INCIDENTALS. 513 IN C<ENA DOMINI. la music, the notes of a chord which are nut absolutely essential to its harmonic complete- ness. Incidentals are thus opposed to essentials (q.v.). They are divided into two classes, con- sonant or strong incidentals, and dissonant or weak incidentals. INCLEDON, iu'k'1-don, Chables Benjamin (1763-1820). An English singer, born at .Saint Keverne, Cornwall. He received his musical edu- cation in the choir of the E.xeter Cathedral, to which he was admitted in 1771. A few years afterwards he entered the navy, and served un- til 1783. His professional career as a musician began when he appeared at the Southampton Theatre in the Castle of Andalusia. In 1817 he visited America, and sang the role of Hawthorn in Love in a Village, at the Park Theatre, in New York City. Soon after his return to England he left the stage, and from that time traveled in the provinces as a musical entertainer. His voice was best adapted to ballads, and it was in this kind of singing that he excelled. Three songs which contributed greatly to his popularity were "The Storm," "Black-Eyed Susan," and "Arethusa." INCLINATION, Magnetic, or Dip. The angle made with the horizontal by the axis of a magnetic needle swinging freely in a vertical plane. The inclination of a magnetic needle varies at different places of the earth's surface, ranging from 90° at the magnetic poles to zero at the magnetic equator. The varying amount of magnetic inclination will be found indicated on the isoclinic charts accompanying the article Magnetism, Terrestrial. This property of a magnetic needle was first discovered by Robert Norman in 1576, and an instrument was de- vised by him by which the amount could be measured. The phenomenon had previously been noticed by George Hartman, in Nuremberg, in 1544, but he was neither able to measure the amount of inclination accurately nor to explain the phenomenon. The amount of inclination is determined by the dipping needle (q.v.) and is measured when the magnetic needle is freely swinging in a vertical plane containing the me- ridian. If the plane of the needle is placed at right angles to the magnetic meridian, the axis needle will form an angle of 90° with the hori- zontal. The dip of the needle is subject to the same periodic variations as its declination (q.v.), but these changes play a far less important part. In order that an ordinary compass-needle may swing in a horizontal plane, it is customary in northern latitudes to make the southern end of the needle heavier; or the same effect may be secured by using a symmetrical needle which has been weighted with a small bit of brass on its southern half. See Compass ; Declination; Dip op the INIaonetic Needle : Dipping Needle ; Magnetism ; Magptotism, Terrestrial. INCLINED PLANE. A smooth plane in- clined to the horizontal plane at any point on the earth's surface. Imagine a plane section through this inclined plane and the horizontal one, perpendicular to their line of intersection. Let the plane be supported by an upright; and let two bodies of masses m, and m,. joined by an inextensible string, be placed, as .shown, one on the plane, and one hanging freely, the string passing over a pulley. If the bodies are in equilibrium, the forces on the body of mass mi, parallel to the plane, must balance each other. There is a force m-^aiae down the plane and a c INCLINED PLANE. force nuj) up the plane; hence m^gs'me ^zm^g; or, in general, the force up the plane equals the weight of the body on the plane multiplied by the sine of the angle of inclination of the plane. To produce motion up the plane of a heavy body requires, therefore, less force than its weight. 1 The 'mechanical advantage' is ^j^ Another method for solving this problem is to consider as before the two bodies in equilibrium, and to produce a small displacement; let the body whose mass is m-, move up the plane a dis- tance iE,, and the body whose mass is m^ move vertically down, owing to this, a distance x,. By the principle of energy m,gsm0 Xi = m^x^; but Xi^x^; hence, as before, m, gains =:nug. In- clined planes are still used daily for rolling up heavy weights. They were used by all ancient peoples for raising heavy stones for building purposes. The screw is nothing but an inclined plane rolled around a cylinder. INCLOSED ABC LAMP. See Electric Lighting. INCLOSURES OF COMMONS. At common law, the only method by which the right to in- close lands subject to common rights could be gained was by mutual agreement between all who had commonable privileges therein. It was a tedious and unsatisfactory method. Oftentimes some of the interested persons were subject to disabilities, in which event a special act of Parliament was required. The benefits of in- elosure became evident centuries ago. and as early as the reign of Henry III. a general act of Parliament, known as the Statute of Merton, was passed, authorizing the 'inclosure and ap- provement' of commons of pasture, upon certain conditions. In the reign of Edward I. the Statute of Westminster the Second was passed in amend- ment and extension of the former act. Compara- tively little progress was made under the laws in the partition of common lands. Not until 1801 was a general inclosure act passed. This has been followed by a large amount of legislation, all tending in the direction of facilitating the division of commons, their conversion into sepa- rate and independent land holdings, the inclosure of such holdings, and the improvement of those portions that are retained for the common use of to«-ns or villages. Consult: Williams. Rights of Common (London, 1880) ; Scrutton. Commons and Common Fields (London, 1887). IN CCE'NA DOMINI (Lat.. at the Supper of the Lord). A celebrated Papal hull, so called be- cause designed to he read in the Church on every Holy Thursday, the day on which the Lord's Supper was instituted, "it is not. as other bulls, the work of a single pope, but with various ad-
