century, even before the Norman Conquest, the mark had already been transformed into the manor, although the term was not yet in use. The country was covered with a great number of domains (maneria), of very different extent, from the maneriolum of one plough to the lati-

fundium of fifty ploughs.